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Chapter 5

Symptoms and Signs of Brain Tumors

Tumors arising in the brain continue to grow, producing two major groups of symptoms and signs:

1. General symptoms. These result from raised intracranial pressure. The three principal symptoms (the symptom triad) are headache, vomiting, and blurred vision due to papilledema (choked disc). As the tumor enlarges, other manifestations appear: personality change, a reduced level of consciousness, double vision (diplopia) or strabismus due to abducens nerve palsy, enlargement of the head in young children, dizziness, generalized epilepsy, and the Cushing reflex. These manifestations have been discussed in detail in the chapter on raised intracranial pressure. They are not, in fact, specific to brain tumors; they are manifestations of raised intracranial pressure, which may have many other causes, including an intracerebral hematoma, brain abscess, and cerebral edema.

2. Focal symptoms. These reflect loss of the specific functions of the part of the brain destroyed or compressed by the tumor. Focal manifestations are important diagnostic clues because they indicate the location of the tumor. Physicians should therefore understand the anatomy and function of each part of the brain in order to recognize abnormalities. In general, patients do not present with purely focal symptoms; their symptoms often also reflect impaired function in the brain surrounding the tumor. Because a brain tumor continues to enlarge, it compresses adjacent brain tissue, progressively impairing its function. Thus, a history of progressively increasing loss of brain function is important in diagnosing a brain tumor. Careful history-taking can identify the first focal functional deficit.

In addition to manifestations of brain destruction, a brain tumor may produce manifestations of cerebral irritation in the form of various types of seizures. A focal seizure can be just as important as a deficit caused by brain destruction, because it helps locate the tumor, as discussed in detail below.

Focal Symptoms and Signs of Brain Tumors

The brain is divided into regions, each with specific functions and connections to other regions. A tumor causes loss of brain function, but this loss may not be conspicuous because of several modifying factors, including the patient’s age, whether the tumor is benign or malignant, the rate of tumor development, and the occurrence of herniation. Frequently, no focal manifestations are evident; the patient has only symptoms of raised intracranial pressure, and the tumor can be localized only by radiological investigation.

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FRONTAL LOBE

The frontal lobe is the largest part of the brain. It lies anterior to the central sulcus (of Rolando), which separates it from the parietal lobe. Laterally, the frontal lobe is separated from the temporal lobe by the lateral or Sylvian fissure. This fissure begins at the temporal pole and runs posteriorly and slightly upward. The cortex forming the fissure is called the operculum and comprises parts of the frontal, parietal, and temporal lobes. Large sulci divide the frontal lobe into four gyri. On the lateral surface of its anterior portion are the superior, middle, and inferior frontal convolutions, separated by the superior and inferior horizontal sulci (Figure 5.1). The inferior frontal gyrus is further divided into orbital, triangular, and opercular parts. The gyrus immediately anterior to the central sulcus is the precentral gyrus, which forms the motor cortex; this also includes the part of the paracentral lobule anterior to the central sulcus on the medial surface of the hemisphere. Anterior to the motor cortex is the premotor sulcus. The cortex anterior to this sulcus and posterior to the superior, middle, and inferior frontal convolutions is the premotor area, corresponding to Brodmann area 6, also called the extrapyramidal cortex. The premotor area helps control the muscles on the opposite side of the body and has a distribution of centers similar to that of the motor area.⁽¹⁾ The posterior portion of the middle frontal convolution contains the frontal eye field, which controls movement of both eyes in the same direction (conjugate gaze). The posterior portion of the inferior frontal convolution, corresponding to its opercular and triangular parts in the dominant hemisphere, is the motor speech area or Broca’s area and is concerned with speech. The frontal lobe anterior to the premotor and motor speech areas is the frontal association or prefrontal area. It is concerned with higher intellectual function and is particularly well developed in humans. On the basal or orbital surface, the olfactory sulcus divides the frontal lobe into the rectus gyrus medially and the orbital gyrus lateral to the sulcus.

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The functional deficits associated with the individual regions of the frontal lobe are discussed separately below.

The motor area produces voluntary movement on the opposite side of the body. It is divided into centers, each controlling the muscles of a particular body part. The center for the larynx and throat lies lowest, adjacent to the Sylvian fissure. Successively higher are the centers for the jaw, tongue, face, eyes, fingers, hand, arm, shoulder, trunk, hip, and leg. The leg area lies medially in the motor area (Figure 5.2). The shoulder center is near the vertex. This anatomy explains shoulder weakness following surgery for a parasagittal meningioma in this part of the motor cortex. The cortical representations of the tongue, face, and fingers are particularly large because these structures perform extensive and complex movements. Fibers from the motor area form the corticobulbar and corticospinal tracts, descending through the corona radiata, the genu and anterior two-thirds of the posterior limb of the internal capsule, and the cerebral peduncle. The corticobulbar tract terminates in nuclei in the pons and medulla. The corticospinal tract continues toward the spinal cord and decussates in the lower medulla: approximately 70–90% of its fibers cross to the opposite side and descend as the lateral corticospinal tract, ending on anterior horn cells in the spinal cord.⁽²⁾ The remaining minority descend without crossing as the ventral corticospinal tract.

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The symptoms and signs of frontal lobe tumors are as follows:

1) MONOPLEGIA, HEMIPLEGIA

Tumors in the motor area often bring patients to medical attention relatively early because they cause weakness of a body part or seizures. A tumor on the surface or in the subcortex causes a focal deficit in the compressed region, described as monoplegia (Figure 5.2). Compression of the arm and hand area causes weakness of the opposite arm and hand; a tumor in the medial motor area causes weakness of the opposite leg. Tumors in these locations do not usually cause hemiplegia. A tumor of the falx in the region of the paracentral lobules, such as a falx meningioma, causes weakness of both legs (Figure 5.3). One leg is usually weaker than the other, and the foot is weaker than the proximal thigh. Some patients also have difficulty passing urine because the micturition center is compressed. These manifestations must be distinguished from those of a spinal cord lesion. The distinction is not difficult: a parasagittal brain tumor causes raised intracranial pressure and seizures, without a sensory level. A spinal cord lesion causes neither raised intracranial pressure nor seizures, but produces a level of sensory loss and motor dysfunction.

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A unilateral lesion in the motor representation of the larynx, throat, palate, upper face, diaphragm, anus, or bladder seldom produces an obvious deficit, because these structures receive bilateral innervation.

A tumor in the lower frontal lobe of the dominant hemisphere, at the facial muscle center and Broca’s area, causes difficulty speaking (dysphasia) or inability to speak (aphasia), together with facial weakness. In right-handed people this speech center is in the left hemisphere; in left-handed people it is in the right hemisphere. If a tumor in this region causes seizures, the patient cannot speak during the seizure and for a time afterward.

A tumor in the deep white matter, where the corticospinal fibers converge, causes hemiplegia (Figure 5.2), even if it is small.

The history is one of gradually developing weakness that progressively spreads to other parts of the body. This is a very important history in diagnosing a brain tumor.

2. Seizures (epilepsy, convulsion, seizure, fit)

Seizures are important, particularly when they first occur in an adult who has never previously had one. Focal seizures and marching seizures (Jacksonian epilepsy or marching epilepsy) are especially significant because they provide clues to the cause and location of the lesion. Tumors in the motor and premotor areas cause seizures more frequently than tumors elsewhere. A focal seizure begins in the body part corresponding to the tumor’s location. It is clonic, with rhythmic jerking that may stop or continue for a prolonged period. In some patients, the jerking spreads to other parts of the same side of the body; this is called marching or Jacksonian epilepsy. For example, jerking may begin in the hand and spread to the arm, mouth, and eyelid. If the tumor is in the dominant hemisphere, the patient becomes unable to speak. The seizure then stops. Consciousness is retained in such cases, but the body parts that jerked remain temporarily weak afterward. This is Todd’s paralysis, attributed to temporary exhaustion of the neurons responsible for the seizure. Within a few hours, the weakness resolves and function returns to its pre-seizure state. The body part in which jerking began regains strength last. In this example, the hand, arm, and face are weak after the seizure, with the hand showing the greatest and longest-lasting weakness. A history identifying the site of onset of the jerking and the distribution of Todd’s paralysis therefore helps localize the tumor.

In some cases, a seizure involves an entire side of the body before spreading to the opposite side. At that stage the patient loses consciousness, and the seizure is called a generalized or grand mal seizure. It takes the form of a clonic-tonic convulsion, which stops after a time. The patient commonly sleeps for a while before awakening.

Jacksonian epilepsy may affect a single body part continuously without loss of consciousness; this is called “epilepsia partialis continua.” In some cases, there are pauses between attacks or many dozens of attacks a day, termed serial Jacksonian epilepsy. Recurrent attacks without recovery of consciousness between them are called Jacksonian status epilepticus.

3) FRONTAL ATAXIA

The premotor and motor areas of the frontal lobe are connected to other brain regions, particularly the pons and cerebellum. Frontopontine fibers arise from the middle frontal convolution anterior to areas 6 and 8 and form an important part of the corticopontocerebellar tract.⁽¹⁾ Impulses descend from the cortex to the pons; after synapsing there, they pass through the middle cerebellar peduncle (brachium pontis) to the opposite cerebellar hemisphere. Destruction of these fibers by a frontal lobe tumor causes frontal ataxia. It may be difficult to distinguish this from cerebellar ataxia. The guiding distinction is that destruction of the frontal cortex or frontopontine fibers causes contralateral ataxia without dysmetria, whereas destruction of a cerebellar hemisphere causes ipsilateral ataxia with dysmetria, usually accompanied by nystagmus.

4) ABNORMAL CONJUGATE GAZE

The frontal eye field (Brodmann area 8), in the posterior middle frontal gyrus anterior to the premotor area, controls voluntary movement of both eyes together in the same direction (conjugate gaze). Stimulation produces conjugate deviation of both eyes to the opposite side and may also turn the head and trunk in the same direction. Eye movements elicited by visual stimulation require impulses to pass from area 17 in the occipital lobe through the inferior occipitofrontal fasciculus to the frontal eye field (Figure 5.40). Destruction of this center causes paresis of conjugate gaze toward the opposite side, so both eyes look toward the side of the lesion.⁽⁶⁾ This is temporary in a conscious person because adaptation can occur; in an unconscious person the deviation persists.

In general, frontal lobe tumors in this region do not cause gaze palsy, conjugate ocular deviation, or nystagmus. If the tumor causes an adversive seizure, however, the attack begins with the eyes and face turning toward the side of the convulsing limbs. Thus, deviation of the eyes and face to the left while the left arm and leg are convulsing indicates an irritative lesion in the right frontal eye field and motor areas.

5) PERSONALITY CHANGE

The prefrontal or frontal association area is the part of the frontal lobe anterior to the premotor area and motor speech center, including its orbital surface. It is connected to the visual, auditory, and other sensory centers through association fibers and also sends fibers to the thalamus and hypothalamus. The prefrontal area is highly developed in humans and is responsible for higher intellectual functions, including memory, judgment, reasoning, emotional restraint, mental activity, and personality. Tumors here therefore cause changes in personality and thinking.^(3,4) Generally, they cause no clearly recognizable focal symptoms until very large, because neither patients nor their families notice the early changes. Patients may complain of deteriorating memory, difficulty concentrating on work, progressively poorer work performance, neglect of their usual duties, and impaired thinking. These changes gradually progress to dementia. Later personality changes include loss of initiative, lack of interest, untidiness, and neglect of habitual personal hygiene such as brushing the teeth, shaving, and bathing. Some patients use coarse language or become irritable; they eat slowly and messily. In later stages they pass urine and stool without awareness, in inappropriate places and without embarrassment, and may sometimes handle their feces. They become lethargic, expressionless, and unresponsive to stimulation.

Intrinsic frontal lobe tumors, such as gliomas and metastases, cause these manifestations earlier and more severely than extracerebral tumors such as meningiomas. With benign gliomas, such as astrocytoma or oligodendroglioma, symptoms develop more slowly and are less severe than with glioblastoma multiforme, which grows rapidly and destroys fibers. Meningiomas grow from outside the brain and compress it before destroying it, so symptoms develop slowly and gradually.

A common orbital-surface tumor is the olfactory groove meningioma. It causes loss of smell (anosmia) by compressing and damaging the olfactory bulb or tract. Depending on tumor size, anosmia may be unilateral or bilateral. Gliomas at the base of the frontal lobe may likewise abolish smell by destroying the olfactory pathway. A large olfactory groove meningioma may also cause personality change, although this is usually not marked. Posterior growth may compress the ipsilateral optic nerve, causing primary optic atrophy. Funduscopic examination shows a distinctly pale optic disc and narrowed vessels. The opposite disc shows papilledema because the large tumor raises intracranial pressure. This combination is called Foster-Kennedy syndrome.

6) TREMOR

Tremor may occur with a large, deep frontal lobe tumor. It may be contralateral or bilateral. It resembles the tremor of parkinsonism but is less severe and lacks the pill-rolling movement seen in parkinsonism. There is no satisfactory explanation for this tremor resembling extrapyramidal motor dysfunction.

7) GRASPING AND GROPING REFLEXES

A grasping reflex on examination is an important finding, regarded as a pathognomonic sign of a frontal lobe lesion. It occurs in the hand opposite the lesion and may also occur in the foot if the tumor is in the superior frontal lobe.⁽⁷⁾

The grasping reflex is flexion of the fingers and thumb in response to an object stimulating the palmar surfaces of the fingers, particularly between the index finger and thumb. The patient grasps the object and does not release it; attempts to pull it away make the grip tighter. In some patients, with both eyes closed, a light touch to the palm or fingers produces grasping and searching or fumbling movements, called the groping reflex. Grasping and groping are infantile reflexes. A frontal lobe lesion causes a return to this infantile pattern, allowing a grasping reflex to appear on the opposite side. A unilateral grasping and groping reflex in a conscious patient is therefore a valuable localizing sign. It is much less significant in a patient with impaired consciousness or when present bilaterally. If the tumor causes progressively increasing hemiparesis, the grasping reflex disappears once complete hemiplegia develops.

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PARIETAL LOBE

The parietal lobe lies posterior to the central sulcus (Rolandic fissure), superior to the temporal lobe or Sylvian fissure, and anterior to the occipital lobe. Anteriorly, the postcentral sulcus runs parallel to the central sulcus, separating the postcentral gyrus from the remainder of the parietal lobe. In the middle of the lobe, a transverse sulcus runs from the postcentral sulcus to the transverse occipital sulcus, dividing the posterior parietal lobe into superior and inferior parietal lobules. These include the supramarginal gyrus, which curves around the end of the Sylvian fissure, and the angular gyrus, which curves around the end of the superior temporal sulcus. In the dominant hemisphere, the supramarginal and angular gyri serve as the sensory or perceptive speech center, also called Wernicke’s center (Figure 5.1).

The postcentral gyrus is concerned with somatosensation. Most of its fibers come from the lateral nuclei of the thalamus, which relay impulses from the spinothalamic tract, medial lemniscus, and secondary trigeminal tract. Fibers from the thalamus pass through one-third of the posterior limb of the internal capsule to the postcentral gyrus. Sensations from different body parts are represented in the postcentral gyrus in an arrangement similar to that of the motor area (Figure 5.2). The superior and inferior parietal lobules constitute the psychosensory area, concerned with the perception and interpretation of sensation, or sensory association area. They connect to the postcentral gyrus through association pathways and also receive fibers from the lateral dorsal and posterior thalamic nuclei. The precise functions of the individual subdivisions of this part of the parietal lobe are not clearly known.

The parietal lobe receives and interprets sensations from the thalamus, particularly touch, pressure, and position sensation.

Focal Symptoms and Signs of Parietal Lobe Tumors

A tumor that destroys the postcentral gyrus causes loss of several somatosensory or cortical sensory functions, including touch, pressure, and position sensation on the opposite side of the body, while pain sensation is retained. Joint position sense, vibration sense, tactile localization, light touch, two-point discrimination, and stereognosis are impaired.⁽⁸⁾ Common sensory deficits include the following:

1. ASTEREOGNOSIS

Astereognosis, or tactile agnosia, is the most common cortical sensory deficit. It occurs opposite the tumor. The patient cannot identify a familiar, frequently used object by touch. For example, with the eyes closed, a key placed in the affected hand cannot be recognized as a key, even though tactile and pressure-touch perception remain intact, because the patient does not recognize the object’s size, weight, shape, and composition.

2. IMPAIRED TWO-POINT DISCRIMINATION

The patient cannot distinguish two simultaneous stimuli. This indicates combined impairment of touch and pressure sensation and occurs on the side opposite the lesion.

3. SENSORY INATTENTION

This is another important finding in a patient with a tumor or other parietal lobe lesion. When corresponding sites on both sides are stimulated simultaneously, the patient does not perceive the stimulus opposite the lesion. For example, a patient with right-sided sensory inattention does not perceive right-palm stimulation when both palms are stimulated together, but perceives stimulation on either side when they are tested separately.

4. SENSORY EPILEPSY

The attack begins with a sensation that is difficult to describe and may take various forms, such as numbness, tingling, an electric-shock-like sensation, or paresthesia. It begins in one body part and spreads to others, a pattern called a sensory Jacksonian fit. For example, numbness may begin in the right hand and subsequently involve the arm and right side of the face. Sensory epilepsy may remain localized and then cease, or spread to the motor area and produce jerking. The motor seizure may be focal or generalized, with loss of consciousness (generalized convulsion). The sensory symptoms may sometimes be interpreted as the aura of motor epilepsy. As with motor epilepsy, the site of onset of sensory symptoms helps locate the tumor in the postcentral gyrus. Deep parietal lobe tumors seldom cause seizures.

5. PSEUDO-ATHETOSIS

A tumor or other lesion in the postcentral gyrus causes hypotonia and wasting of the muscles of the affected body part, with ataxia both at rest and during movement. Involuntary limb movements may occur at rest, termed pseudo-athetosis. Ataxia is evident on finger-nose testing and is called sensory ataxia.⁽⁷⁾

6. CONTRALATERAL HOMONYMOUS INFERIOR QUADRANTANOPIA

This occurs when a large posterior parietal tumor extends deeply into the white matter near the lateral wall of the lateral ventricle, compressing or destroying the upper optic radiation and producing this pattern of visual field loss (Figure 5.4). Here the optic radiation passes upward near the posterior limb of the internal capsule; its fibers then spread along the lateral aspect of the lateral ventricle at the beginning of the occipital horn and terminate at the calcarine fissure of the occipital lobe. A visual field defect is an important sign that requires careful examination to detect.

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7. GERSTMANN’S SYNDROME

A tumor or other lesion in the posterior parietal lobe, at the angular gyrus of the dominant hemisphere, produces finger agnosia (inability to identify the fingers), dysgraphia (inability to write), dyscalculia (inability to calculate), and right-left disorientation.^(6,8) Of these manifestations, finger agnosia is the most important.

8. SENSORY APHASIA OR DYSPHASIA

This results from a tumor in the posteroinferior parietal lobe corresponding to Wernicke’s center in the dominant hemisphere. The patient has impaired comprehension of spoken language (dysphasia), written language (dysgraphia), and meaning, as well as impaired reading (dyslexia) and calculation (dyscalculia). As the tumor enlarges, the deficits become more severe, producing global dysphasia: speech becomes meaningless and incomprehensible, and verbal communication is impossible.

9. AGNOSIA AND APRAXIA

These occur with tumors in the posterior parietal lobe near the temporal and occipital lobes. Agnosia is the inability to understand the meaning of, or recognize, objects presented visually or by touch because of a receptive defect. Apraxia is the inability to perform a desired action, such as unfastening a pin, despite understanding the task and having no motor paralysis, sensory loss, or ataxia of the arm or hand.

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OCCIPITAL LOBE

The occipital lobe is the most posterior part of the cerebral hemisphere, lying behind the parieto-occipital fissure. Anteriorly it adjoins the parietal and temporal lobes. On its medial surface, the calcarine fissure runs from front to back. The portion above the fissure is the cuneus, and that below it is the lingual gyrus. The optic radiation from the lateral geniculate body terminates in the primary visual cortex (the striate area or Brodmann area 17) (Figure 5.5), which lies on both sides of the calcarine fissure and extends onto the lateral aspect of the occipital pole. Fibers carrying impulses from each half-retina divide into two groups: those from its lower half terminate below the calcarine fissure, and those from its upper half terminate above it. Macular fibers terminate in the most posterior part of the calcarine fissure bilaterally (bilateral representation), accounting clinically for macular sparing with a unilateral lesion. A distinctive feature of the visual cortex on a transverse section through the occipital lobe is a white band of fibers, the stripe of Gennari, comprising optic radiation fibers and secondary association fibers.⁽⁹⁾ The visual cortex is concerned only with the reception of visual information, not its interpretation.

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Beyond the visual cortex lie the visual association areas (Brodmann areas 18 and 19) (Figure 5.5). Area 18 connects with areas 17 and 19 and interprets impulses received from area 17. Its important function is to recognize and distinguish the objects seen. Area 18 also exchanges fibers with the prefrontal, sensory, motor, and auditory association areas. Of particular importance are fibers forming the superior longitudinal and inferior fronto-occipital bundles to the frontal lobe, providing the pathway for voluntary conjugate eye deviation in response to visual stimulation (Figure 5.40). Area 18 also sends internal corticotectal or corticomesencephalic fibers to the superior colliculi, providing a pathway for vertical eye movements.⁽⁹⁾ Area 19, the peristriate area, extends from area 18 to the boundary of the occipital lobe and connects with areas 17 and 18 and other cortical regions. It serves as the visual psychic area, with complex functions involving visual recognition and perception. Together with area 18, it is also a cortical center for eye movements and the optic fixation reflex in response to vision.

Focal Symptoms and Signs of Occipital Lobe Tumors

Tumors are uncommon in the occipital lobe. It is considered a silent area because symptoms usually do not appear early, but only after the tumor has become very large. The large size produces raised intracranial pressure, with headache, papilledema, and vomiting; papilledema is common. Focal manifestations may result either from destruction or from irritation (epilepsy), as follows:

1. CONTRALATERAL HOMONYMOUS HEMIANOPIA

The patient cannot see the same half of the visual field of each eye (Figure 5.6) because of destruction of the optic radiation or the region of the calcarine fissure. Homonymous hemianopia may be complete or incomplete, depending on the tumor’s position and size. Compression of the upper or lower part of the calcarine fissure produces homonymous inferior or superior quadrantanopia, respectively. Such tumors are small and are often falx meningiomas compressing the calcarine fissure. Intrinsic tumors, such as an occipital glioblastoma, usually cause complete homonymous hemianopia because they destroy the entire optic radiation as it approaches the calcarine fissure. A tumor at the occipital pole destroys fibers from the retinal macula, producing a hemianopic scotoma.

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1. Optic nerve = ipsilateral amaurosis
2. Chiasm = bitemporal hemianopsia
3. Optic nerve-chiasm junction = ipsilateral amaurosis and contralateral temporal hemianopsia
4. Optic tract = contralateral incongruous homonymous hemianopsia
5. Anterior (Meyer’s) loop of the optic radiation in the temporal lobe = incongruous contralateral homonymous superior quadrantanopsia
6. Optic radiation in the parietal lobe = incongruous contralateral homonymous inferior quadrantanopsia
7. Optic radiation in the anterior occipital lobe = contralateral homonymous hemianopsia
8. Occipital pole = contralateral congruous homonymous hemianoptic central scotoma
9. Occipital horn. intraventricular tumor extending into the ventricular wall = contralateral homonymous hemianopsia

Homonymous hemianopia is an important manifestation of an occipital lobe tumor, but some patients are unaware that vision on one side is lost. Others give a suggestive history, such as repeatedly walking into a door frame. One of the author’s patients reported grazing a three-wheeled vehicle while cycling three times in four months, always on the patient’s right side. When reading, some patients see only half a word or sentence; when writing, they continue to the far right edge of the page, a manifestation of right hemianopia.

2. CORTICAL BLINDNESS

This is blindness caused by a tumor destroying both occipital lobes at the calcarine fissures. It may occur with a large falx meningioma extending to both sides and compressing the calcarine fissures. Cortical blindness is complete bilateral blindness with preserved pupillary light responses.⁽¹⁰⁾ Convergence when viewing a near object and ocular movements remain normal.

3. SEIZURES

Seizures from an occipital lobe tumor take the form of unformed visual experiences or sudden visual hallucinations, such as flashing lights. These differ from hallucinations due to temporal lobe tumors, which are formed images. Visual hallucinations may be accompanied by eye deviation to the opposite side and are an important localizing manifestation of an occipital lobe tumor.

4. VISUAL AGNOSIA, ALEXIA, AGRAPHIA

A large occipital lobe tumor extending into the peristriate area (area 19) or the parietotemporal region of the dominant hemisphere causes alexia (word blindness), or visual receptive aphasia. Despite intact vision, the patient cannot understand the meaning or significance of written words. Some degree of agraphia, the inability to express thoughts in writing, is also usually present.⁽¹²⁾ These manifestations also occur with parietal or temporal lobe tumors, so they alone cannot readily distinguish an occipital tumor from a parietotemporal tumor.

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TEMPORAL LOBE

The temporal lobe lies below the Sylvian fissure and rests in the middle cranial fossa. Laterally, the superior, middle, and inferior sulci divide it into the superior, middle, and inferior gyri, respectively. The inferior temporal gyrus lies on the undersurface and is therefore not visible. The superior temporal gyrus forms the operculum of the insula (island of Reil). On the upper surface of its posterior portion is the transverse or Heschl’s gyrus, which serves as the auditory receptive center⁽¹⁵⁾ (Figure 5.1). This center receives the auditory radiation from the medial geniculate body and auditory fibers from both sides (bilateral representation) (Figure 5.7). Destruction of the center on one side therefore does not cause deafness, but impairs sound localization. Bilateral destruction causes deafness. This center connects with other cerebral centers concerned with speech, memory, eye movements, body movements, and so forth. For example, a loud sound causes the eyes and face to turn toward its source.

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The posterior third of the superior temporal gyrus in the dominant hemisphere is Wernicke’s area (the perceptive speech center) (Figure 5.1). It is concerned with perceiving speech, recognizing words, and understanding and interpreting spoken language. The posterior portions of the middle and inferior temporal convolutions connect with the opposite cerebellum through the temporopontocerebellar pathway. Destruction of this region or pathway produces contralateral ataxia.

The optic radiation passes through the temporal lobe to the occipital lobe (Figures 5.4 and 5.6). On leaving the lateral geniculate body, its fibers run closely together behind the sensory fibers of the internal capsule, forming the optic peduncle, before spreading out. Fibers from the upper retinal quadrant pass upward into the white matter of the parieto-occipital lobe and terminate above the calcarine fissure. Fibers from the lower retinal quadrant pass downward into the temporal lobe and loop anteriorly around the temporal horn of the lateral ventricle, forming Meyer’s temporal loop. They then run posteriorly along the lateral side of the temporal horn, pass the occipital horn, and terminate below the calcarine fissure (Figure 5.8). Destruction of the optic radiation in the temporal lobe produces contralateral homonymous superior quadrantanopia. Irritation produces visual hallucinations with more clearly formed images than those arising from the occipital lobe.

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Inferomedially, the temporal lobe contains the parahippocampal gyrus, uncus, and amygdala, which projects into the anterior temporal horn. These structures are concerned with learning, recent memory, smell, taste, emotion, and sexual feeling.

Focal Symptoms and Signs of Temporal Lobe Tumors

Patients with temporal lobe tumors usually present when the tumor is large because changes in this region produce few conspicuous signs, particularly in the anterior temporal lobe and the nondominant hemisphere. A tumor in the dominant hemisphere may lead to earlier consultation because speech disturbance often appears first. The focal manifestations are as follows:

1. VISUAL FIELD DEFECT

This is an important manifestation of a temporal lobe tumor. As noted above, fibers from the lower retina loop around the temporal horn as Meyer’s loop. An anterior temporal lobe tumor therefore damages this loop, producing homonymous superior quadrantanopia, a characteristic visual sign of a temporal lobe tumor. As the tumor enlarges posteriorly, it destroys fibers from the upper retina and produces homonymous hemianopia. This is more common than superior quadrantanopia because most patients present with a large tumor. Unlike hemianopia caused by an occipital lobe tumor, the defects in the two eyes differ in a temporal lobe lesion (incongruous homonymous hemianopia). For example, one eye may lose half its field while the other loses only a quadrant. An occipital lobe tumor, by contrast, usually causes complete homonymous hemianopia⁽¹³⁾ (Figure 5.6).

2. DYSPHASIA, APHASIA

A tumor in the posterior temporal lobe of the dominant hemisphere, at or near Wernicke’s center, causes sensory dysphasia or aphasia: the patient cannot understand spoken language. An anterior tumor near Broca’s area causes motor dysphasia. A very large tumor may cause global aphasia.

3. UNCINATE FITS AND TEMPORAL LOBE EPILEPSY

A tumor in the medial temporal lobe, at the uncus and parahippocampal gyrus, which are concerned with smell and taste, produces the syndrome called uncinate fits. An attack begins with an unusual smell or taste, usually unpleasant, followed by tasting movements and lip licking. At the same time, the patient stares blankly and appears disconnected from the surroundings. Afterward, the patient describes a dreamlike experience.⁽¹⁴⁾

Temporal lobe epilepsy, or psychomotor seizure, occurs with a lesion in the medial temporal lobe, involving the uncus, parahippocampal gyrus, amygdala, or their subcortical connections. The patient shows automatisms: unusual movements with an appearance of partial awareness. Some patients abruptly stop their current activity and stare in bewilderment, without jerking or collapsing unconscious. Others may walk a considerable distance without remembering where they went or what they did (amnesia). Some experience illusions or hallucinations involving hearing, smell, or taste, sometimes with chewing or swallowing movements. Some describe a dreamlike state with the feeling that they have seen or experienced the present situation before, termed déjà vu. After a psychomotor seizure, confusion may persist for a time, and some patients fall asleep.⁽¹⁾

4. MEMORY IMPAIRMENT

A deep medial temporal lobe tumor destroys the hippocampus or its connections, impairing recent memory. With progression, the manifestations may resemble dementia.

5. HALLUCINATIONS

Both visual and auditory hallucinations may occur. Visual hallucinations are relatively clearly formed images, unlike the unformed hallucinations of an occipital lobe tumor, such as flashing lights. With auditory hallucinations, the patient reports a sound in the ear, such as ringing resembling a bell or a whistle.

6. HEMIPARESIS

A large medial temporal lobe tumor displaces the corticospinal tract fibers supplying the opposite facial muscles, which lie laterally, producing contralateral weakness. Compression extending to the internal capsule may cause contralateral hemiparesis (Figure 5.9). A large tumor may also displace the brain stem to the opposite side, pressing the contralateral cerebral peduncle against the edge of the tentorium cerebelli. Hemiparesis may therefore occur on the same side as the tumor. The combination of homonymous hemianopia and hemiparesis is very important in localizing a temporal lobe tumor (Figure 5.10).

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7. TRIGEMINAL & OCULOMOTOR NERVE PALSY

The Gasserian ganglion of the trigeminal nerve lies medially in the middle cranial fossa and may be compressed by the tumor, causing ipsilateral facial numbness and loss of the corneal reflex. A tumor may also descend past the tentorial edge and compress the oculomotor nerve adjacent to the uncus, causing ptosis and a dilated pupil unresponsive to light on the same side as the tumor.

8. UNILATERAL EXOPHTHALMOS

This occurs with tumors anterior to the temporal lobe, such as meningiomas of the lesser wing of the sphenoid. They may impair venous drainage from the eye, cause reactive thickening of the orbital wall and narrowing of the orbit, or extend into the orbit. These changes cause proptosis. A more lateral meningioma in this region may cause thickening of the temporal bone, making that temple appear fuller than the opposite one (Figure 6.17).

9. ATAXIA

This is uncommon. It resembles frontal ataxia, with swaying or falling toward the side opposite the tumor. It occurs with tumors in the posterior portions of the middle and inferior temporal gyri that destroy the temporopontocerebellar pathway.^(5,16)

Original pages 275–280

THALAMUS AND BASAL GANGLIA

The thalamus is an ovoid nuclear mass near the midline of the brain, at the upper end of the cerebral peduncle. Its anterior medial surface forms the wall of the third ventricle. Its enlarged posterior portion, the pulvinar, lies close to the quadrigeminal plate, pineal gland, and medial and lateral geniculate bodies and serves as a visual association area of the cortex. Together with the caudate nucleus, its superior surface forms the floor of the lateral ventricle. Laterally it adjoins the internal capsule, containing the corticospinal tract connecting the cerebral motor area with lower levels of the central nervous system. Inferiorly, the thalamus rests on the subthalamus and mesencephalic tegmentum. Here fibers ascending from lower levels of the central nervous system enter the thalamus: the spinothalamic tract (pain and temperature), medial lemniscus (touch, vibration, and proprioception), and brachium conjunctivum from the cerebellum.

The thalamic nuclei are divided into midline, anterior, medial, lateral, and posterior groups. The lateral nuclei are further divided into a large ventral and a smaller dorsal group. An important nucleus in the posterior ventral group is the nucleus ventralis posterior, where sensory pathways terminate. The secondary trigeminal sensory pathway carries facial sensation to the nucleus ventralis posteromedialis, while spinothalamic and medial lemniscal fibers terminate in the nucleus ventralis posterolateralis. Cells in these two nuclei send fibers to the postcentral gyrus.⁽¹⁷⁾ A lesion of the lateral thalamic nucleus causes contralateral sensory loss. In some patients, intractable pain also occurs in the affected body parts, termed thalamic syndrome. Even a slight stimulus in the region of sensory loss produces severe pain, often with an emotional response. This phenomenon is not yet satisfactorily explained.⁽¹⁷⁾

The internal capsule is another clinically important structure. It consists of fibers entering and leaving the cerebral cortex, with the thalamus and caudate nucleus medially and the lenticular nucleus (globus pallidus and putamen) laterally. Most of the internal capsule consists of the thalamic radiation, fibers passing from the thalamus to the cerebral cortex.⁽¹⁸⁾ The remainder consists of efferent cortical fibers descending to the brain stem and spinal cord: the corticospinal, corticobulbar, and corticopontine tracts, together with small groups of fibers to the hypothalamus, substantia nigra, and red nucleus. Below the thalamic level, the internal capsule becomes the crus cerebri or cerebral peduncle of the midbrain.

On horizontal section (Figure 5.11), the internal capsule has anterior and posterior limbs meeting at an angle at the genu. The anterior limb contains the anterior thalamic radiation and prefrontal corticopontine tract. The genu contains corticobulbar and corticoreticular fibers. The posterior limb contains the corticospinal tract, frontopontine fibers, and superior thalamic radiation carrying somatic sensation to the postcentral gyrus. The superior thalamic radiation lies posterior to the corticospinal tract.⁽¹⁸⁾

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In this region, the geniculocalcarine tract leaves the lateral geniculate body, passes posteriorly and inferior to the internal capsule, and spreads out as the optic radiation to the calcarine (striate) cortex, area 17, of the occipital lobe. The medial geniculate body gives rise to the auditory radiation, which runs near the geniculocalcarine tract behind the internal capsule to the temporal auditory cortex. These two groups of fibers are important in localizing lesions, as discussed below.

The BASAL GANGLIA comprise gray matter in the caudate nucleus, lenticular nucleus (globus pallidus and putamen), amygdaloid nuclei, and claustrum. The lenticular nucleus is separated from the caudate nucleus by the anterior limb of the internal capsule and from the thalamus by the posterior limb. The basal ganglia connect with many other structures and perform several functions, summarized as follows:⁽¹⁹⁾

i) They are important in voluntary movement. Together with the precentral motor cortex, the basal ganglia can produce useful muscular activity even when the corticospinal fibers from this cortex are lost.

ii) They participate in many automatic and associated movements.

iii) They inhibit postural reflexes, as demonstrated by the muscular rigidity produced by basal ganglia lesions.

iv) They inhibit motor centers. Destruction of the basal ganglia produces abnormal involuntary movements: choreoathetosis with damage to the caudate nucleus and putamen; intention tremor with damage to the dentorubrothalamic pathway; resting tremor with damage to the globus pallidus and substantia nigra; and hemiballismus with damage to the subthalamic nucleus of Luys.

Focal Symptoms and Signs of Tumors of the Thalamus and Basal Ganglia

Because the thalamus and basal ganglia lie very close together, lesions in these regions produce similar manifestations and are discussed together. Tumors are uncommon here, but symptoms often appear relatively early because of the proximity of motor structures (the corticospinal tract) and sensory pathways (Figure 5.12). A tumor arising in one of these regions may extend into the other.

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1. Thalamus
2. Internal capsule
3. Superior colliculus
4. Medial geniculate body
5. Lateral geniculate body
6. Optic radiation
7. Auditory radiation

The manifestations of tumors in this region are as follows:

1. HEMIHYPESTHESIA OR HEMIANESTHESIA

There is numbness on the side opposite the tumor, with impairment of all sensory modalities, due to destruction of thalamic nuclei and all types of sensory fibers entering the thalamus. With a tumor originating in the thalamus, sensory symptoms precede weakness. With a basal ganglia tumor, hemiplegia usually precedes numbness because the sensory fibers lie posterior to the basal ganglia. The author has not encountered thalamic syndrome caused by a tumor.

2. HEMIPLEGIA

This is common in tumors of the thalamus and basal ganglia and usually appears early. Because of its proximity, the corticospinal tract in the internal capsule is destroyed relatively early. A basal ganglia tumor usually presents first with hemiplegia, which is spastic.

3. HOMONYMOUS HEMIANOPIA

This occurs when the tumor compresses the lateral geniculate body or the optic radiation passing below and behind the thalamus and internal capsule.

4. UPWARD CONJUGATE GAZE PALSY AND ANISOCORIA

The tumor grows to compress the upper midbrain, including the quadrigeminal plate (superior and inferior colliculi) and pretectal area. As the superior colliculus is the upward gaze center, the patient cannot look upward. The pretectal area is where pupillary fibers from the optic nerve synapse; compression causes unequal pupils with poor light responses.

5. ATAXIA

Contralateral incoordination may result from destruction of the nucleus ventralis lateralis, where fibers from the cerebellum through the brachium conjunctivum (superior cerebellar peduncle) terminate, together with loss of proprioceptive sensation in the thalamus. This ataxia is uncommon and usually appears late in the disease.

Tremor and abnormal involuntary movements, such as choreoathetosis or hemiballismus, are very rarely caused by a tumor.

6. MENTAL SYMPTOMS

Although not specific to this region, mental symptoms may occur with a thalamic tumor. Destruction of the thalamus and subthalamus produces drowsiness, excessive sleep, mental dullness, and memory impairment.⁽⁷⁾ These may also reflect associated raised intracranial pressure. Because the thalamus lies next to the third ventricle, a tumor here may obstruct cerebrospinal fluid circulation relatively early.

Original pages 280–283

CORPUS CALLOSUM

The corpus callosum is the largest commissural fiber bundle connecting different regions of the two cerebral hemispheres. It has four parts: the rostrum, genu, body, and splenium (Figure 5.13). It forms the roof of the anterior horn and body of the lateral ventricle. Fibers passing anteriorly through the genu to the two frontal poles are called the anterior forceps; those passing through the splenium to the two occipital lobes are the posterior forceps. Other fibers passing through the body connect cortical centers in the frontal, parietal, and temporal lobes (Figure 5.14). The corpus callosum enables functional communication between the hemispheres, allowing the various cortical centers to function fully. Its destruction causes different disconnection syndromes according to the part damaged.⁽²⁰⁾ If the splenium is destroyed, for example, only visual communication is lost. A clear example is occlusion of the left posterior cerebral artery, causing infarction of the occipital lobe and splenium. The patient has right homonymous hemianopia and cannot read. Because the left occipital lobe is damaged, the speech center must receive visual information from the right occipital lobe, but this information cannot reach the left angular gyrus. Destruction of the corpus callosum anterior to the splenium, as with anterior cerebral artery occlusion, disconnects tactile perception and language between the hemispheres. With the eyes closed, the patient cannot compare objects held in the two hands. On verbal command, the right hand performs a task correctly but the left hand cannot. For example, writing to dictation with the left hand produces unformed, illegible writing, while the right hand writes normally.⁽²⁰⁾

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Along the midline, the cingulate gyrus and anterior cerebral arteries lie above the corpus callosum throughout its length. Below it, the septum pellucidum adjoins the corpus callosum at the level of the anterior horn of the lateral ventricle, and the fornix lies below its body.

Several important structures lie below the splenium: the internal cerebral vein, great vein of Galen, pineal gland, quadrigeminal plate, and midbrain aqueduct of Sylvius. These structures account for the syndromes discussed below.

Symptoms and Signs of Corpus Callosum Tumors

Tumors in this region are very uncommon, and clearly defined focal manifestations are difficult to identify. They usually present with dysfunction of neighboring brain invaded by the tumor, or arise in nearby brain and extend into the corpus callosum and then the opposite hemisphere. Thus, manifestations of a corpus callosum tumor are essentially those of dysfunction in neighboring brain and depend on the adjacent hemispheric region. A tumor of the body produces weakness and numbness of both legs because the leg motor cortex lies medially in the frontal lobe. A tumor of the splenium (Figure 5.15) compresses the quadrigeminal plate, pretectal area, and aqueduct of Sylvius, producing manifestations resembling a pineal tumor or Parinaud’s phenomenon. The patient cannot look upward (upward conjugate gaze palsy) because the upward gaze center in the superior colliculus is impaired. Both pupils are dilated and respond poorly to light. Raised intracranial pressure also develops early because the aqueduct is compressed. A tumor of the genu or rostrum may extend into both frontal lobes, producing the previously described manifestations of a prefrontal tumor: personality change and progressive dementia. A corpus callosum tumor should therefore always be considered when dementia is prominent.

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Original pages 283–284

LATERAL VENTRICLE

Lateral ventricular tumors are uncommon. Symptoms and signs generally do not appear until the tumor is very large, because the ventricle is a cerebrospinal fluid-filled cavity in which a tumor can grow without compressing brain tissue or producing a focal deficit. The lateral ventricle is therefore another silent area. When the tumor becomes large, the conspicuous symptoms are those of raised intracranial pressure—headache, blurred vision, and vomiting—which bring the patient to medical attention. In cases where the tumor obstructs cerebrospinal fluid circulation or produces cerebrospinal fluid, as with a choroid plexus papilloma, presentation with raised intracranial pressure occurs relatively early. Some patients have intermittent severe headaches due to a ball-valve action of the tumor. In certain head positions, the tumor blocks cerebrospinal fluid flow, greatly increasing intracranial pressure and causing severe headache. In another position, the tumor may move and allow fluid to pass, relieving the raised pressure and headache; the symptoms may recur. This pattern is important in diagnosing an intraventricular tumor. If the tumor causes hydrocephalus and enlargement of the lateral ventricles, the patient may also present with bilateral leg weakness because corticospinal fibers from the leg motor cortex run close to the lateral ventricular wall and are compressed (Figure 5.20).

A tumor arising from the lateral ventricular wall may grow into the ventricle and also extend into adjacent brain tissue, causing focal deficits determined by its location. A tumor in the body of the lateral ventricle may cause contralateral hemiparesis and hemihypesthesia by compressing the corticospinal and sensory tracts. A tumor in the occipital horn may cause homonymous hemianopia by destroying the optic radiation, which runs close to the wall of the lateral ventricular occipital horn.

Original pages 284–292

HYPOTHALAMUS

The hypothalamus lies in the wall of the third ventricle below the hypothalamic sulcus. Its anteroinferior aspect adjoins the optic chiasm and optic tract. Behind the optic chiasm, the infundibulum on the inferior surface of the hypothalamus extends downward to join the hypophysis as the pituitary stalk (Figure 5.16). The portion forming the floor of the third ventricle is called the median eminence and is divided into two parts. The portion anterior to the infundibulum is the anterior median eminence, and the portion posterior to it is the posterior median eminence. The median eminence is the final important part of the hypothalamus that converts the pathway of the central venous system into the peripheral endocrine system. The arterial capillaries of the hypophyseal portal vessels, beginning at the median eminence, collect blood from this area containing both releasing and inhibitory hormones from the hypothalamus and convey it to the target cells of the anterior pituitary gland.⁽²¹⁾

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Within the hypothalamus, groups of cells form several hypothalamic nuclei. The supraoptic region contains the paraventricular, supraoptic, anterior hypothalamic, and suprachiasmatic nuclei. The paraventricular and supraoptic nuclei are readily distinguishable; both send fibers to the posterior lobe of the hypophysis. The tuberal region also contains several nuclei: the ventromedial, dorsomedial, arcuate, posterior hypothalamic, and mamilloinfundibular nuclei.

The hypothalamus exerts most of its influence on the pituitary gland through the supraopticohypophyseal and tuberohypophyseal tracts. The supraopticohypophyseal tract consists of fibers from the supraoptic and paraventricular nuclei passing to the posterior lobe of the pituitary gland, where oxytocin and antidiuretic hormone are released. This region is important because it is concerned with the body’s fluid balance. Its destruction causes diabetes insipidus; therefore, great care must be taken to avoid damaging it during surgery for tumors in this region. The tuberohypophyseal tract begins in the tuberal area and passes to the median eminence and infundibular system. Together with the hypophyseal portal system, it links the nervous and hormonal systems, connecting the hypothalamus with the anterior pituitary gland. Destruction of the tuberal area causes abnormalities of carbohydrate and fat metabolism, resulting in hyperglycemia and adiposogenital syndrome.⁽²²⁾

Lesions destroying the anterior hypothalamic nuclei cause hyperthermia accompanied by sweating, vasodilatation, and rapid, deep breathing—mechanisms that lower body temperature—as well as emaciation. Lesions destroying the posterior hypothalamic nuclei cause hypothermia accompanied by mechanisms attempting to conserve body temperature, including vasoconstriction and shivering to generate heat. Abnormalities of the posterior hypothalamic nuclei also cause excessive sleep (hypersomnia).

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The medial hypothalamus controls satiety, whereas the lateral hypothalamus controls the desire to eat. Abnormalities of the medial hypothalamus cause marked obesity, while abnormalities of the lateral hypothalamus cause loss of appetite.

Although the hypothalamus is very small compared with other parts of the brain, its functions are essential to survival. It continually regulates and adjusts the body’s internal balance in response to changes both inside and outside the body through three important systems:⁽²³⁾

1. The endocrine system. The hypothalamus directly controls the pituitary gland and indirectly controls the body’s other endocrine glands. It secretes various releasing hormones (factors) that stimulate the pituitary gland to release the corresponding hormones, or secretes inhibitory hormones (factors) to suppress excessive production of pituitary hormones. In this way, it maintains the hormonal balance required for normal life. The hypothalamus thus plays an important role in controlling all the endocrine glands, including the pituitary, thyroid, pancreas, adrenal glands, and gonads.

2. The autonomic nervous system (ANS). The hypothalamus keeps the functions of all the body’s visceral organs within normal limits through reflexes passing to parasympathetic and sympathetic cells in the brainstem and at various levels of the spinal cord. It therefore regulates the cardiovascular, respiratory, and gastrointestinal systems, body temperature, sweat glands, sexual organs, and other functions.

The anterior and medial hypothalamic nuclei, together with the tuber cinereum, control parasympathetic activity. The posterior and lateral hypothalamic nuclei are concerned with sympathetic activity.⁽²⁴⁾

3. The limbic system. This system is important in emotion, protective responses, and memory, through connections with the hippocampus, uncus, anteromedial thalamus, and amygdala.

The hypothalamus also communicates with the tegmentum of the midbrain, an important region concerned with consciousness.

The hypothalamus therefore controls the anterior and posterior pituitary glands, body temperature, water balance, food intake, consciousness, sleep, emotion, behavior, and the autonomic nervous system. Abnormalities or tumors of the hypothalamus may produce the following manifestations:⁽²⁵⁾

A. Hormonal abnormalities

1. Manifestations involving anterior pituitary hormones

2. Manifestations involving the neurohypophysis

2.1 Diabetes insipidus

B. Nonhormonal abnormalities

1. Abnormalities of body temperature regulation

1.1 Hypothermia

1.2 Hyperthermia

1.3 Body temperature varying with the external temperature (poikilothermia)

2. Abnormalities of food intake

2.1 Reduced or absent appetite (anorexia)

2.2 Reduced food intake (hypophagia)

2.3 Absence of food intake (aphagia)

3. Abnormalities of drinking

3.1 Persistent excessive drinking

3.2 No drinking or reduced drinking

3.3 Essential hypernatremia

4. Abnormalities of sleep and consciousness

4.1 Excessive sleepiness (hypersomnia)

4.2 Insomnia

4.3 Absence of movement and speech (akinetic mutism)

4.4 Unconsciousness (coma)

5. Autonomic nervous system abnormalities

5.1 Pulmonary edema

5.2 Cardiac arrhythmia

5.3 Gastrointestinal disturbance

5.4 Sphincter disturbance

6. Abnormalities of caloric balance

6.1 Obesity

6.2 Emaciation

7. Emotional abnormalities

7.1 Anger

7.2 Fear

7.3 Emotional indifference or listlessness (apathy)

8. Sexual abnormalities

8.1 Hypogonadotropic hypogonadism

8.2 Precocious puberty

9. Memory impairment

Symptoms and signs of hypothalamic tumors

As described above, the hypothalamus is very small and contains many closely adjacent groups of nuclei with different functions. It is therefore difficult to identify the precise point at which a tumor originated. Most patients seek medical attention only after the tumor has become large. The findings then represent a combination of hormonal abnormalities, metabolic abnormalities, and loss of function of neural structures neighboring the hypothalamus, including the optic nerves and chiasm, other cranial nerves, cerebral peduncle, pituitary gland, and cerebrospinal fluid pathways. The manifestations vary according to the tumor’s location within the hypothalamus and the patient’s age.

With respect to age, experience has shown different manifestations in younger and older children even when tumors occupy the same location. For example, an anterior hypothalamic tumor may cause emaciation in a young child but abnormal obesity in an older child. This difference remains unexplained.

Anterior hypothalamic tumors cause failure to thrive or the diencephalic syndrome^(26,27) in young children. The patient is emaciated (Figure 5.18), has no subcutaneous fat, and fails to gain weight despite eating well. Some have nausea and vomiting. The child is usually alert and cheerful despite a sickly appearance. These manifestations are generally absent in older children, for reasons that remain unexplained. Visual abnormalities are common, with optic atrophy resulting from compression of the nearby optic chiasm. Impaired vision produces searching nystagmus as the patient moves the eyes in an attempt to find an object to look at. In older children, tumors in this region commonly cause obesity together with diabetes insipidus and visual field defects. Excessive urination and impaired thirst mechanisms may cause dehydration, serum hyperosmolarity, and hypernatremia.⁽²⁸⁾ Some patients also have persistently elevated body temperature.

Tumors in the posterior hypothalamic region, including the tuber cinereum and median eminence, produce precocious puberty (Figure 5.19). The child’s body and bones grow rapidly, the penis becomes adult-sized, pubic hair appears, and both testes enlarge. These changes occur because the tumor destroys the part of the hypothalamus that suppresses secretion of gonadotropic substance,⁽²⁹⁾ resulting in excessive gonadotropin secretion. Upward extension of the tumor causes excessive sleeping or, in some cases, impaired consciousness.

Some hypothalamic tumors also produce several of the other abnormalities described above. Downward extension into the interpeduncular fossa may impair the oculomotor and abducens nerves and produce corticospinal tract signs. Some patients develop raised intracranial pressure because the tumor obstructs cerebrospinal fluid pathways in the third ventricle and foramen of Monro.

In summary, a hypothalamic tumor should be suspected in patients with diencephalic syndrome or precocious puberty accompanied by visual field defects and optic atrophy. Radiological investigation with CT or MRI should be undertaken.

Original pages 292–295

THIRD VENTRICLE

The third ventricle lies in the midline of the brain (Figures 5.16 and 5.17). The anterior portions of its lateral walls are formed by the hypothalamus and the posterior portions by the thalamus. Its anterior boundary consists of the lamina terminalis and anterior commissure. Inferiorly, the pituitary stalk connects the base of the third ventricle with the pituitary gland, with the optic chiasm anterior to the stalk. Behind the third ventricle lie the midbrain and the pineal gland, which rests above the superior colliculus. Above the third ventricle are the tela choroidea, fornix, and internal cerebral veins. The third ventricle communicates with both lateral ventricles through the foramina of Monro. Cerebrospinal fluid leaves it through the aqueduct of Sylvius, beneath the quadrigeminal plate of the midbrain. The third ventricle is an important region because it is surrounded by vital structures, including the hypothalamus, pituitary gland, optic chiasm and other cranial nerves, and cerebral blood vessels. It is also small and deeply situated, making surgical access to tumors difficult. As in other ventricles, tumors in this region may arise within the ventricular cavity itself (intraventricular), or arise in the ventricular wall or neighboring region and grow into the third ventricle (paraventricular). The latter produce manifestations attributable to those structures and will not be discussed here; only tumors within the ventricle are considered.

Localizing manifestations of third ventricular tumors

Tumors in this region do not produce specific localizing symptoms. Most manifestations result from raised intracranial pressure. Tumors in the anterior third ventricle commonly obstruct CSF flow at the foramen of Monro, causing obstructive hydrocephalus. Patients have severe headache, vomiting, blurred vision, and papilledema. A colloid cyst originating near the foramen of Monro often produces a distinctive presentation: intermittent severe headache, vomiting, weakness of both legs, inability to stand, and possible collapse to the ground. Some patients become drowsy or unconscious. When the head assumes another position, however, the symptoms disappear immediately. This is explained by the cyst obstructing CSF flow in one position, causing acute obstructive hydrocephalus. A change in head position displaces the cyst, opening the foramen of Monro and allowing CSF to pass; the headache and other symptoms then disappear. Some patients develop dementia, possibly from compression and destruction of the fornix, septum pellucidum, hypothalamus, and memory pathways, or from raised intracranial pressure. Some also present with weakness of both legs because the enlarged lateral ventricles compress the corticospinal tract fibers to the legs, which lie close to their lateral walls (Figure 5.20).

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Large tumors in the anterior third ventricle (Figure 5.21) compress the hypothalamus and the base of the third ventricle. Patients develop the manifestations of hypothalamic dysfunction described above, including marked obesity, excessive sleep, drowsiness, diabetes insipidus, failure to thrive, and autonomic and endocrine abnormalities. Large tumors extending downward compress the optic chiasm and cause visual field defects.

Tumors in the posterior third ventricle (Figure 5.21) compress the quadrigeminal plate and obstruct CSF flow at the aqueduct of Sylvius, producing Parinaud’s phenomenon. The patient cannot look upward; both pupils are dilated, with absent or diminished light reactions. This occurs because the superior collicular region is the center for upward conjugate gaze, while the pretectal area just anterior to the superior colliculus is the center for the pupillary light reflex. Tumor compression impairs these functions. Raised intracranial pressure from obstruction of CSF flow is regularly associated, producing headache, papilledema, and vomiting. At this stage, tumors in this part of the ventricle are difficult to distinguish from tumors of the pineal gland or quadrigeminal plate itself. In some patients, marked enlargement of the third ventricle from aqueductal obstruction impairs hypothalamic function and causes bitemporal hemianopia through compression of the optic chiasm.

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1. An anterior third ventricular tumor causes hypothalamic dysfunction, visual field defects, and hydrocephalus.
2. A posterior third ventricular tumor causes Parinaud’s phenomenon and obstructive hydrocephalus.

Original pages 295–309

PITUITARY GLAND

The pituitary gland lies in the sella turcica and is connected to the hypothalamus above by the pituitary or infundibular stalk. The stalk passes through an opening in the diaphragma sellae, a sheet of dura mater stretched between the clinoid processes that separates the pituitary gland from CSF in the basal cistern. In some individuals, this opening is large enough to allow the suprasellar arachnoid and CSF to protrude into the pituitary fossa, producing the abnormality known as empty sella syndrome.

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The pituitary gland (Figure 5.22) comprises the adenohypophysis and neurohypophysis. The adenohypophysis, or anterior lobe of the pituitary gland, also called the pars distalis, develops from Rathke’s pouch, an upward extension of the primitive stomodeum toward the neural tube. Cells of Rathke’s pouch form the craniopharyngeal duct. At about 12 weeks of gestation, the proximal part of this duct disappears, eliminating its connection with the buccal cavity. Subsequently, the distal portion of the anterior wall of Rathke’s pouch becomes the pars distalis; 90–95% of this portion becomes the adult anterior pituitary gland. The posterior wall becomes the pars intermedia, adjacent to the posterior lobe of the pituitary gland. A group of anterior lobe cells also extends upward in front of the pituitary stalk to form the pars tuberalis.

The neurohypophysis, or posterior lobe of the pituitary gland, develops from the diencephalic portion of the neural tube at the floor of the third ventricle. A pouch grows downward to form the infundibulum. Its upper portion fuses to become the pituitary stalk, while its distal portion enlarges to form the posterior pituitary lobe, or neurohypophysis.

Two principal arteries supply the hypophysis: the superior and inferior hypophyseal arteries. The superior hypophyseal artery arises from the internal carotid artery. After crossing the diaphragma sellae, it passes toward the pituitary stalk and divides into anterior and posterior branches supplying the median eminence and upper infundibulum. A large branch, the trabecular artery, runs along the anterior aspect of the pituitary stalk and enters the pars distalis superiorly. Within the pars distalis, it does not supply the glandular tissue of the anterior lobe but passes through connective-tissue trabeculae to supply the infundibular stem.⁽²⁹⁾ The inferior hypophyseal artery arises from the intracavernous internal carotid artery. On reaching the hypophysis, it divides into medial and lateral branches that join their counterparts on the opposite side to form a ring around the pars nervosa (posterior lobe). It supplies the pars nervosa and infundibulum.

The arteries supplying the median eminence and infundibular stem terminate in capillary tufts. In humans, blood from these capillary plexuses enters larger vessels on the anterosuperior surface of the pituitary stalk and then reaches sinusoids in the pars distalis of the adenohypophysis. The vessels carrying blood from the capillaries of the median eminence and infundibulum to the sinusoids in the pars distalis are collectively called the hypophyseal portal vessels.⁽²⁹⁾

Many important structures surround the sella turcica. A large pituitary tumor may damage them and produce detectable manifestations, so they warrant description here. These structures include the optic nerves, optic chiasm, and hypothalamus above the sella turcica, and the cavernous sinuses, third, fourth, fifth, and sixth cranial nerves, internal carotid arteries, and temporal lobes lateral to the sella (Figure 5.23).

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Optic nerves and optic chiasm. The right and left optic nerves pass through the optic foramina medial to the anterior clinoid processes, run backward, and unite in the midline to form the optic chiasm. The chiasm lies above the pituitary gland and diaphragma sellae, with the pituitary stalk behind it. From the chiasm, the optic tracts pass below and lateral to the cerebral peduncles toward the lateral geniculate bodies. The optic chiasm forms the anteroinferior wall of the third ventricle. Above it lie the lamina terminalis, anterior commissure, and third ventricle; behind it lie the pituitary stalk, tuber cinereum, mammillary bodies, and oculomotor nerves. Because the optic nerves and chiasm are closely related to other structures in this region, most patients with tumors here present with visual abnormalities. Pituitary tumors in particular produce characteristic visual field defects, discussed below.

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Cavernous sinus. The cavernous sinus lies lateral to the sphenoid sinus, sella, and pituitary gland, extending from the superior orbital fissure to the apex of the petrous temporal bone. It communicates with and receives blood from the orbit through the superior and inferior ophthalmic veins, and communicates with the cerebral hemisphere through the sphenoparietal sinus and middle cerebral veins. The two cavernous sinuses communicate through anterior and posterior intercavernous sinuses. Blood drains through the superior petrosal sinus into the transverse sinus, through the inferior petrosal sinus into the jugular bulb, and also through the basilar and pterygoid plexuses.

The lateral wall of the cavernous sinus contains several cranial nerves. From superior to inferior, these are the oculomotor nerve (III), trochlear nerve (IV), and ophthalmic (V₁) and maxillary (V₂) divisions of the trigeminal nerve. Within the trabeculae of the cavernous sinus lies the internal carotid artery, closely accompanied by the abducens nerve (VI), with sympathetic fibers surrounding the artery (Figure 5.24).

The cavernous sinus is important to surgeons operating on the pituitary gland or tumors in this region because its medial wall may tear and bleed. Furthermore, some tumors extend into the cavernous sinus, making surgical removal of that portion impossible.

Internal carotid artery. The artery passes through the foramen lacerum and enters the cavernous sinus, running forward and upward before emerging from its superior aspect near the anterior clinoid process. Immediately after leaving the cavernous sinus, it gives off the ophthalmic artery to supply the optic nerve, retina, and orbital structures. The internal carotid artery lies inferolateral to the optic nerve and chiasm and runs obliquely laterally. At the beginning of the Sylvian fissure, it divides into the anterior and middle cerebral arteries. The middle cerebral artery follows the Sylvian fissure, while the anterior cerebral artery passes medially above the optic nerve and chiasm and joins its counterpart through the anterior communicating artery. As the anterior cerebral artery crosses the optic nerve and chiasm, it gives off small branches supplying their superior surfaces; their inferior surfaces receive blood from the posterior communicating artery. The anterior cerebral artery is therefore closely related to the optic nerve, chiasm, diaphragma sellae, pituitary gland, pituitary stalk, and hypothalamus, and its position changes when tumors arise in these structures.

Temporal lobe. The anterior medial portion of the temporal lobe, called the uncus, lies close to the cavernous sinus and cranial nerves. A sellar tumor may extend to compress this part of the temporal lobe and produce temporal lobe epilepsy.

Frontal lobe. The posterior basal portion of the frontal lobe lies above the anterior cerebral artery, optic nerve, chiasm, and pituitary gland. A sellar or parasellar tumor extending upward may compress the frontal lobe and olfactory nerve, producing frontal lobe manifestations and anosmia (loss of smell). Seizures may occur in some patients.

Symptoms and signs of tumors in the pituitary region

Based on the anatomy described above, the manifestations of tumors in this region may be divided into two groups.

1. General manifestations caused by tumor extension and compression of the brain and cranial nerves in this region (mass effect).
2. Specific manifestations of pituitary tumors consist of various hormonal abnormalities (endocrinopathies) caused by tumors of pituitary cells. Both hyperpituitarism and hypopituitarism may occur.

A. General symptoms and signs

Most manifestations result from tumor compression of structures surrounding the sella: the optic nerve, chiasm, optic tract, hypothalamus, third, fourth, fifth, and sixth cranial nerves, cavernous sinus, pituitary gland, brain tissue, and ventricular system. Not all manifestations of dysfunction in these structures necessarily occur. They depend on the tumor’s size, location, and direction of extension, which determine the structures compressed. Those nearest the tumor lose function first, and other symptoms gradually develop. In the author’s experience, visual abnormalities are the most common presentation of lesions in this region.

1. Visual abnormalities. Pituitary tumors and other tumors, such as craniopharyngiomas, arising in the sella and extending upward compress the optic nerves and chiasm, causing loss of visual acuity and visual fields. Fundoscopy reveals primary optic atrophy, and the visual field defect is bitemporal hemianopia, a localizing manifestation of tumors in this region and an important diagnostic feature. Some patients presenting early have bitemporal superior quadrantanopia; with time, the inferior temporal quadrants are also lost. This results from compression of the fibers crossing at the optic chiasm (Figure 5.6.2). Later, the tumor also destroys the uncrossed fibers, causing loss of the inferior nasal fields followed by the superior nasal fields. Eventually, both eyes become blind. In some patients, the tumor grows toward the junction of one optic nerve with the chiasm and causes a junctional scotoma (Figure 5.6.3), comprising an ipsilateral central scotoma from compression of that optic nerve and contralateral superior temporal quadrantanopia from compression of inferior nasal fibers arriving from the opposite optic nerve.⁽³¹⁾

Many other patterns of visual loss may occur, depending on the part of the visual pathway damaged. Blindness in one eye with temporal hemianopia in the other indicates extension from the chiasm to damage the optic nerve or optic tract on the blind side. The blind eye is always on the side toward which the tumor has extended. This pattern may also occur with extrasellar tumors, such as meningiomas of the tuberculum sellae or medial sphenoidal ridge.

2. Hypothalamic and pituitary dysfunction. Sellar tumors, whether arising within the pituitary gland or from other tissues in the sella, grow to compress the gland, pituitary stalk, and suprasellar hypothalamus, producing various hormonal abnormalities. In addition to controlling both anterior and posterior pituitary lobes, the hypothalamus regulates fluid balance, temperature, emotion, sleep, behavior, consciousness, and autonomic function. Its manifestations have been described in detail in the section on hypothalamic tumors. Destruction of the pituitary gland and stalk produces hypopituitarism of varying severity, depending on how much of the gland is lost and which hormones are deficient. Large nonfunctioning pituitary tumors, whose cells do not secrete hormones, or large intrasellar craniopharyngiomas commonly destroy the functions of the various pituitary cells, causing panhypopituitarism with reduced pituitary trophic hormones, including growth hormone, gonadotropin, TSH, ACTH, and ADH. Patients lose weight and appear pale. Gonadotropic hormone deficiency causes loss of sexual desire. Women have absent milk secretion and menstruation, with uterine and vaginal atrophy. Men develop testicular atrophy and absence of sperm, with absent or diminished erections and loss of axillary and pubic hair. Thyrotropic hormone deficiency causes hypothyroidism resembling myxedema: swollen eyelids, dry wrinkled skin, dry brittle nails and hair, bradycardia, constipation, hoarseness, mental changes, and cold intolerance.

Loss of adrenocortical function causes weakness, a tendency to hypoglycemia, nausea and vomiting, and hypotension. Complete loss of adrenal function produces shock and unconsciousness.

Growth hormone deficiency before puberty causes dwarfism and hypoglycemia.

The manifestations of functioning pituitary tumors are discussed below.

3. Cranial nerve abnormalities. The cranial nerves involved in this region are II, III, IV, VI, and V. Most patients with pituitary tumors have visual abnormalities from compression of the optic nerves and chiasm, which are the principal symptoms prompting medical consultation. Most present before the tumor extends to compress other cranial nerves. Consequently, pituitary tumors only rarely produce dysfunction of cranial nerves III, IV, VI, and V. When a large tumor extends beyond the sella into the parasellar region, it may impair these nerves, producing strabismus, diplopia, pupillary dilatation, ptosis, facial pain, and related manifestations.

4. Obstructive hydrocephalus and raised intracranial pressure. These result from suprasellar tumor extension compressing the hypothalamus and obstructing the foramen of Monro at the third ventricle. Late in the disease, patients develop manifestations of raised intracranial pressure, including headache and vomiting. Blurred vision due to papilledema is absent because tumor compression has already caused primary optic atrophy and visual loss. Eventually, consciousness progressively deteriorates. The obstruction must be relieved by tumor removal or CSF diversion with a shunt.

Headache may result from raised intracranial pressure, compression of pain-sensitive structures in this region, or both. Pituitary tumor patients commonly have retro-orbital pain due to pressure on the diaphragma sellae, which is supplied by the ophthalmic division of the trigeminal nerve.

Vomiting is uncommon with tumors in this region unless hydrocephalus is severe.

5. Compression of surrounding brain tissue. A large tumor may extend to compress the frontal lobe, temporal lobe, or brainstem (Figure 3.116). Frontal extension produces personality changes, memory impairment, and anosmia from olfactory nerve compression. Irritation of either the frontal or temporal lobe may cause seizures.

6. Rarely, downward tumor extension produces a nasopharyngeal mass and CSF rhinorrhea.

B. Specific symptoms and signs of pituitary tumors

Pituitary tumors produce manifestations of excessive hormone secretion (endocrinopathy), according to the type of tumor cell. The pituitary gland contains three cell types: chromophobe, acidophilic, and basophilic cells, each secreting different hormones. A tumor of a particular cell type therefore produces manifestations of excess hormone from those cells, while compressing the other cell types and reducing their hormone secretion.

Historically, pituitary tumors were classified by cytoplasmic staining as chromophobe, acidophilic, or basophilic adenomas. Chromophobe adenomas were considered nonsecretory and therefore not responsible for hormonal abnormalities; acidophilic adenomas were considered growth hormone-producing, and basophilic adenomas ACTH-producing. Because staining characteristics do not correlate with hormone-secretory capacity, this classification has been abandoned in favor of classification by the endocrine function of the tumor cells.⁽³²⁾ This approach is appropriate because circulating hormone levels can be measured.

Classification of pituitary adenomas by endocrine function is as follows:

1. Growth hormone - secreting adenoma
2. Prolactin - secreting adenoma
3. ACTH - secreting adenoma
4. TSH - secreting adenoma
5. FSH- and LH-secreting adenoma
6. Plurihormonal adenoma
7. Adenoma with no apparent hormonal function

1. Growth hormone-secreting adenoma. This tumor of acidophilic cells secretes growth hormone, causing gigantism (Figure 5.25) when it develops in a child before epiphyseal closure, or acromegaly when it develops in an adult. The patient becomes large in all parts of the body (Figure 5.26). Associated abnormalities include hypertension, heart disease, diabetes mellitus, pulmonary disease, and back and joint pain due to peripheral nerve compression.

2. Prolactin-secreting adenoma (prolactinoma). This is the most common pituitary tumor. Its manifestations result from excessive prolactin secretion by tumor cells, producing hyperprolactinemia. In women, this causes galactorrhea, amenorrhea, and infertility. Galactorrhea is the discharge of whitish, milk-like fluid from the nipple (Figure 5.27), either spontaneously or after stimulation by squeezing the nipple. Galactorrhea occurs in 30% of prolactinoma cases,⁽³³⁾ whereas amenorrhea or oligomenorrhea is the most common manifestation, occurring in up to 95%.⁽³⁴⁾

In men, prolactinomas cause diminished sexual desire, impotence, low sperm counts, and galactorrhea. Galactorrhea is less common in men than in women.^{(35, 36)} Prolactinomas in men are generally larger than those in women and therefore commonly produce hypopituitarism and mass-effect symptoms. In women, they are detected earlier because the endocrine manifestations are more conspicuous.

3. Adrenocorticotropic hormone-secreting adenoma. Its manifestations result from elevated blood ACTH and constitute Cushing’s syndrome. This syndrome can also arise from other causes, including corticosteroid administration, adrenal adenoma, and lung cancer. When caused by a pituitary adenoma, it is called “Cushing’s disease.” Characteristic features include increased appetite; a rounded, red moon face; double chin; truncal obesity; facial acne; long sideburns and a slight mustache, sometimes a beard (hirsutism); a buffalo hump; purple abdominal striae, sometimes extending to the thighs; thin skin, easy bleeding, and slow wound healing; diabetes; weakness; osteoporosis; and amenorrhea or oligomenorrhea. Hypertension and left ventricular enlargement commonly coexist.

An ACTH-secreting adenoma may develop after bilateral adrenalectomy for hypercortisolism. This is called Nelson’s syndrome. Patients develop progressively increased skin pigmentation and elevated blood ACTH. CT and physical examination reveal evidence of a pituitary adenoma.

4. TSH-secreting adenoma. This produces hyperthyroidism.

5. FSH- and LH-secreting adenoma. Composed of gonadotropic cells, this has no specific clinical symptoms or signs, but blood FSH and LH levels are elevated.

6. Plurihormonal adenoma. This adenoma secretes two or more adenohypophyseal hormones. Growth hormone and prolactin are the usual combination. These two hormones are secreted by three types of pituitary adenoma: mixed growth hormone cell–prolactin cell adenoma, acidophil stem cell adenoma, and mammosomatotropic cell adenoma.⁽³²⁾

Original page 309

OPTIC NERVE AND OPTIC CHIASM

Tumors arising in the optic nerve or chiasm impair vision. When one optic nerve is involved, vision in that eye gradually deteriorates and ultimately is lost. An intraorbital optic nerve tumor may push the globe forward, producing nonpulsatile unilateral exophthalmos and restricted eye movements. Fundoscopy reveals primary optic atrophy on the affected side.

A tumor extending into or originating in the chiasm impairs visual fields and visual acuity in both eyes. The pattern of field loss varies according to the fibers destroyed and may be similar or different in the two eyes. Some patients have bitemporal hemianopia, with bilateral optic atrophy on fundoscopy. Children often do not recognize their visual loss, but searching nystagmus may be noticed and may be the first sign prompting medical consultation.

A chiasmal tumor may extend into the hypothalamus, causing hypothalamic dysfunction. Further growth obstructing the CSF pathway at the foramen of Monro produces raised intracranial pressure.

As noted above, tumors of the pituitary gland, hypothalamus, or parasellar region can also impair the optic nerves and chiasm, producing visual field loss, diminished visual acuity, and optic atrophy. These must be considered in the differential diagnosis, although differentiation is sometimes difficult.

Original pages 309–310

CAVERNOUS SINUS

As described in the anatomy section, cranial nerves III, IV, VI, and V pass through the cavernous sinus. Three supply the extraocular muscles, while the trigeminal nerve supplies facial sensation. These cranial nerves lie very close together in the cavernous sinus. A tumor here impairs their function, producing “cavernous sinus syndrome.” Patients have orbital and temporal pain, followed by numbness in the trigeminal distribution and diplopia from compression of the ocular motor nerves, causing ophthalmoplegia. Third nerve palsy is most common: the upper eyelid droops on the tumor side (ptosis), and the pupil is dilated and unreactive to light. When the eyelid closes completely, diplopia disappears because the affected eye cannot see; reopening the eye restores the diplopia. Upward tumor extension may impair the ipsilateral optic nerve and cause blindness. Malignancies such as nasopharyngeal carcinoma extending upward to the skull base may cause bilateral manifestations.

Original pages 310–311

SUPERIOR ORBITAL FISSURE

The superior orbital fissure lies anterior to the cavernous sinus, near the orbital apex and at the medial border of the greater wing of the sphenoid bone. It transmits the oculomotor, trochlear, and abducens nerves and the ophthalmic division of the trigeminal nerve into the orbit to supply the ocular muscles. The fissure is closely related to the optic canal and nerve.

A tumor in this region produces superior orbital fissure syndrome: loss of eye movements, a dilated pupil unreactive to light, and ptosis from compression of the oculomotor, trochlear, and abducens nerves (Figure 5.28). Pain or numbness occurs in the forehead within the ophthalmic division of the trigeminal nerve, and the corneal reflex on the tumor side is lost. Vision on that side may deteriorate to complete blindness while the opposite eye remains normal. Some patients have temporal or nasal visual field loss in the affected eye, depending on the site of optic nerve compression. Fundoscopy shows optic atrophy.

Some tumors also cause unilateral exophthalmos on the affected side.

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Original pages 311–317

PINEAL GLAND

The pineal gland is a small gland attached to the posterior roof of the third ventricle near the posterior commissure. It is closely related to the quadrigeminal plate and aqueduct of Sylvius in the midbrain, resting on the superior colliculi (Figure 5.29). Above it lie the internal cerebral veins and splenium of the corpus callosum; behind it lie the great vein of Galen and anterior vermis. The pulvinar of the thalamus lies laterally, and the posterior third ventricle lies anteriorly. The function of the pineal gland remains uncertain, so the true localizing manifestations of pineal tumors cannot yet be specified. Clinical findings suggest a direct or indirect relationship with gonadotropin, although this remains unproven: some children with pineal tumors have precocious puberty, while others do not, and the difference remains unexplained.

Localizing symptoms and signs result from tumor compression of the quadrigeminal plate, aqueduct of Sylvius, and oculomotor nucleus. Pineal tumors therefore resemble tumors arising within the upper midbrain, or tectum, and the two are difficult to distinguish clinically.

The important manifestations of pineal tumors are as follows:

1. Ocular manifestations. These are important localizing signs, resulting from compression and destruction of the quadrigeminal plate and producing “Parinaud’s syndrome.” This comprises loss of conjugate vertical eye movements (vertical gaze palsy), usually beginning with inability to look upward (upward vertical gaze palsy), and dilated pupils with absent or, in some cases, minimal light reactions (Figure 5.30). The pupils still constrict during near viewing (accommodation).

In this region, corticotectal fibers from the lower part of area 18 and upper part of area 19 in the occipital lobe pass to the upward vertical gaze center at the rostromedial aspect of the superior colliculi.⁽³⁷⁾ Tecto-oculomotor fibers then pass to the portions of the oculomotor nuclei (Figure 5.31) responsible for upward movement of the eyes and eyelids. Pineal tumor compression of the superior colliculi therefore prevents upward eye movements. Corticotectal fibers from the middle of area 19 and upper part of area 18 pass to the downward vertical gaze center caudolateral to the superior colliculi.⁽³⁷⁾ A large pineal tumor compresses this center and prevents downward gaze. Fibers passing to the horizontal gaze center in the pons lie deep in the midbrain tegmentum and escape compression. Horizontal gaze palsy is therefore not seen in patients with pineal tumors.

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The pupillary light reflex pathway begins in the retina and passes through the optic nerve, chiasm, and optic tract to the pretectal nucleus without synapsing in the lateral geniculate body. The pretectal nuclei lie immediately anterior to the superior colliculi and communicate across the posterior commissure. Fibers then pass to both Edinger–Westphal nuclei, whose parasympathetic fibers accompany the oculomotor nerves to the iris (Figure 5.32), causing pupillary constriction. Shining light into one eye causes both pupils to constrict simultaneously and equally. A pineal tumor compressing the pretectal area produces dilated pupils unreactive to light.

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Both eyes can still turn medially to view a near object (convergence) because the convergence center, or nucleus of Perlia, lies deep in the midline between the posterior parts of the two oculomotor nuclei. It is therefore usually spared by a pineal tumor unless the tumor is large. At that stage, upward gaze, downward gaze, and convergence are all lost.

Diplopia may initially be experienced as blurred or indistinct vision because vertical gaze impairment is unequal between the eyes and pupillary dilatation prevents good focus. The double images are vertically separated. Alternatively, diplopia may result from abducens nerve dysfunction due to raised intracranial pressure, in which case the images are horizontally separated (horizontal diplopia). Compression of the oculomotor nucleus can also cause diplopia, but this is uncommon because the nucleus lies deep.

Some patients have upward vertical nystagmus early in the loss of vertical gaze; it disappears once upward gaze paralysis is complete. Pineal tumors may also cause convergence spasm and nystagmus retractorius.⁽³⁸⁾ Both globes retract rapidly and return slowly to their normal position. Greater activity of the medial recti also produces convergence.

2. Raised intracranial pressure. Tumor compression of the aqueduct of Sylvius beneath the quadrigeminal plate causes obstructive hydrocephalus. Patients develop headache, vomiting, blurred vision, papilledema, and diplopia from abducens nerve palsy, with drowsiness late in the disease. Raised intracranial pressure often occurs early and precedes other manifestations because the aqueduct is a very narrow CSF passage closely adjacent to the pineal gland. Some patients have bitemporal hemianopia caused by compression of the optic chiasm by an enlarged third ventricle (Figure 3.57).

3. Deafness. This occurs when a very large pineal tumor extends downward to compress the inferior colliculi, auditory relay stations in the midbrain. Auditory signals pass along the cochlear nerves to the dorsal and ventral cochlear nuclei on both sides, then through the lateral lemnisci to the inferior colliculi, onward to the medial geniculate bodies, and finally to the temporal cortex. The inferior colliculi thus have bilateral innervation (Figure 5.7), and their compression causes bilateral deafness. Some patients have tinnitus before becoming deaf, sometimes with dizziness.

4. Gait ataxia. A large pineal tumor extending downward and backward may compress the cerebellar vermis and superior cerebellar peduncle, causing an unsteady gait. This generally occurs late, when intracranial pressure is markedly elevated. If gait ataxia occurs without prominent Parinaud’s syndrome, a posterior fossa tumor may be suspected instead.

5. Endocrine changes. As noted above, some patients have precocious puberty: the genitalia develop earlier than expected for age and acquire an adult appearance, pubic and axillary hair develops, and the voice breaks (Figure 5.19). These changes do not occur in every patient and remain inadequately explained.

A pineal tumor may grow or seed into the third ventricle, or an ectopic pinealoma may occur there. Compression of the hypothalamus, optic chiasm, and infundibulum then produces the hypothalamic manifestations described above and bitemporal hemianopia.

Original pages 317–326

CEREBELLUM

The cerebellum lies in the posterior fossa behind the fourth ventricle and brainstem, covered superiorly by the tentorium cerebelli. Its two main components are the midline vermis and the two cerebellar hemispheres. The primary fissure divides it into anterior and posterior lobes. Behind the posterior lobes on both sides lies the flocculonodular lobe.

The flocculonodular lobe is also called the vestibulocerebellum (archicerebellum) because it communicates with the vestibular system, which is concerned with balance. It also receives impulses from brain regions involved in eye movements.^{(39, 40)}

The vermis (paleocerebellum) is sometimes called the spinocerebellum because it receives most of its input from the spinal cord through spinocerebellar afferents. It is concerned with equilibrium and posture.

The cerebellar hemisphere (neocerebellum) is sometimes called the pontocerebellum because most of its fibers arrive from the pons. It sends fibers to the thalamus and cerebral cortex and is concerned with motor coordination.

Within the cerebellar white matter are groups of gray-matter cells forming the dentate, fastigial, globose, and emboliform nuclei. The dentate nucleus is the largest and lies near the midline. The fastigial nucleus lies close to the midline beneath the vermis, or on the roof of the fourth ventricle. The globose and emboliform nuclei, collectively called the nucleus interpositus, lie between these two nuclei.

The cerebellum connects with the brainstem through three cerebellar peduncles (Figure 5.33): the inferior cerebellar peduncle (restiform body), middle cerebellar peduncle (brachium pontis), and superior cerebellar peduncle (brachium conjunctivum). Afferent fibers from various parts of the CNS enter through these peduncles. Most efferent fibers leave through the superior cerebellar peduncle; a smaller number leave through the juxtarestiform body, the medial part of the restiform body.

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Inferior cerebellar peduncle. This connects the cerebellum with the spinal cord and medullary centers, carrying the following afferent fibers:

1. The dorsal spinocerebellar tract begins in the dorsal nucleus of Clarke in spinal cord segments L₃–C₈ and enters the cerebellum to terminate in the vermis.⁽⁴¹⁾ It carries impulses from stretch, touch, and pressure receptors, providing proprioceptive and exteroceptive information for coordination of standing and individual limb muscle movements.
2. The cuneocerebellar tract. Because the column of Clarke is absent above C8, cervical spinal nerve fibers entering the cord ascend ipsilaterally in the fasciculus cuneatus. Impulses then reach the accessory cuneate nucleus in the medulla, analogous to the dorsal nucleus of Clarke. Its cells give rise to the cuneocerebellar tract, which carries proprioceptive information from the arm and neck to the cerebellum.
3. The vestibulocerebellar tract begins in the vestibular nerve root and vestibular nuclei, sending fibers to the flocculonodulus, uvula, and paraflocculus. It conveys information from vestibular receptors on both sides to the cerebellum for balance.
4. The olivocerebellar tract begins in the inferior olivary nucleus and sends fibers to all parts of the opposite cerebellar cortex, conveying somatosensory information from the contralateral inferior olivary nucleus to the cerebellum.
5. The reticulocerebellar tract begins in the lateral reticular nucleus of the medulla and terminates in the vermis.

The important efferent fibers passing through the restiform body are cerebellovestibular, fastigiobulbar, and cerebello-olivary fibers, located in the juxtarestiform body.

Middle cerebellar peduncle, or brachium pontis. The largest of the three peduncles, it connects the cerebellum with the pons and cerebral cortex. Most afferent fibers belong to the pontocerebellar tract, arising from pontine cells. The cerebellum communicates with the cerebral cortex through the cerebropontocerebellar pathway. This begins in the frontal, temporal, parietal, and occipital cortices, conveys impulses to the pons, and then relays them through the pontocerebellar tract to the opposite cerebellar hemisphere.

Superior cerebellar peduncle, or brachium conjunctivum. This consists mainly of cerebellar efferent fibers. Fibers from the cerebellar cortex pass to the cerebellar nuclei, chiefly the dentate nucleus. Dentate efferents then pass through the superior cerebellar peduncle to the contralateral red nucleus and ventrolateral thalamic nucleus through the dentorubral and dentothalamic tracts, respectively.

The cerebellum is therefore concerned not only with equilibrium and muscle tone but also with integrating and coordinating muscular activity to produce smooth, accurate intended movements. Cerebellar dysfunction from any cause produces the following manifestations:

1. Asynergy: muscle groups fail to act in coordination, preventing smooth, accurate movement, particularly fine tasks. Examination reveals dysmetria (inaccurate judgment of movement range) and dysdiadochokinesia (inability to alternate pronation and supination of the hand).
2. Hypotonia: reduced muscle tone and rapid fatigability.
3. Intention tremor: the hand trembles during an intended action but not at rest.
4. Unsteady gait and leaning. Destruction of one cerebellar hemisphere causes the head and body to lean toward the affected side when standing, with veering and falling toward that side when walking. A vermian lesion prevents stable sitting or standing, causing forward or backward falls or a staggering, broad-based gait.

5. Nystagmus and ocular deviation. Nystagmus is the most frequent finding in cerebellar lesions and indicates damage to the vestibulocerebellar pathway. The cerebellar hemisphere and nuclei are important in maintaining conjugate gaze toward the ipsilateral side, while the vermis helps maintain vertical gaze. Destruction of one hemisphere prevents sustained conjugate gaze toward that side. The eyes drift slowly back toward the midline, then rapidly return to the intended target, producing jerky nystagmus. Clinically, most cases are horizontal nystagmus, with the fast component toward the lesion.

A unilateral cerebellar hemispheric lesion also causes the eyes at rest, or during attempted straight-ahead gaze, to deviate approximately 10–30° toward the unaffected side because conjugate gaze toward the affected side is impaired.⁽⁴²⁾

6. Speech abnormalities. Speech becomes slow and irregular because the muscles involved in articulation do not act in coordination.

Localizing symptoms and signs of cerebellar tumors

The manifestations may be divided into two groups:

1. Midline tumors. These destroy the vermis and flocculonodular lobe, where vestibular fibers terminate, and therefore resemble vestibular system disease. The midline vermis is important in controlling the head, neck, and trunk. A tumor here impairs their coordination, producing characteristic truncal ataxia (Figure 5.34). Patients cannot sit or stand upright, fall forward or backward, and cannot hold the neck and head upright. They stagger like an intoxicated person when walking and, if severely affected, cannot sit up at all. Dizziness is common, but nystagmus is uncommon unless the tumor extends into a cerebellar hemisphere, in which case ipsilateral cerebellar signs also occur.

A large vermian tumor may compress the brainstem, particularly the midbrain, producing a cerebellar fit: opisthotonos, rigid extension of both arms and legs, and backward arching of the head. Some patients remain conscious while others do not (Figure 4.31). The term “cerebellar fit” is actually inaccurate because the cerebellum itself does not cause seizures; the phenomenon is more likely due to brainstem dysfunction. Some tumors in this region compress the posterior midbrain at the quadrigeminal plate, causing vertical gaze palsy resembling Parinaud’s syndrome, as described above. This is a false localizing sign.

Vermian tumors commonly produce raised intracranial pressure relatively early because they lie very close to the fourth ventricle and can readily obstruct its inlet and outlets. Headache, vomiting, blurred vision, and papilledema are prominent. Young children develop enlargement of the head and separation of the cranial sutures.

2. Cerebellar hemispheric tumors. These produce cerebellar dysfunction in the ipsilateral limbs. Use of the arm and hand is clumsy, with hypotonia and drift toward the tumor side when the arm is extended. Dysmetria, intention tremor, and dysdiadochokinesia occur. The patient walks with the legs spread apart and veers or falls toward the tumor side (Figure 5.35). Unsteadiness is particularly evident when standing with the eyes closed or walking heel-to-toe in a straight line.

Nystagmus is present in nearly every case and is horizontal, with the quick phase toward the affected side and the slow phase toward the midline.

Sometimes a cerebellar hemispheric tumor produces relatively few signs despite its size, particularly when slowly growing, presumably because adaptation has occurred.

In addition to cerebellar signs, a cerebellar tumor may extend to compress ipsilateral cranial nerves V–XII. Involvement of V, VI, VII, and VIII is more common than involvement of IX, X, XI, and XII, although cranial nerve manifestations are uncommon with cerebellar tumors.

Some children develop meningism with neck and occipital pain because the tumor and cerebellar tonsils herniate through the foramen magnum, irritating the cervical nerve-supplied dura of the posterior fossa. The neck becomes stiff, the head tilts backward and may rotate slightly to one side, and opisthotonic arching of the back is frequent (Figure 5.36).

Original pages 326–327

Fourth ventricle

Tumors arising within the fourth ventricle itself produce raised intracranial pressure relatively early because they obstruct CSF flow. Patients have headache, vomiting, blurred vision, and papilledema. Vomiting is more frequent than with tumors elsewhere because the vomiting center in the medulla is affected. Headache usually begins early in the occipital and neck regions, sometimes with neck stiffness, and later becomes generalized as intracranial pressure rises markedly. Abducens nerve palsy may accompany the raised pressure. A large tumor compressing the vermis causes truncal ataxia, with inability to maintain balance and forward or backward falls; cerebellar hemispheric manifestations may be slight. Compression of the fourth ventricular floor, formed by the posterior pons, may impair cranial nerve function. The sixth and seventh nerves have been affected in cases encountered by the author.

Some tumors originate in the floor of the fourth ventricle or the vermis above and then grow into the ventricle. Manifestations of the site of origin appear first; for example, a vermian tumor produces truncal ataxia followed by raised intracranial pressure.

Original pages 327–338

BRAINSTEM

Anatomically, the brainstem comprises the midbrain, pons, and medulla. These three regions have similar components: four important groups of nuclei and five important groups of fibers (Figures 5.37 and 5.38).

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The important nuclei are as follows:

1. Cranial nerve nuclei. These are the sensory and motor nuclei of cranial nerves III–XII. The midbrain contains nuclei III and IV; the pons contains V, VI, VII, and VIII; and the medulla contains IX, X, XI, and XII. Their locations are important for tumor localization, as discussed below.

2. Sensory tract relay nuclei. The cuneate and gracile nuclei in the medulla are concerned with somatic sensation. The inferior colliculus and medial geniculate body in the midbrain are concerned with hearing, as are the superior olivary and trapezoid nuclei in the pons. The superior colliculus is concerned with vision and eye movements.

3. Motor tract relay nuclei. These include the pretectal area, concerned with the pupil and oculomotor system; the red nucleus, connected with the cerebral cortex and cerebellum; the reticular formation nuclei, similarly connected with the cortex and cerebellum; and the vestibular nuclei, concerned with the cerebellum and equilibrium.

4. Cerebellar relay nuclei. These include the inferior olivary, pontine, and red nuclei.

The important fibers are as follows:

1. Cranial nerves. These emerge from their nuclei. Most cranial nerves—V, VII, VIII, IX, X, XI, and XII—leave the brainstem inferolaterally. Nerves III and VI emerge inferiorly. Nerve IV is unusual in emerging superiorly and crossing to the opposite side.

The oculomotor nerve (III) supplies all extraocular and intrinsic ocular muscles except the superior oblique and lateral rectus.

The trochlear nerve (IV) supplies the superior oblique muscle.

The abducens nerve (VI) supplies the lateral rectus muscle.

The sensory root of the trigeminal nerve (V) receives sensation from the face and head. Its motor root supplies the muscles of mastication. The mesencephalic tract receives proprioceptive input from the jaw and ocular muscles; the spinal descending tract receives sensation from the face and head.

The motor root of the facial nerve (VII) supplies facial muscles, and its intermediate root provides parasympathetic innervation to facial glands.

The acoustic nerve (VIII) comprises the vestibular nerve for balance and the cochlear nerve for hearing.

The glossopharyngeal nerve (IX) receives sensation from the pharynx.

The vagus nerve (X) supplies the pharyngeal and laryngeal muscles and provides parasympathetic innervation to thoracic and abdominal organs.

The accessory nerve (XI) supplies the trapezius and sternocleidomastoid muscles, with a small contribution to the pharyngeal muscles.

The hypoglossal nerve (XII) supplies the tongue muscles.

2. Important sensory tracts

The spinothalamic tract conveys pain and temperature sensation from the spinal cord to the thalamus.

The medial lemniscus conveys somatic sensation to the thalamus and parietal cortex.

The trapezoid body, lateral lemniscus, and brachium of the inferior colliculus are concerned with hearing.

3. Clinically important motor tracts

The corticopontine tract runs from the cerebral cortex to the pons. The corticospinal tract consists of fibers from the motor cortex to the spinal cord and controls movement of the body’s muscles.

The rubrospinal tract is associated with the red nucleus and regulates muscle tone.⁽⁴¹⁾

The vestibulospinal tract is concerned with vestibular function.

4. Cerebellar projections. Clinically important projections include the middle cerebellar peduncle, or brachium pontis, associated with the cerebral cortex.

The restiform body, or inferior cerebellar peduncle, is associated with spinal cord function.

The superior cerebellar peduncle, or brachium conjunctivum, carries efferent fibers from the cerebellum to the red nucleus and thalamus.

The juxtarestiform body, the medial portion of the restiform body, connects the cerebellum with the brainstem.

5. Intrinsic fiber systems. The clinically important medial longitudinal fasciculus connects the oculomotor and vestibular nuclei.

Symptoms and signs of brainstem tumors

Based on the anatomy described above, the manifestations of an intrinsic brainstem tumor can be divided into five groups according to the structures destroyed:

1. Dysfunction of one or more cranial nerves from III to XII, depending on tumor location.
2. Corticospinal tract dysfunction, causing hemiparesis with unilateral damage or quadriparesis with bilateral damage.
3. Long sensory tract dysfunction, causing hemianesthesia or hemihypesthesia.
4. Dysfunction of internuclear or supranuclear tracts within or entering the brainstem.
5. Dysfunction of cerebellar pathways entering the pons and medulla or leaving the cerebellum for the midbrain and thalamus.

The key diagnostic pattern is progressively worsening contralateral spastic hemiparesis, with hemianesthesia or hemihypesthesia, accompanied by ipsilateral cranial nerve dysfunction. One or several cranial nerves may be affected. This crossed paralysis is an important diagnostic sign of a brainstem lesion, and the nerves involved indicate tumor location: III and IV indicate the midbrain; V, VI, VII, and VIII indicate the pons; IX, X, XI, and XII indicate the medulla. As the tumor enlarges and crosses the midline, it destroys corresponding structures on the opposite side, producing bilateral cranial nerve and long tract deficits. In the author’s experience, however, the manifestations are not equal or identical on the two sides. Large tumors may produce rigid extension of both arms and legs (Figure 7.39), resembling decerebrate rigidity, while consciousness may remain unchanged until late in the disease.

Brainstem tumors usually do not cause raised intracranial pressure, except for midbrain tumors, which can cause it early because the narrow aqueduct of Sylvius is easily obstructed. Pontine and medullary tumors generally grow along the brainstem fibers rather than into the ventricle; furthermore, brainstem dysfunction prompts patients to seek medical attention early. Nevertheless, raised intracranial pressure may develop late.

Tumors in different parts of the brainstem produce different manifestations, described separately below.

Midbrain. The midbrain comprises the tectum, tegmentum, and basis pedunculi. The tectum, or quadrigeminal plate, lies above the aqueduct of Sylvius and includes the superior colliculus, concerned with eye movements and containing the upward conjugate gaze center, and the inferior colliculus with its adjacent brachium, concerned with hearing. The pretectal area anterior to the superior colliculus is concerned with pupillary function.

On the inferior surface of the midbrain are the two cerebral peduncles, containing corticospinal, corticobulbar, and frontopontine tracts. Between them lies the interpeduncular fossa, where the oculomotor nerves emerge. Above the peduncles, within the tegmentum, lie the substantia nigra and red nucleus. Oculomotor fibers pass through this region, and fibers of the brachium conjunctivum terminate here. Laterally within the tegmentum lie the medial lemniscus and lateral spinothalamic tract, conveying sensation to the thalamus.

At the level of the superior colliculus, beneath the periaqueductal gray, lie the oculomotor nuclei and medial longitudinal fasciculus (MLF). Oculomotor fibers pass through the red nucleus to emerge in the interpeduncular fossa. At the inferior collicular level lies the trochlear nucleus. Its fibers curve around to emerge from the posterior brainstem on the side opposite their nucleus, behind the inferior colliculus, and supply the superior oblique muscle. Near the inferior colliculus are the downward conjugate gaze and convergence centers, controlling downward gaze and inward gaze respectively.

Symptoms and signs of midbrain tumors

Tumors of the tectum or quadrigeminal plate produce Parinaud’s phenomenon, as do pineal tumors: loss of upward conjugate gaze and dilated pupils unreactive to light, due to dysfunction of the superior colliculi and pretectal area (Figures 5.39 and 5.30). Extension destroying the inferior colliculi and lateral lemnisci causes tinnitus and bilateral deafness, together with loss of downward gaze and convergence, so the patient cannot look down or focus on a near object. Destruction of the oculomotor and trochlear nuclei produces diplopia, ptosis, and complete ophthalmoplegia except for the lateral rectus muscles supplied by the abducens nerves. Raised intracranial pressure occurs relatively early because the aqueduct becomes obstructed (Figure 5.39.1).

A tegmental tumor destroying the red nucleus, oculomotor fibers, medial lemniscus, and superior cerebellar peduncle produces contralateral limb tremor and ataxia together with ipsilateral oculomotor palsy. Contralateral sensory loss may occur from medial lemniscal damage (Benedikt’s syndrome; Figure 5.39.2).

A tumor originating in the cerebral peduncle produces contralateral spastic hemiparesis with ipsilateral oculomotor palsy (Weber’s syndrome; Figure 5.39.3).

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Midbrain tumors may extend to both sides, producing bilateral long tract and cranial nerve manifestations, usually of unequal severity.

PONS AND MEDULLA. The pons contains cranial nerves V, VI, VII, and VIII; the medulla contains IX, X, XI, and XII. Clinically important fibers include the corticospinal and corticobulbar tracts; pontocerebellar fibers through the brachium pontis; the medial longitudinal fasciculus (MLF) for eye movements; the medial lemniscus and spinothalamic tract for sensation; the lateral lemniscus for hearing; and the restiform body, or inferior cerebellar peduncle.

In addition to these cranial nerve nuclei, the pons contains a horizontal gaze center on each side near the abducens nucleus. Each center coordinates lateral movement of both eyes toward its own side. It sends fibers directly to the ipsilateral abducens nucleus and through the MLF to the medial rectus portion of the contralateral oculomotor nucleus. Each pontine center receives impulses from the opposite cerebral hemisphere and relays them to the ipsilateral lateral rectus nucleus and contralateral medial rectus nucleus (Figure 5.40). Destruction of one center prevents both eyes from turning toward the lesion; the eyes deviate to the opposite side. If the corticospinal tract is also destroyed, the eyes look toward the side of hemiparesis.

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The medial longitudinal fasciculus (MLF) is another structure whose dysfunction produces detectable signs. It lies beside the midline and, at the midbrain level, close to the oculomotor nucleus. It is clearly identifiable from the oculomotor to the vestibular nuclear region. Most MLF fibers originate in the vestibular nuclei. This tract links cranial nerves III, IV, and VI with one another and with the vestibular nuclei, and also connects the pontine lateral conjugate gaze center to the oculomotor nucleus. Tumor destruction of the MLF causes internuclear ophthalmoplegia, discussed below.

Symptoms and signs of pontine and medullary tumors

Most tumors in this region originate in the pons and extend into the medulla; primary medullary tumors are very rare. Common early manifestations are diplopia and lower motor neuron facial weakness because the closely adjacent abducens and facial nerves and nuclei are destroyed. Later, horizontal conjugate gaze toward the tumor is lost and the eyes look away from it, an important localizing finding for a pontine tumor. In the author’s experience, this contralateral eye deviation persists and does not subsequently return to normal as may occur with frontal eye field lesions. Pontine tumors impair horizontal but not vertical conjugate gaze because the vertical gaze center lies in the midbrain. However, extension into the midbrain (Figure 3.23) can also impair vertical gaze.

Tumor damage to the MLF produces internuclear ophthalmoplegia. The characteristic findings are failure of the ipsilateral medial rectus during gaze toward the opposite side and horizontal nystagmus in the contralateral abducting eye.^{(43, 44)} For example, on attempted rightward gaze, the right lateral rectus functions normally and the right eye turns right, but the left medial rectus fails to act despite no actual palsy of that muscle. The left eye remains in the primary position, yet convergence is preserved. Horizontal nystagmus is greater in the right eye than in the left; this asymmetry is another indication of an MLF or brainstem lesion. With progression, both horizontal and vertical nystagmus occur and internuclear ophthalmoplegia becomes bilateral. Vertical nystagmus is an important sign indicating a lesion within the brainstem; it is not found with lesions outside it and may therefore help distinguish these locations.

Failure of the medial rectus in internuclear ophthalmoplegia may be accompanied by other findings, depending on the location of MLF damage. Cogan⁽⁴⁴⁾ divided MLF lesions into three locations:

1. Posterior MLF lesions (medullary portion): convergence remains normal. Attempted lateral gaze produces nystagmus and sometimes paresis of the lateral rectus as well as the medial rectus.
2. Anterior MLF lesions (midbrain portion): convergence is absent or diminished in both eyes, without lateral rectus dysfunction. Nystagmus persists on lateral gaze but is less conspicuous than with posterior MLF lesions.
3. MLF lesions intermediate between sites i and ii produce the characteristic internuclear ophthalmoplegia described above. Thus, finding internuclear ophthalmoplegia indicates a tumor or lesion within the brainstem.

When the tumor enlarges to destroy the trigeminal and acoustic nerves and their nuclei, patients develop facial numbness, loss of the corneal reflex (V), and hearing loss (VIII), which may be unilateral or bilateral.

Medullary tumors impair cranial nerves IX, X, XI, and XII, causing vomiting, hiccups, progressive hoarseness, and choking when swallowing food or liquids, often resulting in aspiration pneumonia. Examination shows abnormal gag reflex, uvular movement, and vocal cord function. The tongue is paralyzed and atrophic, with fasciculations, and deviates toward the affected side on protrusion. Medullary tumors generally do not weaken the sternocleidomastoid and trapezius because these muscles receive most of their innervation from cervical nerves.

Spastic hemiparesis is commonly encountered with pontine and medullary tumors because the corticospinal tract in the lower pons is destroyed. Pontocerebellar fibers are also damaged, so gait ataxia may accompany limb weakness. Some patients have bilateral limb weakness, but its severity is unequal. Late in the disease, both sides may show rigid extension. Hemisensory loss accompanies the hemiparesis.

Original pages 338–343

CEREBELLOPONTINE ANGLE

The cerebellopontine angle is another common site of tumors. It contains several important structures whose involvement produces localizing symptoms and signs.

The C-P angle is bounded superiorly by the cerebellar hemisphere, medially by the pons, and anteriorly and laterally by the dura over the temporal bone.

Important structures in this region include the cerebellum, middle cerebellar peduncle, brainstem, cranial nerves IV–XI, and arteries and veins: the vertebrobasilar artery, superior cerebellar artery, anterior inferior cerebellar artery, posterior inferior cerebellar artery, petrosal sinus, cerebellar and pontine veins, and sigmoid sinus. The cerebrospinal fluid pathways include the aqueduct of Sylvius, fourth ventricle, and basal cistern.

The trochlear nerve (N IV) emerges from the dorsal midbrain behind the inferior colliculus and runs beneath the tentorium to supply the superior oblique muscle of the eye. During a transtentorial approach, every effort must be made to identify N IV.

The trigeminal nerve (N V) emerges from the lateral pons anterior to the facial and acoustic nerves and passes to Meckel’s cave at the middle of the petrous ridge. Meckel’s cave contains the Gasserian ganglion of the sensory root. Three divisions arise from this ganglion: i) the ophthalmic division receives sensation from the forehead, upper eyelid, and cornea; ii) the maxillary division receives sensation from the cheek, nose, and upper lip; iii) the mandibular division receives sensation from the chin, the inside of the mouth and tongue, and part of the ear.

The motor root runs beneath the sensory root and joins the mandibular division to supply the muscles of mastication (masseter, pterygoids, and temporalis).

The sensory nucleus and descending tract in the pons lie near its lateral surface and may be compressed by a C-P angle tumor.

The abducens nerve (N VI) emerges ventrally at the pontomedullary junction and runs along the underside of the pons into the cavernous sinus and superior orbital fissure to supply the lateral rectus muscle.

The facial nerve (N VII) emerges from the lateral pons close to the acoustic nerve and passes to the internal auditory canal. It lies anterior and inferior to the acoustic nerve and supplies the facial muscles and platysma.

The nervus intermedius is the part of the facial nerve that runs between the facial and acoustic nerves. It has two functions: sensory and parasympathetic. It carries pain and touch sensation from the ear, particularly the external auditory canal, and taste from the anterior two-thirds of the tongue via the chorda tympani. The ganglion of its sensory root is the geniculate ganglion. Its parasympathetic function controls secretion from the lacrimal and submaxillary glands.

The acoustic nerve (N VIII) has two components: the cochlear component for hearing and the vestibular component for balance. The vestibular nerve begins at Scarpa’s ganglion, which receives impulses from the hair cells of the semicircular canals, saccule, and utricle. It then enters the vestibular nuclei at the pontomedullary junction. These nuclei connect with many structures, including the MLF, cerebellum, spinal cord, and contralateral vestibular nuclei. These connections provide balance, changes in posture, and movements of the eyes, head, and neck. The cochlear nerve begins at the spiral ganglion and runs alongside the vestibular nerve to the cochlear nuclei in the brainstem, serving hearing.

The glossopharyngeal (N IX) and vagus (N X) nerves are related cranial nerves with similar functions. Both have motor and autonomic nuclei in the medulla and carry exteroceptive, general, and visceral sensations into the brainstem. They emerge from the medulla slightly below N VIII and pass into the jugular foramen together with the accessory nerve (N XI).

The motor component of N IX supplies the pharyngeal, soft-palate, and stylopharyngeus muscles involved in swallowing. Autonomic efferent fibers arise from the inferior salivatory nucleus and pass as preganglionic fibers to the otic ganglion. Postganglionic fibers then supply the parotid gland and stimulate salivary secretion. The sensory branch carries pain and temperature sensation from the posterior part of the tympanic membrane and the external auditory canal. General visceral sensory fibers receive sensation from the mucosa of the pharyngeal wall, uvula, tonsil, and posterior third of the tongue. It also carries special visceral sensation—taste—from the posterior third of the tongue. The fibers terminate in the nucleus of the fasciculus solitarius.

The vagus nerve (N X) has motor fibers from the nucleus ambiguus supplying the muscles of the soft palate, pharynx, and larynx (vocal cords). Its parasympathetic or visceromotor component begins at the dorsal efferent nucleus and sends postganglionic fibers to control the heart, gastrointestinal tract, and respiratory tract. The sensory fibers have cell bodies in the jugular ganglion and ganglion nodosum below the jugular foramen. They carry visceral sensation from the pharynx, larynx, bronchi, and abdominal viscera into the tractus solitarius in the medulla. There is also a component carrying sensation from the external ear.

The spinal accessory nerve (N XI) is a motor cranial nerve with two origins, one in the medulla and the other in the spinal cord. The medullary component arises from the nucleus ambiguus. After emerging from the medulla, it joins the spinal component, whose fibers arise from motor cells in the anterior horn from the fifth cervical segment upward to the medulla. N XI then enters the jugular foramen with N IX and N X to supply the sternocleidomastoid and trapezius muscles.

The hypoglossal nerve (N XII) arises from the hypoglossal nucleus in the medulla. It is a motor nerve supplying the muscles of the tongue on the same side.

Symptoms and signs of cerebellopontine angle tumors

The anatomy described above shows that tumors in this region produce signs of cranial nerve, brainstem, and cerebellar dysfunction, as well as obstruction of cerebrospinal fluid flow (Figure 5.41).

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1. Symptoms of cranial nerve dysfunction are important from the earliest stage because most tumors in this region are extra-axial. They compress the portions of the cranial nerves outside the brain, which therefore produce the first symptoms. Additional cranial nerves become involved as the tumor enlarges. Brainstem and cerebellar symptoms develop later, when the mass is very large. Whatever the tumor type, the nerve from which it arises or the nerve nearest it will produce symptoms first. The most common C-P angle tumor is acoustic neurinoma, followed by meningioma, trigeminal neurilemmoma, and others.

Tumors of the acoustic nerve begin in the vestibular nerve. The initial symptom is therefore dizziness related to balance, followed by tinnitus and progressively diminishing hearing on the side of the tumor until deafness develops. These are important early symptoms of acoustic nerve tumors, and the physician must make a particular effort to elicit them in the history. Dizziness is usually mild and does not cause severe spinning vertigo. The tinnitus varies: some patients describe buzzing, while others hear a bell-like sound. It is intermittent rather than continuous, and in most cases its timing is irregular. Patients describe progressively declining hearing until they can hear nothing on the affected side. Some do not realize they have lost hearing until they use the telephone.

As the tumor subsequently enlarges, it compresses adjacent cranial nerves, including N V, VII, IX, X, and XI. N V and N VII are most commonly affected. In some patients, N V symptoms occur before those of N VII. There is numbness or paresthesia on the side of the face ipsilateral to the tumor. A few patients report pain in the distribution of N V and may be mistaken for cases of trigeminal neuralgia. When N V is compressed, the corneal reflex is diminished or absent. Although N VII lies close to the acoustic nerve, facial weakness is uncommon unless the tumor is very large. A few patients present with facial twitching. The earliest sign of N VII dysfunction is loss of taste over the anterior two-thirds of the tongue, indicating compression of the nervus intermedius of N VII⁽⁴⁵⁾. N IX and N X dysfunction is uncommon unless a large mass extends downward and compresses both nerves, causing dysphagia and hoarse, indistinct speech.

2. Symptoms caused by cerebellar and brainstem dysfunction. A large tumor compresses the cerebellar hemisphere, nuclei, and peduncle, causing an unsteady gait and incoordination. Cerebellar signs are found in the ipsilateral limbs, together with nystagmus. At the same time, compression of the corticospinal tract in the pons causes contralateral spastic hemiparesis.

3. In the final stage, raised intracranial pressure results from obstruction of cerebrospinal fluid flow at the fourth ventricle and basal cistern. The patient develops headache, blurred vision, vomiting, and progressively worsening consciousness, eventually leading to death.

When a tumor arises from another cranial nerve, loss of that nerve’s function occurs first. For example, an N V tumor causes facial numbness or paresthesia, impairment of the corneal reflex, and dysfunction of the muscles of mastication early in its course. Other cranial nerves become affected later. The history is therefore important in identifying the original site of the tumor. As the mass enlarges, it compresses the brainstem, cerebellum, and other cranial nerves, just as an acoustic nerve tumor does.

Original pages 343–344

JUGULAR FORAMEN

As noted above, the jugular foramen is the exit for N IX, X, and XI. A tumor here therefore impairs all three cranial nerves. The patient has difficulty swallowing, hoarse and indistinct speech, vocal cord paralysis, and loss of taste and general sensation in the posterior third of the tongue. Sensation is also lost in the soft palate, uvula, pharynx, and larynx. The sternocleidomastoid and trapezius muscles on the side of the tumor become weak and atrophic.

Original pages 344–346

FORAMEN MAGNUM

The foramen magnum is the opening through which the medulla continues into the cervical cord. Two cranial nerves pass through this region: i) the spinal component of the accessory nerve arises from spinal cord levels C1–5 and ascends through the foramen magnum to join the component emerging from the medulla. It then leaves the skull through the jugular foramen to supply the sternocleidomastoid and trapezius muscles. ii) The hypoglossal nerve emerges from the medulla and enters the hypoglossal foramen at the margin of the foramen magnum to supply the ipsilateral tongue muscles. In the lower medulla, the corticospinal tract (pyramid) crosses to the opposite side (decussation). Fibers destined for the arm cross before those destined for the leg and lie lateral to the leg fibers (Figure 5.42). The lateral medulla contains important structures whose dysfunction can be detected clinically: the spinal tract and nucleus of the trigeminal nerve and the spinothalamic tract, which carries pain sensation from the lower body. Posteriorly, the medulla contains the fasciculus cuneatus and fasciculus gracilis, which carry proprioception, vibration, and touch.

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Symptoms and signs of foramen magnum tumors

Most tumors in this region lie outside the medulla and grow to compress it, the cranial nerves, and the upper spinal cord and spinal nerves. Patients present with the following symptoms.

1. Occipital and neck pain is a common initial symptom. It is explained by compression of the C2 spinal nerve, which gives rise to the greater occipital nerve. The pain worsens with changes in head position and movements of the neck. Patients therefore tense their neck and keep their head still.

2. Numbness. As the mass enlarges, contralateral hemihypesthesia or hemianesthesia develops because of compression of the lateral spinothalamic tract. Sensation is also lost on the side of the face ipsilateral to the tumor because the descending spinal tract of the trigeminal nerve is compressed. Paresthesia usually affects the arms more than the legs because the tumor commonly arises lateral or anterolateral to the medulla and displaces the fasciculus cuneatus. Some patients have Lhermitte’s sign: flexion of the head produces an electric-shock sensation extending into the lower body.

3. Spastic weakness. Muscle weakness may take several forms, depending on the tumor’s location. As noted above, motor fibers to the arm and leg do not decussate at the same level. A tumor lateral to the medulla compresses fibers to the ipsilateral arm and contralateral leg, causing weakness of an arm on one side and a leg on the other. This is called hemiplegia cruciata. Some patients describe weakness beginning in an arm and spreading to the leg on the same side, followed by the opposite leg and finally the opposite arm, producing quadriparesis. This pattern is explained by the arrangement of the pyramidal decussation (Figure 5.42).

Atrophy of the hand muscles, particularly the intrinsic muscles, is common. It may suggest a lesion in the part of the cervical cord supplying the arm and hand. The explanation remains uncertain, but ischemia caused by compression of the anterior spinal artery may be responsible⁽⁴⁶⁾.

4. Dysfunction of N XI and N XII causes weakness and atrophy of the ipsilateral sternocleidomastoid, trapezius, and tongue muscles. Upward extension of the tumor may compress N IX and N X, causing dysphagia and hoarseness later in the course.

5. Difficulty breathing occurs when a large tumor compresses the respiratory center in the medulla. Associated quadriparesis makes breathing still more difficult.

6. Horizontal nystagmus is found in 25% of patients⁽⁴⁷⁾.

7. In the late stage, patients develop raised intracranial pressure because cerebrospinal fluid pathways around the fourth ventricle are obstructed.

Original pages 346–347

CLIVUS

The clivus is the part of the skull base anterior to the brainstem. It extends from the posterior wall of the sella turcica to the anterior margin of the foramen magnum. It is closely related to cranial nerves II–XII, the basilar artery, cerebral peduncle, pons, and medulla.

Symptoms and signs of clival tumors

A tumor in this region compresses several cranial nerves and the corticospinal tract. A tumor in the upper clivus, anterior to the midbrain, causes headache and blurred vision. Compression of the optic chiasm and optic tract produces visual field defects. Compression of the oculomotor, trochlear, and abducens nerves causes extraocular muscle palsy and diplopia. In some cases, extension above the sella causes hypopituitarism. Extension to Meckel’s cave causes ipsilateral facial numbness or pain. Simultaneous compression of the cerebral peduncle in the midbrain causes associated limb weakness.

With a tumor arising in the lower clivus, or extending there from above, headache becomes more severe and is invariably accompanied by neck and occipital pain. Cranial nerves VI–XII may be affected unilaterally or bilaterally. N VI is affected most often because it runs from the lower border of the pons along its underside to the cavernous sinus⁽⁴⁸⁾.

Original pages 347–350

FALSE LOCALIZING SIGNS

In patients with brain tumors, false localizing signs arise from dysfunction of brain regions distant from the tumor rather than from the tissue at its actual location. They therefore cause confusion in determining the true site. Even careful history-taking and repeated examinations may lead to incorrect localization. These signs should be recognized. Those encountered include the following.

1. Dementia. Patients show deterioration in memory, reasoning, judgment, emotion, and personality, resembling a frontal lobe tumor. This dementia results from raised intracranial pressure or hydrocephalus.

2. Frontal lobe sign. The grasp reflex, a frontal lobe sign, may occur with raised intracranial pressure. In these cases it is bilateral and has no localizing value. A unilateral grasp reflex, however, is highly significant for localization.

3. Cranial nerve signs

3.1 Visual field defect. Compression of the optic chiasm by a markedly enlarged third ventricle may occur when a posterior fossa tumor obstructs cerebrospinal fluid flow and causes hydrocephalus. Bitemporal hemianopia may be found.

A supratentorial tumor unrelated to the optic pathways may cause homonymous hemianopia because raised intracranial pressure produces tentorial herniation. The tentorial edge compresses the posterior cerebral artery, causing occipital infarction (Figure 4.27). If the brain tissue has not infarcted, the homonymous hemianopia may disappear after removal of the tumor.

3.2 Oculomotor nerve signs. Ptosis, pupillary dilatation, and extraocular muscle paresis may result from uncal herniation compressing N III. These are important signs requiring prompt removal of the causative tumor before brainstem dysfunction develops.

3.3 Abducens nerve palsy is the most common false localizing sign. Raised intracranial pressure displaces the brainstem downward, stretching the abducens nerve against the petrous ridge. Lateral rectus dysfunction causes inward deviation of the eye. It may be unilateral or bilateral and has no value in localizing the lesion.

3.4 Trigeminal nerve palsy. A tumor outside the brainstem may push it to the opposite side. The contralateral trigeminal nerve is stretched and kinked where it enters Meckel’s cave, causing pain or numbness on the side of the face opposite the tumor⁽⁹⁾.

4. Cerebellar signs may occur with supratentorial tumors, such as frontal or temporal lobe tumors, because of damage to frontopontocerebellar or temporopontocerebellar fibers projecting to the cerebellum.

5. Pyramidal tract signs. A supratentorial tumor, particularly in the temporal lobe, displaces the brainstem to the opposite side. The opposite cerebral peduncle is compressed against the tentorial edge, producing hemiparesis ipsilateral to the tumor. This is called Kernohan’s phenomenon.

A tumor causing hydrocephalus may produce paraparesis. Markedly enlarged lateral ventricles compress corticospinal fibers from the leg area of the motor cortex that run close to the lateral ventricular walls. The resulting spastic paraparesis resembles a spinal cord lesion.

6. Conjugate gaze palsy. The quadrigeminal plate may be compressed by the posterior portion of the third ventricle in hydrocephalus, or by the vermis during upward transtentorial herniation caused by a posterior fossa tumor. This produces Parinaud’s phenomenon, resembling the signs of a pineal tumor.

7. Endocrine dysfunction. A tumor elsewhere, unrelated to the pituitary gland, may cause hydrocephalus with marked third ventricular enlargement and produce hypopituitarism. The floor of the enlarged third ventricle presses down on the pituitary gland. At the same time, displacement or ischemia of the hypothalamus causes diabetes insipidus. In longstanding cases, marked enlargement of the pituitary fossa may be visible on X-rays.

8. Neck stiffness may suggest subarachnoid hemorrhage or meningitis. It is frequently found with posterior fossa tumors that cause tonsillar herniation and irritate the dura mater and upper spinal sensory nerves. Some patients experience an electric-shock sensation extending elsewhere in the body when the neck is strongly flexed (Lhermitte’s sign).

9. Paraparesis. Bilateral frontal parasagittal meningiomas cause paraparesis, which is a true localizing sign. It is included here because such patients have sometimes been misdiagnosed as having spinal cord lesions. The distinction is actually straightforward: a brain tumor is associated with raised intracranial pressure, seizures (if present), and absence of a sensory level, unlike a spinal cord lesion.

10. Cerebellar fits consist of arching of the back and neck (opisthotonos) with extensor rigidity of the limbs. They are not localizing signs of the cerebellum, because the cerebellum does not cause seizures. Rather, they indicate brainstem involvement due to a large cerebellar tumor with upward transtentorial herniation of the vermis, compressing the brainstem, particularly the midbrain.

Original pages 350–352

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29. Martin J.B., Reichlin S. Neuroendocrinology of reproduction. In Clinical Neuroendocrinology 2nd edit. F.A. Davis Co. p 331-334, 1987.
30. Plum F., and Van Uitert R.: Nonendocrine Diseases and Disorders of the Hypothalamus. In Reichlin, S., Baldessarini R.T. and Martin J.B., The Hypothalamus. New York, Raven Press. p 415-473, 1978.
31. Tindall G.T., Barrow D.L., Clinical and endocrinologic evaluation of patients with pituitary tumors. In Disorders of the Pituitary. The C.V. Mosby Co. p 123-143, 1986.
32. Kovaces K., Horvath E., Asa S.L.: Classification and pathology of pituitary tumors. In Neurosurgery. Wilkins R.H., Rengachary S.S. eds. Mc Graw-Hill Book Co. p 834-842, 1985.
33. Frank S., Nabarro JDN., Jacobs H.S.: Prevalence and presentation of hyperprolactinemia in patients with “functionless” pituitary tumors. Lancet 1: 778, 1977.
34. Faria M.A., Jr., Tindall G.T.: Transphenoidal microsurgery for prolactin-secreting pituitary adenomas. J. Neurosurgery 56: 33, 1982.
35. Carter J.N., Tyson J.E., Tolis G. et al: Prolactin-secreting tumors and hypogonadism in 22 men N. Engl J. Med 299: 847, 1978.
36. Finn J.E., Mount L.A.: Galactorrhea in males with tumors in the region of pituitary gland. J. Neurosurg. 35: 723, 1971.
37. Kahn E.A., Crosby E.C.: Lesions of the posterior ventricle and the midbrain. In Correlative Neurosurgery, 3rd edition. Charles C. Thomas Publisher p 283, 1982.
38. Huber A.: Tumors of the pineal body and the midbrain. In Eye Symptoms in Brain Tumors 2nd edition. The C.V. Mosby Co. p 259-264, 1971.
39. Selhorst J.B., et al: Disorders in cerebellar ocular motor control. I Saccadic overshoot dysmetria. An oculographic, control system, and clinico-anatomical analysis. Brain 99: 497, 1976.
40. Selhorst, J.B., et al: Disorders in cerebellar ocular motor control II Macrosaccadic oscillation. Brain 99. 509, 1976.
41. Truex R.C., Carpenter M.B.: The fiber tracts of the spinal cord. In Human Neuroanatomy, The Williams & Wilkins Co. 6th edition p 269, 1970.
42. De Jong R.N., The cerebellum In The Neurologic Examination 3rd edit. Harper and Row Publisher p 438, 1967.
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46. Yasuoka S., Okazaki H., Daube J.R., et al.: Foramen magnum tumor. Analysis of 57 cases of benign extramedullary tumor J. Neurosurg. 49: 828-838, 1978.
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Original pages 353–354

Chapter 6: text and illustrations from original pages 353–514

Chapter 6

INVESTIGATION

When a patient presents with neurological symptoms suggesting a brain tumor, the physician should take a detailed history and perform thorough neurological and general physical examinations. The resulting symptoms and signs help identify the tumor’s location and the extent of neurological dysfunction. The surgeon must carefully consider the various aspects of treatment in order to restore as much lost function as possible, or achieve a cure, while avoiding further deterioration. Before surgery, radiological investigations are therefore needed to support the clinical diagnosis. The images help determine the site, size, and type of tumor, as well as the many changes it has caused in the brain and blood vessels. This information guides surgical planning: where to operate, the extent of the procedure, and whether to remove the entire tumor or only part of it.

Several radiological investigations are available for tumors. The physician should choose methods that provide an accurate diagnosis, offer the greatest benefit for treatment, and do not endanger the patient, while also considering appropriate costs. The investigations used for brain tumors are as follows:

1. Skull X-rays
2. Cerebral angiography
3. C.T. (Computerized tomography)
4. MRI (magnetic resonance imaging)
5. Ventriculography

Pneumoencephalography (PEG), radioisotope brain scanning, echoencephalography, and EEG are now obsolete investigations because they do not clearly demonstrate the pathological lesion, and some carry risks.

Original pages 354–374

SKULL X-RAYS

Before C.T. became available, skull radiography was a useful initial investigation that provided certain information about brain tumors without endangering the patient. Routine views were anteroposterior (A-P), lateral, and Towne’s views. Additional views could examine particular sites, such as the optic foramen or sella turcica. A posteroanterior (P-A) view showed changes in the frontal bone, orbit, and lesser wing of the sphenoid; Stenvers’ view examined the auditory canal; and the submentovertical view examined the skull base.

The changes in skull radiographs caused by brain tumors are as follows:

1. Changes due to raised intracranial pressure. Tumors are among the many causes of raised intracranial pressure. The pressure must remain elevated for a prolonged period before skull changes develop. Pulsations of the cortex, CSF, and blood vessels with the heartbeat cause bone resorption, producing the following abnormalities.

1.1 Convolutional markings appear as indentations in the skull because its inner surface has become thinner. These are sometimes called digital impressions because they resemble indentations made by pressing fingers into modeling clay (Figure 6.1). This change is seen in adults. Prominent markings in the parietal region have particular diagnostic significance, because some digital impressions may normally occur in the occipital and frontal regions.

1.2 Erosion of the dorsum sellae is a frequent abnormality. The dorsum sellae and posterior clinoid become thin and fade from view (Figure 6.2). This is common in adults but uncommon in children, who can accommodate raised intracranial pressure by separation of the cranial sutures. With prolonged and progressively increasing pressure, the sellar floor becomes thinner, and the sella enlarges. In some cases, it disappears completely, together with atrophy of the tuberculum sellae (Figure 6.3).

1.3 Suture separation. The sutures between the skull bones separate. This occurs in children whose skull bones have not yet fused with bone, but not in adults, whose sutures are firmly joined. The coronal suture is the first to separate because it is the last to fuse (Figure 6.4, A and B).

1.4 Enlargement of the head results from separation of the cranial sutures and occurs in young children (Figure 6.4).

1.5 Localized skull bulging occurs in children with a slowly growing tumor at the brain surface. The bulging bone is thinner than the surrounding skull (Figure 6.5).

2. ABNORMAL VASCULAR GROOVES. Normal skull radiographs show grooves for the middle meningeal artery and its branches, diploic venous channels, and emissary veins. Tumors arising at the brain surface in contact with the dura and skull, such as meningiomas, usually receive their blood supply from the middle meningeal artery. Two changes may be seen: i) neovascularity, and ii) enlargement of arterial and venous grooves on the inner skull surface (Figure 6.6).

Neovascularity consists of new vessels around the tumor that supply it. It is an important sign for tumor localization (Figure 6.7).

Enlargement of vascular grooves and vessels is more common than neovascularity and usually occurs with tumors of the cerebral convexity and parasagittal region. Tumors at the brain base usually do not show this change. Three changes in the middle meningeal arterial grooves are significant: i) enlargement on only one side; ii) enlargement of a single branch; and iii) tortuosity. Unilateral enlargement suggests that the vessel supplies a tumor on that side. Enlargement may occasionally be bilateral, as when a falcine meningioma grows to both sides. Enlargement of one branch of the middle meningeal artery likewise raises suspicion that it supplies a tumor.

Enlargement of emissary venous grooves and their skull openings may occur with tumors causing raised intracranial pressure, or when the vein drains a tumor. Sites include the occipital emissary vein (Figure 6.8) and the region of the Pacchionian granulations.

3. CALCIFICATION. Calcium deposits in intracranial structures, including pathological lesions, can assist diagnosis. Several brain tumor types calcify, particularly slowly growing (benign) tumors such as meningioma, craniopharyngioma, and oligodendroglioma. Recognizing the pattern and location of calcification helps distinguish tumor types.

Physiological calcification may occur in the pineal gland, choroid plexus, falx cerebri, tentorium cerebelli, and diaphragma sellae. Pineal and choroid plexus calcification are particularly important in relation to tumors. On an A-P view, the calcified pineal gland normally lies in the midline of the skull. A tumor or other expansile mass may displace it to the opposite side (Figure 6.9, B), indicating a supratentorial mass. It may also be displaced anteriorly, posteriorly, superiorly, or inferiorly, depending on the tumor’s position. Pineal calcification is found in approximately 55% of people over 20 years of age⁽¹⁾, although it is less common in Thai people. Pineal calcification in a child, unusually large calcification, or calcification unlike the normal gland should always be regarded as suspicious for pineal pathology. A detailed neurological examination and further investigations are required.

Choroid plexus calcification usually occurs in its glomus. It may be unilateral or bilateral and is less common than pineal calcification. Calcified glomera normally lie midway between the midline and the lateral skull margins and are symmetrical. A tumor may displace them from their normal positions, producing asymmetry (Figure 6.10, A and B). A choroid plexus papilloma may occasionally produce a large calcified mass on one side.

Tumor calcification varies with the tumor type. Gliomas, including oligodendroglioma, astrocytoma, and ependymoma, show clusters of small and large calcific fragments or curved lines scattered throughout the tumor (Figure 6.11). Oligodendroglioma calcifies more commonly than the other types. In some cases, extensive calcification merges into an appearance resembling cigarette smoke.

Craniopharyngioma frequently calcifies and can show several patterns. Curved lines indicate calcification of a tumor cyst wall (eggshell calcification); small and large fragments may also coalesce into a mass. The important feature is its suprasellar location (Figure 6.12, A, B, and C), although some lesions lie within the sella.

Slowly growing meningiomas, especially psammomatous meningiomas, develop numerous calcified psammoma bodies. Their radiographic calcification is therefore uniformly white (homogeneous) (Figure 6.13), allowing the size and shape of the mass to be seen without angiography. In addition to calcification, two other radiographic abnormalities may coexist: i) hyperostosis and ii) increased vascularity, described earlier. Hyperostosis (Figure 6.14) develops in the skull adjacent to the tumor. This new bone formation is a reaction to the tumor, although the precise mechanism is unknown. Some cases show no tumor cells in the thickened bone or in the dura against the tumor surface; in others, tumor cells extend through the dura into the skull. Hyperostosis is usually accompanied by hypervascularity. Changes in the outer table produce a visible bony prominence on the head (Figure 6.15). A tuberculum sellae tumor may produce brushlike hyperostosis⁽¹⁾ (Figure 6.16). Another diagnostically important finding is upward bulging of the cortical bone above the ethmoid and sphenoid sinuses, enlarging the air sinus beneath the tumor upward. This is termed blistering⁽¹⁾ (Figure 6.16). With a sphenoid tumor, particularly meningioma en plaque, hyperostosis may cause exophthalmos and temporal bony prominence (Figure 6.17).

4. Local bone erosion. Bone at the site of a tumor consistently shows destruction or a reactive change. Rapidly growing tumors, such as skull metastases, destroy bone rapidly and extensively. Slowly growing tumors, such as meningioma, neurilemmoma, and pituitary adenoma, cause slow, localized destruction. Most tumors that erode bone lie at the skull base. Common examples include pituitary tumors, optic nerve glioma, acoustic nerve tumors, and glomus jugulare tumors. The changes are visible on skull radiographs.

4.1 Changes in the sella turcica. An intrasellar tumor, such as a pituitary adenoma, enlarges the sella into a rounded shape extending beneath the tuberculum sellae and anterior clinoid. This is called ballooning of the sella (Figure 6.18). A double sellar floor may be seen, indicating greater growth on one side than the other (Figure 6.19). This appearance may also occur with a medial lesser-wing meningioma or an intracavernous aneurysm.

An early intrasellar tumor erodes the junction of the dorsum sellae and sellar floor. The bone gradually thins and ultimately disappears. With a slowly growing tumor, reossification may produce a thin bony outline, creating the ballooned appearance.

4.2 Changes in the internal auditory canal are demonstrated by Towne’s and Stenvers’ skull views. They are important in diagnosing acoustic nerve tumors, most of which arise near the meatus of the internal auditory canal. As the mass enlarges, the following canal changes occur (Figure 6.20, A, B, and C): i) the internal meatus enlarges to more than 8 mm vertically; ii) the canal becomes funnel-shaped, with the wider end medially; iii) its upper margin becomes indistinct; iv) one canal exceeds the other in size by more than 2 mm; and v) a large tumor may destroy the petrous apex.

4.3 Changes in the jugular foramen. Enlargement occurs with glomus jugulare tumors. Some also destroy the posterior petrous bone (Figure 6.21).

4.4 Changes in the optic foramen. Both sides must be imaged and compared. Normally they should be equal or differ by no more than 2 mm. With optic nerve glioma, the optic foramen enlarges and has a thin, sharply defined margin (Figure 6.22) because the tumor grows slowly. A lateral skull radiograph shows a J-shaped sella (Figure 6.23), named for its shape. The tumor presses on and flattens the anterior sella and tuberculum sellae. The combination of an enlarged optic foramen and a J-shaped sella is important in diagnosing optic nerve glioma.

Optic nerve meningiomas may produce hyperostosis or erosion of the foramen. Nasopharyngeal carcinoma extending upward destroys the optic foramen together with the adjacent skull base (Figure 6.24).

4.5 Changes in the clivus. A clival chordoma may extend into the middle cranial fossa, C-P angle, and foramen magnum, causing destruction of the petrous bone together with the clivus.

Nasopharyngeal carcinoma extending into the base of the brain can likewise destroy bone in this region.

Original pages 374–375

CEREBRAL ANGIOGRAPHY

Before C.T. and MRI became available, this was an important investigation performed alongside skull radiography. It provided a high rate of accurate diagnosis, but was invasive and potentially hazardous, with several possible complications that could be severe enough to cause paralysis. A physician performing this investigation therefore required adequate training. In experienced hands, important complications would not occur. The introduction of C.T. and MRI (around 1973 and 1987, respectively) greatly reduced the use of angiography to diagnose brain tumors and other expanding masses. It continued to be performed in selected cases to determine the location of important vessels and the vascularity of a tumor, information useful in planning surgery for maximum patient safety, and in vascular disorders such as aneurysms and AVMs. Nevertheless, where C.T. is unavailable, angiography remains a very useful investigation and should therefore be learned.

When angiography is used to investigate a tumor, three types of change in the cerebral vessels must be examined:

1. Local stretching of cerebral vessels at the site of the tumor
2. Vessels affected by herniation or displacement of midline structures toward a region of lower pressure; and
3. Abnormal circulation within the tumor

Before discussing abnormalities on an angiogram, the normal appearances of carotid and vertebral angiograms will be described to provide a basis for understanding. The technique of cerebral angiography will not be discussed.

Original pages 375–382

Normal appearance of the carotid angiogram

The internal carotid artery branches from the common carotid artery at the level of the upper part of the thyroid cartilage and enters the carotid canal in the petrous bone. Its cervical portion has no branches. The artery runs through the carotid canal into the cavernous sinus; this is called the cavernous sinus portion. On a lateral skull radiograph it runs horizontally at approximately the level of the floor of the sella turcica. It then emerges from the cavernous sinus medial to the anterior clinoid process and enters the subarachnoid space. The artery passes upward and backward between the optic and oculomotor nerves. This is called the supraclinoid portion. On the lateral view, the cavernous and supraclinoid portions form a curved, pipe-like configuration called the carotid siphon. On the AP view, its shape is less clear because the vessels overlap, but the supraclinoid portion can be seen passing upward and slightly laterally before dividing into the anterior and middle cerebral arteries (Figure 6.25).

As the internal carotid artery passes through the carotid canal and cavernous sinus, it gives off small branches that are normally invisible on an angiogram. A branch may enlarge and become visible when it supplies a tumor or other lesion in that region.

Branches of the internal carotid artery

1. Ophthalmic artery. This is the first branch visible on the angiogram. It arises immediately after the internal carotid artery emerges from the cavernous sinus and enters the orbit through the optic foramen. On a lateral angiogram it is seen running forward from the internal carotid artery (Figure 6.27).

2. Posterior communicating artery. This arises from the posterior aspect of the internal carotid artery and passes backward and medially to join the posterior cerebral artery approximately 1 cm from the basilar bifurcation. These two arteries form part of the circle of Willis. On a lateral view, the posterior communicating artery runs horizontally or curves slightly downward and is about 1.5 cm long. Its origin may be enlarged, a feature called junctional dilatation that can sometimes be confused with an aneurysm. If this enlargement does not exceed 3 mm and the posterior communicating artery arises from its apex, it is considered normal rather than an aneurysm. On the AP view, the proximal posterior communicating artery is hidden by the internal carotid artery, while its posterior portion lies medial to the internal carotid artery (Figure 6.26). This relationship is important: a change in position should be regarded as abnormal.

3. Anterior choroidal artery. This arises from the internal carotid artery slightly behind the posterior communicating artery. It is a small vessel that runs backward and laterally into the choroidal fissure of the anterior temporal lobe to supply the choroid plexus, hippocampus, and basal ganglia.

On a lateral angiogram, this artery passes backward and slightly downward before curving upward (Figure 6.26b). On the frontal (AP) view, it passes upward and slightly medially for a short distance before turning laterally into the temporal horn (Figure 6.25).

In tumors of the choroid plexus or basal ganglia, this artery may be enlarged and form a visibly elongated curve.

4. Anterior cerebral artery. This is one of the two terminal branches of the internal carotid artery. It runs forward and toward the midline, passes over the anterior perforated substance above the optic nerve and optic chiasm, and connects with the opposite anterior cerebral artery through the anterior communicating artery. It then runs backward along the corpus callosum as far as the parieto-occipital fissure. Because it lies close to the midline of the cerebral hemispheres, it is an important vessel for demonstrating midline shift (herniation) of the brain.

The important branches of the anterior cerebral artery visible on angiography are:

4.1 The frontopolar artery arises before the anterior cerebral artery reaches the genu of the corpus callosum and runs forward to supply the anterior frontal lobe (Figure 6.27).

4.2 The callosomarginal artery is a large branch arising behind the frontopolar artery. It follows the callosomarginal sulcus and divides into anterior, middle, and posterior internal frontal branches, supplying the medial frontal lobe as far as the paracentral lobule (Figure 6.27).

4.3 The pericallosal artery is the distal continuation of the anterior cerebral artery and runs backward to the parieto-occipital fissure (Figure 6.27).

5. Middle cerebral artery. After arising from the internal carotid artery, it runs laterally and slightly forward into the beginning of the Sylvian fissure, where it divides into three branches (trifurcation). The major branches pass upward and backward over the surface of the insula (island of Reil), giving off further branches while on the insula. There are about 5–8 branches from front to back. These ascend to the cleft between the insula and operculum, then turn downward to emerge on the surface of the Sylvian fissure and supply the frontal, parietal, and temporal cortex.

On a lateral angiogram, these branches are arranged from front to back. Three lines—one joining the points where the branches turn back toward the Sylvian fissure, one along the middle cerebral artery, and one along the first (most anterior) insular branch—form a triangle called the Sylvian triangle (Figure 6.27). This is very important for localizing tumors and other expanding masses.

Tumors at different sites produce characteristic changes in the shape of this triangle. Its most posterior point is called the angiographic Sylvian point.

On the frontal view, the middle cerebral artery branch over the anterior insula lies lowest and most medially. Successive branches lie progressively higher and farther laterally, so that the most posterior branch is highest and most lateral. This arrangement reflects the fact that the anterior insula is nearer the cerebral midline than the posterior insula (Figure 6.28). The middle cerebral artery itself lies approximately 20–30 mm from the inner skull, while the angiographic Sylvian point lies about 30–43 mm away. The latter point is approximately halfway along a line drawn from the upper border of the petrous bone to a horizontal line along the inner skull at the vertex⁽¹⁾ (Figure 6.29). Changes in these relationships indicate the location of a tumor, as described below.

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The small branches arising from the horizontal segment of the middle cerebral artery are the medial and lateral lenticulostriate arteries. Approximately 2–6 can be seen on an angiogram. They ascend into the anterior perforating substance. The medial lenticulostriate arteries supply the medial ganglia, including the lentiform nuclei, internal capsule, thalamus, and caudate nucleus. The lateral lenticulostriate arteries supply the putamen, lateral part of the globus pallidus, and internal capsule. On a frontal angiogram, the lenticulostriate arteries form an S-shaped curve (Figure 6.25). They are usually not visible on the lateral view because the internal carotid bifurcation obscures them. With tumors of the basal ganglia, these vessels become enlarged and their position and shape are abnormal.

Original pages 382–387

Normal appearance of the vertebral angiogram

VERTEBRAL ARTERY arises from the subclavian artery and enters the foramina transversaria from C₆ to C₁. It then pierces the dura at the foramen magnum, enters the posterior fossa, and joins the opposite vertebral artery at the pontomedullary junction to form the basilar artery. The basilar artery lies in the midline anterior to the pons. At the upper border of the pons, or the level of the dorsum sellae, it divides into the two posterior cerebral arteries. The important vertebrobasilar branches that should be recognized and are visible on angiography are (Figure 6.30):

1. posterior inferior cerebellar a.
2. anterior inferior cerebellar a.
3. superior cerebellar a.
4. posterior cerebral a.
5. posterior choroidal a.

Posterior inferior cerebellar artery. This arises from the vertebral artery approximately 1–2 cm before the latter joins to form the basilar artery. It runs backward along the side of the medulla and divides into medial and lateral branches. The lateral branch supplies the inferior cerebellum. The medial branch lies along the medial aspect of the tonsil and curves around its lower border, forming the caudal loop. It then ascends to the upper tonsil, corresponding to the posterior aspect of the fourth ventricle, and forms the rostral loop. Beyond this, it supplies the medial cerebellar hemisphere and vermis. A choroidal branch arising at the rostral loop supplies the fourth ventricular choroid plexus and can sometimes be seen. On the lateral view, the posterior inferior cerebellar artery and its caudal loop are clearly visible as described (Figure 6.31). On the AP view, the vessel is initially some distance from the midline at its origin from the vertebral artery, then approaches the midline. The arteries on the two sides are approximately 3 mm apart. Their separation indicates a tumor developing between them.

The caudal and rostral loops are important landmarks for posterior fossa lesions because they indicate the positions of the tonsil and posterior fourth ventricle, respectively. A posterior fossa tumor causes tonsillar herniation, with the caudal loop displaced through the foramen magnum into the cervical canal (Figure 6.32), visible on the lateral skull view. Normally, the caudal loop is at the lower border of the tonsil and lies no lower than the margin of the foramen magnum. In some patients it may descend as far as C2–3. The rostral loop may also change position: a tumor within the fourth ventricle displaces it backward (Figure 6.69).

Anterior inferior cerebellar artery. This small vessel arises from the proximal basilar artery and runs laterally toward the internal auditory meatus. It can be seen on a frontal vertebral angiogram. On the lateral view it is obscured by bone, and in some patients it is not visible on angiography.

Superior cerebellar artery. This arises from the basilar artery just before its termination and runs laterally and slightly downward around the lateral midbrain to the side of the quadrigeminal plate. It then curves upward to supply the superior cerebellum. On a lateral vertebral angiogram, it lies below the posterior cerebral artery. Over the cerebellum it forms a dome with its apex superiorly, but below the medial branch of the posterior cerebral artery (Figure 6.31). If this dome lies above the posterior cerebral artery, a cerebellar tumor should be suspected. On the frontal view, the superior cerebellar artery initially lies below the posterior cerebral artery. After passing around the midbrain, it lies more medially than the posterior cerebral artery (Figure 6.30). The superior cerebellar arteries on the two sides have matching configurations and relationships to the posterior cerebral arteries.

Posterior cerebral artery. This is a terminal branch of the basilar artery. The portion that curves around the midbrain is infratentorial. At the tentorial edge, it ascends into the supratentorial compartment to supply the temporal and occipital lobes.

Posterior choroidal artery. This arises from the proximal posterior cerebral artery and curves around the midbrain alongside it. This portion is not visible on the vertebral angiogram because it is obscured by the posterior cerebral artery. There are two posterior choroidal branches, medial and lateral (Figure 6.33). The medial posterior choroidal artery passes to the back of the midbrain. On reaching the side of the pineal gland, it enters the tela choroidea of the third ventricle to supply its choroid plexus. The lateral posterior choroidal artery passes around the posterior border of the thalamus to supply the choroid plexus of the lateral ventricle.

On a frontal vertebral angiogram, the posterior cerebral artery lies above the superior cerebellar artery, then passes lateral to it (Figure 6.30). In the supratentorial compartment, it gives off temporal and occipital branches whose positions vary. The posterior choroidal arteries are usually not visible. On the lateral vertebral angiogram, the posterior cerebral artery lies above the superior cerebellar artery throughout; any change in this relationship is abnormal. The posterior choroidal arteries are usually visible on the lateral view. Both curve backward and upward, with the lateral posterior choroidal artery forming a wider arc and lying posterior to the medial posterior choroidal artery. Changes in the configuration or size of these vessels indicate lesions of the thalamus, ventricle, or pineal gland.

Original pages 387–393

Normal appearance of the cerebral veins

The cerebral veins are divided into superficial and deep cerebral veins. Venous blood drains into the superior sagittal, inferior sagittal, and transverse sinuses and then into the internal jugular vein.

SUPERFICIAL CEREBRAL VEINS

1. SUPERIOR SUPERFICIAL CEREBRAL VEINS lie on the cortex of the cerebral hemispheres and run upward and backward. Before emptying into the superior sagittal sinus, they turn forward and then enter the sinus. At the central sulcus, a large vein called the superior anastomotic vein of Trolard (Figure 6.34) marks the position of the motor cortex. In the anterior frontal lobe, the superficial cerebral veins are less conspicuous than posteriorly.

2. MIDDLE CEREBRAL VEIN lies in the Sylvian fissure and receives blood from the lower frontal lobe and upper temporal lobe. It descends along the Sylvian fissure into the sphenoparietal sinus at the medial sphenoid ridge. Blood then drains into the cavernous sinus (Figure 6.34).

3. INFERIOR ANASTOMOTIC VEIN OF LABBÉ communicates with the superior anastomotic vein of Trolard and the middle cerebral vein. It runs downward and backward over the posterior temporal lobe to enter the transverse sinus (Figure 6.34).

Important DEEP CEREBRAL VEINS

1) INTERNAL CEREBRAL VEIN begins at the foramen of Monro through the union of the thalamostriate and septal veins. It runs in the roof of the third ventricle close to the midline, parallel to the internal cerebral vein on the opposite side. The veins curve upward and then downward to unite above the suprapineal recess, forming the great vein of Galen (Figure 6.34).

2) GREAT VEIN OF GALEN passes into the quadrigeminal cistern and then curves upward into the straight sinus, which joins the transverse sinus at the torcular Herophili. In some patients, the posterior callosal vein is visible as a small vessel running along the posterior border of the splenium to join the anterior part of the great vein of Galen. This vessel helps identify the position of the splenium.

3) THALAMOSTRIATE VEIN lies between the thalamus and caudate nucleus and receives blood from the wall of the lateral ventricle. It therefore indicates the size of the lateral ventricle. On the lateral carotid angiogram it lies above and parallel to the internal cerebral vein (Figure 6.34). On the frontal view, the two thalamostriate veins form curves on either side of the internal cerebral veins, resembling buffalo horns (Figure 6.35). If the ventricles are enlarged, these curves extend farther from the midline. This is a more reliable sign of ventricular enlargement than changes in the anterior cerebral artery. Conversely, a vein lying unusually close to the midline indicates a smaller ventricle or one compressed by a tumor lateral to it.

The junction of the thalamostriate vein with the internal cerebral vein and the septal vein from the septum pellucidum is called the “venous angle.” It corresponds to the foramen of Monro and normally lies directly above the dorsum sellae or slightly posterior to this line. Displacement of the venous angle indicates pressure from an expanding mass. In some patients, the thalamostriate vein joins the internal cerebral vein behind the foramen of Monro, placing the venous angle farther posteriorly than usual. This is called a “false venous angle” (Figure 6.36), and caution is required in interpretation. If a frontal lobe tumor truly displaces the venous angle backward, the internal cerebral vein must also be displaced into an upward arch.

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4) BASAL VEIN OF ROSENTHAL originates in the anteromedial temporal lobe, the interpeduncular fossa of the midbrain, and the anterior perforated substance. It passes backward and upward around the midbrain to join the internal cerebral vein on each side before these unite as the great vein of Galen. Its appearance in the lateral and AP views is shown in Figures 6.34 and 6.35.

5) VEINS OF THE POSTERIOR FOSSA are seen on vertebral angiography and are divided into three groups⁽¹⁾: i) the superior group drains the superior cerebellum into the vein of Galen; ii) the anterior group drains the anterior cerebellum into the petrosal sinus; and iii) the posterior group drains the posterior cerebellum into the torcular, straight sinus, and transverse sinus. Two other important veins are the anterior pontomesencephalic vein, lying anterior to the pons, and the precentral cerebellar vein, running in the precentral cerebellar fissure (Figure 6.37a, b). Visualization of these two veins helps localize tumors.

DURAL SINUSES

These are important because they receive venous blood from the brain. Obstruction causes cerebral venous congestion and brain swelling and may be fatal. The important dural sinuses are:

1) SUPERIOR SAGITTAL SINUS lies beneath the superior sagittal suture. It begins at the nasion and passes backward, progressively increasing in size, to join the transverse sinus at the torcular Herophili; drainage then continues into the internal jugular vein. Most blood passes into the right transverse sinus. This sinus receives blood from cortical veins, which enter in a direction opposed to the flow within the superior sagittal sinus.

2) INFERIOR SAGITTAL SINUS lies along the lower edge of the falx cerebri and is visible on some carotid angiograms. At the junction of the falx and tentorium, the great vein of Galen joins it to form the straight sinus, which runs backward in the midline to the torcular.

3) TRANSVERSE SINUS begins at the torcular, receiving blood from the superior and inferior sagittal sinuses and the straight sinus. It extends to either side along the junction of the supratentorial and infratentorial compartments, continuing into the sigmoid sinus and internal jugular vein. The right transverse sinus is usually larger than the left.

Original page 393

Angiographic abnormalities in brain tumors

A brain tumor is an expanding lesion that compresses brain tissue, vessels, and cerebrospinal fluid pathways. Adverse consequences include cerebral edema, hydrocephalus, increased intracranial pressure, and herniation of brain tissue and vessels. Angiography can demonstrate the following changes:

1. Herniation of vessels and brain tissue across the midline toward the side with lower intracranial pressure.
2. The location and size of the tumor, indicated by displacement of vessels at the tumor site from their normal positions.
3. The tumor type, judged from its blood supply, the rate of blood flow, and the pattern of vascular abnormalities within it.

Original pages 393–400

Angiographic appearances of cerebral herniation

A tumor may produce four important forms of herniation: i) midline shift, ii) transtentorial herniation, iii) tonsillar herniation, and iv) upward cerebellar herniation. These can be demonstrated by angiography, with the characteristic appearances described below.

MIDLINE SHIFT is displacement of the brain across the midline toward the side with lower intracranial pressure, passing beneath the falx. It is called subfalcine or cingulate herniation because the displaced structure is the cingulate gyrus, accompanied by the anterior cerebral artery. The inferomedial frontal lobe and anterior portion of the anterior cerebral artery are not covered by the falx, so they are displaced to the opposite side more readily than posterior structures, which are almost completely covered by the broader posterior falx. The pericallosal artery on the corpus callosum is not covered by the falx along its course, although its branches are. On a frontal carotid angiogram, the anterior cerebral arteries run parallel on either side of the midline. When an anterior cerebral artery and its branches are displaced to the opposite side, the lower edge of the falx forces them back toward the midline, creating an angular, step-like appearance (Figures 6.39–6.41).

Midline shift also affects the internal cerebral vein, septal vein, and vein of Galen. In deep-seated brain tumors, displacement of these deep veins is more conspicuous than displacement of the anterior cerebral artery (Figure 6.38).

Displacement of the anterior cerebral artery from the midline takes several forms that also help localize the tumor. The appearances on carotid angiography are as follows:

1. PROXIMAL SHIFT is displacement of the anterior portion of the anterior cerebral artery beneath the falx to the opposite side, with its distal portion gradually returning to the midline without an angular bend (Figure 6.39). It is clearly seen on the frontal view and indicates a tumor in the anterior and inferior frontal lobe.

2. ROUNDED SHIFT is a bowing of both the anterior and posterior portions of the anterior cerebral artery to the opposite side (Figure 6.40). It indicates a large frontal lobe tumor at or near the origin of the pericallosal artery.

3. SQUARE SHIFT is equal displacement of the anterior and posterior portions of the anterior cerebral artery to the opposite side (Figure 6.41). It indicates a tumor in the posterior frontal lobe. Although pressure from the tumor is greater posteriorly, the broader posterior falx limits displacement of the posterior anterior cerebral artery; consequently, the brain and vessels are displaced by equal amounts.

4. DISTAL SHIFT shows displacement of the posterior anterior cerebral artery to the opposite side, followed by an abrupt return to the midline where it is restrained by the falcine edge. The anterior portion remains in the midline (Figure 6.42). This indicates a parietal lobe tumor, especially in the parasagittal area. The anterior portion remains central because the pressure does not reach it. A very large mass may displace it somewhat, but less than the posterior portion.

The internal cerebral vein lies at the midline in the center of the brain, making it an important vessel in which contralateral displacement may be seen. Displacement of the internal cerebral vein without a corresponding change in the anterior cerebral artery indicates a deep tumor in the posterior frontal lobe or thalamic region. Changes in its shape may also localize a tumor, as discussed later.

TRANSTENTORIAL HERNIATION changes the configuration of the posterior communicating and posterior cerebral arteries. On the lateral carotid angiogram, uncal herniation produces increased downward bowing of the posterior communicating artery because the uncus presses on it from above (Figure 6.43a). If the parahippocampal gyrus also herniates, both the posterior communicating and posterior cerebral arteries sag in a broad downward curve. At the tentorial edge, the vessel makes an angular upward turn into the supratentorial compartment (Figure 6.43b). The anterior choroidal artery is stretched horizontally. On the AP view, both the posterior cerebral and anterior choroidal arteries shift toward the midline (Figure 6.44), an important diagnostic feature. The anterior choroidal artery also forms a wider arc.

TONSILLAR HERNIATION is demonstrated by the caudal loop of the posterior inferior cerebellar artery lying below the margin of the foramen magnum, clearly visible on a lateral vertebral angiogram (Figure 6.32). The tonsil may descend as far as C2–3. In posterior fossa tumors, the tonsil on the tumor side usually herniates farther downward than the opposite tonsil.

UPWARD CEREBELLAR HERNIATION displaces the basilar artery forward on the lateral vertebral angiogram because the upward-herniating tissue lies behind the brainstem. The superior cerebellar artery rises above the posterior cerebral artery (Figure 6.45), on one or both sides. The most important venous-phase finding is elevation of the great vein of Galen and the posterior basal vein of Rosenthal by the upward-herniating cerebellar tissue.

Original pages 400–430

Local vascular changes caused by brain tumors

Wherever a tumor develops, it compresses nearby vessels and alters their configuration and position. Arteries and veins adjacent to it may be stretched in an arc around its margin, sometimes outlining the mass. The tortuosity of vessels following the gyri disappears; the vessels become narrower and straighter. An infiltrative tumor without cerebral edema may cause relatively little vascular change. When a tumor produces local cerebral edema, vessels in the sulci are compressed into curves by the mass and swelling. On the lateral carotid angiogram, groups of vessels form concentric curved layers resembling an onion cut across (Figure 6.46). With a subcortical tumor, pressure from the mass and edema spreads the cortex, stretching and separating the vessels (Figure 6.47).

In the posterior fossa, tumors can alter the positions of the superior cerebellar, basilar, and posterior inferior cerebellar arteries, just as supratentorial tumors alter vessels in that compartment.

Deep cerebral hemisphere tumors can alter the size and shape of the septal vein, internal cerebral vein, thalamostriate vein, great vein of Galen, and basal vein of Rosenthal (Figure 6.50).

Taveras used the Sylvian fissure as a reference⁽¹⁾ for angiographic localization of tumors (Figure 6.48), as follows:

a. SUPRATENTORIAL TUMORS at the following sites:

1. anterior frontal lobe
2. supra-Sylvian (posterior frontal and anterior parietal)
3. infra-Sylvian (temporal lobe)
4. retro-Sylvian (temporo-occipital, parieto-occipital, and occipital lobe)
5. latero-Sylvian (lateral to the Sylvian fissure, extracerebral)
6. intra-Sylvian (within the Sylvian fissure)
7. centro-Sylvian (thalamus, basal ganglia, deep posterior frontal)
8. hydrocephalus
9. intraventricular, periventricular structures
10. suprasellar and parasellar

b. INFRATENTORIAL TUMORS

c. INCISURAL TUMORS

Dividing the brain into regions related to the Sylvian fissure and Sylvian triangle is useful for tumor localization. Physicians should therefore observe and remember the normal Sylvian triangle. Tumors at different sites alter its shape in different ways, as described below.

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ANTERIOR FRONTAL LOBE TUMORS produce changes in three vascular structures: the anterior cerebral artery, the distal internal carotid artery, and the Sylvian triangle vessels. The anterior cerebral artery changes are particularly important. A tumor causes proximal shift, or rounded shift if large. A frontobasal tumor elevates the frontopolar and anterior cerebral arteries (Figure 6.49). An olfactory groove meningioma arches the anterior cerebral artery upward with little or no contralateral displacement, although a predominantly unilateral tumor also displaces it to the opposite side. A frontal lobe tumor bows the anterior cerebral and frontopolar arteries backward. The Sylvian triangle may be unaffected, but a large tumor or one extending posteriorly pushes the anterior insular branches backward, compressing the triangle posteriorly (Figure 6.49). The carotid siphon narrows as the internal carotid artery is depressed and its bifurcation displaced backward. The internal cerebral vein becomes more arched upward, and the venous angle is displaced backward (Figure 6.50).

An anterior parasagittal tumor may depress the anterior portions of the pericallosal and callosomarginal arteries.

Supra-Sylvian tumors lie in the posterior frontal or anterior parietal lobe. They cause square or distal shift of the anterior cerebral artery, depending on location, and depress the supraclinoid internal carotid artery. A tumor on the frontoparietal convexity stretches and separates the middle cerebral artery branches supplying that region. The upper border of the Sylvian triangle is depressed (Figure 6.51a), best seen on the lateral view. A large tumor or extensive edema spreading into the parietal lobe also depresses the angiographic Sylvian point and shifts the internal cerebral vein to the opposite side.

Parietal lobe tumors depress the angiographic Sylvian point and move it toward the midline, changes visible on both frontal and lateral carotid angiograms (Figure 6.52). The posterior cerebral artery is often displaced downward and medially. The internal cerebral vein is flattened and displaced contralaterally, increasing its distance from the thalamostriate vein. Tumors here generally shift the internal cerebral vein more than the anterior cerebral artery because the broad falx restricts arterial displacement. This relationship is important in localization.

A parasagittal parietal tumor produces important changes in the pericallosal and callosomarginal arteries: both are depressed and deflected to the opposite side. The upper (distal) middle cerebral artery branches are stretched, separated, and distorted. A large parietal parasagittal tumor invariably depresses the angiographic Sylvian point. The internal cerebral vein is flattened and may not shift contralaterally. A parasagittal meningioma may extend into the superior sagittal sinus, narrowing or occluding it. A surface tumor can stretch cortical veins around its border (Figure 6.53).

Temporal lobe tumors are infra-Sylvian tumors. Their characteristic carotid angiographic changes vary somewhat with the site and size of the mass in the middle cranial fossa, but generally include (Figure 6.54a, b): i) elevation of the middle cerebral artery and its branches, clearly seen laterally; ii) medial displacement of the middle cerebral artery; iii) medial displacement of the supraclinoid internal carotid artery with elevation of its bifurcation; iv) medial displacement of the anterior choroidal artery, which may also move upward or downward; v) medial displacement of the basal vein of Rosenthal; vi) midline shift of the anterior cerebral artery and internal cerebral vein, usually a proximal shift; and vii) when parahippocampal herniation occurs, downward and medial displacement of the posterior communicating and posterior cerebral arteries.

Tumors in different parts of the temporal lobe have the following angiographic appearances:

An anterior temporal lobe tumor elevates the horizontal middle cerebral artery. The anterior choroidal artery is also displaced upward and medially. The anterior Sylvian triangle is elevated while the angiographic Sylvian point remains unchanged (Figure 6.55).

With a posterior temporal lobe tumor, the lateral carotid angiogram shows elevation of the middle cerebral artery branches, with only slight change in the proximal horizontal segment. The angiographic Sylvian point is displaced upward and forward. The frontal view likewise shows elevation and medial displacement of this point (Figure 6.56).

An intraparenchymal temporal lobe tumor not only arches the middle cerebral artery branches within and outside the Sylvian fissure upward, but also stretches the branches on the affected temporal cortex around the tumor margin. This is called the “draping sign” (Figure 6.57). It may also occur with a large extracerebral tumor at the floor of the middle cranial fossa, which pushes the temporal lobe and its vessels into a draped configuration.

Retro-Sylvian tumors lie behind the angiographic point and include occipital, parieto-occipital, and temporo-occipital tumors (Figure 6.58). The prominent feature on the lateral carotid angiogram is forward displacement of the angiographic Sylvian point, accompanied by upward or downward displacement depending on the tumor site. An occipitoparietal tumor moves the point forward and downward, whereas an occipitotemporal tumor moves it forward and upward. On the frontal view, the point appears lower because forward displacement projects as downward displacement in the AP view. An occipital tumor pushes the brain forward, so the distal cortical middle cerebral artery branches are invariably bowed as well. The posterior cerebral artery supplying the occipital lobe is stretched and displaced.

INTRA-SYLVIAN TUMORS arise within the Sylvian fissure. On the lateral carotid angiogram, middle cerebral artery branches within the fissure are stretched and separated, some lying above the tumor and others below—a characteristic appearance (Figure 6.59a, b). A tumor extending to the brain surface may displace the middle cerebral artery medially (Figure 6.59b).

LATERAL SYLVIAN TUMORS lie outside the Sylvian fissure and displace the middle cerebral artery branches and angiographic Sylvian point medially. If the tumor lies toward the anterior Sylvian fissure, however, the point may remain unchanged, with displacement confined to the insular middle cerebral artery branches.

Thalamic tumors. Because the thalamus is deep, the important changes involve the deep veins, particularly the thalamostriate and internal cerebral veins. Anatomically, the thalamostriate vein follows the groove between the caudate nucleus and thalamus, which form the lateral wall and floor of the lateral ventricle. In a thalamic tumor, the venous angiographic phase is important for localization: the thalamostriate vein is elevated, widening the venous angle. On the lateral angiogram, the thalamostriate vein lies unusually high above the internal cerebral vein, which itself becomes more curved. On the frontal carotid angiogram, the thalamostriate vein is elevated and deflected medially, while the internal cerebral vein shifts to the opposite side (Figure 6.60a, b). In the arterial phase, the anterior cerebral artery generally remains at the midline, although hydrocephalus may arch it upward. The middle cerebral artery branches and angiographic Sylvian point move farther laterally. This pattern occurs with deep intracerebral tumors generally, is not specific to thalamic tumors, and may also occur with hydrocephalus. The lenticulostriate arteries supplying the basal ganglia are displaced laterally and obliquely downward. The anterior choroidal artery enlarges and is stretched around the posterior thalamus, visible on both lateral and frontal carotid angiograms (Figure 6.61a, b). The posterior cerebral artery may be depressed. The lateral posterior choroidal artery enlarges and forms a wider arc.

The key carotid angiographic findings in a thalamic tumor are displacement of the internal cerebral and thalamostriate veins without displacement of the anterior cerebral artery, together with enlargement and widening of the arc of the anterior choroidal artery.

Pineal gland tumors elevate the posterior internal cerebral vein, separating it from the basal vein of Rosenthal (Figure 6.62). A large tumor may make the internal cerebral vein meet the great vein of Galen at an angle rather than an S-shaped curve, and may depress the great vein of Galen. Changes in the internal cerebral vein are important for diagnosing pineal tumors. Backward displacement of the posterior choroidal artery on the lateral view provides further support for this location (Figure 6.63).

Suprasellar tumors. The important related vessels are the internal carotid and anterior cerebral arteries. The intracavernous and supraclinoid internal carotid artery lie beside the sella, while the anterior cerebral artery lies above it. Any sellar tumor expanding upward arches the anterior cerebral artery upward and stretches the carotid siphon and supraclinoid segment upward and laterally, best seen on the frontal view. The lateral carotid angiogram shows widening of the siphon, called opening of the siphon (Figure 6.64a, b). Intrasellar tumors displace the intracavernous internal carotid artery laterally more conspicuously than extrasellar tumors. If a suprasellar tumor extends high enough to obstruct the foramen of Monro, hydrocephalus develops, with increased arching of the anterior cerebral artery and elevation of the septal and internal cerebral veins. This pattern may be difficult to distinguish from a third ventricular tumor.

A tumor arising at the tuberculum sellae or planum sphenoidale, such as a meningioma, displaces the anterior cerebral artery upward and backward while depressing the supraclinoid internal carotid artery. This narrows the carotid siphon, a pattern called closing of the siphon (Figure 6.65a, b).

A posteriorly situated suprasellar tumor elevates the internal carotid bifurcation and moves it forward. The anterior choroidal and posterior communicating arteries are displaced laterally, visible on the frontal carotid angiogram.

A tumor lateral to the sella turcica, such as a medial lesser wing meningioma, displaces the supraclinoid internal carotid artery medially. The internal carotid bifurcation and horizontal middle cerebral artery are elevated, best seen in the AP view. The anterior choroidal and posterior communicating arteries are simultaneously displaced medially and downward (Figure 6.66a, b).

Hydrocephalus. Tumors near or within the ventricular system, especially posterior fossa tumors, cause obstructive hydrocephalus. Carotid angiography shows: i) an anterior cerebral artery that is straight at the midline without shift on the AP view and arched upward like a bow on the lateral view; ii) elevation of the angiographic Sylvian triangle when the temporal horn is enlarged, resembling a temporal lobe tumor; iii) lateral displacement of the middle cerebral artery and its branches by the enlarged ventricle, increasing separation between the anterior and middle cerebral arteries on the frontal view; iv) outward bowing of the lenticulostriate arteries; and v) outward bowing of the thalamostriate vein with increased separation from the internal cerebral vein, indicating lateral ventricular size (Figure 6.67a, b, c).

Posterior fossa tumors. The vessels affected are the posterior inferior cerebellar, superior cerebellar, and basilar arteries. A tumor in one cerebellar hemisphere stretches and displaces the normally midline vermian branches of the posterior inferior cerebellar artery contralaterally. The superior cerebellar artery is usually elevated above the posterior cerebral artery by upward cerebellar herniation (Figure 6.68). The posterior inferior cerebellar artery descends below the foramen magnum because of tonsillar herniation, with the tumor side usually descending farther than the normal side. The basilar artery is pushed forward against the clivus (Figure 6.68). An inferior vermian tumor stretches the vermian arterial branches backward and displaces the rostral loop of the posterior inferior cerebellar artery downward and backward, best seen laterally (Figure 6.69). The frontal view shows separation of the posterior inferior cerebellar arteries. A superior vermian tumor separates the superior cerebellar arteries and their branches; the lateral view shows upward bowing of the superior cerebellar artery.

Fourth ventricular tumors displace the rostral loop backward and move the basilar artery against the clivus. A large mass also displaces the vermian branches of the posterior inferior cerebellar artery backward (Figure 6.69).

Brainstem tumors push the basilar artery against the clivus and separate the posterior cerebral and superior cerebellar arteries on the two sides as they pass around the brainstem (Figure 6.70a, b). These changes usually occur in advanced cases. Occasionally, a brainstem tumor grows anteriorly against the clivus, paradoxically placing the basilar artery farther posteriorly away from the clivus (Figure 6.71).

Clival tumors displace the brainstem and basilar artery backward away from the clivus, curving them around the tumor margin. A laterally situated tumor may also deflect them to the opposite side (Figure 6.72).

Cerebellopontine angle tumors elevate and medially displace the superior cerebellar artery alongside the brainstem (Figure 6.73). A large tumor displaces the rostral loop of the posterior inferior cerebellar artery and its vermian branches backward and contralaterally. The anterior inferior cerebellar artery may be displaced upward or downward and straightened.

The petrosal vein, if visible in the venous phase, is an important diagnostic landmark. This short vein lies superior and lateral to the internal auditory canal and receives the transverse pontine, mesencephalic, and cerebellar veins. A cerebellopontine angle tumor stretches the petrosal vein or makes it disappear entirely, an important angiographic sign of a lesion in this region.

Tumors at the tentorial edge are commonly meningiomas and may grow supratentorially, infratentorially, or in both compartments. They displace the posterior cerebral, superior cerebellar, and basilar arteries. An anterior tentorial tumor depresses the still-infratentorial portions of the posterior cerebral and superior cerebellar arteries downward and medially (Figure 6.74a, b, c, d). A more posterior tumor, where the posterior cerebral artery crosses into the supratentorial compartment, elevates that artery while depressing and medially displacing the superior cerebellar artery, increasing their separation (Figure 6.75a, b). A posterior midline tentorial tumor displaces the great vein of Galen forward. Upward extension may also displace the posterior internal cerebral vein. Infratentorial extension depresses superior cerebellar artery branches, visible on the lateral view. A large mass displaces the basilar artery contralaterally.

Original pages 430–431

Abnormal Tumor Circulation

Studying the vessels supplying a brain tumor and the circulation within it may reveal the type of tumor. Angiography therefore requires serial images showing the arterial, capillary, and venous phases to permit more reliable interpretation. Some tumors contain abnormally formed vessels and rapid blood flow, features of malignancy, whereas others have slow blood flow, and in some no intratumoral vessels are visible at all. These findings can indicate both the type and the malignancy of the tumor. The important angiographic features to observe are: i) the vessels supplying the tumor, which become enlarged and tortuous; ii) abnormalities of newly formed intratumoral vessels, which may be large, show arteriovenous shunting, or have a beaded appearance characteristic of malignancy; iii) tumor stain, also called tumor capillary blush, produced by an increased number and size of intratumoral vessels and thus increased blood flow. On the angiogram this appears as a whitish mass. The duration of tumor staining can also indicate malignancy. Prolonged staining favors a benign tumor, whereas rapid disappearance of staining favors malignancy, except in angioblastic meningioma and hemangioblastoma, which have rapid blood flow but are not malignant; iv) the appearance of veins draining the tumor or the surrounding area. Early visualization of veins in the arterial phase suggests malignancy. This can be distinguished from an AVM because an AVM does not form an expanding mass like a tumor.

Only a few tumors have circulatory abnormalities that allow them to be distinguished by angiography using the principles described above: meningioma, hemangioblastoma, malignant glioma, metastatic tumors, and glomus jugulare tumor.

Original pages 431–438

Meningioma

This tumor arises from arachnoid cells and receives blood from two systems, the external and internal carotid arteries. Its sites are relatively characteristic, most commonly the parasagittal region; other locations include the convexity, olfactory groove, lesser wing of the sphenoid, tuberculum sellae, petrous ridge, tentorium, foramen magnum, and ventricles. Displacement of vessels near the tumor is similar to that described under local vascular changes caused by tumors in general. The characteristic angiographic features of meningioma, however, are as follows:

1. Supply from the external carotid system: branches of the middle meningeal artery or meningeal arteries at other tumor sites are enlarged, sometimes tortuous, and appear relatively earlier than other vessels in the arterial phase because of their increased flow. These feeding arteries become progressively larger as they approach the tumor, an important sign that they supply it (Figure 6.76). Branches of the middle meningeal artery are more clearly seen on external carotid angiography.

External carotid angiograms show the characteristic sunburst or sunray appearance of meningioma, with capillaries radiating from a central point where the meningeal artery enters the tumor from its outer surface (Figure 6.76).

The internal carotid artery supplies the inner aspect of the tumor, and its branches near the tumor are enlarged. In intraventricular meningioma of the lateral ventricle, the anterior choroidal artery is enlarged and more tortuous, clearly visible on both lateral and frontal angiograms (Figure 6.77). Intraventricular meningiomas receive no blood supply from the middle meningeal artery.

2. Meningioma produces a well-defined, uniformly opaque white mass of homogeneous staining. Its intratumoral vessels resemble normal capillaries, but are numerous and do not have a beaded appearance. The white tumor stain remains visible for approximately 8–10 seconds, beginning in the arterial phase and continuing through the capillary and venous phases. Such prolonged staining is characteristic of meningioma (Figure 6.78), unlike malignant glioma or metastatic tumor, in which staining lasts for a shorter period. This principle is therefore used in diagnosing the tumor.

3. Early venous drainage is usually absent in meningioma. An exception is angioblastic meningioma, in which several large early draining veins may be seen because circulation is relatively rapid, as in malignant glioma. Nevertheless, staining remains prolonged, as in ordinary meningioma (Figure 6.79).

4. Meningiomas near the superior sagittal sinus often extend into it and cause partial or complete occlusion, clearly seen in the venous phase of the angiogram. Other tumors do not show this feature (Figure 6.80).

5. Even without tumor staining, the pattern of local vascular displacement in a falx meningioma may suggest the diagnosis. As an extracerebral tumor, a falx meningioma pushes the callosomarginal artery away from the falx toward the side of the tumor, because this artery lies lateral to the falx. The pericallosal artery, however, is pushed to the opposite side because it lies below the falx⁽³⁾ (Figure 6.81a, b). A tentorial meningioma may elevate the posterior cerebral artery because part of it is supratentorial, while depressing the superior cerebellar artery, which lies in the infratentorial compartment.

Original pages 438–439

Malignant Glioma

Glioblastoma multiforme is a brain tumor with abundant, rapid intratumoral blood flow because numerous new vessels of varying sizes form within it. These vessels are abnormal, with proliferation of intimal cells in their walls, a beaded appearance, and shunting between arteries and veins, causing rapid flow into the veins. The angiographic features of malignant glioma are as follows (Figure 6.82a, b):

1. The vessels supplying this tumor vary in size and have a beaded appearance.

2. Tumor staining begins in the arterial phase and disappears before the venous phase, sooner than in meningioma.

3. Abnormal intratumoral vessels are usually numerous at the tumor periphery but sparse centrally. They may appear as patches of vascular clusters surrounding central tumor necrosis, resulting in uneven staining.

4. Early venous drainage is visible late in the arterial phase. There may be one or several draining veins, or drainage into the deep cerebral veins. These are important signs of the malignant nature of this tumor.

Original pages 439–441

Metastatic Tumors

These tumors spread from cancer in other organs, most commonly the lung and breast. Their principal angiographic features are as follows (Figure 6.83):

1. Finding more than one tumor mass is the most important diagnostic feature. Cancer cells reach the brain through the bloodstream and may spread to several sites at different times, producing multiple brain metastases of varying sizes. A solitary lesion may be difficult to distinguish from glioblastoma because the intratumoral vessels, tumor staining, and early venous drainage are similar. However, finding a primary cancer elsewhere, such as in the lung or breast, favors metastatic tumor over glioblastoma.

2. There is usually a single enlarged feeding vessel, because the cancer cells enter that vessel as an embolus. As the tumor grows, the vessel containing the embolus becomes its feeding artery, so only one vessel is enlarged. The angiogram shows this feeder directed toward a pole of the tumor (Figure 6.83).

3. Tumor staining is not homogeneous as in meningioma, and circulation is faster. Central tumor necrosis leaves fewer vessels in the center than at the periphery. Newly formed vessels resemble those in glioblastoma.

4. Early venous drainage appears as rapidly as in glioblastoma and cannot distinguish the two.

Original pages 441–442

Cerebellar Hemangioblastoma

This is a highly vascular tumor consisting of a solid tumor component, the mural nodule, and a surrounding cyst, although some cases have no cyst. The solid component has a rich vascular supply, so tumor staining is prominent and sometimes homogeneous (Figure 6.84). The cyst contains no vessels, but vessels are present in its wall. Early venous drainage occurs at the mural nodule. In cases without a cyst, the entire tumor contains numerous abnormal vessels. Intratumoral circulation is relatively rapid, like that of malignant tumors in general, sometimes making the distinction difficult. Clinical findings and other investigations must assist the diagnosis.

Original page 442

Glomus Jugulare Tumor

This is another highly vascular tumor. It lies at the jugular foramen and destroys the petrous bone. It receives blood from the external carotid system. Carotid angiography shows large feeding branches, staining resembling an AVM, and prominent early venous drainage. Circulation is also relatively rapid. The important angiographic diagnostic feature is its supply from the external carotid artery. Subtraction films clearly show both the feeding vessels and the tumor (Figure 6.85).

Original pages 442–449

Computed Tomography (C.T.)

Since 1972 (B.E. 2515), CT has been introduced for diagnosing diseases of the brain and spinal cord, greatly reducing the use of older investigations such as skull radiographs, angiography, ventriculography, and pneumoencephalography. Some, including ventriculography and pneumoencephalography, are now hardly performed because they carry substantial risks and cause considerable pain and distress. Skull radiographs and angiography are still used in selected patients and where CT is unavailable. Skull radiographs can provide direct or indirect evidence of a brain tumor. Direct signs include tumor calcification and tumor-induced blastic or lytic skull changes or ballooning of the sella. Indirect signs include displacement of a calcified pineal gland and changes in the sella turcica or cranial sutures resulting from tumor-related intracranial hypertension. However, these radiographic findings are insufficiently detailed to characterize the tumor, so further investigation is necessary. Before CT, angiography was the next investigation; ventriculography and pneumoencephalography were used when angiography was nondiagnostic or a tumor within or near a ventricle was suspected. At present, when physical examination suggests a brain tumor, CT is requested directly without skull radiographs, saving time and money. Angiography is also used much less often to diagnose brain tumors. It is reserved for selected cases in which the major feeding vessels and tumor vascularity must be assessed to plan surgery with the least possible risk. For example, in meningioma of the medial lesser sphenoid wing, the positions of the internal carotid artery and its branches must be known.

CT is a safe, painless examination that causes no suffering and depicts tumor location, size, and shape very well; sometimes it can also suggest the tumor type. It shows tumor-related changes in the skull, soft tissues, brain parenchyma, and ventricular system. CT should be performed before and after contrast administration, with standard axial sections. Tumors in the sellar, parasellar, tentorial, and posterior fossa regions may be better seen in coronal sections. Computer reconstruction can also provide sagittal images, but these are not particularly clear and are inferior to MRI (magnetic resonance imaging), as discussed later.

For brain tumors, noncontrast CT is less useful than contrast-enhanced CT, but it reveals calcification and intratumoral hemorrhage, which help identify the tumor type.

A brain tumor at any site produces mass effect on brain tissue, ventricles, subarachnoid spaces, cisterns, and blood vessels. CT assessment should consider the following changes to guide treatment planning and determine how urgently treatment should begin:

1. Tumor location. Enhanced CT usually shows tumor location and size very well. The neurosurgeon must determine whether the tumor is intra- or extracerebral, infratentorial or supratentorial, superficial or deep, and solitary or multiple. These findings inform the decision whether to operate, which approach will permit complete and safe removal, or whether only palliative treatment is appropriate. CT provides considerable guidance in these decisions.

2. Enhancement pattern. Different tumor types have different patterns. Irregular peripheral enhancement, appearing hyperdense or very white on the film, with a hypodense or dark center favors malignancy. Rapid tumor growth causes central necrosis because of inadequate blood supply.

3. Calcification, visible on nonenhanced CT, favors a benign rather than malignant tumor (Figure 6.86).

4. Brain edema. Edema is usually visible around brain tumors. CT clearly demonstrates it, an advantage over cerebral angiography. Malignant glioma, glioblastoma multiforme, and metastatic brain tumors may cause extensive surrounding edema. Metastatic tumors in particular can cause marked edema even when the tumor itself is small (Figure 6.87). Nevertheless, extensive edema is also observed around benign parasagittal meningiomas, possibly because the tumor compresses cortical veins entering the superior sagittal sinus and impedes venous drainage (Figure 6.88). It may also occur around large meningiomas of the lesser sphenoid wing and olfactory groove (Figures 6.89, 6.90). Intraventricular and other midline tumors usually do not cause brain edema. Marked edema on CT is important because the patient may deteriorate rapidly. Thus, whether extensive or limited, edema on CT helps indicate the need for prompt, appropriate treatment.

5. Brain herniation. CT is a very useful radiological investigation for identifying the sites and extent of brain herniation. These findings prompt the surgeon to treat the patient urgently before brainstem function is lost. As discussed earlier, subfalcine, transtentorial, tonsillar, and upward cerebellar herniations occur at different sites and can be demonstrated on CT.

Subfalcine herniation occurs with supratentorial tumors. Important CT findings are as follows (Figure 6.93): i) the falx is displaced to the opposite side; ii) the lateral ventricle is compressed and displaced to the opposite side; iii) the anterior cerebral artery and cingulate gyrus pass beneath the falx to the opposite side, clearly seen in the coronal plane; iv) the anterior suprasellar cistern is distorted and narrowed; v) a relatively small superficial tumor may cause only local loss of the subarachnoid space over the tumor.

Transtentorial herniation has the following CT features: i) the lateral suprasellar cistern disappears because the uncus herniates downward into it; ii) further downward displacement of the uncus and parahippocampal gyrus pushes the brainstem to the opposite side. The ambient cistern on the herniation side widens, while the opposite cistern narrows or disappears; iii) marked brainstem compression elongates its anteroposterior diameter, and associated hydrocephalus also obliterates the interpeduncular and suprasellar cisterns⁽⁵⁾; iv) if the herniating tissue occludes the posterior cerebral artery, occipital infarction appears as a low-density area; v) severe, rapidly developing transtentorial herniation with marked brain edema compresses the ventricles until they are no longer visible. The suprasellar, interpeduncular, and ambient cisterns also become invisible.

Tonsillar herniation. A posterior fossa tumor can cause the cerebellar tonsils to herniate downward through the foramen magnum and compress the medulla. Neither nonenhanced nor enhanced CT can show this unless opaque contrast medium has been injected into the spinal subarachnoid space. However, a posterior fossa tumor is a contraindication to lumbar puncture because it may increase herniation. Vertebral angiography shows tonsillar herniation better.

Upward cerebellar herniation. A posterior fossa tumor pushes the upper cerebellum upward through the posterior margin of the tentorial notch. CT shows: i) obliteration of the quadrigeminal cistern; ii) disappearance of the superior cerebellar cistern; iii) truncation of the posterior third ventricle, with hydrocephalus involving the third and lateral ventricles; iv) with a large mass, anterior displacement of the brainstem and loss of the prepontine and cerebellopontine angle cisterns; v) altered shape and size of the fourth ventricle, depending on tumor location and size (Figure 6.91).

Original pages 449–450

Metrizamide Cisternography and CT

This consists of CT after intrathecal injection of metrizamide, a water-soluble contrast medium. The patient is placed in the Trendelenburg position so that the opaque medium enters the posterior fossa cisterns and fourth ventricle. This demonstrates the cisterna magna, cerebellopontine and chiasmatic cisterns, as well as the medulla, pons, midbrain, and cerebellar tonsils. The technique is suitable for detecting small posterior fossa tumors, such as acoustic tumors, and tumors at the foramen magnum. Small tumors in these areas are generally difficult to see with conventional CT alone because of extensive artifacts.

In some cases, 4–5 cc of air may be injected intrathecally instead of metrizamide, a technique called air cisternography. The patient is positioned to let the air rise into the cerebellopontine angle, followed by CT. This can clearly demonstrate acoustic tumors smaller than 1 cm (Figure 6.92).

Metrizamide and air cisternography are now rarely used to detect tumors, because current CT scanners provide better image quality and higher resolution, and MRI offers better diagnosis than CT.

Original page 450

CT Features of Different Tumor Types

It is generally accepted that CT is much better than angiography for diagnosing brain tumors. It shows tumor location, size, and effects on adjacent brain, including edema and herniation. Combining these findings with the tumor’s enhanced and nonenhanced CT appearances may identify its type. Although determining tumor type by CT is difficult, it can improve treatment planning. In practice, neurosurgeons correctly identify the tumor type before surgery in most cases; only a few prove to be something else.

The principal CT features of commonly encountered tumor types are described below.

Original pages 450–453

Malignant Glioma

This tumor arises from astrocytic cells and is classified as astrocytoma grade III–IV, also called glioblastoma multiforme. It grows rapidly and contains numerous new abnormal vessels. Rapid growth invariably causes central necrosis. Nonenhanced CT shows a tumor margin slightly denser than brain tissue (Figure 6.93a). The tumor center and surrounding brain are low-density areas, darker than normal brain, due to necrosis and edema respectively. Enhanced CT shows tumor hyperdensity in every case. Most commonly, an irregular hyperdense ring of uneven thickness surrounds a low-density center. There may be several low-density areas. Low-density edematous brain surrounds the mass (Figure 6.93b). Two other appearances may occur: homogeneous enhancement of the entire mass, sometimes containing small low-density spots (Figure 6.94), or an entirely cystic lesion with a small hyperdense solid mural tumor component in the cyst wall (Figure 6.95a, b).

The pattern of peritumoral edema may also suggest malignancy. Malignant gliomas and metastatic tumors can have extensive surrounding low density, unlike grade 1–2 astrocytomas or other benign tumors, which have little surrounding low density.

These CT appearances of glioblastoma multiforme must be distinguished from metastatic brain tumors, brain abscesses, and intracerebral hematomas several weeks old. The history is needed to distinguish these conditions. A primary cancer in the lung or breast favors metastasis, and multiple brain lesions make this more certain. For brain abscess, both the history and CT help: its ring is smoother and more uniform than that of glioblastoma.

Original pages 453–455

Astrocytoma

Grade 1 and 2 astrocytomas are classified as low-grade, benign astrocytomas. They grow slowly, infiltrate tissue without clear margins, and are less vascular than glioblastoma multiforme. They occur in the cerebral hemispheres, cerebellum, brainstem, optic nerve and chiasm, and hypothalamus. Nonenhanced CT (Figure 6.96) shows irregular low density without clear margins. Some are isodense with brain tissue. Any calcification is clearly visible on nonenhanced CT. Astrocytomas may contain cystic components, particularly in the cerebellum. Enhanced CT usually shows little increase in density⁽⁷⁾; when present, it is less marked than in glioblastoma and occurs in the solid tumor, while the cyst does not increase in density. Other causes of this low-density CT appearance include other tumors, cerebral infarction, traumatic brain edema, demyelination, and focal cerebritis.

In brainstem astrocytoma, nonenhanced CT shows an enlarged pons and flattening and posterior displacement of the fourth ventricle. Most tumors are low density (Figure 6.97). Enhanced CT appearances vary: some show only a slight increase in density, while others become hyperdense.

Cerebellar astrocytomas differ from those in the cerebral hemispheres in having well-defined margins. They may be solid, cystic, or mixed; most consist of a cyst with a mural nodule. Nonenhanced CT may show slightly increased density or mixed low- and high-density areas. Enhanced CT clearly defines the tumor, showing a cyst with a hyperdense mural nodule (Figure 6.98a, b). If the cyst wall also contains tumor, a high-density ring may be visible. In such cases, the neurosurgeon must try to remove the cyst wall as well, otherwise the tumor may recur.

Original pages 455–457

Oligodendroglioma

This is a benign, slowly growing tumor, usually in the cerebral hemispheres and commonly in the frontal lobe. Nonenhanced CT shows hypodensity with mass effect and relatively little surrounding edema. This resembles astrocytoma and is difficult to distinguish from it. Calcification is common in oligodendroglioma (Figure 6.99). Enhanced CT shows high density at the tumor periphery, while its center may be low density.

Original page 457

Ependymoma

This tumor arises from ependymal cells lining the ventricles. Its location in the ventricular wall or within a ventricle is therefore a diagnostic clue. Ependymoma can occur anywhere in the ventricular system, most commonly in the fourth ventricle, where it causes obstructive hydrocephalus. Nonenhanced CT shows an isodense or slightly hyperdense fourth ventricular mass, sometimes with calcification. Enhanced CT may show homogeneous or heterogeneous enhancement (Figure 6.100). Supratentorial ependymomas often contain cysts and calcification. The differential diagnosis includes medulloblastoma and choroid plexus papilloma.

Original pages 457–459

Choroid Plexus Papilloma

This highly vascular choroid plexus tumor commonly occurs in the trigone of the lateral ventricle and in the fourth ventricle. CT shows a well-defined hyperdense intraventricular mass, invariably with hydrocephalus because the tumor produces CSF or because it may bleed (Figure 6.101). Some cases contain calcification. The differential diagnosis includes intraventricular meningioma, ependymoma, medulloblastoma, and hemangioblastoma.

Original page 459

Medulloblastoma

This tumor is common in children and lies in the cerebellar midline, extending into the fourth ventricle or foramen magnum, or spreading through CSF into the subarachnoid space. CT shows a hyperdense mass in the vermis extending toward the fourth ventricle, displacing it anteriorly or obstructing it and causing obstructive hydrocephalus (Figure 6.102a). Cysts are generally absent, although very large tumors may develop small cysts (Figure 6.102b).

Original pages 459–460

Colloid Cyst

A mucoid-containing cyst situated in the third ventricle near the foramen of Monro. This characteristic location is a diagnostic clue. CT shows a small, round, smooth-margined mass of homogeneous high density⁽⁶⁾.

Original page 460

Hemangioblastoma

This benign vascular tumor most commonly lies in a cerebellar hemisphere near the midline and may contain a cyst. CT shows a hyperdense solid component. When a cyst is present, it is low density, with solid tumor in its wall, usually adjacent to the pia mater on the superior or posterior cerebellar surface (Figure 6.103). This is difficult to distinguish from cystic astrocytoma, but angiography can differentiate them by the numerous intratumoral vessels of hemangioblastoma.

Original pages 460–464

Meningioma

Meningioma is not difficult to diagnose on CT because of its characteristic sites, including the parasagittal region, falx, olfactory groove, lesser sphenoid wing, tentorium, and convexity, and associated skull changes. It is a benign, well-defined tumor. Psammomatous meningiomas often contain calcification. Nonenhanced CT shows increased density due to densely packed cells and calcification, with no hypodense areas within the tumor. Some tumors are extensively calcified throughout and clearly visible on nonenhanced CT (Figure 6.104). Enhanced CT shows a well-defined hyperdense mass, sometimes with its surface attached to the falx (Figure 6.105) or hyperostotic bone. The broad surface of attachment to the dura also aids diagnosis. Since meningioma is an extracerebral tumor, surrounding low-density edema is often visible. Parasagittal meningiomas in particular may have extensive surrounding low density because compression of cortical veins impairs venous return and causes edema (Figure 6.88), as observed during surgery at this site. In other locations, such as the olfactory groove, tuberculum sellae, and tentorium, surrounding low density may be absent or slight.

Another CT feature suggesting meningioma is mass effect that is disproportionately small for tumor size, such as only slight midline shift despite a large mass. Because meningioma grows slowly, adjacent brain atrophies through local water loss, allowing the tumor to expand without raising intracranial pressure.

Intraventricular meningioma shows homogeneous isodensity or slight hyperdensity on nonenhanced CT. It is well defined within the ventricle, commonly at the glomus of the lateral ventricle, and becomes hyperdense on enhanced CT (Figure 6.106), making it difficult to distinguish from choroid plexus papilloma.

A cerebellopontine angle meningioma is difficult to distinguish from an acoustic tumor. Bone CT may help: in meningioma, the internal auditory canal is not enlarged, and adjacent bone may be hyperostotic, whereas acoustic tumors usually enlarge the internal auditory canal. Sellar meningioma must be distinguished from pituitary adenoma and craniopharyngioma, both of which alter the sella turcica; craniopharyngioma also contains cysts.

Meningioma en plaque appears on enhanced CT as hyperdensity spreading along the brain surface, sometimes with associated hyperostosis (Figure 6.107).

Original pages 464–467

Metastatic Brain Tumors

Most spread from lung or breast cancer. They can occur anywhere in the brain, commonly in the frontal lobe, and may be solitary or multiple. Growth often begins at the gray–white matter junction, where capillaries supply the tissue. CT is very useful for brain metastases because it shows their number, location, and associated edema in greater detail than other methods. Generally, CT shows well-defined homogeneous hyperdensity. Another important feature is extensive surrounding low-density edema, even when the tumor is small (Figure 6.108a). The tumor center may be hypodense. These appearances, together with multiple masses (Figure 6.108b), are the main diagnostic criteria for brain metastases. A solitary metastasis is difficult to distinguish from malignant glioma, and a history of the primary cancer is needed. Ring-shaped lesions must be distinguished from brain abscesses, which may also be solitary or multiple. A very thick, irregular wall on CT favors metastasis. Four types of metastatic tumors commonly hemorrhage: choriocarcinoma, melanoma, and lung and renal carcinomas⁽⁸⁾. Nonenhanced CT shows a hyperdense hematoma within the tumor.

Original page 467

Pituitary Adenoma

This tumor grows in the pituitary fossa, enlarging the sella turcica. It usually extends upward, but may also grow laterally, posteriorly, or anteriorly. A small intrasellar tumor is called a microadenoma; a large tumor is a macroadenoma. CT shows enlargement of the sella turcica in macroadenoma, but no sellar change in microadenoma. Nonenhanced CT shows increased tumor density, and enhanced CT shows well-defined hyperdensity (Figure 6.109a). Occasionally, a low-density cyst is present within the tumor (Figure 6.109b). Suprasellar or parasellar extension is best seen in coronal sections (Figure 6.110a, b), which clearly show the tumor’s relationships to the sphenoid sinus, sellar floor, pituitary gland and stalk, suprasellar cistern, optic chiasm, and third ventricle. These sections also reveal microadenomas, usually as low-density areas within the pituitary gland. The pituitary stalk may deviate away from the tumor. Marked suprasellar extension can obliterate the third ventricle and obstruct the foramen of Monro, producing obstructive hydrocephalus.

Original pages 467–470

Craniopharyngioma

This tumor arises above the sella turcica and does not cause sellar ballooning unless it originates within the sella. It usually consists of solid and cystic components. The cyst fluid contains cholesterol, and calcification is common. Nonenhanced CT therefore shows hyperdense calcification (Figure 6.111), which may be eggshell-like or form scattered small clumps, together with low-density cystic areas measuring below 0 because they contain fat. This combination with calcification is an important diagnostic criterion⁽⁹⁾. Enhanced CT shows hyperdensity of the solid component. Without a cyst, the tumor may be difficult to distinguish from pituitary adenoma. As with pituitary adenoma, coronal imaging demonstrates suprasellar hyperdense tumor and calcification and low-density cysts (Figure 6.112). Some cases show parasellar extension.

Original page 470

Dermoid and Epidermoid

These ectodermal tumors are cystic and may have calcification in the cyst wall. Enhanced CT shows low-density cysts (Figure 6.113a, b) and hyperdense wall calcification. The two types are difficult to distinguish by CT.

Original page 470

Pineal Gland Tumors

These tumors arise from two cell groups⁽¹⁰⁾. Pineal parenchymal cells give rise to pineocytoma and pineoblastoma, while germ cells give rise to germinoma, teratoma, and embryonal carcinoma. The tumor compresses the quadrigeminal plate, aqueduct of Sylvius, and posterior third ventricle. Pineal tumors generally contain both calcification and cysts, and distinguishing their types by CT is very difficult. Nonenhanced CT shows isodensity or slight hyperdensity, with obliteration of the posterior third ventricle and quadrigeminal cistern. There may be hyperdense calcification or hemorrhage, or small low-density cysts. Enhanced CT shows hyperdensity (Figure 6.114). Some patients have a pineal tumor together with a tumor near the anterior third ventricle or optic chiasm, called an ectopic pinealoma (Figure 6.115).

Original pages 470–474

Acoustic Neurinoma (Schwannoma or Neurilemmoma)

This tumor arises from the vestibular division of the acoustic nerve, either within the internal auditory canal or intracranially, most commonly beginning at the internal auditory meatus. It enlarges the surrounding bone and extends into the cerebellopontine angle cistern. A large tumor compresses cranial nerves, the brainstem, cerebellar peduncle, and ventricle, obstructing CSF flow. Nonenhanced bone CT shows clear enlargement of the internal auditory canal on the tumor side compared with the normal side (Figure 6.116a). If the tumor arises outside the auditory canal, the canal may remain normal in size. Bilateral acoustic neurinomas may enlarge both canals (Figure 6.116b). Acoustic neurinomas generally contain no calcification visible on CT, unlike meningiomas, which may be calcified. Enhanced CT shows homogeneous hyperdensity. Large tumors may contain low-density degenerative areas, with compression of the brainstem, middle cerebellar peduncle, and fourth ventricle (Figure 6.116c).

An acoustic neurinoma smaller than 1.5 cm may not be clearly visible on CT alone because hyperdense petrous bone obscures it. It can be demonstrated more clearly by introducing air or water-soluble contrast medium in conjunction with CT (Figure 6.92).

Petrous ridge meningioma is also hyperdense, like an acoustic neurinoma, but does not enlarge the internal auditory canal. Some cases cause hyperostosis or contain visible calcification.

Original pages 474–475

CT in Treatment Follow-up

CT is useful for monitoring tumors both after surgery and when they have not been operated on. Some tumors are difficult to reach or still small; surgical exploration may cause further loss of brain function. CT should therefore be used to monitor their changes because it is harmless to the patient. A benign, slow-growing tumor may show little change over many years. If neurological symptoms do not worsen, surgery is not yet necessary.

Some tumors, such as pineal germinoma, are radiosensitive and can disappear after radiotherapy. CT is useful for assessing the response.

Postoperative complications, including hemorrhage or herniation, may cause death. CT demonstrates these complications very well.

For cystic tumors, CT can guide aspiration of cyst fluid to improve the patient’s symptoms. It can also guide stereotactic needle biopsy in some cases.

Original pages 475–477

MRI (MAGNETIC RESONANCE IMAGING)

MRI, also called NMR (nuclear magnetic resonance), is the newest investigation. It differs from C.T. in that it does not use ionizing radiation. MR imaging results from the interaction between the body’s hydrogen nuclei, placed in a strong external magnetic field generated by the MRI scanner, and radiofrequency waves. The patient is therefore not exposed to radiation, and being within the magnetic field is highly safe. Like C.T., MRI uses a digital computer to display tomographic images of the desired thickness. Because MR data are stored as MR signals, MRI has the advantage of producing clear axial, coronal, sagittal, oblique, and curved images as required. C.T. cannot do this as well; in particular, it cannot produce oblique or curved images.

The appearance of an MR image depends on the density of mobile hydrogen nuclei and their physical changes, expressed by T₁ and T₂ magnetic relaxation times (also referred to as T₁- and T₂-weighted images). Different MR sequence parameters produce tissue signals of varying brightness according to the tissue type. In routine clinical practice, T₁-, T₂-, or proton-density-weighted images are obtained to distinguish diseased tissue from normal brain.

On T₁-weighted brain images, gray matter appears gray, white matter white, and CSF black. Skull bone produces no signal, whereas bone marrow fat produces a very bright signal. On T₂-weighted images, gray matter appears white, white matter is less bright, and CSF is white. The degree of brightness depends on the degree of T₂ weighting.

MRI diagnoses many diseases of the brain and spinal cord better than C.T. and clearly demonstrates lesions in different planes. It is particularly useful to neurosurgeons because it shows the relationship between a lesion and nearby structures before surgery, thus facilitating operative planning. The physics of MRI may be studied in general MRI textbooks and will not be discussed here.

Although MRI offers many advantages in diagnosing brain lesions, it also has shortcomings and is inferior to C.T. for some conditions. For example, C.T. provides excellent, detailed diagnosis of acute hemorrhage, whether outside the brain, within the brain substance, in the ventricles, or in the subarachnoid space. C.T. also demonstrates calcification and bony details well. MRI does not show bone because its low mobile-hydrogen content produces no signal (a signal void). This characteristic is also an advantage, however: MRI does not produce the bone artifacts commonly encountered on C.T. at the skull base or foramen magnum. MRI is therefore particularly suitable for investigating skull-base lesions, showing them more clearly and in greater detail than C.T. It also better demonstrates several other conditions, including hemorrhage at different stages, multiple sclerosis plaques, intracanalicular acoustic neuromas, occult brainstem abnormalities, cavities within the spinal cord, and normal and abnormal cerebral vessels, such as AVMs. All these are well demonstrated by MRI without contrast injection and without bone artifacts, even when a lesion lies immediately adjacent to bone.

MRI is routinely performed in three planes: axial, coronal, and sagittal. Coronal sections clearly demonstrate lesions of the pituitary gland, orbits, petrous pyramids, skull base, and regions near the vertex. Sagittal sections show the details and relationships of midline tumors to adjacent structures particularly well, more clearly than C.T. They are therefore suitable for investigating lesions of the pituitary gland, diencephalon, brainstem, and spinal cord. In practice, when the clinical examination suggests a lesion in one of these locations, MRI should be performed because it provides better results and greater benefit than C.T.

Original pages 477–478

CONTRAST INJECTION

The intravenous contrast material currently accepted as safe for MRI is Gd-DTPA (gadolinium-labeled diethylenetriamine pentaacetic acid, also known as gadopentetate dimeglumine). It enhances T₁ and T₂ relaxation, producing T₁ hyperintensity (Figure 6.126c) and T₂ hypointensity. The indications for contrast injection are similar to those for contrast-enhanced C.T.: extra-axial brain tumors, tumors at the skull base, and intra-axial tumors, particularly metastatic brain tumors.

Contrast enhancement in MRI is especially useful for demonstrating the relationship between a brain tumor and surrounding cerebral edema⁽¹⁵⁾ and for better defining the tumor’s characteristics. In general, tumors with a high malignancy grade enhance more than low-grade tumors.⁽¹⁶⁾ However, the intensity of enhancement does not necessarily correlate with tumor grade. Extra-axial tumors consistently show marked enhancement.

MRI detects and localizes brain tumors much more clearly than C.T., but it still cannot unequivocally demonstrate the specific features of every tumor type. Accurate diagnosis requires consideration of differences in signal intensity. Most brain tumors have a high proton density, with prolonged T₁ and T₂ on spin-echo sequences. Tumors therefore appear hypointense on T₁-weighted images and hyperintense on T₂-weighted images. Studies show that T₁ hyperintensity occurs with subacute and chronic hemorrhage (methemoglobin), melanin, fat, high protein concentration, slowly flowing blood, iodinated or paramagnetic intravenous contrast enhancement, and paramagnetic cations such as manganese, iron, and copper. T₂ hypointensity occurs with low proton density (for example, calcification, dense cellularity, and fibrocartilage), paramagnetic effects (iron, hemosiderin, deoxyhemoglobin, melanin, and intracellular methemoglobin), macromolecular content (high protein concentration), and signal void caused by rapidly flowing blood.^(17,18) Knowledge of these signal intensities, considered together with the characteristic features of each lesion and the clinical history, enables more accurate and definite MRI diagnosis of brain tumor types.

The MRI characteristics of a brain tumor depend mainly on its water content, particularly extracellular water. Occasionally, other components develop within a tumor, including calcium, fat, blood, necrosis, edema, and cysts. These alter its MRI appearance according to their composition. Considered together with other features, they improve the accuracy of tumor diagnosis. The MRI appearances of tumors containing these various components are briefly described below.

Original pages 478–479

Cerebral Edema

As discussed in earlier chapters, brain tumors can cause cerebral edema. This occurs with metastatic and malignant brain tumors, as well as with benign tumors such as meningiomas. MRI demonstrates edema very well. On T₁-weighted images, edematous tissue has lower intensity than brain tissue and appears darker; on T₂-weighted images, it has higher intensity and appears white (Figure 6.126b). This high intensity sometimes makes it difficult to distinguish the tumor margin from surrounding edema, because the extracellular spaces in both the tumor and white matter contain water. Low-grade astrocytomas have relatively little vascular permeability to contrast material and therefore show no enhancement on contrast C.T., despite increased water within the tumor. In such cases, MRI demonstrates tissue abnormalities and their extent better than C.T. MRI often shows a different signal in the tumor from that in the surrounding edematous brain. On T₂-weighted images, edema has higher intensity (appears whiter) than the tumor, indicating more extracellular water in white matter than in the densely cellular tumor region.⁽¹⁹⁾ Necrotic or cystic portions of a tumor appear markedly hypointense (darker) on T₁-weighted images, whereas edema is better demonstrated on T₂-weighted images.

Original pages 479–480

Cyst

Many brain tumors contain cysts, including craniopharyngiomas, colloid cysts, and various malignant tumors. Some are cystic from the outset, such as colloid and epidermoid cysts. Others develop cysts from tumor-cell necrosis or hemorrhage in the center of the tumor, producing a high-protein cyst with a variable MRI appearance. In general, cysts in malignant tumors have irregular walls and may show fluid levels. Their fluid signal differs from CSF, with a shorter T₁ relaxation time and a brighter appearance on film. MRI’s ability to characterize cyst fluid allows better assessment of cystic brain tumors than C.T.⁽²⁰⁾ For example, C.T. cannot distinguish the density of fluid in a cystic astrocytoma from that of CSF, whereas MRI clearly distinguishes a CSF-containing cyst from a high-protein cyst such as a cystic astrocytoma or a hemorrhagic cyst. High-protein fluid has a shorter T₁ relaxation time than CSF, so the cyst appears brighter than CSF on MRI (Figure 6.120a). When cyst fluid separates into two layers, the layers have different MRI appearances. The upper, lower-protein layer has a longer T₁ relaxation time than the lower, higher-protein layer. On T₁-weighted images, the upper layer consequently appears darker than the lower layer, though not as dark as CSF.

Original page 480

TUMOR HEMORRHAGE

Intratumoral hemorrhage generally involves only part of a tumor. MRI demonstrates characteristic blood appearances well in subacute and chronic hemorrhage. On T₁-weighted images, an acute hematoma (0–2 days) is isointense to brain tissue, while surrounding vasogenic edema is less intense (darker) because of its longer T₁. In the subacute stage, the periphery of the hematoma changes to methemoglobin, which has a very short T₁. T₁-weighted images therefore show increased intensity,⁽²¹⁾ or a whiter appearance (Figure 6.117a, b). In the chronic stage, all deoxyhemoglobin in the center of the hematoma has changed to methemoglobin, and the surrounding vasogenic edema disappears. The hematoma is hyperintense,⁽²²⁾ with surrounding isointense hemosiderin. With further passage of time, the former hematoma becomes hypointense.

Original page 480

Calcification

Calcification in a tumor is important in diagnosing its type. C.T. demonstrates calcification better than MRI.⁽¹⁴⁾ Calcification produces no MRI signal (a signal void) and therefore appears dark (Figure 6.118).

Original pages 480–483

Fat

Fat-containing tumors such as lipomas and teratomas appear bright on T₁-weighted MRI and fade on T₂-weighted images.

Original page 483

MRI Characteristics of Individual Brain Tumors

Different intra-axial and extra-axial brain tumors have different MRI appearances, depending on their internal components as described above. Knowledge of the pathological and MRI characteristics of each type permits more accurate and definite diagnosis. The MRI appearances of individual brain tumors are briefly described below.

Original page 483

Glial Tumors

These tumors arise within the brain substance. Common members of this group include astrocytoma, oligodendroglioma, and ependymoma, with further variation according to malignancy. Abnormal signals produced by glial tumors can be divided into five categories:⁽¹⁷⁾ signals from the tumor itself, cystic change, necrosis, edema, and neovascularity with loss of the blood–brain barrier, clearly demonstrated by contrast enhancement. All these changes increase brain water content and thus prolong T₁ and T₂ relaxation times. Consequently, MRI shows hypointensity on T₁-weighted images and hyperintensity on T₂-weighted images. Gliomas with central cystic change and necrosis show hypointensity on T₁-weighted images.

Original pages 483–484

Astrocytoma

Astrocytomas may be divided into low-grade (benign) astrocytoma, anaplastic astrocytoma, and glioblastoma multiforme (malignant). MRI improves localization of these tumors. For example, a low-grade astrocytoma has almost the same density as brain tissue on C.T., making its location and extent indistinct. Even contrast C.T. shows no enhancement. MRI defines its margins more clearly (Figure 6.119) because it distinguishes water within the tumor from water in the surrounding edematous brain. Nevertheless, MRI remains no better than C.T. at identifying the tumor type. Tumors in this group are more conspicuous after Gd-DTPA contrast injection.

Original pages 484–486

Glioblastoma Multiforme

MRI demonstrates differences among the components of this tumor (Figure 6.120a, b, c). i) Central necrosis is hypointense on T₁-weighted images and hyperintense on T₂-weighted images. ii) Densely cellular, highly vascular tumor often forms an irregular ring around the central necrosis. It is hypointense on T₁-weighted images and hyperintense on T₂-weighted images, but the T₂ hyperintensity is relatively modest (not very white on film) because of the glial cells, vascular proliferation, and abundant blood flow characteristic of glioblastoma multiforme. Contrast MRI shows marked enhancement of this component. iii) Abnormal vessels supplying the tumor and large draining veins produce signal voids and appear dark. iv) Edematous brain is hypointense on T₁-weighted images and hyperintense on T₂-weighted images. v) Areas of intratumoral hemorrhage appear hyperintense on both T₁- and T₂-weighted images.

Original page 486

Oligodendroglioma

This is a slowly growing glioma, usually containing calcification. Intratumoral hemorrhage may occur, so MRI can show several different appearances. Calcified areas are hypointense, whereas areas of previous hemorrhage are hyperintense on T₁-weighted images.

Original page 486

Brainstem Glioma

MRI is very useful for brainstem glioma. It shows the tumor more clearly than C.T., without interference from bone artifacts, and produces excellent sagittal images. The brainstem tumor is hypointense on T₁-weighted images and hyperintense on T₂-weighted images (Figure 6.121a, b, c). The pons is enlarged and the fourth ventricle compressed. Intravenous contrast produces conspicuous enhancement.

Original page 486

Cerebellar Astrocytoma

This is a common childhood tumor, second to medulloblastoma, and includes benign pilocytic and fibrillary astrocytomas. The tumor may be solid without a cavity, or cystic with a mural nodule in the cyst wall. On MRI, the solid tumor is hypointense on T₁-weighted images and hyperintense on T₂-weighted images. The cystic portion has lower intensity than the solid portion on T₁-weighted images and higher intensity on T₂-weighted images. Cyst fluid has higher intensity (is whiter) than water on T₁-weighted images and may form fluid levels. Intravenous contrast produces very clear enhancement.

Original pages 486–488

Ependymoma

On MRI, this tumor is hypointense on T₁-weighted images and hyperintense on T₂-weighted images. Patches of T₁ hyperintensity may indicate previous intratumoral hemorrhage. Some tumors contain scattered signal voids caused by calcification. Important diagnostic features are an intraventricular location, clearly defined margins, and obstruction of CSF flow causing hydrocephalus. Contrast MRI may show tumor seeding along the ventricular ependyma and in the subarachnoid space.

Original page 488

Choroid Plexus Papilloma

This intraventricular tumor commonly occurs in the trigone of the lateral ventricle and in the fourth ventricle. It has a cauliflower-like appearance and is always associated with hydrocephalus, because the tumor produces excessive CSF and may occasionally bleed into it. A fourth-ventricular tumor can rapidly obstruct CSF flow. The intraventricular location, together with these features, helps establish the diagnosis. Choroid plexus papilloma is highly vascular and may contain calcification. It is hypointense or isointense to brain on T₁-weighted images, and hypointense to CSF on T₂-weighted and proton-density-weighted images. Contrast MRI shows very marked enhancement.

Original pages 488–489

Medulloblastoma

This tumor consists of densely packed primitive cells and is usually located in the cerebellar vermis. Obstruction of the fourth ventricle causes hydrocephalus. Most tumors are solid without cysts, although large tumors may contain cysts or necrosis. MRI shows hypointensity on T₁-weighted images and isointensity or slight hyperintensity on T₂-weighted images (Figure 6.122). The isointensity or limited hyperintensity on T₂-weighted images reflects the high cellular density and low interstitial water content.⁽²⁴⁾ This distinguishes medulloblastoma from cerebellar astrocytoma on MRI. Intravenous gadolinium produces conspicuous tumor enhancement and can also demonstrate tumor cells disseminated through the subarachnoid space.⁽²⁵⁾

These signal characteristics, together with a vermian location and subarachnoid dissemination, are important in diagnosing this tumor.

Original pages 489–491

Colloid Cyst

This is a round, smooth-walled cyst containing mucinous fluid, located in the third ventricle near the foramen of Monro. MRI shows hyperintensity on both T₁- and T₂-weighted images. However, the signal varies with the amounts of mucin, iron, and hemosiderin in the cyst, so its appearance is not constant.^{(26,27,28,29)} The key diagnostic feature is therefore a smoothly marginated mass in the third ventricle close to the foramen of Monro.

Original page 491

Hemangioblastoma

This benign vascular tumor commonly occurs in the posterior fossa, especially the cerebellum. It contains numerous small and large sinusoidal vessels, so intratumoral hemorrhage is common. The tumor may be solid or a cyst with a mural nodule; the cystic form is less common. Multiple hemangioblastomas may occur in one patient. MRI shows a mixture of T₁ and T₂ intensities reflecting solid tumor, cyst, vessels, intratumoral hemorrhage, and fat. The following appearances may therefore be seen:⁽³⁰⁾ i) A cyst, or a cyst with a mural nodule; the cyst is hypointense on T₁-weighted images and hyperintense on T₂-weighted images. ii) Areas of T₁ hyperintensity within the tumor indicate previous hemorrhage or fat within the tumor stroma, which shortens T₁. iii) Previous hemorrhage produces hemosiderin within and around the hemangioblastoma, appearing as curved hypointense areas. iv) Vascular signal voids appear as hypointense structures within or around the tumor. Their size varies with the vessels supplying or draining the tumor (Figure 6.123a, b).

Important diagnostic features of hemangioblastoma are a cyst with a mural nodule and vascular signal voids. Contrast MRI clearly demonstrates the mural nodule.

Original pages 491–492

Meningioma

This is an extra-axial tumor, usually attached to the dura and clearly circumscribed. When large, it compresses the cortex, subarachnoid CSF, and cortical vessels; some cases also have cerebral edema. MRI demonstration of these changes is important for diagnosis. Meningiomas are generally isointense to brain or slightly hypointense on both T₁- and T₂-weighted images, although some may be slightly hyperintense on T₂-weighted images. After contrast injection, there is marked enhancement and a “dural tail sign”: thickened, enhancing dura adjacent to the tumor margin resembles a tail extending from the meningioma (Figure 6.124b). Enhancement is often heterogeneous because the tumor may contain calcification, varying vascularity, and sometimes small cysts. A hypointense band of subarachnoid CSF and vessels separates the meningioma from the compressed gyri (Figure 6.124a). Some cases show surrounding edema, with T₁ hypointensity and T₂ hyperintensity. MRI demonstrates extension into a dural venous sinus better than C.T.⁽³¹⁾ MRI may also show skull thickening from hyperostosis as a signal void.

Original pages 493–494

Schwannomas

The most common tumor in this group is an acoustic nerve schwannoma. It is a well-circumscribed extra-axial tumor surrounded by CSF in the basal cistern. It may lie within the internal auditory canal (intracanalicular) or extend outside the canal into the intracranial cerebellopontine angle (extracanalicular). MRI is the best method for diagnosing acoustic neurinoma. It does not require intrathecal air or metrizamide contrast as C.T. does, and there is no artifact from adjacent bone, even with a small tumor. It clearly shows the details of both intracanalicular and extracanalicular tumors. The tumor is hypointense on T₁-weighted images and hyperintense on T₂-weighted images, more so than meningioma. The cistern on the affected side is enlarged; occasionally a cyst lies over the posterior surface of the tumor. Contrast injection produces marked enhancement, particularly of the intracanalicular component.^(32,33,54) (Figure 6.125a, b, c)

Original pages 494–497

Metastatic Tumors

The pathological characteristics of metastatic brain tumors are: i) They are commonly located at the junction of gray and white matter. ii) They may be solitary or multiple. iii) Marked edema always surrounds the tumor. iv) Some tumors contain hemorrhage. v) They show marked contrast enhancement, which may be homogeneous, heterogeneous, or ring-like when there is central necrosis. vi) Tumor cells may spread into the ventricles and subarachnoid space. MRI clearly demonstrates all these features. Contrast MRI is the best examination for metastatic tumors in the brain, ventricles, subependymal and ependymal regions, cisterns, and subarachnoid space. Bone produces no signal, so an enhancing tumor adjacent to bone is clearly visible (Figure 6.126c). This is particularly useful in the posterior fossa. Metastatic tumors are hypointense on T₁-weighted images and hyperintense on T₂-weighted images. On T₂-weighted images the surrounding edema is hyperintense (Figure 6.126a, b, c), and is more readily distinguished from the tumor than in primary brain tumors.⁽¹⁹⁾

Two types of metastatic tumor have characteristic appearances: mucinous adenocarcinoma and malignant melanoma. Both are hypointense on T₂-weighted images.

MRI best demonstrates hemorrhage within metastatic tumors because it is sensitive to blood and hemoglobin breakdown products, helping to distinguish these lesions from ordinary hemorrhage.⁽³⁴⁾ The distinguishing features are: i) Reduced T₂ signal persists longer because deoxyhemoglobin continues to be produced.^(34,35) ii) Hypointensity may persist for weeks or months. iii) Repeated hemorrhage produces a heterogeneous appearance, with blood of different ages in different locations: recent hemorrhage is hypointense, subacute hemorrhage hyperintense, and old hemorrhage has a hypointense hemosiderin rim. iv) There is marked contrast enhancement.

Malignant melanoma contains melanin, a paramagnetic substance,⁽³⁶⁾ and tends to bleed. Its appearance depends chiefly on whether hemorrhage is present. Without hemorrhage, it is hyperintense on T₁-weighted images and slightly hypointense or isointense on T₂-weighted images. When hemorrhage is present, the appearance varies with its age. Contrast enhancement is homogeneous.

Mucinous adenocarcinoma is hypointense or isointense on T₁-weighted images and hypointense on T₂-weighted images, probably because of its high protein content.⁽³⁷⁾

Original page 497

Leptomeningeal Metastasis

Tumor cells spread to the leptomeninges and through the CSF in the subarachnoid space, involving the basal cisterns, Sylvian fissures, cortical sulci, and ventricles and causing hydrocephalus. Primary CNS tumors that commonly spread in this way include medulloblastoma, ependymoma, pinealoblastoma, and retinoblastoma.^(38,39) Lymphoma, leukemia, and melanoma can also do so. Noncontrast MRI generally cannot demonstrate this dissemination at all. Contrast injection produces marked enhancement, and MRI demonstrates it better than C.T.⁽⁴⁰⁾ Enhancement in the basal cisterns, Sylvian fissures, cortical sulci, and tentorium is usually nodular, rather than the smooth diffuse enhancement seen with inflammation.⁽⁴¹⁾

Original pages 497–499

Pituitary Adenoma

MRI clearly demonstrates tumor margins, particularly in coronal and sagittal sections, showing its size, extent, and relationship to nearby important structures and thus helping the surgeon plan treatment. Pituitary adenomas are classified as microadenomas, smaller than 1 cm, and macroadenomas. MRI is better than C.T. for microadenomas. Most are hypointense relative to the normal gland on T₁-weighted images, with variable T₂ signal. They enhance less than normal pituitary tissue (Figure 6.127a, b). Most lie laterally, causing bulging of the gland and displacement of the stalk to the opposite side.⁽⁴²⁾ (Figure 6.127c) Most prolactin-secreting microadenomas do not enhance.^(43,44) ACTH-secreting microadenomas enhance late after Gd-DTPA injection.

For macroadenomas, MRI clearly shows the size, extent, and relationships, as well as cysts, necrosis, and hemorrhage. Solid tumor is hypointense or nearly isointense on T₁- and T₂-weighted images and enhances homogeneously (Figure 6.128a, b, c). Cystic and necrotic areas have T₁ intensity between that of CSF and solid tumor and are hyperintense on T₂-weighted images. Hemorrhage is clearly demonstrated; in the subacute stage, methemoglobin causes hyperintensity on both T₁- and T₂-weighted images.⁽⁴⁵⁾ Coronal and sagittal images excellently demonstrate compression of the optic chiasm, cavernous sinus, and internal carotid artery, and extension into the interpeduncular fossa.

Original pages 499–502

Craniopharyngioma

This tumor occurs in the region of the sella turcica. It may be intrasellar, suprasellar—the most common location—or, less commonly, intraventricular in the third ventricle. The tumor usually contains cysts and calcification. The cyst fluid is brown, with a high protein content and numerous cholesterol crystals. In children, craniopharyngioma is the most common tumor in the sellar region with these characteristics. MRI is the best investigation because it differentiates tissue types and clearly demonstrates the relationship of the tumor to adjacent structures in coronal and sagittal planes. C.T., however, demonstrates calcification better. In general, the cystic component of a craniopharyngioma is hyperintense on T₁-weighted images because of cholesterol crystals within it; a cyst without cholesterol is slightly hypointense. On T₂-weighted images it is hyperintense (Figure 6.129a, b). Noncalcified solid tumor is isointense on T₁-weighted images and hyperintense on T₂-weighted images. Calcification is hypointense on both T₁- and T₂-weighted images because bone produces no signal (signal void). After contrast injection, the solid tumor and cyst wall enhance clearly on T₁-weighted images.

Original page 502

Pineal Tumors

Tumors in this region fall into three groups.

1. Tumors arising from germ cells: germinoma and teratoma
2. Tumors arising from pineal cells: pineocytoma and pineoblastoma
3. Tumors arising from glial cells, such as gliomas, and others

The most common tumor in this region is germinoma, followed in descending order of frequency by teratoma, pineoblastoma, and pineocytoma.

On MRI, germinomas are isointense to gray matter on T₁-weighted images and isointense or slightly hyperintense on T₂-weighted images.^(49,50) (Figure 6.130) Germinomas generally do not contain calcification, although they may coexist with pineal gland calcification. Contrast MRI shows hyperintensity. These tumors tend to extend into the third ventricle and disseminate through the CSF; consequently, deposits on the ventricular walls and in the subarachnoid space may be demonstrated on contrast MRI.

Original page 502

Teratoma

This tumor contains several types of tissue, including bone and fat, and often contains cysts. On MRI, fat produces hyperintensity on T₁-weighted images, whereas bone or calcium and cysts are hypointense.

Original pages 502–503

Pineocytoma & Pineoblastoma

Both are tumors of pineal cells. Pineoblastoma is malignant and more common than pineocytoma. It consists of densely packed immature cells and is currently classified in the primitive neuroectodermal tumor (PNET) group. Both tumors are hypointense on T₁-weighted MRI and hyperintense on T₂-weighted MRI. Because these tumors contain calcification, hypointense areas of bone may be seen on both T₁- and T₂-weighted images.

Original pages 503–504

Epidermoid Tumors (Pearly Tumors)

These are the most common congenital intracranial tumors, followed by dermoids, lipomas, and teratomas, in that order. They commonly occur in the cerebellopontine angle and parasellar region. The tumor consists of an epithelial cyst wall and fluid containing keratin. Calcification is uncommon. Epidermoids generally appear hypointense on T₁-weighted MRI and hyperintense on T₂-weighted MRI,⁽⁵¹⁾ (Figure 6.131a, b) without enhancement after Gd-DTPA injection. Horowitz et al.⁽⁵²⁾ described two MRI types: black epidermoids and white epidermoids. The former are solid masses of pearly keratin without triglycerides, and therefore appear hypointense on T₁-weighted images. The latter are cystic lesions containing triglycerides and consequently have a higher signal intensity (a whiter appearance) on T₁-weighted images.

Original page 504

Dermoid Tumors

These thick-walled cysts occur along the midline of the brain, commonly in the posterior fossa, and often have calcification in their walls and contents. The cyst contents have two components: the lighter, fat-containing component lies above, while the keratin protein component lies below. A dermoid therefore has a heterogeneous MRI appearance (Figure 6.132). The fatty component is hyperintense on T₁-weighted images; the lower component is hypointense or dark, although not as dark as CSF. On T₂-weighted images, all the contents are hyperintense.⁽⁵³⁾ Calcified areas produce signal voids and appear dark. If a dermoid ruptures, fat droplets disseminate to multiple sites in the subarachnoid space. On T₁-weighted MRI they appear as hyperintense foci in the basal cisterns and throughout the subarachnoid space.

Original pages 504–506

Lipomas

These commonly occur in midline structures such as the corpus callosum and quadrigeminal plate. Some have eggshell-like calcification. MRI clearly demonstrates the characteristic fat within the lipoma: hyperintensity on T₁-weighted images and isointensity or hyperintensity on T₂-weighted images. A lipoma of the corpus callosum may be associated with a visible abnormality of the corpus callosum.

Original pages 506–507

Chordoma

This tumor arises from notochordal remnants. Within the skull it commonly occurs at the clivus and sphenoid bone. It is a locally destructive tumor, appearing as a mass anterior to the brainstem and displacing it posteriorly. MRI shows hypointensity or isointensity on T₁-weighted images and hyperintensity on T₂-weighted images. Some tumors contain hemorrhagic foci that are hyperintense on both T₁- and T₂-weighted images. In others, fragments of bone and bone marrow within the tumor produce mixed intensities on both sequences. Clival chordomas are well demonstrated in the sagittal plane.

Original page 507

Obsolete Investigations

Before C.T. and MRI were introduced for detecting brain tumors, several other examinations could establish the diagnosis, including:

• ventriculography
• pneumoencephalography
• radioisotope brain scan
• echoencephalography
• EEG

These examinations have now been discontinued because they do not provide the detail obtained with C.T. Some cause distress and pain, and occasionally serious complications. C.T. is far superior: it is reliable and clearly demonstrates the location, size, sometimes the type of tumor, and its effects, such as cerebral edema, hydrocephalus, and herniation, without pain or danger to the patient.

Nevertheless, these examinations will be described briefly to provide an understanding of investigations that have become historical. If necessary, they may still be used to investigate tumors on certain occasions and in particular circumstances.

Original pages 507–509

Ventriculography

Air or radiopaque contrast is injected to replace CSF in the ventricles, to demonstrate hydrocephalus, the site of CSF pathway obstruction, and tumors within or adjacent to the walls of the lateral, third, and fourth ventricles. Examination using air is called air ventriculography; that using radiopaque material is called positive-contrast ventriculography. Ventriculography is performed when angiography does not clearly demonstrate an intracranial abnormality. The surgeon must always be prepared to operate immediately if necessary, because complications may be fatal.

Technique: Under local anesthesia, a frontal burr hole is made over the nondominant hemisphere, anterior to the coronal suture and approximately 2–2.5 cm from the midline. The dura is opened and a catheter containing a stylet is passed toward the ventricle, almost perpendicular to the surface and angled slightly medially toward the ipsilateral inner canthus. At a depth of approximately 5 cm, the catheter tip enters the frontal horn of the lateral ventricle and CSF is obtained. Alternatively, the burr hole may be placed in the posterior temporal region, 3 cm above and 3 cm behind the ear, or in the posterior parietal region, just above the lambdoid suture and 3–3.5 cm from the midline.

For air ventriculography, before air is injected the opposite side of the head is placed uppermost, or the patient is positioned prone, to prevent air escaping through the catheter. The volume of CSF removed must balance the volume of air injected; otherwise, air pressure may dangerously increase intracranial pressure. After the required amount of air has been introduced, the head is repositioned to direct it to the desired site and reveal the abnormality, and skull radiographs are obtained. If the foramina of Monro are unobstructed, air enters both lateral ventricles and the third ventricle (Figure 6.133).

For positive-contrast ventriculography, the radiopaque agents used include Myodil, Pantopaque, and Conray 60. Only 3–4 c.c. of Myodil or Pantopaque is required; the head is then repositioned to allow Myodil to enter the third ventricle, aqueduct, and fourth ventricle (Figure 6.134). When Conray 60 is used, 6 c.c. is mixed with 6 c.c. of CSF and injected back into the ventricle. Conray flows through the ventricular system, allowing the whole system to be seen on radiographs.

Original pages 509–511

Pneumoencephalography

Air is injected into the ventricular system through a lumbar puncture. This examination causes headache, distress, sweating, and faintness, and is hazardous, particularly in patients with raised intracranial pressure or a posterior fossa tumor, because it may cause tonsillar herniation, respiratory arrest, and loss of consciousness. In the author’s opinion, this should be the last investigation considered.

Technique: The patient sits with the head slightly flexed so that air can readily rise into the fourth ventricle. A lumbar puncture is performed, and air is injected in a volume equal to the CSF removed, approximately 5 c.c. at a time. Skull radiographs are obtained in the sitting position after each additional injection. If air does not enter the ventricles, the head must be repositioned. To show the third ventricle, aqueduct, and fourth ventricle clearly, tomography is performed by having the patient turn the head from side to side while remaining seated and obtaining a lateral image (Figure 6.135). This method clearly depicts only the midline structures. The patient may then be repositioned to move the air into other desired locations, followed by radiographs to demonstrate abnormalities.

If a tumor is suspected at the base of the brain, such as in the suprasellar region or cerebellopontine angle, it may be demonstrated by injecting air with the patient seated and the head extended. Air then enters the basal cisterns and subarachnoid space (Figure 6.135).

Original page 511

Brain Scan

A radioisotope is injected intravenously, and a scanning detector records an image on paper or X-ray film, demonstrating intracranial pathology. This is suitable as a screening examination to identify patients with brain lesions and may be performed on outpatients. The isotope used is technetium (Tc 99m). When an abnormality is found, further investigations are performed to establish the diagnosis, using angiography or ventriculography according to the individual case (Figure 6.136).

Original pages 511–512

Echoencephalography

Ultrasound is used to locate the brain’s midline and intracerebral masses. When ultrasound strikes the skull, midline structures, or a mass, reflected echoes allow their positions to be identified. A mass on one side of the skull shifts the midline to the opposite side. The ultrasound reflections have no features specific to tumors, so this method is insufficient for preoperative diagnosis and must always be supplemented by angiography or another investigation. Echoencephalography is therefore used only for screening.

Original page 512

EEG

This records the electrical activity of the brain and is appropriate only for patients with epilepsy. It is not useful for determining whether a patient has a brain tumor, because the changes in brain electrical activity are not specific to tumors. EEG indicates only the location of abnormal electrical activity; other investigations are required to determine the cause.

Original pages 512–514

References · Chapter 6

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5. Lee, S.H., Rao K.C.V.G. Primary tumors in adults. In Cranial Computed Tomography, Mc Graw-Hill Book Co., pp. 241-293, 1983.
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13. Darwin R.H., Drayer B.P., Riederer S.J., et al: T2 estimates in healthy and diseased brain tissue: a comparison using various MR pulse sequences Radiology 160 : 375-381, 1986.
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18. Atlas S.W.: Magnetic resonance imaging of the brain and spine, New York, Raven Press, 1991.
19. Zawadzki M.B., Kelly W., : Brain tumors in Magnetic Rosonance Imaging of Central Nervous System ed. by Zawadzki M.B., Norman D., Raven Press, p. 151-185, 1987.
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21. Bradley W.G., Schmidt P.C., Effect of methemoglobin formation on the MRI appearance of subarachnoid hemorrhage. Radiology, 156 : 99-103, 1985.
22. Gomori J.M., Grossman R.I., Goldberg H.I., et al : Intracranial hematomas : imaging by high field MR. Radiology 156, 1985.
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24. Zimmerman R.A., : Pediatric brain tumors. In Cranial MRI and C.T. ed. by Lee H, Rao, K.C.V.G. Zimmerman R.A. 3rd ed. Mc Graw-Hill Inc. p. 389. 1992.
25. Heideman R.L., Packer R.J., Albright, L.A., et al: Tumors of the central nervous system in Pizzo PA, Poplack D.G. (eds), Principles and Practice of Pediatric Oncology, Philadelphia, Lippicott, pp. 505-553, 1989.
26. Maeder P.P., Holtas S.L., Basibuyuk L.N., : Colloid cyst of the third ventricle : Correlation of MRI & C.T. findings with histology and chemical analysis AJNR 11 : 575-581, 1990.
27. Wilms G., Marchal G., Van Hecke P., et al colloid cysts of the third ventricle : MR findings J. comput. Assist. Tomogr. 14 : 527-531, 1990.
28. Roosen N., Gahlen D., Stork W., et al: Magnetic resonance imaging of colloid cysts of the 3rd ventricle. Neuroradiology 29 : 10-14, 1987.
29. Scotti G., Scialfa G., Colombo N., Landoni, L. : MR in the diagnosis of colloid cysts of the 3rd ventricle. AJNR 8: 370-372, 1987.
30. Lee S.R., Sanches J., Mark A.S., et al : Posterior fossa hemangioblastomas : MR imaging. Radiology 171 : 463-468, 1989.
31. Spagnoli M.V., Goldberg H.I., Grossman R.I., : Intracranial meningiomas : High-field MR imaging Radiology 161 : 369-375, 1986.
32. Breger R.K., Papkei R.A., Pojunas K.W., Benign extraaxial tumors : Contrast enhancement with Gd-DTPA, Radiology, 163 : 427-429, 1987.
33. Valvassori G.E., Morales F.G., Palacios F., Dobben G.E., MR of the normal and abnormal internal auditory canal AJR. 9 : 115-119, 1988.
34. Atlas S.W., Grossman R.I., Gomori J.M., : Hemorrhagic intracranial malignant neoplasms. Spin-echo MR imaging. Radiology 164 : 71-77, 1987.
35. Destian S., Sze G., Krol G., et al : MR imaging of hemorrhagic intracranial neoplasms. AJNR 9 : 1115-1122, 1988.

36. Wooddruff W.W. Jr., Djang W.T., Mc Lendon R.E., et al : Intracranial malignant melanoma : High-field strength MR imaging. Radiology 165 : 209-213, 1987.
37. Egelhoff J., Ross, J.S., Modic M.T., et al: Finding of MR imaging of adenocarcinoma metastatic to the brain, presented at the radiological society of North America annual meeting, Chicago, November. p. 25-30, 1990.
38. Rippe D.J., Boyko O.B., Friedman H.S., et al : Gd-DTPA enhanced MR imaging of leptomeningeal spread of primary intracranial CNS tumors in children AJNR 11: 329-332, 1990.
39. Mackay C.J., Abramson H.D., Ellsworth R.M., metastatic patterns of retinoblastoma. Arch. Ophthalmol. 102 : 391-396, 1984.
40. Sge G., Soletsky. S., Bronen R. et al : MR. imaging of the cranial meninges with emphasis on contrast enhancement and meningeal carcinomatosis AJNR 10 : 965-975, 1989, AJR 153 : 1039-1049, 1989.
41. Phillips M.E., Ryals T.J., Kambhu S., et al : Neoplastic V.S. inflammatory meningeal enhancement with Gd-DTPA. J. Comput. Assist. Tomogr. 14(4) : 536-541, 1990.
42. Kucharczyk W., Davis D.O., Kelly W.M., Pituitary adenomas : High resolution MR imaging at 1.5 T. Radiology 161 : 761-765, 1986.
43. Dwyer A.J., Frank J.A., Doppman J.L., et al : Pituitary adenomas with Cushing’s disease : Initial experiences with Gd-DTPA-enhanced MR imaging. Radiology 163 : 421-426, 1987.
44. Davis P.C., Hoffman J.C., Malko J.A., : Gadoliniun-DTPA and MR imaging of pituitary adenoma : a preliminary report AJNR 8 817-823, 1987.
45. Chakeres D.W., Curtin A., Ford G., : magnetic resonance imaging of pituitary and parasellar abnormalities. Radio. Clin. North Am. 27 (2) : 265-281, 1989.
46. Kyle C.L., Laster R.A., Burton E.M., et al : subacute pituitary apoplexy : MR. and C.T. appearance. J. Comput. Assist. Tomogr. 14 (1) : 40-44, 1990.
47. Karnaze M.G., Sartor K., Winthrop J.D., et al: Suprasellar lesion : Evaluation with MR imaging. Radiology 161 : 77-82, 1986.
48. Pusey E., Kortman K.E., Flannigan B.D., et al : MR of craniopharyngiomas tumor delineation and characterization. AJNR 8 : 439-444, 1987.
49. Tien R.D., Barkovich A.J., Edwards M.S.B., MR imaging of pineal tumors. AJNR 11: 557-565, 1990.
50. Zee C.S., Segall H., Apuzzo M., et al: MR. imaging of pineal region neoplasm. J. comput. Assist. Tomogr., 15 : 56-63, 1991.
51. Tampieri D., Malanson D., Ethier R. : MR imaging of epidermoid cysts AJNR 10 : 351-356, 1989.
52. Horowitz B.L., Chari M.V., James R., et al : MR of intracranial epidermoid tumors : Correlation of in vivo imaging with in vitro C. spectroscopy. AJNR 11 : 299-302, 1990.
53. Howard Lee Primary tumors in adults in Cranial MRI and C.T. p. 295-280, 1992.
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Original page 515

Chapter 7 · Treatment of Brain Tumors

As discussed earlier, a brain tumor impairs the function of the region in which it arises and, as it enlarges, adjacent regions. It also causes cerebral edema, obstruction of CSF pathways, and raised intracranial pressure. Various medical illnesses may further worsen the patient’s condition or compromise the results of surgery. All these factors must be considered when treating patients with brain tumors. The aim of treatment is complete removal without increasing the neurological deficit present before surgery, with the greatest possible recovery of lost function. Once the tumor has been completely removed, its effects—cerebral edema, obstruction of CSF pathways, and raised intracranial pressure—resolve toward normal. However, tumors in some locations cannot be completely removed, and some cannot be treated surgically at all, such as those in the brainstem, thalamus, and hypothalamus. These are vital brain regions, and surgery may cause death. Other methods must therefore be used to provide palliation for a period of time.

The treatment of brain tumors may be discussed in two parts:

1. General principles of treatment
2. Specific management of individual tumors according to their type and location

Original pages 515–518

General Principles of Brain Tumor Treatment

Brain tumors grow, and allowing time to pass permits them to enlarge, with progressive loss of neurological function. Once examination and investigation establish that a brain tumor is present, treatment must be carefully planned. Considerations include its location, size, and probable type based on imaging, cerebral edema, hydrocephalus, midline shift, and the patient’s condition. The general treatment plan is as follows:

1. Completely remove the brain tumor if its location permits this without loss of neurological function or life. This can cure the disease and is usually possible with well-circumscribed benign tumors. Malignant or infiltrative tumors are difficult to remove completely; even with an operating microscope, all tumor cells infiltrating brain tissue cannot be dissected away. When the tumor is completely removed, intracranial pressure, cerebral edema, tumor-related hydrocephalus, and midline shift may return to normal.

2. Perform subtotal excision, removing as much as possible without increasing neurological deficit. This relieves compression of the brain and is appropriate when complete removal is impossible. During surgery, the surgeon must exercise judgment as to whether removal is worth the risk, how much should be removed, and when an attempt at complete excision should be abandoned in the face of difficulty. The patient’s neurological function and life must always take priority. If complete removal of a benign tumor in a critical location might cause death or major disability, it should not be attempted; as much as safely possible should be removed instead. The patient may then improve for a period and continue living, but may eventually face a second operation. At that point, the question of reoperation must be reconsidered through a fresh neurological examination and imaging, such as C.T., comparing the findings with those before the first operation and carefully weighing the benefits and disadvantages. If a second operation would offer no benefit, other treatments should be sought. In general, the period of improvement after a second operation is shorter than after the first unless additional treatments are used. Lost neurological functions often do not recover, particularly with infiltrative tumors.

New, highly effective instruments now assist brain tumor surgery, including bipolar coagulating forceps, microscopes, microinstruments, ultrasonic aspirators, and lasers. These make removal easier and less hazardous. Tumors in some locations that previously could not be completely removed can now be treated more successfully, with higher success rates.

3. Divert CSF through a shunt or ventriculostomy when its pathways are obstructed and the causative tumor cannot be completely removed. This improves the patient’s condition by lowering intracranial pressure and is often combined with radiotherapy for radiosensitive tumors. Shunts are frequently used in children, whose tumors commonly occur in the posterior fossa or midline and obstruct CSF flow.

CSF drainage before tumor removal has several benefits. It lowers intracranial pressure, potentially saving the patient’s life and improving neurological function. It also provides time to correct malnutrition and electrolyte abnormalities before major surgery. With posterior fossa tumors, however, a shunt or ventriculostomy may cause upward cerebellar herniation. Conversely, posterior fossa craniectomy for tumor removal without first draining CSF by ventriculostomy may worsen downward herniation, with similarly harmful consequences.

4. Obtain tumor tissue for pathological examination to determine its type, helping to plan surgery and subsequent additional treatment. Biopsy is indicated: i) when the tumor is deep or in a critical location where complete removal might endanger the patient; and ii) for malignant tumors that may require radiation and chemotherapy, so that the tumor type should be established. Tissue may be obtained by three methods: i) craniotomy and open biopsy; ii) needle biopsy; and iii) stereotactic biopsy. Open biopsy allows the surgeon to see the tumor, identify and avoid major vessels, and obtain additional tissue for diagnosis. It also allows bleeding points to be seen and controlled. Needle biopsy often yields a small sample that may be insufficient for diagnosis or may come from nontumorous tissue. More importantly, it may cause internal hemorrhage that cannot be controlled.

5. For radiosensitive tumors, follow surgery with radiotherapy, possibly combined with chemotherapy, according to the individual case.

Original pages 518–519

Preoperative Preparation

Before surgery, the surgeon must perform a thorough general and neurological examination to identify abnormalities in the various body systems. Unless urgent surgery is necessary, medical illnesses should first be treated and stabilized. This helps ensure successful surgery without intraoperative or postoperative complications. Once examination and investigations establish a brain tumor diagnosis, the surgeon must weigh the expected outcome and risks, considering the tumor’s location and type and the degree of cerebral edema. A reasoned plan must be made before operating: the approach to the tumor, the extent of removal, and whether surgery should be replaced by another treatment because of pre-existing medical illness. It is essential always to consider what additional loss of brain or cranial nerve function removal might cause. For example, acoustic neuroma surgery may cause facial palsy, while tentorial meningioma surgery may cause third, fourth, or sixth nerve palsy.

Psychological preparation and the relationship between the doctor, patient, and family are also important. The surgeon should explain the disease, indications for surgery, operative method, benefits, disadvantages, risks, and possible complications so that the patient and family understand them. At the same time, encouragement and confidence should be fostered to obtain cooperation and prepare the patient to face surgical risks.

The following important factors relating to brain surgery should be assessed and corrected before the operation.

Original page 519

1. The Cardiovascular System

This is particularly important because the brain requires an adequate blood supply at all times, both during and after surgery. Surgery may cause blood loss and hypotension, and pre-existing cardiac disease increases the risk. A history of angina pectoris, chest pain, easy fatigue on exertion, myocardial infarction, or arrhythmia indicates risks during anesthesia. EKG and chest X-rays should therefore be obtained, particularly in patients over 40 years old, to detect abnormalities. A cardiologist should be consulted and treatment provided until surgery is considered safe.

In elderly patients, blood pressure should be measured both supine and sitting to assess whether brain surgery in the sitting position would compromise cardiac function. If cardiac function is inadequate, surgery should be performed in a recumbent position.

Original pages 519–520

2. The Respiratory System

This is another important system that ensures adequate O₂ delivery to the brain. The preoperative history should cover chronic lung diseases such as asthma, emphysema, and bronchiectasis, chronic productive cough, noisy breathing, difficulty breathing, and tuberculosis. These conditions can cause CO₂ retention and inadequate oxygenation. Excess CO₂ causes cerebral vasodilatation, raising intracranial pressure and making surgery difficult and hazardous to the brain. Chest radiographs should be obtained to detect abnormalities. If pulmonary function is suspected to be inadequate, pulmonary function tests and blood gas analysis should be performed, and treatment continued until lung function improves satisfactorily before surgery.

In patients with markedly elevated intracranial pressure, positive-pressure breathing should not be used, because it raises venous pressure and consequently increases intracranial pressure further, creating a potential danger.

Original page 520

3. Blood Tests

Obtain a complete blood count, including hemoglobin, hematocrit, and platelet count. Anemia and a low platelet count should first be corrected by transfusion of blood and platelets. If a disorder causing a coagulation defect, such as liver disease, is suspected, measure the prothrombin time and partial thromboplastin time, and correct the abnormality with intravenous vitamin K1 (Mephyton) and fresh frozen plasma.⁽¹⁾

Other hematological problems that must be sought in the preoperative history include ecchymoses, prolonged bleeding, petechial rashes, purpura, epistaxis, and current aspirin use. These abnormalities endanger the patient during and after surgery; their causes must be identified and corrected.

Original pages 520–521

4. Fluids and Electrolytes

Tumors in certain locations may cause fluid and electrolyte disturbances. For example, hypothalamic tumors may cause diabetes insipidus or impair the thirst mechanism. Children with posterior fossa tumors may vomit excessively and eat poorly. Administration of osmotic diuretic solutions and furosemide can also cause dehydration and hypovolemia. At induction of anesthesia, blood pressure may fall, reducing cerebral blood flow and causing cerebral ischemia. Furosemide causes greater losses of Na⁺ and K⁺ than mannitol.⁽²⁾ These disturbances must be corrected before anesthesia.

Several brain diseases, including tumors, may cause the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Excessive water retention results in hyponatremia and water intoxication,⁽³⁾ which can cause cerebral edema and seizures, making surgery difficult and dangerous. Fluid restriction should therefore first restore Na⁺ to normal.

K⁺ abnormalities are also important in surgery. Patients receiving diuretics for hypertension may develop hypokalemia, which can cause cardiac arrhythmias during surgery. It must therefore be corrected before the operation.

Original page 521

5. The Endocrine System

Two important diseases affect surgery: diabetes insipidus and diabetes mellitus. Blood glucose must therefore be measured in every patient. If diabetes mellitus is found, it must be treated until blood glucose is within the normal range, because diabetes impairs wound healing and increases susceptibility to infection. Moreover, the stress of anesthesia and surgery, or steroids given before and after surgery, may greatly increase blood glucose and endanger the patient.

Corticosteroids must sometimes be given before surgery. In patients with a tumor and cerebral edema, they are used to reduce swelling:⁽⁴⁾ dexamethasone 10 mg I.V., followed by 5 mg I.V. every 6 hours, beginning 1–2 days before surgery. Patients with pituitary gland or hypothalamic tumors often have hypopituitarism and require hydrocortisone 100–200 mg by intravenous drip before surgery to prevent an Addisonian crisis.

Original page 521

6. Anticonvulsants

Preoperative anticonvulsants remain controversial for patients with brain tumors who have never had seizures. Some neurosurgeons give agents such as Dilantin and phenobarbital before and after every supratentorial tumor operation, although seizures during or immediately after surgery are uncommon. The author considers routine preoperative anticonvulsants unnecessary for all supratentorial tumors and selects only patients undergoing surgery in areas readily provoking seizures, such as the motor area, and those with a history of seizures. Dilantin or phenobarbital must be given for several days before surgery to control seizures, and should be continued for a time afterward. If no seizures occur, medication is discontinued.

Original page 521

7. Antibiotics

The administration of antibiotics before and during surgery remains controversial. However, intraoperative antibiotics in clean cases have now been found effective in preventing postoperative neurosurgical infection.⁽⁵⁾

Original pages 521–522

8. Head Shaving and Hair Washing

Before the day of surgery, the hair should be washed thoroughly to reduce staphylococcal organisms. The head is then shaved on the day of surgery, cleaned with antiseptic, and covered with a clean cloth. The entire head should be shaved rather than only part, since partial shaving provides inadequate cleanliness and makes wound dressing difficult. After anesthesia and positioning, before surgery begins, the operative scalp area must be scrubbed twice with antiseptic soap for approximately 5–10 minutes, followed by sterile draping of the surrounding unclean areas.

Original page 522

9. Enemas

An enema should not be given to a patient with a large tumor and raised intracranial pressure. It may induce forceful straining at defecation, abruptly raising intracranial pressure enough to cause brain herniation. The patient may lose consciousness and deteriorate, requiring emergency surgery.

Original page 522

10. Urinary Catheterization

Brain tumor operations often take a long time, and some patients require diuretics to lower intracranial pressure. A Foley catheter should therefore be inserted in every patient with raised intracranial pressure who is expected to undergo a prolonged operation. Generally it is inserted after induction of anesthesia and removed postoperatively once the patient has recovered well and frequent timed measurements of urine output are no longer necessary.

Original pages 522–523

Anesthesia for Patients with Brain Tumors

Besides providing smooth anesthesia, the anesthesiologist must understand the various changes that may occur in the brain during anesthesia, particularly changes in intracranial pressure and cerebral circulation. These must be recognized immediately and corrected urgently during anesthesia; otherwise brain surgery cannot continue.

Before anesthesia, the anesthesiologist should assess the patient and consult the operating surgeon about the disease, operation, patient position, risks, and precautions, to prevent intraoperative complications and ensure a good result. The anesthesiologist must know the patient’s history regarding illness, level of consciousness, drug allergies, and seizures. The respiratory and circulatory systems must be examined for respiratory disease that could interfere with anesthesia or obstruct the airway. Cardiac and blood pressure abnormalities, such as myocardial infarction and hypertension, should be treated before anesthesia. Abnormalities in the laboratory and other investigations—CBC, electrolytes, blood glucose, blood gases, coagulation profile, urinalysis, EKG, and chest X-rays—must also be corrected to prevent complications.

Original pages 523–528

Considerations in Anesthesia for Patients with Brain Tumors

The surgeon and anesthesiologist must always take three interrelated factors into account: intracranial pressure, cerebral blood flow, and respiration. Changes must be recognized and corrected promptly. Raised intracranial pressure is a major obstacle to brain tumor surgery, making removal difficult and dangerous.

Changes in intracranial pressure depend on several factors that must be understood so that an increase during anesthesia can be prevented:

1. Premedication. This is important in patients whose tumor has already produced very high intracranial pressure, approaching decompensation (see Chapter 4). Drugs should not increase cerebral blood flow or intracranial pressure. Respiratory depressants should be avoided because they cause carbon dioxide retention and reduced oxygen; carbon dioxide dilates cerebral blood vessels and raises intracranial pressure. Narcotics, particularly morphine, should be avoided: they depress respiration, constrict the pupils, reduce consciousness, delay postoperative awakening, and interfere with assessment of consciousness. They may also cause vomiting, raising intracranial pressure to a dangerous level. The anesthesiologist may give atropine alone. Drowsy or unconscious patients do not require premedication.

2. Coughing and straining during induction. In patients with a large tumor or very high intracranial pressure, the surgeon must warn the anesthesiologist to avoid provoking coughing. Coughing and straining during intubation abruptly raise intracranial pressure and may cause uncal or tonsillar herniation, compressing the brainstem during anesthesia. Patients with raised intracranial pressure also tolerate poorly the hypoxia caused by coughing or prolonged intubation. Induction should therefore be smooth, with adequate oxygenation and rapid intubation without coughing.

3. Airway obstruction. This is the most important cause of an abrupt rise in intracranial pressure. Hypercapnia and hypoxemia cause cerebral vasodilatation and engorgement. Unless the airway is cleared promptly, diffuse cerebral edema may lead to brain herniation and brainstem compression, preventing recovery of consciousness. Brain cells cannot tolerate prolonged oxygen deprivation; obstruction must therefore be diagnosed promptly.

When the skull and dura have been opened, obstruction of the endotracheal tube by secretions or kinking causes the brain to bulge progressively beyond the craniotomy, without pulsation. Capillaries rupture, producing subarachnoid hemorrhage over the protruding brain. Surgery cannot continue. The airway must be cleared and the patient hyperventilated to correct hypercapnia; the brain then visibly subsides and begins to pulsate. Thus, when sudden intraoperative brain swelling occurs and hemorrhage into the tumor or brain and obstruction of the ventricles have been excluded, the airway should be checked first. Restoring its patency allows the brain to subside.

During tumor removal, intracranial pressure should be lowered by hyperventilation to a PCO2 of 25–30 mmHg. This provides the desired reduction in pressure without the cerebral ischemia caused by excessive vasoconstriction at a very low PCO2. Its advantages are: (1) cerebral vasoconstriction lowers intracranial pressure and relaxes the brain, facilitating tumor removal; (2) it counteracts the vasodilating effect of halothane; (3) it reduces the amount of anesthetic required; and (4) it permits control of PCO2. The disadvantage is that vasoconstriction at a PCO2 of 20 mmHg may cause cerebral hypoxia and infarction.

Spontaneous respiration during anesthesia is inappropriate in patients with a tumor and high intracranial pressure, since respiration is already depressed, especially with posterior fossa tumors near the respiratory center. Inadequate ventilation prevents brain relaxation and makes surgery difficult. Controlled respiration offers the following advantages: (1) adequate oxygen delivery and carbon dioxide elimination when the heart and lungs are normal; (2) less cerebral venous congestion and bleeding; (3) a smaller anesthetic requirement; (4) lighter anesthesia and more rapid awakening; (5) improved ventilation in the prone position; and (6) the use of muscle relaxants to prevent coughing and straining, which benefits the brain. Some surgeons prefer spontaneous respiration during posterior fossa surgery to monitor the respiratory center while manipulating the medulla. Even during controlled respiration, however, cardiac arrhythmias on the EKG can indicate disturbance of the medulla.⁽⁶⁾

A patent airway must be maintained at all times, including after surgery, when surgical edema and poor respiration may aggravate the problem. If the patient remains unconscious after the operation, the endotracheal tube should remain in place to prevent obstruction by the tongue and permit suction of secretions.

4. Anesthetic agents. Several injectable and inhaled anesthetics, including ketamine and halothane, dilate cerebral vessels, increasing cerebral blood flow and intracranial pressure.

KETAMINE is not favored in patients with tumors or other brain disorders associated with raised intracranial pressure, because it increases cerebral blood flow by more than 50%^(7,8) and markedly increases intracranial pressure.

HALOTHANE is widely used in general surgery because it provides smooth anesthesia and allows rapid awakening.^(9,10) It is nonexplosive and can be used with electrocautery. However, it dilates cerebral vessels and increases cerebral blood flow and intracranial pressure. It should therefore be used at a concentration below 0.75%, together with hyperventilation.⁽¹¹⁾

5. Patient position. Position affects intracranial pressure, particularly the prone position and the supine position with excessive head rotation. Breathing is more difficult prone than supine; increased intrathoracic pressure raises cerebral venous pressure and intracranial pressure. Compression of the abdomen and thorax should be avoided, and the head should be slightly above the heart to improve venous drainage and prevent a rise in pressure. In the supine position, excessive head rotation may obstruct the neck veins. A pillow should elevate the shoulder on the operative side above the other shoulder, reducing the amount of head rotation and preventing venous obstruction. If intracranial pressure is already very high and cerebral perfusion is maintained only by elevated blood pressure, venous obstruction may raise intracranial pressure to a life-threatening level.

6. Blood pressure. Marked hypertension should be avoided after the dura has been opened. It is dangerous because blood pressure is no longer opposed by intracranial pressure; cerebral blood flow increases, and the brain swells to fill the craniotomy opening. Touching or retracting it causes extravasation of blood and fluid, increasing the swelling.⁽¹²⁾ Conversely, lowering blood pressure relaxes the brain.

Hypertension. The main cause is painful stimulation during excessively light anesthesia, particularly during dissection around the trigeminal nerve.⁽¹³⁾ Interference with vessels of the brainstem, such as the anterior inferior cerebellar artery, or basal branches of the anterior cerebral artery supplying the anterior hypothalamus,⁽¹³⁾ may also raise blood pressure. At the start of surgery, injection of local anesthetic containing adrenaline to reduce bleeding may cause hypertension. Hypertension before craniotomy or after completion of the operation should suggest raised intracranial pressure.

Hypotension. Initially, thiopentone, muscle relaxants, and controlled ventilation may cause a temporary fall in blood pressure, followed by recovery. During posterior fossa surgery, such as removal of an acoustic neuroma, traction on the adjacent vagus nerve or traction on a medullary tumor may produce hypotension with a slow, irregular pulse. Stopping the stimulus restores normal values. The sitting position for posterior fossa surgery lowers blood pressure and intracranial pressure. Air embolism causes an abrupt fall in blood pressure and is a life-threatening complication, discussed in detail in the section on surgery.

The cerebral circulation has already been discussed in the chapter on intracranial pressure.

Original page 528

Postoperative Care

If the patient was alert before surgery, the operation was smooth without injury to important areas of the brain, and consciousness returns well, postoperative care resembles that following other operations. With smooth care and no complications, recovery proceeds normally. Nevertheless, many technically successful operations are followed by complications caused by errors in postoperative care. Close and correct care must continue until the patient is safe. Postoperative hematoma and cerebral edema can be fatal and require prompt diagnosis and treatment.

Important aspects of postoperative care for patients with brain tumors are as follows:

Original pages 528–529

1. Immediate Postoperative Care

Emergence from anesthesia is a critical period. Before removing the endotracheal tube, adequate respiration, blood pressure, and consciousness must be assured. Premature extubation may cause carbon dioxide retention and hypoxemia, resulting in cerebral edema, raised intracranial pressure, and poor recovery of consciousness. If awakening or respiration remains poor, ventilation should be continued with frequent reassessment. If the condition does not improve, its cause must be investigated. The tube can be removed later, when the patient is alert and breathing normally.

After anesthesia has been discontinued, the endotracheal tube may provoke coughing, causing hypertension, intracranial bleeding, and raised intracranial pressure. Once the patient is adequately awake, extubation should be smooth, preventing or minimizing coughing.

An intensive care unit is essential after brain surgery, providing close care by doctors and nurses trained in neurological observation. They must recognize changes in consciousness, vital signs, weakness, and pupils. The earlier a complication is diagnosed, the better. Nurses are especially important because they remain continuously with the patient, and require extensive training to provide effective care. Untrained nurses may be unable to interpret changes and may miss the opportunity for prompt treatment.

Original pages 529–535

2. Four Standard Observations

Immediately on arrival in the intensive care unit, four important observations must be made to establish the baseline for monitoring changes. Everyone must use the same criteria so that subsequent observations can be compared:

1. Vital signs: pulse, blood pressure, and respiration
2. Consciousness
3. Limb movement
4. Pupil size and reactions

These four observations reveal intracranial complications, namely postoperative hemorrhage (postoperative clot) and cerebral edema. Both raise intracranial pressure and require urgent treatment.

Vital signs should be checked frequently, every 15–30 minutes during the first 1–2 hours. If the condition is then stable, observations should continue hourly for another 2–3 days.

Blood pressure and pulse. When a cause of raised intracranial pressure develops, the pulse progressively slows while blood pressure progressively rises: Cushing’s reflex. An accompanying deterioration in consciousness, with increasing drowsiness, further supports the diagnosis. The author consistently follows this principle in practice.

Generally, after brain tumor surgery without major blood loss, or with major blood loss adequately replaced by transfusion, hypotension does not occur even if intracerebral hemorrhage develops. The amount of postoperative intracranial bleeding is insufficient to lower blood pressure, although it can impair consciousness. If postoperative hypotension occurs, extracranial causes should therefore be considered, such as cardiac disease, diabetes insipidus with excessive urine output causing hypovolemia, and hypopituitarism. These require appropriate treatment. In some patients, inadequate hemostasis during closure of the skull and scalp results in 400–500 cc of blood collecting in the suction bottle within 10–15 minutes, potentially causing hypotension. The patient must be returned urgently to the operating room for hemostasis.

Respiration. This is extremely important in caring for patients after brain surgery. The airway must remain patent at all times to provide adequate O₂. Patients who are fully conscious after surgery have no respiratory difficulty, but this may change if postoperative hemorrhage or cerebral edema raises intracranial pressure. A posterior fossa hematoma produces conspicuous respiratory changes: breathing becomes progressively slower and shallower, followed shortly by respiratory arrest. This is an important sign requiring diagnosis and intervention before respiration ceases. After supratentorial tumor surgery, respiratory changes may be less obvious. Breathing may slow somewhat, and some patients develop Cheyne–Stokes respiration. These are important signs requiring investigation of the cause.

To determine whether respiration is adequate, assess the breathing pattern, cough, and blood gases. Shallow, slow breathing or dyspnea indicates abnormal ventilation. A patient able to cough strongly has sufficient vital capacity to maintain normal oxygenation. Blood gases provide a good indication of pulmonary function. Since inspired air contains no CO₂, an increased blood PaCO₂ indicates hypoventilation and the need for mechanical ventilation. Normally, while breathing room air, PaCO₂ is 35–45 torr and PaO₂ 80–100 torr. This PaCO₂ range maintains blood pH within the normal range of 7.35–7.45. A reduced PaCO₂ indicates hyperventilation. Generally, if the brain is not compressed after surgery, patients mildly hyperventilate. This is beneficial, avoiding CO₂ retention and providing adequate O₂, and does not require correction.

Maintaining a patent airway. In patients who remain drowsy or poorly conscious after brain tumor surgery, whatever the cause, the first concern and intervention must be to maintain a patent airway. This permits good lung expansion without hypoxia or hypercarbia, saves life, and prevents intracranial complications.

Methods of maintaining a patent airway are as follows:

i) Position the patient with the head extended. This draws the relaxed jaw forward and lifts the tongue that has fallen back to obstruct the pharynx, opening the airway. Preferably, the patient should lie on either side with the head extended, allowing sputum, saliva, and vomitus to drain out.

ii) Insert an oropharyngeal or nasopharyngeal airway, placing its inner end between the posterior pharynx and the base of the tongue. The oropharyngeal airway is inserted through the mouth; the nasopharyngeal tube through one nostril. Besides opening the airway, both allow suction of sputum and saliva. An oropharyngeal tube also prevents an unconscious patient from biting the endotracheal tube. Conscious patients, however, usually tolerate it poorly because it provokes vomiting and laryngospasm. A nasopharyngeal tube is well tolerated by both conscious and unconscious patients. Neither type prevents aspiration into the trachea, which may cause pneumonia, so caution is required. In a drowsy patient who vomits, an endotracheal tube is preferable because it provides good protection against aspiration.

The airway must be appropriately sized for the patient. If too long, it may push the epiglottis over the airway; if too short, it may push the tongue backward and worsen obstruction.

iii) Insert an endotracheal tube. For poorly conscious or unconscious patients, this is the best way to maintain a patent airway. It can be passed through the nose (nasoendotracheal tube) or mouth (oroendotracheal tube). These tubes have cuffs to prevent aspiration and can be connected to a ventilator. Adequate training is necessary for smooth insertion without complications. In a patient with raised intracranial pressure, an inexperienced operator may provoke struggling and resistance, raising pressure dangerously. If possible, a muscle relaxant and Pentothal facilitate insertion without resistance, but a ventilator must be immediately available for safety.

After intubation, always check that air enters both lungs equally. Insertion into one bronchus ventilates only one lung, with serious effects on the brain: hypercarbia, cerebral vasodilatation, and raised intracranial pressure. Leaving an excessively long external portion of the tube can also cause problems. The author has often encountered a tube displaced inward into one bronchus while its outer end still appeared long, obscuring recognition of the displacement. The patient breathes with only one lung and becomes breathless. Withdrawing the tube to the correct position restores normal breathing. The author therefore makes it a rule to take the following steps after intubation:

i) Auscultate both sides; air entry must always be equal in both lungs.

ii) Once the tube’s correct position has been verified, mark it at the nostril or lip and secure it so that it remains in position.

iii) Cut the tube so that approximately 2 inches remain outside. If less than this protrudes later, inward displacement will be apparent.

iv) Tracheostomy is performed when unconsciousness persists for a long time after brain tumor surgery. An endotracheal tube should not remain in place for more than 10 days because nasal necrosis may develop, or dried secretions may narrow its lumen and cause inadequate ventilation. For an unconscious patient, a tracheostomy tube with a low-pressure cuff and an inner tube should be used. The cuff can be inflated to fill the trachea, preventing aspiration and allowing connection to a ventilator without leakage. The inner tube can also be removed and inspected for obstruction. A metal tube is unsuitable for an unconscious patient because it does not prevent aspiration and cannot be connected to a ventilator. It should be used when consciousness has recovered and removal of the tracheostomy tube is planned. A metal tube must not be too long, because it may injure a major blood vessel, causing fatal hemorrhage as blood obstructs the trachea and bronchi.

Tracheostomy must be performed by an experienced operator; otherwise complications may occur, sometimes rapidly fatal. The author has encountered tension pneumothorax in a child after injury to the pleural dome, which lies close to the trachea; the patient subsequently died.

Consciousness. This is the most important observation in postoperative care because it indicates changes in the brain. Immediately after recovery from anesthesia, assess consciousness by asking questions and giving commands, then record what the patient can actually do—for example, correctly stating the day, month, year, and location, and recounting the history of illness. Terms such as conscious, drowsy, stupor, semicoma, and coma may be interpreted differently by the next person taking over care. This can lead to misinterpretation of changes: consciousness may be judged unchanged when it has in fact deteriorated. Treatment is then delayed, and the patient may eventually become unconscious.

In some cases, postoperative hemorrhage develops early. A patient approaching full recovery from anesthesia deteriorates again and must be returned to the operating room for reopening of the skull and evacuation of the blood. In others, consciousness begins to deteriorate around the third or fourth day, possibly because of cerebral edema, a slowly developing hematoma, or hyponatremia. Imaging investigations are required to identify the cause, followed by urgent treatment.

Limb movement. This is another sign requiring repeated assessment after surgery. As soon as the patient awakens from anesthesia, record any weakness and which limbs are affected. In principle, monoparesis or hemiparesis already present on leaving the operating room suggests injury to some part of the corticospinal tract during surgery. If there is no weakness on awakening, but hemiparesis develops later, consider a postoperative complication: hemorrhage, cerebral edema, or infarction. If this is the cause, changes in consciousness and signs of raised intracranial pressure will also be present. The cause must be investigated and treated immediately.

If weakness was present before surgery and persists afterward, subsequent progressive worsening should likewise suggest a postoperative complication.

After posterior fossa tumor surgery, complications may produce increasing incoordination and relatively rapid deterioration of consciousness, together with progressively slower respiration.

Pupil size and reactions. Pupillary changes occur with brain herniation, as discussed in detail under raised intracranial pressure. It is wrong to wait until one pupil has dilated (anisocoria), because treatment is then delayed and recovery is less satisfactory than when treatment precedes herniation. As already mentioned, actual pupillary dilatation is often preceded by constriction, due to stimulation of the parasympathetic constrictor fibers on the surface of the oculomotor nerve or interference with the hypothalamus. Such changes, together with deteriorating consciousness, require urgent investigation so that the cause can be corrected early. After posterior fossa surgery, anisocoria does not occur as it does after supratentorial surgery; both pupils remain equal and continue to react to light.

Original pages 535–536

3. Patient Position

Generally, the patient is positioned with the head elevated approximately 30° to improve cerebral venous return and prevent cerebral edema and raised intracranial pressure. The disadvantage is possible aspiration of vomitus, making this position less suitable for patients who remain unconscious after surgery. If an endotracheal tube is present, however, it is safe. Lying flat with the head low provides poorer venous drainage than head elevation, promoting cerebral edema and raised intracranial pressure, which may facilitate bleeding at the operative site. Its advantage is a lower likelihood of aspiration.

Removal of a large tumor on one side leaves a large cavity. Placing the operative side downward may shift the brain toward this space, tearing cortical bridging veins and causing an acute postoperative subdural hematoma. The patient should therefore lie on the side with the operative hemisphere uppermost for several hours, allowing the brain in the operative area to swell and narrow the cavity, while CSF also accumulates to support the brain. Turning to other positions then becomes less dangerous. Similarly, turning a patient after removal of a large posterior fossa tumor may cause complications; the author has encountered respiratory arrest and hypotension.

Elderly and unconscious patients must be turned every 2 hours to prevent pneumonia.

Original pages 536–538

4. Fluids and Electrolytes

The brain is very sensitive to water retention and edema. In the early period after brain tumor surgery, cerebral edema remains a concern and excessive fluid should be avoided. Generally, during the first 3–4 days, mild dehydration should be maintained by giving approximately two-thirds of the daily requirement, about 1500 cc per day for an adult. Fluid is given as 5% dextrose in half-normal saline (0.5 NSS), with K⁺ added as required. It is generally accepted that 5% dextrose in water should not be given when postoperative cerebral edema is anticipated, because it may worsen swelling. If the patient is fully conscious after surgery, does not vomit, and does not aspirate because of ninth- or tenth-cranial-nerve dysfunction, oral feeding can begin on the second postoperative day. Intravenous fluids are unnecessary if intravenous medication is not needed. Patients who are not fully conscious should not yet be fed orally, because vomiting and aspiration may occur. Intravenous fluids should continue as required, and tube feeding should begin once vomiting has ceased.

During the first 1–2 postoperative days, urine output may be reduced as a normal response to surgery. Increasing fluid intake to restore urine output to normal is unnecessary and may aggravate cerebral edema.

Hyponatremia. A low blood Na⁺ concentration may result from excessive water retention due to the syndrome of inappropriate ADH secretion (SIADH). This is frequently encountered after brain surgery or with brain disease, particularly tumors near the third ventricle and hypothalamus. The syndrome may also occur after traumatic intracranial hemorrhage, with oat cell carcinoma of the lung, or with pulmonary tuberculosis. Diagnosis rests on the history and blood Na⁺ measurement. Its features are: (i) weight gain; (ii) progressive drowsiness around the end of the first postoperative week, after intracranial hematoma has been excluded; (iii) possible seizures; (iv) low serum Na⁺; (v) low serum osmolarity; (vi) increased urinary Na⁺; (vii) increased urine osmolarity; and (viii) absence of renal or adrenal disease. The principal treatment is restriction of fluid intake to no more than 500–1000 cc daily. In mild cases, Na⁺ returns to normal within 1–2 days, with restoration of consciousness. In severe cases, with Na⁺ below 120 mEq/L, hypertonic saline, such as 3% or 5% solution, 200–300 cc daily, may be required in addition to fluid restriction. The author has found that this improves consciousness and raises Na⁺ more rapidly than fluid restriction alone. Nevertheless, hyponatremia may recur intermittently after correction. The patient must therefore be monitored and blood Na⁺ measured periodically until normality is maintained.

Diabetes insipidus (DI). This occurs after surgery for tumors in the pituitary and hypothalamic regions. Most postoperative cases last approximately 2–3 weeks before gradually improving. Characteristic diagnostic features are polyuria, polydipsia (excessive thirst and drinking), very low urine specific gravity, and signs of dehydration.

Treatment depends on severity. With mild polyuria and polydipsia, the patient may drink enough water to replace losses as required, and the condition usually improves. If urine output is excessive and the patient becomes markedly dehydrated, drowsy, and unable to retain water, intravenous replacement and Pitressin injections are required. There are two preparations. Aqueous Pitressin is given intramuscularly at 0.1 unit/kg, or approximately 5 units for an adult. Its action lasts approximately 4–6 hours, so it may need repeating every 4–6 hours to keep urine output below 200 cc per hour. The other preparation, Pitressin tannate in oil, is given to adults as 5 units intramuscularly and acts for 16–24 hours. One daily injection can therefore reduce urine output as required. Preparation before injection is extremely important because the drug settles as particles at the bottom of the ampoule. The ampoule must be warmed for approximately 10 minutes and then shaken vigorously for another 10–15 minutes before the contents are drawn into a syringe and immediately injected intramuscularly. This ensures delivery of the intended dose. Otherwise only oil may be drawn up and injected, providing inadequate Pitressin. A Foley catheter must be inserted, and fluid intake and output carefully measured and recorded to prevent dehydration. Electrolytes must also be checked regularly and abnormalities corrected.

If diabetes insipidus persists, intranasal treatment is more convenient: DDAVP (1-desamino-9-D-arginine vasopressin [chemical name as printed in the original]), 0.05 cc intranasally once or twice daily as required.⁽¹⁴⁾

Original pages 538–540

5. Fever

Elevated body temperature harms the brain by increasing metabolism and the cerebral blood flow needed to supply sufficient O₂, thereby raising intracranial pressure. Postoperative care must therefore maintain temperature within the normal range at all times, using antipyretics, cold-water sponging, or a hypothermia blanket.

Fever usually occurs on the first postoperative day and lasts approximately one day as a bodily response to surgical injury. It resolves spontaneously without medication. If high fever recurs on subsequent days, consider postoperative hematoma and infection. A postoperative hematoma always causes accompanying signs of raised intracranial pressure. Investigate with CT, MRI, or angiography; if a hematoma is found, evacuate it surgically, after which the fever subsides. Infection generally causes fever around postoperative days 4–5. Uncovering the wound reveals inflammation, swelling, and redness, with an increased white blood cell count and polymorphonuclear cells.

Blood in the CSF may also cause fever, particularly after posterior fossa tumor surgery. Fever may persist for several days, sometimes accompanied by meningism and Kernig’s sign. Meningism can be difficult to identify because neck stiffness may also result from the operative wound. In such cases, lumbar puncture may be necessary in addition to antipyretics. If the CSF is heavily bloodstained, approximately 20–30 cc or more should be removed. Repeated punctures over several days help clear the blood from the CSF and reduce the raised intracranial pressure caused by hydrocephalus resulting from blood in the CSF.

Another important cause of high fever is surgery near the third ventricle and hypothalamus, disrupting the temperature-regulating mechanism. Characteristically, the temperature rises abruptly and remains high without returning to normal, sometimes reaching 40°C. Treatment is often ineffective even when several measures are combined: oral and rectal antipyretics, a hypothermia blanket, and sponging with ice water or alcohol. Temperature may remain uncontrollably high and the patient may die.

Original pages 540–541

6. Steroids

Postoperative steroids serve two purposes: (i) hormone replacement in patients with tumors of the pituitary and hypothalamic regions; and (ii) reduction of edema in the operated portion of the brain.

Patients undergoing tumor surgery in the pituitary and hypothalamic regions must always receive adequate steroid replacement before and after surgery. They frequently lack ACTH and cannot tolerate the operation and postoperative stress. Steroid deficiency causes a shock-like state and deterioration of consciousness.⁽¹⁵⁾ Patients develop hypotension, tachycardia, fever, abdominal pain, nausea, vomiting, and oliguria. Blood tests show low or absent plasma cortisol, as well as hyponatremia and hypoglycemia—important laboratory findings.⁽¹⁵⁾

Steroids should begin one day before surgery for sellar and parasellar tumors. Options are dexamethasone 5 mg I.V. every 6 hours, hydrocortisone 100–200 mg by intravenous drip over 24 hours, or cortisone acetate 100 mg I.M. daily.⁽¹⁶⁾

Treatment must continue postoperatively, with gradual reduction of the dose. If there was no preoperative hormone deficiency and surgery did not damage the pituitary or hypothalamus, tapering may be rapid, with discontinuation within 3–4 days. If hormone deficiency existed preoperatively, the initial postoperative dose should gradually be reduced to an adequate maintenance dose within 7 days. Once the patient can eat, oral prednisolone or dexamethasone may be given according to the patient’s requirements.

The edema-reducing benefit of steroids is particularly apparent in metastatic brain tumors or malignant gliomas with marked vasogenic edema. Steroids reduce swelling and improve the patient’s condition. Dexamethasone 5 mg I.V. every 6 hours is generally given before surgery for these tumors and continued afterward. If the tumor has been satisfactorily removed, postoperative dexamethasone should continue for 5 days, followed by tapering and discontinuation over 2–3 days. Prolonged dexamethasone treatment causes complications such as gastric bleeding, hyperglycemia, and hypertension.

Original pages 541–542

7. Anticonvulsants

Patients with brain tumors who have previously had seizures, or whose tumors occupy seizure-prone areas such as the motor area, require anticonvulsants before and after surgery. Each seizure increases cerebral metabolism, oxygen requirements, cerebral blood flow, and venous engorgement, raising intracranial pressure. For this reason some neurosurgeons give anticonvulsants to every patient undergoing supratentorial tumor surgery. The author, however, selects only patients with previous seizures or tumors in seizure-prone regions such as the motor area, because postoperative seizures have been very uncommon in the author’s patients without a previous history.

Postoperative seizures require urgent and effective control. Diazepam 10 mg in adults, given slowly intravenously over 1 minute, can stop a seizure immediately. Intravenous diazepam may impair respiration; a ventilator should always be ready. Inadequate respiration is particularly important after tumor removal because it can raise intracranial pressure and cause hemorrhage. Once diazepam has stopped the seizure, longer-acting anticonvulsants—Dilantin and phenobarbital—must follow. Dilantin may be started with 400 mg, or 5–7 mg/kg, intravenously at a very slow rate, no more than 50 mg per minute; thus 400 mg should take 8–10 minutes. Cardiac activity must be monitored because arrhythmias may occur. Thereafter, Dilantin 100 mg and phenobarbital 30 mg are given orally or through a nasogastric tube three or four times daily.

Whenever seizures occur, remember that the operative site may have developed a complication, such as postoperative hemorrhage, cerebral edema, or infarction; metabolic disorders are another possible cause. These require investigation with CT and treatment directed at the cause.

Original page 542

8. Headache

Headache after brain tumor surgery has two possible causes: (i) pain from the operative wound, and (ii) a change in intracranial pressure. Wound pain is localized to the incision and responds to analgesics such as paracetamol or aspirin. Headache from raised intracranial pressure—for example, due to hemorrhage, cerebral edema, or hydrocephalus—is generalized and does not respond to analgesics alone. Its cause must be removed or intracranial pressure restored to normal before the headache resolves. A hematoma requires evacuation, for example, while elevated CSF pressure requires drainage of CSF from the brain.

Morphine and other analgesics with narcotic or sedative effects should not be used because they cause drowsiness and mask deterioration due to raised intracranial pressure. Morphine also depresses the respiratory center and should not be used when intracranial pressure is already elevated.

Original pages 542–543

9. Urinary and Bowel Care

Brain tumor operations generally take a long time, and some patients need diuretics to lower intracranial pressure. A Foley catheter must therefore be inserted before surgery and left in place during the postoperative period. If consciousness is normal, remove it as soon as possible and allow spontaneous urination, reducing bladder infection. If recovery is poor, or surgery involved the pituitary region where diabetes insipidus often develops, retain the catheter to measure hourly urine output. After removal of a frontal lobe tumor, patients may have poor urinary control despite being conscious, wetting the bed without awareness. Their voiding mechanism remains normal. A condom catheter connected to a collecting bottle prevents bedwetting and can be removed once frontal lobe function improves.

Bowel care is not difficult, but is often overlooked. Patients may go 4–5 days without defecating, particularly those who are poorly conscious after surgery, and may strain or develop hypertension. A laxative or enema should therefore be given within the first 2 postoperative days and repeated as appropriate. If hard impacted stool is found and cannot be expelled with an enema, manual evacuation is required. The author has seen fecal impaction cause multiple rectal ulcers, bleeding, rectal perforation, generalized peritonitis, and death. The attending physician must give this matter attention.

Original pages 543–544

10. Eye Protection

Eyelid swelling may follow frontal lobe surgery. The lids often swell shut, usually more severely on the operative side. A bifrontal bone flap may cause bilateral swelling, sometimes preventing inspection of the pupils. Swelling begins on the second postoperative day, lasts approximately 4–5 days, and gradually subsides. The physician should explain to the patient and family that this is usual after surgery in this region. Head elevation accelerates its resolution.

Corneal drying and abrasion are important problems in unconscious patients. If both eyes remain open, the corneas dry and become abraded; the patient may be unable to see after otherwise recovering from brain tumor surgery. The physician must attend to this, using narrow strips of adhesive tape at the lateral and medial portions of the upper lid and drawing the lid downward to close the eye. Ensure that the tape does not touch the cornea, and inspect regularly. Apply ophthalmic ointment three times daily to coat the cornea. A fan should not blow directly into the eyes because it introduces dust and accelerates drying. Most importantly, do not use an eye pad: its underside may directly contact the cornea and cause an ulcer.

Keratitis may follow acoustic neuroma surgery when loss of the corneal reflex and facial nerve palsy leave the cornea insensitive and the eye widely open. Keratitis and corneal ulceration develop readily. Initially the eye becomes red, followed by a whitish opacity at the ulcer, and eventually loss of vision. Prevention must therefore begin immediately after surgery. An effective measure is temporary tarsorrhaphy, suturing together the lateral third of the upper and lower eyelids. If corneal sensation remains and facial nerve function is expected to recover soon, an eye shield to exclude wind and dust may suffice, with artificial tears every 2–3 hours.

Original pages 544–545

11. Operative Wound Care

Brain tumor surgery produces a clean wound after proper preoperative skin preparation. Nevertheless, infection may occur in 1%^(17,18) despite prophylactic antibiotics. Contributing factors include an operation lasting more than 3 hours, entry into a paranasal sinus or mastoid air cells, diabetes, anemia, wasting or malnutrition from vomiting, CSF leakage, and a drain left in place too long. A blood-soaked dressing must be replaced promptly because blood supports bacterial growth.

At present, a vacuum drain is routinely used after craniotomy. It must be removed after 24–48 hours; leaving it longer increases infection risk. The author usually inspects the wound when removing the drain. After removal, compress the scalp opening until it closes completely. If it remains open, suture it to prevent bacterial entry. If the sutured edge is dusky, remove the offending stitch to improve circulation and healing. Redress the wound properly. Sutures are removed on days 6–7, although an inflamed stitch should be removed earlier and antibiotics given.

Sutures in posterior fossa wounds must be removed later than those in supratentorial wounds, around postoperative days 8–9, because this region moves. If the dura was left open for decompression, or was not closed watertight, CSF may leak through the wound. This must be corrected urgently by lumbar puncture or another method of CSF drainage to lower CSF pressure, stop leakage, and permit sound wound healing.

Original page 545

12. Skin Care

In patients who remain unconscious after surgery, caregivers must prevent pressure sores caused by prolonged immobility in one position. These usually develop over bony prominences such as the femoral greater trochanter, shoulders, heels, and head. Turn the patient every 2 hours and support these areas with soft, jelly-like pads to reduce pressure. If the patient is soiled with stool or urine, clean and dry the skin promptly to reduce rashes.

Original pages 545–546

Complications of Brain Tumor Surgery

Complications are a major reason why surgery and its outcome may fall short of expectations, and may be severe enough to cause death. Surgeons must understand them thoroughly in order to plan prevention, diagnose them rapidly, and correct them appropriately. They arise from two sources. The first is the disease itself—for example, intratumoral hemorrhage, cerebral edema, or obstruction of CSF pathways. The second is the physician’s actions, of which several examples follow. These complications are less frequent in experienced hands. Nevertheless, they still occur despite newer and more effective equipment, including the microscope, microinstruments, laser, ultrasonic aspirator, and bipolar coagulator.

Complications may occur during two periods:

1. The intraoperative period
2. The postoperative period

Original page 546

Intraoperative Complications

These are extremely important. Complications such as brain swelling or air embolism may prevent any further surgery and force abandonment of the operation if they cannot be corrected in time.

Possible intraoperative complications are as follows:

Original page 546

1. A Craniotomy That Does Not Correspond to the Tumor’s Position

This makes access difficult and requires greater brain retraction, potentially tearing brain tissue and vessels. Before making the incision, the surgeon should carefully study the tumor’s location on imaging and correlate it as accurately as possible with the surface anatomy of the patient’s head. Before CT and MRI, correct placement based on angiography, brain scanning, or ventriculography was sometimes difficult, particularly for tumors in the posterior cerebral hemisphere. CT now accurately shows tumor location and size, permitting more precise placement of the craniotomy and sometimes a smaller opening, with fewer complications. Nevertheless, errors remain possible if variations in the angle of the orbitomeatal line used for CT slices are overlooked; this angle may differ between patients.

Original pages 546–547

2. Complications of the Incision

When making the scalp incision, the following must be considered:

i) The blood supply to the scalp flap.

ii) The nerves supplying the muscles and skin.

iii) Cosmetic appearance.

The surgeon must therefore know the vascular and neural anatomy of the scalp; otherwise the following complications may occur.

Original page 547

2.1 Scalp Ischemia

This is an important cause of poor wound healing and dehiscence. The scalp may become dusky or gangrenous. Causes include: (i) a scalp flap with an excessively narrow base or pedicle; (ii) an incision across a major scalp artery; (iii) spring scalp clips applied to the wound edges for hemostasis, particularly when the scalp is thin or already poorly supplied; and (iv) prolonged sharp folding of the reflected flap, impairing flow through its base. A rolled cloth should therefore be placed beneath the flap’s base before reflection to prevent kinking and maintain its blood supply.

Original page 547

2.2 Frontalis Muscle Paralysis

In a frontotemporal craniotomy, a temporal incision extending down to the zygomatic margin and more than 2 cm anterior to the tragus often divides the frontal branch of the facial nerve.⁽¹⁹⁾ The ipsilateral frontalis muscle then loses function, preventing eyebrow elevation. This may cause psychological distress, especially in women.

Original page 547

3. Hemorrhage

Hemorrhage may occur at any stage, from opening the skull to dissecting out the tumor.

Original pages 547–548

3.1 Hemorrhage from the Middle Meningeal Artery

With a meningioma on the cerebral convexity, especially in the frontotemporal or parasagittal region, bleeding during opening of the skull may be profuse. In some patients, this alone causes enough blood loss to produce hypotension. The tumor is supplied by a markedly enlarged middle meningeal artery. This vessel should therefore always be ligated with a suture before opening the skull to reduce blood loss.

Original page 548

3.2 Hemorrhage from the Superior Sagittal Sinus and Arachnoid Granulations

For a parasagittal tumor, the craniotomy must approach the midline, where the superior sagittal sinus lies, and may extend across it. Profuse bleeding may arise from the sinus and arachnoid granulations. Although venous, it can be difficult to control without familiarity with hemostatic techniques in this region and may cause hypotension. Preventing sinus tears is therefore important. Place burr holes a little away from the superior sagittal sinus; never drill directly over it. If a tear occurs, cover it with muscle or Gelfoam, suture the dura across the muscle patch, and apply pressure briefly to stop bleeding. Bleeding from an arachnoid granulation can be controlled by covering it with Gelfoam and pressing with cotton briefly.

Original pages 548–549

3.3 Bleeding from the Tumor

Dissection of highly vascular tumors, such as angioblastic meningioma, glioblastoma multiforme, metastatic tumors, and hemangioblastoma, may cause blood loss severe enough to produce shock and require massive transfusion, with its harmful consequences. The author has encountered this several times. In one patient, a temporal lobe meningioma the size of a small orange received a substantial supply from the middle meningeal and internal carotid arteries. Attempted removal required 15 bottles of blood. After approximately 10 bottles, clotting became delayed, and the blood subsequently appeared very dilute. Hemostasis was unsuccessful because massive transfusion caused dilutional coagulopathy, thrombocytopenia, and hypocalcemia.⁽²⁰⁾ Bleeding stopped only after the decision to clip the internal carotid artery. The patient survived without hemiplegia.

Large glioblastomas and metastatic brain tumors similarly present difficult hemostasis because their numerous abnormal, fragile vessels often bleed profusely.

In brain tumor surgery, complete hemostasis is achieved only after the entire tumor has been removed. Residual tumor may bleed again at any time. The physician must remain alert for a postoperative hematoma causing deterioration.

Original page 549

4. Acute Brain Swelling

During an otherwise smooth operation, the brain may suddenly bulge beyond the craniotomy margin, with patches of subarachnoid hemorrhage on its exposed surface. The brain may even split. The abrupt rise in intracranial pressure prevents access to the tumor and makes further surgery impossible. Its cause must be removed promptly; otherwise brainstem dysfunction and death follow. Causes of acute intraoperative brain swelling include:

Original page 549

4.1 Airway Obstruction

Secretions may obstruct the endotracheal tube, the tube may kink, or a connector may become detached. Oxygen deprivation and carbon dioxide retention cause cerebral vasodilatation and venous engorgement, abruptly raising intracranial pressure. If the anesthesiologist corrects the problem promptly and hyperventilates briefly, the brain subsides well. This is the most frequent complication and is usually easy to correct.

Original pages 549–552

4.2 Intracranial Hemorrhage

4.2.1 Intraventricular and subarachnoid hemorrhage. During dissection of a tumor near or within a ventricle, blood may enter the ventricular system and obstruct CSF pathways, causing the brain to bulge. Prevent this by securely covering any opening in the ventricular wall with cotton so that blood cannot enter. Blood may also spread through the subarachnoid space, another cause of CSF obstruction.

4.2.2 Intracerebral hematoma. When dissection moves from one part of the tumor to another, bleeding may develop in adjacent brain at a previously dissected site because initial hemostasis was incomplete. The resulting hematoma pushes the brain outward. Excessive retraction can also cause intracerebral bleeding.

4.2.3 Subdural hematoma. This important complication may occur when a tumor causes hydrocephalus with enlarged lateral ventricles, as with posterior fossa or supratentorial intraventricular tumors. Before tumor removal, ventriculostomy is needed to drain CSF and lower intracranial pressure, facilitating dural opening and access. Ventricular collapse after drainage may tear cortical bridging veins, producing a unilateral or bilateral acute subdural hematoma. This is common in children, whose tumors often arise in the posterior fossa and enlarge the head, further predisposing bridging veins to tearing. The sitting position aggravates the risk because the brain sags downward, as illustrated by the following cases.

First case. A 5-year-old child had a medulloblastoma obstructing the fourth ventricle, markedly enlarged third and lateral ventricles, and an enlarged head. Surgery was performed sitting. A ventriculostomy was placed before opening the posterior fossa, ready for CSF drainage. When the dura was exposed, it was tense and bulging. The ventriculostomy was opened to drain CSF into a bottle until the tension subsided, then the dura was opened and tumor dissection begun. The cerebellum bulged during dissection, but inspection found no posterior fossa hemorrhage, and the CSF in the ventriculostomy tube was not bloodstained. The pulse accelerated and blood pressure fell. The wound was rapidly closed and the patient laid down. Pallor suggested an acute subdural hematoma. An exploratory burr hole disclosed one on the right; craniotomy revealed a very large clot. In such a young child, this amount of bleeding can cause pallor and hypotension. The hematoma could become so large because the lateral ventricle and cortex collapsed markedly. The patient recovered well after surgery.

Second case. A 7-year-old child had a fourth-ventricular choroid plexus papilloma and hydrocephalus with very large lateral ventricles. Posterior fossa surgery and ventriculostomy were performed sitting. The tumor was removed satisfactorily, the wound closed, and the patient regained consciousness. Approximately half an hour later, drowsiness returned with signs of raised intracranial pressure. Investigation revealed an acute subdural hematoma over the left cerebral hemisphere. The patient returned to the operating room for craniotomy and evacuation, after which the symptoms resolved and consciousness returned. The author believes no subdural hematoma was present during the posterior fossa operation, since there had been no signs of raised pressure, surgery was successful, and the patient awakened. The hematoma probably arose during repositioning, when brain displacement tore a bridging vein, causing renewed unconsciousness after initial recovery.

Third case. A 17-year-old patient with a fourth-ventricular tumor underwent posterior fossa surgery and ventriculostomy in the sitting position. The tumor was removed satisfactorily. After wound closure, before the patient was laid flat, several bouts of coughing occurred. Once the patient was laid down and the anesthesiologist prepared for extubation, the right pupil was found larger than the left and unreactive to light. A burr hole and craniotomy were required to evacuate a subdural clot. The patient recovered well.

Fourth case. A 2-year-old child with a lateral-ventricular choroid plexus papilloma had an enlarged head and ventricular system. Craniotomy was performed supine. After the ventricle was opened and the tumor completely removed, the ventricle and cortex collapsed. Profuse subdural bleeding occurred at multiple sites, not all of which could be visualized. The patient ultimately developed shock and died.

These cases teach the following lessons: (1) When ventriculostomy is used to lower pressure in patients with large ventricles, CSF should not drain continuously; open the drain intermittently as needed. (2) Patients with markedly enlarged lateral ventricles should be operated on lying down rather than sitting, reducing the risk of acute subdural hematoma. (3) Coughing while sitting, with the ventricles still collapsed, jolts the brain and may tear bridging veins. (4) Repositioning or transferring a patient immediately after surgery must always be gentle and careful, avoiding blows to the head. (5) In children, subdural hemorrhage may cause pallor, tachycardia, and hypotension, which are useful diagnostic signs.

Original pages 552–553

4.3 Venous Obstruction

Impaired venous return to the heart causes cerebral venous congestion and marked swelling, which may be fatal. During surgery, this may result from the following:

4.3.1 Tearing of a cerebral vein. A large cortical vein may be torn during tumor dissection, such as a superior cortical vein draining into the superior sagittal sinus, the Sylvian vein, or the vein of Labbé. The brain drained by that vein then swells, making further dissection impossible. Sometimes the swollen brain must be removed unnecessarily, with additional loss of function. Cortical veins must therefore be carefully preserved; tearing them may prove fatal.

For example, a 50-year-old man had a parasagittal meningioma at the postcentral gyrus. The tumor lay adjacent to the cortex and displaced a superior cortical vein anteriorly. During dissection the vein was torn and coagulated. The adjacent brain rapidly swelled and protruded through the craniotomy, with patchy subarachnoid hemorrhage. Surgery could not proceed, and some brain tissue had to be removed. Further removal was difficult because the brain continued to swell and venous bleeding constantly obscured the field. The patient developed postoperative hemiplegia and died on the second day from brain swelling leading to brain stem dysfunction.

This example illustrates the harm caused by injury to a major cortical vein. The surgeon must learn to prevent such injury during dissection and to use the techniques of venous hemostasis described later.

4.3.2 Compression of a vein by a retractor. Strong, prolonged brain retraction impairs circulation. Retractors should not be placed over large cortical veins and should be released periodically. Retraction that presses a vein against the craniotomy margin likewise obstructs venous return and causes brain swelling.

Original page 553

4.4 Other Causes

Excessive fluid administration, administration of hypo-osmolar fluids, or irrigation of the exposed brain with a hypo-osmolar solution may cause brain swelling.

Original pages 553–554

5. AIR EMBOLISM

Air embolism is an important complication of surgery in the sitting position. Air enters the right atrium because venous pressure at the operative site is lower than that within the right atrium. When a vein is opened, air is sucked into the right atrium. Diagnostic manifestations include: 1) hyperventilation preceding air hunger, cyanosis, or apnea; 2) a fall in blood pressure without another explanation; 3) tachycardia and dysrhythmia; 4) increased central venous pressure; 5) EKG changes with atrial and ventricular extrasystoles; 6) a mill-wheel murmur, audible with an esophageal stethoscope or ultrasonic Doppler; 7) a fall in expired CO₂; 8) occasionally, visible air bubbles in cerebral vessels; and 9) cardiac arrest when a large volume of air in the heart produces severe effects.

Several devices are available for detecting air embolism, including ultrasonic Doppler and the capnographic technique for measuring expired CO₂.⁽²¹⁾ Two newer devices are the transesophageal Doppler probe⁽²²⁾ and the transesophageal echocardiographic unit.⁽²³⁾ Both are sensitive and can detect abnormalities on both sides of the heart. They are not yet in use in the Neurosurgical Unit at Siriraj Hospital.

Ultrasonic Doppler is a very sensitive means of detecting air embolism. Both the anesthetist and the surgeon can hear and recognize the embolism simultaneously, allowing the surgeon to act immediately to prevent further air entry. Sometimes, however, the opening in the vein is difficult to locate quickly.

Original pages 554–555

Treatment of Air Embolism

Prevention is most important. If the sitting position is unnecessary, operating with the patient lying down reduces the risk. When the sitting position is used, a catheter should be introduced by venous cutdown at the antecubital fossa, with its tip in the right atrium. Bunegin and colleagues⁽²⁴⁾ described the appropriate position for maximum air aspiration using a catheter with multiple holes near its tip. A chest X-ray must always confirm that the tip lies in the right atrium; sometimes it remains in the superior vena cava or turns upward into the common jugular vein. If surgery in the sitting position proceeds without verification of the catheter tip, air embolism cannot be adequately managed.

The principles of treatment are as follows:

1) The surgeon must immediately close any visible opening in a vein, using a clamp, ligature, or suture as appropriate. If the opening cannot be seen, cover the operative wound with wet gauze and keep the field flooded with fluid to prevent air entry. To locate the opening, temporarily apply positive end-expiratory pressure or compress both common jugular veins. The resulting rise in central venous pressure causes bleeding from the opening and makes it visible.

2) Aspirate air from the right atrium through the catheter. Blood withdrawn into the syringe should be reinjected through another venous line to prevent blood loss.

3) Stop N₂O and administer 100% O₂ with positive-pressure ventilation.

4) If the venous opening cannot be closed and air embolism increases, close the wound rapidly, turn the patient into the left lateral position, and continue aspiration until no air remains.

5) If blood pressure falls, administer a vasopressor, such as ephedrine 10–30 mg intravenously.

Once the condition has returned to normal, surgery may be continued with the patient lying down if tumor removal must be completed that day. If the patient’s condition is unfavorable, the operation should be postponed.

Original pages 555–556

Postoperative Complications of Brain Tumor Surgery

Complications can occur after any operation, and most cause increased intracranial pressure. Early, accurate diagnosis and timely, appropriate treatment preserve life and function. Delay may result in poor recovery or death. Close, continuous observation is particularly important during the first 48 hours. When a complication is suspected, urgent investigation should begin before all its manifestations have appeared; this can make a substantial difference to the outcome.

The surgeon must take meticulous preventive measures, perform the operation properly, secure complete hemostasis, and avoid factors that cause brain swelling. Complications are closely related to the surgeon’s experience and skill; experienced surgeons encounter fewer complications.

Possible complications include:

1) Complications causing increased intracranial pressure

1.1 Hemorrhage

1.1.1 Bleeding from residual tumor

1.1.2 Bleeding outside the dura (epidural hematoma)

1.1.3 Bleeding beneath the dura (subdural hematoma)

1.1.4 Bleeding within the brain (intracerebral and intracerebellar hematoma)

1.2 Brain edema

1.3 Necrotic brain tissue

1.4 Hydrocephalus

1.5 Air within the ventricle

2) Cerebrospinal fluid leakage

3) Infections

4) Fluid and electrolyte imbalance

4.1 Hyponatremia

4.2 Hypernatremia

5) Hormonal Disturbance

5.1 SIADH

5.2 DI

6) Seizures

7) Hyperthermia

Original pages 556–557

1) Hemorrhage

Hemorrhage is a major cause of raised intracranial pressure and many rapid postoperative deaths. Intraoperative blood loss is usually not fatal because adequate transfusion can be given. After surgery, however, a hematoma of only 40–50 cc may cause unconsciousness, death, or loss of functions that the surgeon took great care to preserve during the operation. It is regrettable when successful tumor removal is followed by destruction of function from this complication.

Postoperative hemorrhage may occur at the following sites:

Original page 557

1.1 Bleeding from Residual Tumor

Every surgeon fears and is troubled by incomplete tumor removal, because the residual surface may bleed after surgery from its numerous abnormal, fragile vessels. After the bulk of the tumor has been removed, a fall in blood pressure may allow arterial bleeding from the tumor to stop with pressure or coagulation. When blood pressure rises after wound closure, bleeding may recur. Before closure, the anesthetist should be asked to raise the blood pressure so that bleeding points can be identified and hemostasis secured as an additional precaution. Complete removal is the best prevention of recurrent bleeding. Surgeons often find that, however profuse the hemorrhage during the operation, it stops once the entire tumor has been removed.

Original page 557

1.2 SUBDURAL HEMATOMA

This most commonly results from tearing of bridging veins. After removal of a large tumor, collapse of the brain stretches these veins. Coughing, jolting of the head during transfer onto or off the bed, or positioning the patient with the operative side downward may tear them and cause an acute subdural hematoma, as discussed earlier.

After removal of a falx meningioma, the attachment contains many dural vessels that supplied the tumor. If hemostasis is inadequate, these may bleed into the subdural space later.

Original pages 557–558

1.3 EPIDURAL HEMATOMA

An epidural hematoma may arise from three sources [Translator’s note: the original enumerates four sources below and subsequently refers to all four]: i) the middle meningeal artery and its branches; ii) venous tributaries in the dura and arachnoid granulations; iii) the diploic space at the skull margins and in the bone flap; and iv) the temporalis muscle. Prevention requires secure hemostasis at all four sites. Bleeding from the middle meningeal artery may be controlled by suture ligation. When cutting the dural flap, begin below and pass across the frontal, temporal, and parietal regions, leaving its base at the superior sagittal sinus; this divides the arterial supply to the dura. Small bleeding points on the dura should be controlled with bipolar coagulation. The dura near the craniotomy margin should then be tacked to the galea and muscle to prevent an epidural hematoma beneath the adjacent skull. Bleeding from the diploic space at the skull margins can be stopped by plugging the openings with bone wax. Bleeding openings in the bone flap may likewise be plugged with bone wax. Alternatively, separate the temporalis muscle from the outer table of the bone flap, leaving only its terminal attachment to the bone; this divides the vessels supplying the flap from the muscle. Bleeding from the temporalis must also be stopped. If all these measures are completed properly, an epidural hematoma should not occur.

Original page 558

1.4 INTRACEREBRAL AND INTRACEREBELLAR HEMATOMA

These arise from two causes: i) forceful retraction and operative manipulation contuse and swell the brain, making small vessels liable to rupture both during and after surgery; and ii) venous obstruction, which may occur when retraction compresses a cortical vein against the craniotomy margin or when a vein is torn during surgery. Venous return from that vein’s tributaries is impaired, producing swelling and necrotic brain tissue that bleeds readily.

An intracerebral or intracerebellar hematoma may be solitary or multiple. The clots are usually not large, but associated brain swelling causes rapid deterioration.

Original pages 558–559

Symptoms and Signs of Postoperative Hemorrhage

Whatever its location, hemorrhage causes increased intracranial pressure. Changes are generally evident in the first 24–48 hours, although in some patients they occur within 1–2 hours after surgery. The timing depends on the rate of bleeding and the size and location of the hematoma. As the hematoma develops, headache progressively increases and vomiting occurs. Consciousness gradually deteriorates, the pulse progressively slows, and blood pressure rises. Respiration may become shallow or show a Cheyne–Stokes pattern. With a posterior fossa hematoma, respiration slows and apnea develops rapidly. Some patients with supratentorial hemorrhage develop weakness of one side, usually contralateral to the side from which the tumor was removed. An intracerebral hematoma may also cause seizures. Without timely investigation and treatment, the patient becomes unconscious, the pupil on the side of the hematoma dilates and loses its light reaction, decerebration occurs, and death follows from brain stem dysfunction.

Original pages 559–560

Treatment

As soon as the patient recovers from anesthesia, consciousness, vital signs, limb movements, and pupillary size and reactions must always be assessed, followed by close observation. If consciousness begins to change and Cushing’s reflex appears, urgent angiography or C.T. is required to determine the cause. A hematoma may require reopening the craniotomy for evacuation. Whether to reoperate must, however, be considered individually, according to the speed of deterioration, the size and location of the clot, and other factors contributing to impaired consciousness. In the author’s opinion, progressive deterioration in consciousness with a mass effect on C.T. requires reopening, evacuation of the hematoma, and secure hemostasis; medical treatment alone is insufficient.

Evacuation of blood from the epidural and subdural spaces generally presents little difficulty, and hemostasis is readily achieved. With an intracerebral or intracerebellar hematoma, however, reaching the clot reveals swollen, soft, friable, necrotic brain tissue resulting from the first operation and the postoperative clot. Hemostasis is difficult in this tissue even when the bleeding is capillary. Sometimes portions of this friable brain must be aspirated back to healthy tissue before bleeding can be stopped. This is another cause of additional loss of brain function. When bleeding arises from residual tumor, some patients require an attempt at complete tumor removal to prevent a second hemorrhage.

Original printed page 560

2) Brain swelling

This is another complication responsible for many deaths after tumor removal, and the surgeon must try to prevent it during surgery. The principal causes of intraoperative and postoperative brain swelling are: i) trauma to the brain during tumor dissection. Retraction by an assistant is often unstable, with frequent changes in position and traction force, occasionally tearing the brain. A self-retaining retractor is preferable and causes less injury. In principle, the less the brain is injured, the less it swells. During tumor dissection, therefore, the surgeon should handle the brain as gently and as little as possible. ii) Venous obstruction caused by retraction or control of venous bleeding is an important cause of swelling. iii) Hyponatremia and water intoxication.

In postoperative brain swelling, symptoms of raised intracranial pressure appear about 48–72 hours after surgery. Consciousness gradually deteriorates, with increasing drowsiness and Cushing’s reflex. These changes develop less rapidly than with hemorrhage, although the two may sometimes be difficult to distinguish clinically. CT or MRI is needed for a definite distinction. Hemiparesis or seizures may also occur.

For treatment, see Chapter 4.

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3) NECROTIC BRAIN TISSUE

This is another cause of raised intracranial pressure. It occurs where the cortex has been incised for tumor dissection, damaging brain tissue and occluding arteries and veins. The brain tissue at this site and farther away in the territory supplied by those vessels becomes infarcted and swollen. If extensive, this raises intracranial pressure. Occasionally the affected tissue must be removed before the condition resolves.

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4) HYDROCEPHALUS

This occurs postoperatively for two reasons. i) During surgery for tumors within or near the third and lateral ventricles, small clots or tissue fragments may enter and obstruct the narrow aqueduct of Sylvius, blocking CSF flow and raising intracranial pressure. Prevent this during surgery by packing the ventricular space beyond the tumor with moist cotton. ii) During posterior fossa surgery, blood commonly enters the subarachnoid space, obstructing CSF circulation and impairing absorption at the arachnoid granulations, thus producing communicating hydrocephalus. This is an important cause of tense bulging at the craniectomy wound and CSF leakage through it, followed by postoperative meningitis or ventriculitis.

CT readily demonstrates hydrocephalus. Treatment requires CSF drainage by lumbar puncture, ventriculostomy or a shunt to lower CSF pressure and stop leakage. Select the appropriate method individually.

Original printed pages 561–562

5) PNEUMOCEPHALUS

Whenever the skull is opened, some air remains intracranially, in the epidural or subdural space or in the ventricles. This air exerts pressure but is slowly absorbed. Together with brain swelling and hydrocephalus, it may further increase intracranial pressure. Therefore irrigate these cavities to expel all air before closing the dura.

When nitrous oxide anesthesia is used for posterior fossa surgery in the sitting position, air may rise into the ventricular system and form a closed gas-containing space. Nitrous oxide in the blood exchanges with nitrogen in this closed space. Nitrous oxide is generally 34 times more soluble in blood than nitrogen⁽²⁵⁾. Consequently, nitrous oxide accumulates in the closed space and expands its gas volume, increasing intraventricular pressure. The gas can be removed through a ventriculostomy tube.

Original printed page 562

6) CSF LEAKAGE

This commonly occurs after surgery for tumors at the base of the frontal lobe or in the pituitary fossa. A low skull opening is needed for adequate tumor exposure but may open the frontal air sinus. Dissection of a frontal tumor such as an olfactory groove meningioma may leave a defect in the cribriform plate. These defects cause CSF rhinorrhea. In posterior fossa surgery, craniectomy may open the mastoid air cells, producing CSF otorrhea if the tympanic membrane is perforated. Watertight dural closure helps prevent leakage. Mastoid air-cell openings may additionally be sealed with a thin sheet of bone wax or covered with a muscle patch.

Hydrocephalus or raised CSF pressure is an important cause of leakage. Prevention therefore requires maintaining low CSF pressure, using repeated lumbar punctures, ventriculostomy or a shunt as appropriate for the individual patient.

Original printed pages 562–563

pseudomeningocoele

This may occur after posterior fossa tumor surgery by craniotomy when the dura is not sutured closed as before, but its edges are attached to muscle and galea. CSF then collects between the cerebellum, muscle and dura. Several months after surgery, a bulging fluid-filled sac resembling a meningocele develops. Hydrocephalus makes it particularly tense. It can be resolved by lowering CSF pressure.

Treatment of CSF leakage follows these principles: i) Position the patient to reduce hydrodynamic pressure at the leak, for example with the head elevated. ii) Suture the skin-wound opening closed. iii) Correct the cause of raised CSF pressure, for example by complete tumor removal, lumbar puncture, ventriculostomy or a shunt. Remember that some patients may become drowsier after leakage stops if an expanding mass remains: the leak had lowered intracranial pressure, but when it stops, CSF accumulates and pressure rises. iv) Give antibiotics as appropriate for the individual patient.

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7) Infection

Most postoperative infections involve the scalp wound. Acute epidural, subdural or brain abscesses are very rare, particularly after clean operations such as brain tumor surgery, in which they are now almost never seen because of good technique and antibiotics. Three forms of infection may occur: skin-wound infection, osteomyelitis, and meningitis or ventriculitis resulting from CSF leakage. Predisposing factors for infection and poor wound healing include advanced age, poorly controlled diabetes, a poorly vascularized scalp flap, necrosis of skin edges, prolonged surgery, steroid and immunosuppressive therapy, and repeat craniotomy. Wound inflammation generally becomes evident toward the end of the first week, with fever, leukocytosis, red and warm skin, or palpable abscesses at suture sites. Remove the sutures and give appropriate antibiotics for an adequate duration. Open the wound to drain any pus. In some patients infection appears weeks or months after surgery as protruding infected granulation tissue along the wound, sometimes discharging pus. This usually accompanies infection of the bone flap and epidural infected granulation tissue. Open the scalp flap, remove the bone flap, curette all infected granulation tissue, excise unhealthy wound edges and close the wound to allow healing. The bone flap must be removed because its poor blood supply makes it behave like a foreign body.

During craniotomy closure, the surgeon must achieve a watertight dural closure to prevent infection from spreading into the subdural space or the operated brain region. If this occurs, the patient often dies.

Infection from CSF leakage or intraoperative contamination causes meningitis or ventriculitis, with high fever, drowsiness, neck stiffness, a positive Kernig’s sign and possible death. Stop the CSF leak promptly and give high doses of antibiotics appropriate to the organism, with good CSF penetration, for 3–4 weeks.

Original printed pages 564–565

8) Fluid and electrolyte imbalance

Hyponatremia is a complication of brain tumor surgery and craniotomy for other cerebral diseases. Causes include excessive hypotonic fluid, such as 5% dextrose in water, and SIADH (syndrome of inappropriate antidiuretic hormone). Both cause dilutional hyponatremia and water intoxication. Patients develop vomiting, nausea, deteriorating consciousness and progressively increasing drowsiness, sometimes with seizures or hemiparesis. These findings may be difficult to distinguish from postoperative hemorrhage or brain swelling. They improve when the sodium level returns to normal.

The main treatment is fluid restriction, which works well when hyponatremia and symptoms are mild. In severe hyponatremia, the author has found that an initial 300 cc of 3% or 5% NaCl, together with fluid restriction, hastens recovery. Subsequent administration is determined by the patient’s symptoms and sodium level.

Hypernatremia or hyperosmolarity is less common. The principal causes are dehydration and excessive sodium administration. It occurs in patients with brain disease who are unconscious or drowsy, lack thirst, have difficulty swallowing, vomit, have high fever or rapid breathing, or lose excessive water in the urine (polyuria). Following surgery for tumors around the pituitary gland and hypothalamus, destruction of the source of ADH may cause diabetes insipidus. It may also occur with osmotic diuresis, such as mannitol used to reduce intracranial pressure.

Signs and symptoms of hypernatremia include increasing drowsiness, confusion or unconsciousness, fever, dry mouth and oliguria, except when diabetes insipidus or osmotic diuresis is responsible. Some patients have seizures and weight loss.

Treatment principally consists of electrolyte-free water in amounts exceeding ongoing water losses, with repeated electrolyte measurements until normal values are restored. At the same time, correct the cause of polyuria, for example by treating diabetes insipidus as described earlier, and stop diuretics.

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9) HORMONAL DISTURBANCES

These may occur after surgery for tumors around the pituitary gland and hypothalamus. Common examples are SIADH (syndrome of inappropriate antidiuretic hormone) and diabetes insipidus, discussed earlier in this chapter.

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10) Seizures

Postoperative seizures may be motor or nonmotor. They are most common after surgery in or near the motor area. A preoperative history of seizures increases the likelihood of postoperative seizures. If a seizure occurs, promptly give anticonvulsants until it stops, as discussed earlier, and investigate the cause with CT. During the first 2–3 postoperative days, common causes are postoperative hemorrhage, brain swelling and infarction. Metabolic abnormalities can also cause seizures. Once the cause is identified, treat it accordingly.

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11) HYPERTHERMIA

A persistently elevated temperature from the first postoperative day, without returning to baseline, usually indicates dysfunction of the hypothalamic temperature-regulating center, termed central hyperthermia. Blood in the subarachnoid space, ventricles or brain may also cause fever, but it is usually less marked than central hyperthermia. When the patient has a high fever, lower the temperature by the methods described earlier in the chapter, to reduce cerebral metabolism, CBF and intracranial pressure.

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General techniques of brain surgery

Many new instruments and techniques for diagnosing and operating on cerebral disease have made brain surgery easier and more successful. These include CT, MRI, bipolar forceps coagulators, microinstruments, microscopes, microneurosurgical techniques, ultrasonic aspirators and lasers. CT and MRI accurately locate tumors, allowing the surgeon to make a small skull opening precisely over the tumor. This shortens the operation and reduces complications.

Bipolar forceps coagulation provides effective hemostasis even where unipolar coagulation would be dangerous, such as the brainstem. For tumors at important sites such as the third ventricle, pituitary gland and cerebellopontine angle, with vital structures including the brainstem, cranial nerves and vessels, microscopes and microinstruments allow more confident removal while preserving cranial nerves and important vessels. The newest and very useful developments at present are the ultrasonic aspirator and laser. Ultrasonic aspiration facilitates removal of large tumors or those at important sites by aspirating tissue fragmented by ultrasound, reducing tumor size. Advances in laser technology for neurological surgery also allow surgery without blood loss and shorten operating time.

Before discussing operative techniques, the following basic principles should be understood.

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1. Patient positioning

Before surgery, the surgeon must carefully assess tumor location, side, size, vascularity and feeding vessels on CT, MRI or cerebral angiography. Before anesthesia, display the images that best show the tumor, as they will be needed throughout the operation. Relate them to the surface anatomy of the head and brain to place the skull opening directly over the tumor.

Good positioning must achieve these important objectives:

i) Provide the easiest and most complete exposure of the lesion.

ii) Avoid intraoperative and postoperative complications, such as venous obstruction or compression of spinal nerves.

iii) Allow the anesthetist to correct cardiovascular and respiratory abnormalities during surgery without disturbing the operative field.

iv) Keep the surgeon comfortable during a prolonged operation.

v) Allow convenient placement of the anesthetic machine, surgical instruments, scrub nurse, assistant and microscope.

In general, the operating surgeon should personally position the patient and mark the skull opening to ensure correct tumor exposure and avoid potential injury.

The following positions are used in brain surgery:

Original printed pages 567–568

1.1 Supine position

The patient may face directly upward or be turned slightly toward the opposite side, depending on tumor location. This position is suitable for frontal lobe and sellar tumors. No support beneath the shoulder on the operative side is needed because the neck is not rotated. Avoid compression of either ulnar nerve. A horseshoe headrest may be used for a short operation without causing pressure sores. A pin-type head holder avoids pressure sores even in prolonged operations, leaving only scalp puncture sites. Choose pin sites away from vessels to prevent bleeding when the pins are removed. Place the pins below the frontal and parietal prominences to prevent upward slippage, and avoid the thin temporal squamous bone.

Keep the head slightly above the chest to improve venous drainage. Air embolism is possible, although the author has not encountered it. Moderately extend the head so that gravity allows the frontal lobe to fall toward the vertex, reducing the retraction needed to reach subfrontal and sellar tumors.

Temporal and parietal tumors require substantial rotation of the face and neck toward the opposite side. This may obstruct venous drainage and overstretch neck muscles, increasing intracranial pressure and making surgery difficult and dangerous. Elevate the shoulder on the operative side with a sandbag to reduce neck rotation.

After positioning, always verify the endotracheal tube position and adequate ventilation, then arrange the gas tubing and anesthetic machine appropriately. Apply ophthalmic ointment over the entire cornea and tape the eyelids fully closed to prevent dryness and corneal ulceration from contact with the drapes.

Original printed page 568

1.2 Lateral position

This position is used for posterior fossa and occipital lobe tumors. Place a soft pillow beneath the dependent side of the chest. Extend the lower arm forward to reduce pressure on axillary nerves and vessels, and support the upper arm. Always flex the lower hip and knee to provide a stable base and prevent the patient from rolling backward. Keep the upper leg straight, with a pillow between the legs. Secure the iliac crest and chest to both sides of the operating table with broad adhesive straps. Avoid compression of the peroneal and ulnar nerves. Once the trunk is positioned, secure the head in a pin-type holder with the neck tilted slightly downward. Tape the upper shoulder downward to enlarge the operative space. Rotate the head moderately downward as required by tumor location (Figure 7.1)

Original printed pages 568–569

1.3 Prone position

This position is used for tumors in the posterior fossa, occipital lobe and cervical spine. It is important to avoid pressure on the chest and abdomen, which would increase intrathoracic pressure and impair venous return from the brain. Place the patient prone on a Wilson frame with an open center, or use cylindrical cushions under the pelvis and upper chest. Keep both arms beside the body and both feet against the foot support. Raise the head of the operating table so the head does not hang downward, improving cerebral venous return. Moderately flex the head and neck to facilitate posterior fossa access and secure the head in a pin-type holder, avoiding pressure sores on the forehead and cheekbones. For an occipital lobe tumor, keep the head straight without flexion to expose the occipital region. After positioning, check that the endotracheal tube remains correctly positioned, because flexing the head and neck may advance it into one bronchus, ventilating only one lung and adversely affecting the brain.

If a horseshoe headrest is used, protect the forehead and cheekbones from pressure sores with soft cotton padding. Ensure that neither eye is compressed by the edge of the headrest.

Original printed pages 569–570

1.4 Semiprone position

Position the patient as for the lateral position, then rotate approximately another 45° forward. Extend the lower arm backward and place a pillow anteriorly to support the trunk in the semiprone position. Secure the trunk with adhesive straps and position the head appropriately for the tumor site within the posterior fossa.

Original printed pages 570–571

1.5 Sitting position

This position provides good posterior fossa exposure but carries several possible hazards, including air embolism, hypotension, supratentorial subdural hematoma and pneumocephalus, as discussed under complications. These require particular attention. After anesthesia, gradually raise the head of the table, checking blood pressure at intervals. If it falls, wait for the patient to adapt and the pressure to normalize before proceeding to the sitting position. If blood pressure does not recover, do not operate in this position. Wrap the legs with elastic bandages from feet to groins to limit dependent pooling of blood while sitting. Flex the hips and knees and elevate the legs above the horizontal. Flex the head, leaving at least about two fingerbreadths between the chin and sternum. This provides good posterior fossa access. Flexion until the chin touches the sternum may kink the endotracheal tube and impair ventilation. For a cerebellopontine angle tumor, turning the face toward the tumor side may improve exposure. Finally, secure the head in a pin-type holder (Figure 7.2)

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2. Preparation of the operative skin

Correct skin preparation is important in preventing wound infection. Shave the entire head closely; partial shaving may allow contamination. After positioning, scrub the scalp with Betadine or Hibitane soap for about 10 minutes to remove skin bacteria. Once dry, mark the incision with sterile dye or a light superficial scratch with a knife. Place sterile drapes around the marked incision. Do not omit this marking, since draping obscures surface landmarks and the skull opening may otherwise miss the tumor site. A Steri-Drape, a plastic sheet adhesive on one side, placed over the scalp and upper drapes prevents fluid from soaking the drapes and spreading bacteria along with it.

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3. Hemostasis

Several sites may bleed profusely during brain surgery. The surgeon must know the appropriate hemostatic technique for each. Unless bleeding is completely controlled, brain surgery becomes difficult. Potential sources include the scalp, skull, dura mater, middle meningeal artery, superior longitudinal sinus, transverse sinus, arachnoid granulations, cerebral vessels and tumor vessels.

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3.1 Scalp bleeding

The scalp is highly vascular, and opening and closing it can cause substantial blood loss. Most scalp vessels lie between the skin and galea. Individually clamping and ligating cut vessels, as in general surgery, is ineffective and slow. Methods of scalp hemostasis are as follows:

3.1.1 Have the assistant press firmly with the fingertips along both sides of the planned incision, compressing vessels against the skull to prevent bleeding. Incise a length of about 6–7 cm at a time (Figure 7.3)

3.1.2 Grasp the galea and undersurface of the skin together with arterial clamps about 1 cm apart along both wound edges. Tie the clamps together in groups of approximately 5–6 (Figure 7.4). Continue along the entire planned scalp incision. The clamps fall under gravity and exert traction on the scalp, stopping bleeding.

3.1.3 Clips may be applied to both wound edges, including both skin and galea to stop bleeding. Michel clips (Figure 7.5), Raney clips or Kölner clips may be used. Michel clips come in long, medium and short sizes. The medium size is generally used for an ordinary adult scalp and the short size for the thinner scalp of a child. Place Michel clips about 1 cm apart. They cannot be reused and are therefore costly, but they keep the field tidy and do not obstruct the operation. Raney clips are broad spring clips that indent and darken the scalp edges, potentially impairing healing. Place cloth beneath them on the scalp before application (Figure 7.4). Raney clips can be reused and are therefore economical.

3.1.4 Use bipolar or unipolar coagulation at individual points where vessels remain open. Coagulate only the vessel, avoiding the skin, to promote good healing.

3.1.5 Inject a solution of adrenaline, 1 mg in 200 cc of water, beneath the scalp along the planned incision. Vasoconstriction reduces wound bleeding. Disadvantages include elevated blood pressure from systemic absorption of adrenaline and, in some patients, skin necrosis with failure of wound healing.

3.1.6 Scalp closure is another stage when substantial bleeding may occur. Correct suturing also provides hemostasis. Before closure, thoroughly irrigate all bone fragments from the wound edges, because bone acts as a foreign body and prevents healing. Begin closure proximally along the arterial supply to the scalp, controlling inflow and reducing distal bleeding. Also work from the higher part of the wound toward the lower part so that bleeding does not obscure suturing. Starting below allows blood from above to pool where sutures are being placed. Remove arterial clamps or clips in groups of 5–6 at a time, and approximate the subcutaneous tissue together with the galea at intervals of about 1.5 cm. Then approximate the full thickness of the skin. The author prefers alternating one subcutaneous suture with two skin sutures, with the subcutaneous stitch lying between the two skin stitches. This improves hemostasis because the skin sutures reinforce vessel compression. After completing one group, remove the next group of clamps and repeat until finished. Do not space skin sutures too widely, as bleeding may occur; intervals should not exceed 1.5 cm. Inadequate scalp hemostasis during closure can cause a large hematoma or rapid drainage of hundreds of cc of blood, requiring reopening for hemostasis. This wastes time and provides an opportunity for infection. The surgeon must therefore always secure complete hemostasis during closure.

Original printed page 574

3.2 Muscle bleeding

Muscle bleeds along its cut edges and where it has been detached from the skull. This most often involves the temporalis during supratentorial craniotomy, or the occipital muscles during posterior fossa exposure. Coagulation usually stops the bleeding easily. If it persists, use suture ligation.

Original printed pages 574–575

3.3 Bone bleeding

Since Victor Horsley invented bone wax⁽²⁶⁾ and successfully used it to control bone bleeding, this hemostatic problem has been resolved. Bone wax remains in use today. Without it, brain surgery would be difficult, and even with modern operative techniques, postoperative hemorrhage could still be dangerous. Press bone wax into the bone openings to plug them. If the middle meningeal artery is torn while the bone flap is being elevated, bleeding may emerge from a bony canal containing the retracted arterial end. Do not simply plug it with bone wax: postoperative hypertension may dislodge the wax and cause an acute epidural hematoma. A better method is to remove bone until the artery is visible, then suture-ligate or coagulate it until bleeding stops. Besides using bone wax, bleeding from the bone flap may be stopped by detaching the temporalis from the skull, leaving only its end attached. This interrupts the muscular blood supply to the bone. Bleeding from the muscle must also be controlled.

When applying bone wax along the skull edge, do not push large pieces beneath the skull. They may separate the dura from the inner skull surface and cause bleeding on the dural surface.

Original printed pages 575–576

3.4 Dural bleeding

Dural bleeding comes from the middle meningeal artery, superior sagittal sinus and arachnoid granulations (Pacchionian bodies). It may be profuse and difficult to control, making prevention important. The middle meningeal artery is often torn by a sharp inferior temporal bone edge when the bone flap is turned away from the dura, producing heavy arterial bleeding. Prevent this by slightly lifting the bone flap and inserting a periosteal elevator to separate the skull from the dura all around. After fracturing the temporal bone attachment, do not turn the flap directly downward; first lift it, then turn it downward. This prevents the fractured edge from injuring vessels. The author has often seen simultaneous tears of the middle meningeal artery, dura and cortical vessels caused by incorrectly turning the flap.

Bleeding from the superior sagittal sinus and arachnoid granulations can be avoided by keeping the skull opening at least 3–4 cm from the midline. If midline exposure is necessary, for example for a tumor near the midline, make burr holes about 2 cm from the midline on both sides and join them by removing the intervening bone with a rongeur. This avoids injury to the superior sagittal sinus.

Control a torn middle meningeal artery with a silver clip across its open end or by passing a suture through the dura around the artery and tying it. If the arterial end lies deep to the skull edge, remove a little more bone until it is visible, then suture-ligate, clip or coagulate it. Suspend the dura from muscle or galea with sutures. If these methods fail, it may be necessary to approach the artery at the foramen spinosum. Separate the dura from the inner skull surface in the middle fossa and follow the middle meningeal branches from distal to proximal. At the floor of the middle fossa, identify the foramen spinosum. If the arterial segment between dura and foramen is long enough, apply a silver clip and divide the artery, or simply clip it, to stop bleeding. If the segment is too short to clip, pack a piece of cotton approximately 3 × 5 mm into the foramen spinosum to occlude the artery. The cotton may be left there without harm. Small middle meningeal branches on the dural surface are readily controlled with bipolar coagulation. Avoid unipolar coagulation because it causes marked dural contraction. Finally, suspend the dura along the skull edge from the galea all around to prevent epidural bleeding beneath the skull.

Original printed pages 576–577

3.5 Bleeding from arachnoid granulations

Small bleeding points may be controlled with bipolar coagulation. This is ineffective for larger areas. Cover the bleeding site with an adequately sized piece of Gelfoam, place moist cotton over it and apply pressure for 2–3 minutes to stop bleeding. If the bleeding granulation is at the skull edge, cover it with Gelfoam and suspend the dura from the galea with sutures.

Original printed pages 577–578

3.6 Bleeding from a dural venous sinus

Although the blood is venous, a tear can cause substantial blood loss. The taut sinus walls cannot be approximated to close the defect, and coagulation is ineffective. A good method is to cover the opening with a muscle patch, pass a suture through the dura on either side and tie it so that the thread presses down on the patch. Apply cotton briefly until bleeding stops, then remove the cotton (Figure 7.6)

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If the superior sagittal sinus must be divided, its anterior one-quarter to one-third may be divided without harm. Occlusion farther posteriorly may impair venous return, cause brain swelling and lead to death. To divide the sinus, make small dural openings on both sides, apply two clamps, divide the sinus and securely suture-ligate its ends. Simple ligation alone should be avoided because the ligature may slip.

Original printed pages 578–579

3.7 Bleeding from cerebral and tumor vessels

Bleeding from either arteries or veins on the cerebral or cerebellar cortex is readily controlled with bipolar coagulation for small vessels and silver clips for larger vessels. Before occluding a vessel, always consider the function of the brain territory it supplies. Avoid proximal occlusion of a torn vessel; occlude it at the bleeding site to minimize brain injury.

The author considers bleeding from cortical or bridging veins particularly important. Although bleeding may be easily stopped, swelling in the territory drained by the vein may be fatal. Sometimes the swollen brain must be resected to save the patient, leaving a disability. Therefore, if a large vein has a defect but is not completely divided, wrap Gelfoam around it and apply pressure for 2–3 minutes. Bleeding will stop, and the Gelfoam is unlikely to dislodge because venous pressure is low. This preserves normal venous flow. The author has seen a Sylvian vein torn during craniotomy by bone penetrating through the dura into the vein. The surgeon attempted bipolar hemostasis, but the entire hemisphere eventually swelled and the patient died. Small veins may be coagulated, except those draining important regions such as the brainstem and hypothalamus.

Bleeding during tumor dissection can be controlled with coagulation, silver clips and cotton packing. The best method of controlling tumor bleeding is prompt complete removal of the tumor, which stops the bleeding and leaves the field in good order. There may be slight bleeding from cerebral vessels supplying the tumor, but it is easily controlled. During dissection, systematically occluding and dividing the feeding vessels along the capsule margins minimizes blood loss during removal.

Original printed pages 579–581

4. Suction apparatus (sucker)

This is essential in every brain operation. Two suction units may sometimes be needed when substantial bleeding is anticipated. Suction serves the following purposes:

i) It keeps the operative field clean and dry, removing blood, cerebrospinal fluid and saline used to irrigate the brain, so that the surgeon can clearly see the lesion and important structures.

ii) It removes soft tumor gradually, reducing its size so that the remainder can be removed easily. For firm tumors, suction may be combined with a cutting loop.

iii) It identifies bleeding points. Sometimes the severed vessel can be lifted into view by suction and coagulated to stop the bleeding easily. When the bleeding point is unclear, I usually flood the operative cavity with saline and apply suction away from the bleeding site. The jet of blood and its stream through the water toward the suction tube reveal the point that needs coagulation.

iv) For firm tumors, the suction tube can help lift the tumor and facilitate its separation from the brain.

v) It removes necrotic brain tissue or substitutes for a knife during lobectomy. Suction exposes vessels running between the tissue to be removed and the healthy tissue, allowing convenient coagulation or clipping without causing bleeding.

Suction technique is important because improper use may impair brain and cranial nerve function. Suction tubes are available in several sizes. The choice depends on the operation: microsurgery requires a small tube, whereas tumor aspiration calls for a large one. Most tubes are metal and have a vent at the handgrip to regulate suction. Closing the vent completely with the thumb applies the full suction set on the machine; opening it reduces suction. Fukushima devised a tube with a teardrop-shaped oval vent that allows finer thumb control.

When suction is applied near brain tissue, cranial nerves or blood vessels, a thin cotton pledget should first cover the area, and suction should be applied through it to prevent injury. Gentle pressure while suctioning through the pledget also controls bleeding and dries the field. Gradually lifting the pledget reveals bleeding points for easy coagulation.

A large tube aspirates tumor quickly and removes more tissue. Begin in the least vascular area and gradually work outward. As the tumor shrinks, its margins and feeding vessels become more visible. Coagulating and dividing these vessels reduces its blood supply. If a tumor vessel is drawn onto the suction tip, coagulate it with bipolar forceps; with unipolar coagulation, apply the electrode to the metal suction tube to stop the bleeding.

Hazards of suction Suction may damage cranial nerves, blood vessels and important brain tissue. If these structures are not protected, a nerve or vessel may be drawn onto the tip, causing contusion or transection and loss of function. For example, the facial nerve may be injured during suction dissection of an acoustic neuroma. If the nerve becomes caught on the tip, an alarmed surgeon may pull the tube away and sever it. The correct method is to reduce suction when approaching the nerve. If the nerve adheres to the tip, open the vent or pinch the rubber tubing to interrupt suction, then gently push the nerve off the tip to preserve it. The optic and olfactory nerves are not true peripheral nerves but extensions of the brain and lack toughness. Suction can easily sever them, so they should be completely covered with cotton pledgets.

Striking, pulling or aspirating a vessel with the suction tube may tear it. Cerebral veins are particularly fragile and should remain carefully covered with cotton pledgets throughout tumor dissection.

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5. Coagulator

An electrical coagulator controls bleeding from small vessels. There are two types: i) unipolar and ii) bipolar. Bipolar coagulation is now used for most neurosurgical operations.

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5.1 Unipolar coagulation

Unipolar coagulation can be used for cutting and hemostasis. Its disadvantage is that current passes from the active electrode through the patient to a grounding plate placed against the leg. It therefore cannot be used in vital areas such as the brainstem, because the patient may fail to regain consciousness. Burns may also occur if the grounding plate is absent.

The operative field must be dry for effective unipolar coagulation, so suction is always required. The electrical setting must be appropriate. Besides coagulation, a loop electrode can cut firm tumors that cannot be aspirated, such as fibrous meningiomas. Cutting pieces from the center outward reduces the tumor to its capsule, allowing complete removal. However, using a loop on tumors near the medial part of the lesser sphenoid wing may be dangerous: in some patients the internal carotid artery runs through the tumor and could be cut. This possibility must always be borne in mind.

Original printed pages 581–582

5.2 Bipolar coagulation

Current flows only between the two electrode tips of the forceps, rather than through the patient to ground. If the tips touch, a short circuit occurs and no coagulation takes place. The bleeding point or tissue to be coagulated must therefore lie between the tips, which should remain approximately 2–3 mm apart. Unlike unipolar coagulation, bipolar coagulation can work in a pool of saline. Irrigating the tips during use improves coagulation, protects tissue from heat, reduces tissue shrinkage and prevents the tips from drying and sticking. Without saline, the tips adhere to dry, burned tissue. Tips coated with charred tissue will not coagulate effectively again until the coating has been scraped off.

An advantage of bipolar coagulation in neurosurgery is that it can control vessels in areas where unipolar coagulation would be dangerous, such as the brainstem⁽²⁷⁾. Small bleeding points on the wall of a large vessel may also be controlled with low current and saline irrigation, without vessel contraction or thrombosis. Unipolar coagulation would sacrifice such a vessel through contraction and thrombosis.

Original printed pages 582–584

6. Retractor

Retractors are another essential instrument in brain surgery because they expose the lesion. They include ordinary hand-held brain spatulas used to retract a brain tumor and self-retaining retractors that hold the brain without manual support. These useful devices come in many forms (Figure 7.7). They are generally divided into those attached directly to the skull edge and those attached to the operating table. Self-retaining retractors maintain steady traction, avoiding contusion, and their position and tension can be adjusted as needed. They free both of the surgeon’s hands for other tasks. A hand-held spatula tends to shift during prolonged retraction, readily bruising the brain and interrupting the operation.

Principles of retractor use:

i) Use a self-retaining retractor.

ii) Lower intracranial pressure before applying a retractor; otherwise traction may tear the brain and make tumor exposure difficult.

iii) Choose a suitably small spatula that provides the required tumor exposure.

iv) Apply only enough traction to expose part of the tumor. There is no need to retract the brain until the entire tumor is visible; doing so damages brain tissue.

v) First cover the brain to be retracted with a cotton pledget to protect it from the blade edges.

vi) Whenever possible, position the spatula away from cortical veins to prevent venous occlusion and brain edema.

If hypotension develops, reduce retraction to maintain adequate brain perfusion.

Original printed pages 584–585

7. COTTONOID

Cottonoids are thin cotton pads cut into various sizes. A long black thread is sewn to one side to indicate the pad’s location, with the thread remaining outside the skull. They have the following uses:

i) Covering the brain to prevent drying. The pad retains water and keeps the cortical surface continuously moist.

ii) Covering cranial nerves and vessels near the tumor to protect them during dissection.

iii) Providing a protective layer when suctioning fluid and blood, preventing direct contact between the suction tube and brain, cranial nerves or vessels. Place the pad over the area and apply suction to the pad until dry.

iv) Packing a bleeding site to apply pressure. Wait approximately 3–4 minutes for bleeding to stop, then irrigate the packing with saline. The cotton expands and can be gently removed one piece at a time. If bleeding persists, use another method.

v) Covering Gelfoam while suction is applied to the cotton, drying the Gelfoam and helping it adhere to the bleeding surface.

Care is required when removing cottonoids covering nerves, vessels or brain, because these structures may tear. During suction, they can adhere to the fibers on the underside of the pad; repeated suction and prolonged placement increase this adherence. Lifting the cottonoid may then avulse them. I encountered this during acoustic neuroma surgery, in which cottonoids are routinely placed over cranial nerves IX, X and XI at the jugular foramen. Careless removal before wound closure tore one nerve filament; fortunately, the entire nerve was not severed. The correct method is to keep irrigating the pad while lifting it gradually. At any point of adherence, gently free the nerve, vessel or cortex from the cotton with a nerve root retractor to avoid injury.

Original printed pages 585–586

General methods of opening the skull

There are two methods, classified according to how the skull is opened:

i) Osteoplastic craniotomy creates a bone flap of the required size, depending on the size, location and type of tumor or lesion. Particular techniques for each location will be discussed later. After the brain operation, the bone flap is replaced, leaving no large skull defect. This method is used for supratentorial openings.

ii) Craniectomy removes bone to create an opening of the required size. Usually a burr hole is made first, then enlarged by cutting away surrounding bone. This is suitable for the posterior fossa. It may also be used supratentorially when only a small opening is needed. No bone flap is replaced after the brain operation, and a skull defect remains.

Original printed page 586

Osteoplastic craniotomy technique

The following principles apply to craniotomy at any location:

i) Center the opening over the tumor and make it as small as permits convenient removal. CT and MRI are particularly helpful. Limiting the opening to the necessary size saves time and reduces blood loss. It also limits the cortical area exposed to air, which may be damaged by drying during prolonged exposure.

ii) Always preserve the muscle attachment to the bone flap to maintain its blood supply. Otherwise the flap dies and behaves like a foreign body.

iii) For this reason, fracture the bone with the muscular pedicle of the flap always directed toward the skull base.

iv) Fracture the skull at a thin, narrow site where it breaks easily.

v) Avoid injury to the superior sagittal and transverse sinuses and to the proximal middle meningeal artery.

vi) Whatever the shape of the scalp incision, preserve the major vessels supplying the scalp flap.

vii) Always consider cosmetic results, particularly in frontal operations, without compromising access to the brain tumor.

Original printed pages 586–587

Scalp incision

A scalp incision for craniotomy is generally horseshoe-shaped, with its open end directed inferiorly toward the skull base to maintain a good blood supply to the flap. The pedicle must be sufficiently wide: the narrower it is, the greater the risk of ischemia. A straight or slightly curved incision may be suitable for a relatively small craniotomy.

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The scalp arteries (Figure 7.8) include:

i) The superficial temporal artery, supplying the temporal and parietal regions and part of the frontal region.

ii) The supraorbital and supratrochlear arteries, supplying the frontal region.

iii) The greater occipital artery, supplying the occipital and posterior parietal regions.

A scalp flap must receive blood from at least one of these arteries; preserving two supplies is preferable whenever possible.

Original printed pages 587–590

Examples of scalp incisions (Figure 7.9)

Panel a shows an incision suitable for tumors of the temporal lobe, Sylvian fissure, middle cranial fossa and tentorium. Begin in front of the ear, behind the superficial temporal artery, to preserve the flap’s blood supply. The incision may need to extend to the upper border of the zygoma, but should not lie more than 2 cm anterior to the tragus, as this may sever the frontal branch of the facial nerve and impair frontalis function. Curve the incision posteriorly through the temporal region above the ear, then forward around the temple, ending behind the frontotemporal hairline.

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Panel b shows a horseshoe incision with its open end toward the skull base. It is suitable for tumors on the cerebral convexity and in paramedian regions, as in panel f. Note the good blood supply from the superficial temporal artery.

Panel c is suitable for tumors of the occipital lobe and tentorium. It may be extended inferiorly to expose both supratentorial and infratentorial compartments, using a craniotomy above and a craniectomy below the tentorium. The occipital artery provides a good blood supply to this flap.

In panel d, the anterior limb of the horseshoe lies in front of the ear. This incision is suitable for tumors of the posterior temporal region, lateral tentorium or posterior petrous bone.

Panel e shows a transcoronal incision along the coronal suture, extending from in front of one ear to the other. Keep it behind the frontal hairline for cosmetic reasons. In some cases it need only extend slightly across the midline, rather than all the way to the opposite ear—for example, with a narrow forehead or when subfrontal access is unnecessary. The flap remains supplied by the supraorbital, supratrochlear and superficial temporal arteries.

A transcoronal incision is suitable for a bifrontal bone flap, as shown in panel g.

Panel f shows a horseshoe incision crossing the midline, with its open end still directed toward the skull base. This is suitable for parasagittal tumors such as meningiomas, or midline tumors such as third ventricular tumors.

Panels h and i show straight scalp incisions, which bleed relatively little because they run parallel to the vessels. I prefer this approach when a large bone flap is unnecessary, since CT and MRI now show tumor location and size clearly enough to permit accurate incision placement.

Original printed pages 590–596

Opening the skull

After incising the scalp and controlling bleeding with arterial clamps or clips as described earlier in this chapter, separate the scalp in the loose areolar plane between the galea and pericranium and reflect it inferiorly. Place a rolled cloth beneath the flap to prevent folding and ischemia, and hold it in this position throughout the operation. A frontotemporoparietal craniotomy exposes the temporalis muscle and pericranium; an occipital craniotomy does not expose temporalis.

The steps are as follows:

Step 1. Divide the temporalis muscle with electrocautery along its fibers at both lower wound margins. Strip enough muscle from the skull to permit convenient burr-hole placement (Figure 7.10b). Control bleeding from muscle and bone, and remove the pericranium at each intended burr-hole site.

Step 2. Use a perforator to make approximately 4–6 holes, depending on the required flap size, spaced about 5–6 cm apart (Figure 7.10b). Usually five holes suffice: three superiorly and two inferiorly in the prepared temporalis regions over the temporal squama. When the perforator reaches the dura, it feels caught and becomes difficult to turn. Stop immediately, remove it and move to another site. Forcing it farther may penetrate the dura or brain, particularly through the thin temporal squama. Control bony bleeding with bone wax. Then enlarge each initial opening with a burr. Remove any inward-projecting bone at the lower rim with a rongeur. In a thin skull, this opening is sufficient to pass a dural guide between holes. A thick skull may require slightly wider holes to facilitate passage.

Burr holes can also be made with an electric or pneumatic drill (craniotome) (Figure 7.10). Its shoulder prevents penetration that could injure the brain. When the drill passes the inner table and reaches the dura, loss of resistance stops its rotation. The skull is then divided with a dural guide and Gigli saw, as described below.

Step 3. Use a rongeur to enlarge the two lowest temporal burr holes toward each other, leaving a narrow bridge of bone beneath temporalis that can be fractured easily. Cutting here may cause bleeding from branches of the middle meningeal artery. Use bipolar coagulation or temporarily pack with bone wax or a cottonoid. Definitive hemostasis is achieved after the skull is opened and the bleeding point is visible.

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Step 4. Pass the dural guide with the Gigli saw from one hole to the next (Figure 7.10). The guide must lie between the dural surface and the inner table. Precautions are: i) If the perforator has torn the dura, the guide may enter the subdural space and injure brain or vessels. First separate the dura from bone with a curved dissector, then insert the guide. ii) In elderly patients or those with hyperostosis frontalis interna, frontal dura may adhere firmly to the inner table and tear during guide insertion. If passage from one hole is obstructed, try from the other or first separate the dura with a curved dissector. iii) Large arachnoid granulations often occur near the midline in the parietal parasagittal region. The guide may perforate the dura there and cause venous bleeding. If this happens, withdraw it and reinsert it obliquely downward, passing beyond the granulation before turning the tip toward the intended exit hole. This separates the dura and arachnoid granulation from the inner table. iv) When cutting across the midline, do not pass a dural guide from one side of the superior sagittal sinus to the other, because the sinus may tear.

Step 5. Detach the Gigli saw from the dural guide and saw the skull at an angle of approximately 45° to produce a beveled edge. This allows the replaced flap to rest securely against the skull margin without easily falling inward. After sawing around the flap, except at its base beneath temporalis, use a periosteal elevator to raise the upper edge (Figure 7.10f). Insert a dissector beneath the flap and separate the dura from its inner table. Fold the flap downward until the remaining bone bridge breaks. Before reflecting it downward, lift the bone flap first, then turn it down. Lift the bone flap first, then turn it down. This prevents the sharp fractured edge from pressing on and tearing the middle meningeal artery, dura or cortex. The temporalis muscle remains attached. Smooth the fractured edge, wrap the flap in cloth and secure it to the drapes.

A craniotome can create a flap of the required size and shape. First drill a burr hole in the prepared temporalis region, then replace the burr with a cutting head, consisting of a vertically rotating metal cutter with a dural guard beneath it. Insert the head into the hole and control the switch with the foot. Advance parallel to the skull while keeping the cutter perpendicular to it, continuing to the opposite burr hole. Then fracture the bone beneath temporalis. Where no muscle is attached, one burr hole may suffice: cut a circle of the required size, returning to the initial hole to free the flap.

The craniotome may tear the dura as it passes, particularly over hyperostotic frontal bone where the dura adheres firmly.

Step 6. Control bony bleeding with bone wax. Bleeding from the middle meningeal artery is controlled with bipolar coagulation or a suture ligature. Coagulate bleeding arachnoid granulations or cover them with Gelfoam and briefly apply a cotton pad until bleeding stops.

Step 7. Place dural hitch sutures around the skull margin, securing the dura to the surrounding galea or muscle to control epidural bleeding. Achieve hemostasis before opening the dura so that blood does not interfere with the brain operation.

Step 8. Before opening the dura, always assess whether intracranial pressure remains elevated. If so, lower it, for example by hyperventilation or by administering 200–300 cc of 20% mannitol over 10–15 minutes, then waiting until the dura becomes soft. When hydrocephalus is responsible, ventricular puncture and CSF removal immediately relax the brain. Open the dura only after pressure has been relieved. Opening it while pressure remains high causes brain protrusion and tearing, subarachnoid hemorrhage and further swelling, and should be avoided. Begin the incision frontally or temporally, about 1 cm from the skull edge. Lift the dura away from the cortex with a dural hook and make an approximately 0.5-cm incision with a pointed knife. Insert a dural groove beneath it and cut along the groove, which protects the cortex while the opening is enlarged. If this instrument is unavailable, place a small cotton pledget beneath the dura to protect the cortex and cut with scissors. Continue around the opening, leaving a hinge toward the superior sagittal sinus. Take particular care near the Sylvian fissure, where the dura is thicker and pushed inward by the lesser sphenoid wing. Inserting scissors may tear the Sylvian vein, with serious consequences; protect it carefully with cotton before cutting. Control middle meningeal arterial bleeding with a silver clip or suture ligature, and small bleeding points at the dural edge with bipolar coagulation. Leaving a 1-cm dural margin facilitates closure. If the dura is cut flush with the skull edge, subsequent shrinkage draws its margin beneath the bone and makes suturing difficult.

Original printed pages 596–598

Bifrontal craniotomy

A bifrontal craniotomy opens both frontal bones. It is used for a large midline frontal tumor extending into both frontal lobes, since a unilateral opening makes dissection on the opposite side difficult and dangerous. The general principles of craniotomy apply, with the following differences:

Step 1. Position the patient facing directly upward, with the head moderately extended so that gravity allows the frontal lobes to fall away and exposes the anterior cranial fossa. Make a transcoronal incision from one temple to the other behind the hairline. Reflect the scalp inferiorly until the superior orbital ridge can be seen or palpated. Opening as low as possible improves the view of a subfrontal tumor. Preserve the supraorbital nerve within the scalp flap, although accidental division has no adverse effect. Place a rolled cloth beneath the flap base to prevent folding and ischemia.

Step 2. Divide the right temporalis along its fibers near the junction of the zygoma, orbital rim and temporal fossa. On the left, if the opening does not reach the temporalis insertion, the muscle need not be divided. If the opening must extend to temporalis, divide it close to its fascial insertion at the frontotemporal ridge, leaving enough length for resuturing. Strip the muscle over the width required for the bone flap.

Incise the pericranium 2–3 cm from the orbital ridge so that it can later cover an opened frontal sinus.

Step 3. Make eight burr holes as shown in Figure 7.9g. Cut the bone above the orbital ridge as low as possible. A large frontal sinus may have to be crossed, but avoid it if possible. Remove the bridge between the holes on either side of the superior sagittal sinus with a rongeur to protect the sinus. Never pass a dural guide or Gigli saw between these two holes.

At the frontal sinus, the perforator first passes through the anterior wall. Use a fine-tipped rongeur or laminectomy rongeur to enlarge the anterior opening to the width of the perforator. The sinus mucosa may still be intact. The author prefers to separate it from the sinus wall and push it inferiorly with a cottonoid. Keeping it intact prevents infection from the nose. Then perforate the posterior wall and proceed as for the anterior wall.

Step 4. Divide the bone with a Gigli saw and lift the flap. Always dissect the superior sagittal sinus away from the inner table before lifting it. Fracture the temporal bone bridge, using temporalis as the hinge. Control bleeding from bone, dura and muscle as described above.

Step 5. If the frontal sinus has been opened, cut an appropriately sized piece of temporalis to cover the entire opening. Suture the prepared galea to the dura over the muscle as an additional layer, then close the skull.

Original printed pages 598–600

Closing the skull

After removing the tumor or lesion and securing hemostasis, proper closure is important. Some postoperative complications result from improper closure. Follow these steps (Figure 7.11)

Step 1. Close the dura. Place three or four initial sutures to restore its original shape. If it is taut, cut the initial hitch sutures to prevent tearing during approximation, and replace them after dural closure. Once the dura is adequately relaxed and can be tied without tearing, close it with closely spaced continuous sutures to obtain a watertight seal. Closely spaced interrupted sutures may also be used, but take longer.

If the dura has contracted so that its edges cannot be approximated, or if the brain is swollen, insert a temporalis fascia graft between the edges to reduce tension and cover the brain.

Step 2. Replace the bone flap. If bleeding persists despite bone wax, partially detach temporalis, leaving a small vascular attachment. This reduces blood flow from the muscle into the flap and helps prevent a postoperative epidural hematoma. Use a 2–3-mm drill to make corresponding holes in the skull and flap at three or four positions for secure fixation. The skull holes may pass through its full thickness, but protect the underlying brain. Limit the protruding drill bit to slightly more than the bone thickness to avoid penetrating the dura. The author prefers to drill a horizontal hole almost 1 cm deep into the diploic space, then drill through the outer table about 0.5 cm from the edge to intersect the first hole. Stop at the intersection to avoid penetration toward the brain. Drill full-thickness holes in the flap, together with two central holes for suspending the dura, reducing the epidural space and preventing expansion of a hematoma. Pass fine silver wire through each pair of corresponding holes. Pass a central dural suture through the two central flap holes. An epidural vacuum drain may be placed through a burr hole before closure. Replace the flap and twist the wires tightly. Trim their ends and tuck them into the holes to prevent skin puncture and late infection. Securely tie the central dural hitch suture. Resuture temporalis, replace the pericranium over the bone and close the scalp as described at the beginning of this chapter.

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Original printed pages 600–609

Opening the posterior fossa

Suboccipital craniectomy provides access to tumors or lesions in the cerebellar hemisphere, vermis, fourth ventricle, brainstem, foramen magnum and cerebellopontine angle. The opening may be unilateral or bilateral, depending on the tumor site and size. The steps are as follows.

Step 1. Positioning is important, because the occipital bone is difficult to reach if the patient is incorrectly positioned, making posterior fossa exposure difficult.

Sitting position is the position the author most often prefers. Positioning is described at the beginning of this chapter. In particular, the head must be sufficiently flexed without kinking the endotracheal tube or causing venous obstruction. For a midline or cerebellar hemisphere tumor, flex the head directly forward without rotation. For a cerebellopontine angle tumor, slight rotation toward the tumor side may be necessary. Advantages of posterior fossa surgery in the sitting position are: i) the tumor is clearly visible at eye level, and table height can be adjusted as required; ii) venous bleeding is reduced because venous pressure is low; and iii) blood flows downward rather than pooling in the operative field. Disadvantages are: i) air embolism may occur; ii) hypotension; and iii) downward sagging of the cerebellum necessitates greater retraction.

Recumbent position is suitable for cerebellopontine angle tumors. Its advantages are: i) there is no need to fear air embolism or hypotension; and ii) less cerebellar hemisphere retraction is needed, since the cerebellum falls downward and facilitates access to the cerebellopontine angle. Disadvantages are: i) the surgeon must look downward unless using a microscope; and ii) blood pools in the operative field.

Step 2. Scalp incision. Usually make a midline incision from about 3–4 cm above the external occipital protuberance down to the C3–C4 spinous processes. Use electrocautery in the midline to divide connective tissue between the muscles on both sides and the fascia until the occipital bone and C1–C2 are visible. Detach the muscular attachments from each side of the occipital bone with electrocautery and a periosteal elevator, extending to both occipitomastoid sutures and the foramen magnum margin. A large mastoid emissary vein is present in the mastoid region; if divided, coagulate it and plug its bony opening with bone wax. During muscular dissection, bleeding may occur at individual points. Secure hemostasis before proceeding. Detach the muscle from the posterior arch of C1 no more than 1.5 cm laterally from the midline on each side; extending farther may injure the vertebral artery. After dissection, separate the muscles with a self-retaining retractor to expose the occipital bone and the entire atlas arch.

Hockey-stick and paramedial incisions are suitable for unilateral posterior fossa exposure, such as a cerebellar hemisphere or cerebellopontine angle tumor. As its name suggests, the hockey-stick incision resembles a hockey stick. Begin in the midline as described above, then extend obliquely laterally for about 5 cm at the level of the external occipital protuberance (Figure 7.12). Detach muscle from the ipsilateral occipital bone and posterior arch of C1 as described above.

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Step 3. Removing the skull bone. Make a burr hole on each side of the occipital bone (Figure 7.13). Enlarge each opening circumferentially until they meet in the midline. Extend laterally to the occipitomastoid sutures and superiorly until the transverse sinus is visible. In some patients, the bone near the external occipital protuberance and transverse sinus is too thick for a rongeur. If skull radiographs and CT show marked thickness here, before making burr holes and removing the occipital bone, use a perforator to make multiple closely spaced holes in the protuberance and other thickened areas to a depth of approximately two-thirds of the bone thickness. Removing the intervening bone leaves a thinner plate that can be removed with a rongeur. Do not drill these thick areas after craniectomy, because the perforator could slip and penetrate the brain. Inferiorly, remove the posterior margin of the foramen magnum to almost its full width. If removal of the posterior atlas arch is necessary, remove no more than 1.5 cm on each side, since extending farther could injure the vertebral artery. In a unilateral occipital opening, only the ipsilateral atlas arch may need removal. Alternatively, the occipital bone may be removed without opening the foramen magnum margin. Decide individually.

For a midline tumor, a large craniectomy is unnecessary. Determine the required dimensions from CT or MRI. CT is particularly useful in this respect. Previously, ventriculography and vertebral angiography localized a tumor but did not clearly show its shape and size, so a broad opening was necessary.

After removing the bone, apply bone wax to bleeding bone and coagulate all bleeding points on the dural surface.

Step 4. Opening the dura. Before every dural opening, assess whether the dura is bulging and tense from raised intracranial pressure. If so, remove CSF first. There are two methods. The first is ventriculostomy immediately above the lambdoid suture, 3–4 cm from the midline. Mark and prepare this incision site beforehand so it is ready for use. Inserting a tube into the occipital horn of the lateral ventricle allows CSF to drain. Continue drainage until the dura softens and the brain moves with respiration, then clamp the tube and open the dura safely. The author prefers frontal-horn ventriculostomy before positioning the patient, because it is easier to perform and manage postoperatively, and the head does not compress and kink the tube. The second method is to make a small opening in the dura and arachnoid over the cisterna magna, allowing CSF to drain until posterior fossa pressure decreases.

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Always open the dura only when intracranial pressure is not elevated. The dura must be soft and relaxed, not tense, to avoid injury to the cerebellum and its vessels. Make a Y-shaped incision (Figure 7.14), beginning just below the transverse sinus at the two upper corners of the craniectomy and converging in the midline at the foramen magnum. An occipital dural sinus runs along the midline and may be large, causing bleeding when divided. Therefore, always suture-ligate this sinus at the lower dural corner (Figure 7.14b), then reflect the dural flap upward to expose the cerebellum. Continue the midline incision down to C1 and suture the lateral dura to muscle. In some cases, a transverse incision in this dural margin is needed before securing it to muscle, providing wider cerebellar exposure. Control dural sinus bleeding at the foramen magnum with a silver clip; bipolar coagulation may suffice elsewhere.

After a unilateral craniectomy, a single oblique dural incision followed by a transverse incision, with the dura retracted and sutured to muscle, exposes the ipsilateral cerebellar hemisphere and cerebellopontine angle.

Step 5. Locating the tumor. After opening the dura, always inspect the cerebellar hemispheres, vermis, tonsils, fourth ventricle, brainstem and cerebellopontine angle, because a tumor may lie outside the cerebellum and the cerebellum could otherwise be incised at the wrong site. The author witnessed such an error abroad when the surgeon carelessly omitted a complete posterior fossa inspection before incising the cerebellum. Clinical and radiological examination had shown a lime-sized tumor in the right posterior fossa. Exposure revealed an enlarged right cerebellar hemisphere and tonsillar herniation. Palpation of the cerebellar surface met resistance suggesting an underlying tumor, as did probing with a cannula. The surgeon incised the cerebellar hemisphere to a depth of about 3–4 cm and encountered a well-demarcated tumor. Attempted removal through the cerebellar hemisphere could not achieve complete excision and caused marked cerebellar swelling. The patient died postoperatively from brain swelling and hemorrhage around the residual tumor. Examination of the brain and tumor histology revealed a petrous ridge meningioma. The surgeon had omitted inspection of the cerebellopontine angle before incising the cerebellum and had improperly approached an extracerebellar tumor through the cerebellum. Inspection of the cerebellopontine angle would have allowed better planning.

With the remarkable ability of CT and MRI to show tumor site and size, such an error should now be rare, except when the surgeon truly lacks knowledge.

When a cerebellar hemisphere tumor is not visible on the surface, its site may be indicated by changes in the overlying folia, which become broader and paler. Abnormal vessels may be visible. Palpation may reveal resistance, or a cystic tumor may feel softer than the surrounding tissue. Probing with a cannula is another method. A vermian tumor may similarly broaden and pale the vermian folia and separate the supplying branches of the posterior inferior cerebellar artery.

Incise the cerebellar hemisphere horizontally, parallel to its folia. Always incise the vermis vertically in the midline. A horizontal incision may divide branches of the posterior inferior cerebellar artery and veins and gives poor exposure of the fourth ventricle. Coagulate small vermian vessels first, then divide and separate the vermis. The larger posterior inferior cerebellar artery branches at the junction of the vermis and cerebellar hemispheres remain intact.

For a fourth ventricular tumor or a vermian tumor projecting into that ventricle, separate the tonsils with a spatula to expose the lower fourth ventricle. To expose its upper part, divide the vermis vertically from posterior to anterior for the required distance.

Wider cerebellopontine angle exposure can be obtained by removing the lateral third of the cerebellar hemisphere, which does not add functional loss. Removing more may impair cerebellar function. Techniques for removing individual tumor types are described later.

Step 6. Closing the posterior fossa. This is an important step. Before closure, completely control bleeding from the tumor bed, dura and muscle surfaces dissected from bone. The posterior fossa contains the brainstem, and even a small hematoma may cause unconsciousness and respiratory arrest. A vacuum drain is generally not left in the posterior fossa.

There are two methods of closure: leaving the dura open, or suturing it closed as before.

For closure with the dura left open, approximate the muscles in the midline up to just above the foramen magnum. Suture the lower corner of the V-shaped dural flap, previously reflected upward, to the muscles on both sides in the midline. Secure its lateral edges to the undersurface of the muscles with interrupted sutures so that the flap continues to cover the cerebellum. Leave the dura at the craniectomy margin and atlas attached to muscle as previously sutured. Continue approximating the muscles throughout, then suture the fascia and galea and close the skin. A disadvantage is formation of a CSF collection beneath the muscles, termed a pseudomeningocele. It may bulge posteriorly when hydrocephalus develops. Over time, the uncovered cerebellar hemisphere adheres firmly to muscle, making separation difficult at another operation. Blood from muscle surfaces may also enter the subarachnoid space. A vacuum drain cannot be used because the cerebellar surface is not covered by dura. The advantage is decompression of the posterior fossa and relief of medullary compression in patients with tonsillar herniation.

Closure with the dura sutured is suitable when, after the operative work, there is no evidence of raised posterior fossa pressure or cerebellar swelling, or after a small or unilateral craniectomy. Cut the sutures securing the dura to muscle around the craniectomy, then reapproximate the original dural incision. Sometimes the dura can be closed without tearing or excessive tension. If it is tight, harvest a neck muscle fascia or galeal graft and close the dura with a watertight continuous suture. The graft relieves tension. Then suspend the dural margins from muscle around the craniectomy. Place a central dural suture and secure it to muscle to eliminate the epidural space and prevent a large epidural hematoma. Close muscle and fascia in the midline, then close the skin in two layers. This preserves dural coverage of the cerebellum, prevents pseudomeningocele and permits placement of an epidural vacuum drain if desired.

Original printed pages 609–610

Ventriculostomy

Ventriculostomy creates a communication with a ventricle so that CSF can flow elsewhere or outside the body, reducing CSF pressure. It is used in patients with obstructive hydrocephalus, or to introduce radiopaque media or air to investigate lesions within or near a ventricle. Injection of radiopaque media is no longer performed, since CT and MRI are more useful.

Ventriculostomy is generally performed through a frontal or occipital site. Occasionally a parietal site, as used for a ventriculoatrial shunt, may be necessary.

Original printed pages 610–612

Frontal ventriculostomy

The procedure may be performed under local or general anesthesia. Position the patient supine, facing directly upward, and secure the head with adhesive tape. Even slight rotation may cause an inaccurate ventricular puncture. After preparing the scalp, mark an approximately 3-cm incision just anterior to the coronal suture, which is palpable in some patients, about 2–2.5 cm from the skull midline. Ventricular cannulation is easier here than farther laterally. After sterile draping, incise along the mark and separate the scalp with a mastoid self-retaining retractor. Strip the pericranium with a periosteal elevator and make an exploratory burr hole. Control skull and dural bleeding with bone wax and bipolar coagulation. Make a cruciate dural incision with a pointed knife to expose the cortex. Incise an area without large vessels, making the opening only as wide as the cannula. Insert the cannula with its stylet toward the ventricle, perpendicular to the skull when the ventricle is large, or inclined slightly medially when it is not markedly enlarged (Figure 7.15). When the tip penetrates the ventricular wall, loss of resistance and CSF return are felt and seen. Stop advancing the cannula. Do not allow CSF to spurt out rapidly under pressure; let it drip slowly. Rapid reduction of intracranial pressure may shift the brain, causing upward cerebellar herniation and brainstem dysfunction. A No. 8 stomach tube may be used for CSF drainage. Tie a thread around it 10 cm from its tip as a depth marker during intracerebral placement. After sufficient CSF has drained and its pressure has returned to normal, withdraw the cannula and introduce the prepared tube along the cannula tract until CSF flows through it. Do not insert the tube through brain into the ventricle while intracranial pressure is high: its end and side openings may cut off pieces of brain that block the tube and prevent CSF flow. Once the tip is correctly positioned, cover the dura with Gelfoam, close the wound and secure the tube. It may be tunneled beneath the scalp to exit away from the incision. Connect it to a sterile bottle. Crucially, position the bottle so that the open end of the tube within it is about 10–12 cm above the foramen of Monro, corresponding to normal ventricular pressure. CSF drains into the bottle when pressure exceeds 10–12 cm CSF and stops when it falls to 10–12 cm. Drainage starts and stops automatically as long as the tube remains patent. Once the bottle and head levels are set, avoid changing either, to maintain the desired intracranial pressure. Reset the level whenever their positions change. Never lower the bottle below the head, because continuous drainage would cause intracranial hypotension. Always clamp the tube temporarily when moving the patient, then reset its level and reopen it.

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A ventriculostomy may be maintained for no more than seven days. If it remains necessary, change to a new site on the opposite side. Leaving it longer risks wound and CSF infection. In general, a ventriculoatrial or ventriculoperitoneal shunt is preferable for prolonged CSF drainage.

Original printed pages 612–613

Occipital ventriculostomy

This may be performed with the patient sitting or prone, but is most often done in the sitting position during posterior fossa exposure. Place the burr hole adjacent to the palpable lambdoid suture, 3–4 cm from the midline. Alternatively, place it 7–8 cm above the external occipital protuberance (Figure 7.16). Make the burr hole and open the dura as described above. Direct the cannula toward the ipsilateral medial canthus to enter the occipital horn of the lateral ventricle. Once the ventricle is entered, proceed as for frontal ventriculostomy.

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Original printed pages 613–615

Trephination

This is another method of opening the skull, using a rotating circular saw to remove a bone disk corresponding to the trephine diameter, which ranges from 3 to 5 cm. It is therefore suitable for a small skull opening when extensive brain exposure is unnecessary. A central pin holds the trephine in position as it rotates through the skull.

Open the scalp sufficiently for the selected trephine, and retract the scalp and pericranium with a self-retaining retractor. Attach the trephine to a Hudson brace. Adjust the central pin to project about 2–3 mm beyond the saw teeth and set the guard to limit the cutting depth. Rock and press the trephine until the pin grips the bone, stabilizing it. Then rotate the trephine (Figure 7.17). The teeth gradually cut down to the inner table. Since skull thickness may not be uniform, observe whether one side has been cut more deeply and tilt the trephine to deepen the cut where required. Avoid cutting deeply enough to tear the dura. The external guard, set to the skull thickness, prevents the trephine from plunging inward. Once the bone has been divided, use a periosteal elevator to lift the disk (Figure 7.17). Secure hemostasis in bone and dura before proceeding with brain surgery. For closure, replace the disk, secure it with silver wire and close the scalp in layers.

Original printed pages 615–616

Treatment of individual brain tumor types
(Specific management of individual brain tumors)

As discussed in the pathology chapter, many types of tumor occur in the brain, including primary tumors and metastases from elsewhere. Each has a different natural history. Some are malignant, growing and impairing brain function rapidly; others are benign and grow slowly. Treatment therefore differs among tumor types. Tumor site and size are also important considerations in surgical treatment. Even benign tumors require different treatments and operative approaches when they involve vital brain centers.

Surgical treatment has three main objectives:

i) Complete removal when the tumor is accessible and removal will not cause loss of brain function or life.

ii) Obtaining tumor tissue for histological identification to guide the choice of other treatments in conjunction with surgery.

iii) When complete removal is impossible, reducing tumor size to relieve local and generalized intracranial pressure and improve symptoms for a time.

When tissue cannot be obtained to identify the tumor, whether radiotherapy should be given may be debated. The author believes that the tumor site and appearance on skull radiographs, CT and MRI, together with the patient’s age and clinical syndrome, should be considered. Previous experience with the characteristic age distribution, location, CT appearance and radiosensitivity of each tumor type can support radiotherapy in selected cases. Nevertheless, if the tumor can be approached without a major risk of loss of brain function, or the patient is fit enough for surgery, tissue should be obtained for identification in every case, for three reasons:

i) To support the clinical and radiological diagnosis.

ii) To compile accurate statistics on tumor types.

iii) To provide a sound basis for radiotherapy when the tumor is known to be radiosensitive, with benefit through shrinkage or disappearance.

The surgical approach must take account of the tumor’s site, size, extent, vascularity, histology and radiosensitivity, as well as the patient’s neurological and general condition.

Individual tumor types at their various sites and the corresponding operative techniques are described in detail below.

Original printed pages 616–617

Tumors of neuroglial cells

Tumors arising from the various neuroglial cells—astrocytes, oligodendrocytes, microglia and ependymal cells—are collectively called gliomas. They are the most common brain tumors, accounting for 40–45% of all brain tumors⁽²⁸⁾. Because they arise within brain tissue and infiltrate without clear boundaries, complete surgical removal is difficult. Although modern techniques and instruments permit earlier diagnosis and easier removal, they still cannot cure the disease; surgery only prolongs postoperative survival. No method can distinguish the full extent of these tumor cells from normal brain, even with an operating microscope. Gliomas can therefore be treated but are usually not cured.

Surgical treatment of gliomas generally offers three alternatives:

Original printed pages 617–618

Method 1: Craniotomy with removal of the tumor alone

The tumor is excised or aspirated without lobectomy. Success depends on removing it without adding to the patient’s pre-existing neurological deficits, which is difficult for the surgeon. New instruments, including the operating microscope, carbon dioxide laser, ultrasonic aspirator and bipolar coagulator, make removal easier, even for large tumors, while reducing injury to healthy brain. The surgeon should always stop resection on reaching functionally important brain tissue. In addition to removing as much tumor as possible, this operation immediately reduces intracranial pressure, as shown by relaxation of the brain after removal. The patient may then experience a further period without focal symptoms or symptoms of raised intracranial pressure. In general, prolonged survival after glioma surgery correlates with the extent of resection. This method usually leaves some tumor behind, which later gives rise to recurrence.

There are two reasons for attempting the most complete removal possible. i) In some patients and locations, a glioma is not markedly infiltrative and its boundary can be identified. Hemiparesis or dysphasia may result from compression and associated local edema. Radical removal should therefore permit functional recovery and longer survival than limited removal. ii) If the tumor has infiltrated functionally important brain tissue, that tissue has already been destroyed and rendered nonfunctional. Resection within the visible tumor boundary should therefore not add neurological deficits, while reducing local pressure and intracranial pressure. Nevertheless, radical resection remains impossible in some patients.

The removal technique is described in the illustrative cases that follow.

Original printed page 618

Method 2: Lobectomy

This removes the tumor together with a margin of healthy brain beyond its boundary, in the hope of complete excision. It is suitable for gliomas at the frontal, temporal and occipital poles, which can be removed without loss of brain functions important for daily living. Some sites may incur functional loss, but not disabling impairment; for example, occipital lobe removal causes homonymous hemianopia.

From experience with this method, gliomas can still recur. Some tumors are not truly confined to the pole but infiltrate widely toward important areas, such as Broca’s and motor areas, or, in the temporal lobe, toward the Sylvian fissure or insula. These extensions limit resection. Even when CT shows a well-defined mass, histology reveals tumor cells extending beyond its macroscopic margin into surrounding brain, where they subsequently grow into another mass. This operation prolongs survival.

Original printed pages 618–622

2.1 Frontal lobectomy

This procedure is suitable for gliomas in the frontal pole, particularly unilateral tumors in the non-dominant hemisphere. It can also be performed in the dominant hemisphere.

Technique. Place the patient supine, with the face turned approximately 15–20° away from the side of the tumor. Make a transcoronal incision behind the anterior hairline to conceal the scar. On the side of the craniotomy, extend the incision down to the superior border of the zygoma, no more than 2 cm anterior to the tragus, to avoid injuring the frontal branch of the facial nerve. Dissect and reflect the scalp flap anteriorly to expose the frontal bone, orbital ridge, and temporalis muscle. Make a craniotomy with its anterior edge close to the orbital ridge to provide easy access to the frontal pole. Place its medial edge approximately 1–1.5 cm from the midline, its posterior edge slightly behind the coronal suture (approximately 1 cm), and its inferior edge at the level of the squamosal suture of the temporal bone. This exposes the anterior Sylvian fissure, which helps identify the positions and relationships of the various structures.

After opening the skull, if the dura is tense, institute hyperventilation or administer 300 cc of 20% mannitol intravenously over 10–15 minutes. Once intracranial pressure has decreased and the dura is relaxed, open the dura with its flap based adjacent to the superior sagittal sinus. This opening exposes the superior, middle, and inferior frontal gyri. In the dominant hemisphere, the posterior third of the inferior frontal gyrus contains Broca's motor speech center, which must be preserved and not injured. The anterior temporal lobe, Sylvian fissure, and lesser wing of the sphenoid are also visible.

Resection of brain tissue. In a normal brain without hydrocephalus, resection of the frontal lobe along a vertical line extending upward from the anterior tip of the temporal lobe, or from the edge of the lesser wing of the sphenoid, generally does not enter the anterior horn of the lateral ventricle (Figure 7.18). Frontal lobectomy should therefore be performed transversely along this line or anterior to it, as appropriate. Resection may begin in the cortex of the inferior frontal gyrus, using bipolar cautery to coagulate the vessels and scissors to divide them. Then use suction to remove the brain tissue transversely, proceeding from the inferior to the middle and superior frontal gyri and deepening the resection uniformly to maintain a broad view. Use a spatula to retract the part of the frontal lobe to be removed. Avoid touching or retracting the brain that is to be preserved, as this may cause further damage. During suction resection, vessels may be drawn up with the tissue; coagulate and divide them. Preserve the major branches of the cortical veins draining into the sagittal sinus with the brain that is to remain, to avoid cerebral swelling. Divide cortical veins close to the cortex, rather than near the superior sagittal sinus. As suction resection proceeds deeper, direct it toward the base of the frontal lobe. If the anterior part of the frontal horn is entered, cover the opening carefully with a cottonoid to prevent blood entering the ventricle. Remove the cottonoid at the end of the operation and plug the opening with Gelfoam. Medially, keep the frontal lobe resection anterior to the genu of the corpus callosum and the anterior cerebral artery. Coagulate or clip and divide the ipsilateral frontopolar artery running along the medial frontal lobe. When resecting the inferior frontal gyrus, avoid injuring the Sylvian vessels by keeping the resection anterior to the Sylvian fissure throughout. At the base of the frontal lobe, the olfactory nerve and bulb and the vessels running along the nerve will be seen. Try to preserve these structures, both to prevent CSF leakage through the cribriform plate and to preserve the sense of smell. Coagulate and divide the veins and arteries adjacent to the pia-arachnoid at the frontal base; the frontal pole can then be removed. If the tumor extends posterior to the resection plane, remove as much as possible with suction without damaging functionally important brain tissue. Before closing the dura, irrigate and secure complete hemostasis. Cover the cut surface of the remaining frontal lobe with Gelfoam and close the dura tightly. Before placing the final stitch, fill the cavity with saline to expel all air, to prevent postoperative headache.

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Disadvantages of frontal lobectomy. Generally, this procedure does not cause an obvious loss of cerebral function such as hemiparesis or dysphasia, because the motor speech area and motor area are not damaged. However, patients may become slow in thinking, lack interest in activities, or tend to remain inactive. These changes are especially noticeable after surgery on the dominant hemisphere. Some patients may have impaired recent memory.⁽²⁹⁾

Original printed pages 622–624

2.2 Temporal lobectomy

This procedure is suitable for gliomas in the temporal pole and may be performed in either the dominant or non-dominant hemisphere.

Technique. Place the patient supine with the face turned to the opposite side. Elevate the shoulder on the operative side with a sandbag to avoid excessive neck rotation, which may cause venous obstruction in the neck. After skin preparation and draping, make a question-mark incision starting 1.5 cm anterior to the tragus, above the superior border of the zygoma, curving posteriorly above the ear and then forward (Figure 7.9). This incision preserves the frontal branch of the facial nerve and the superficial temporal artery. Make the craniotomy as low in the temporal fossa as possible, leaving the temporalis muscle attached to the bone flap. After opening the skull, remove the squamous temporal bone down to the floor of the temporal fossa. If bleeding occurs from the middle meningeal artery, control it by suture ligation. Then open the dura, beginning in the temporal region, with the dural flap based toward the vertex.

Resection of brain tissue. After opening the dura, the Sylvian fissure, superior and middle temporal gyri, and part of the inferior temporal gyrus are visible. Most of the inferior temporal gyrus lies on the inferior surface of the temporal lobe. The tip of the temporal lobe is hidden beneath the lesser wing of the sphenoid. The temporal lobe may be resected to a maximum of approximately 5–6 cm posterior to its anterior edge without loss of functions essential to daily living. Remember that approximately 2 cm of the anterior temporal tip lies beneath the lesser wing and must be included in this measurement. In addition to measuring distance, a reliable anatomical landmark can guide the resection: the junction of the Rolandic and Sylvian fissures. Temporal lobe resection must always remain anterior to this point. Resection of the superior and middle temporal gyri posterior to it in the dominant hemisphere would remove part of Wernicke's sensory speech center. The inferior anastomotic vein of Labbé can be an unreliable landmark because its position varies.

Use suction and a bipolar coagulator for the resection. Begin along the length of the superior temporal gyrus, from anterior to posterior, stopping just anterior to the junction of the Rolandic and Sylvian fissures and remaining approximately 1 cm from the Sylvian fissure. Throughout the resection, avoid entering the Sylvian fissure or insular cortex (Figure 7.19). Do not cut through the pia-arachnoid separating the insula and middle cerebral artery, as injury to the artery or its branches may cause postoperative hemiparesis. Coagulate and divide the branches of the middle cerebral artery crossing to supply the temporal lobe. When the superior temporal gyrus has been resected to the planned posterior limit, continue transversely downward through the middle and inferior temporal gyri, again using suction and bipolar coagulation, toward the floor of the middle fossa. Near the temporal horn, avoid opening it because this may lead to postoperative complications such as a tension cyst. If the temporal horn is entered, plug the opening securely with Gelfoam. If a large draining vein is encountered, preserve it until the final stage before dividing it, to avoid cerebral swelling during surgery. The uncus and parahippocampal gyrus on the medial side of the temporal lobe may also be resected if infiltrated by tumor. Leave some of the medial surface of the uncus to protect the optic tract. During surgery in this region, avoid injury to the oculomotor nerve and posterior cerebral artery, which lie medial to the uncus and parahippocampal gyrus.

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Sequelae of temporal lobectomy. Homonymous superior quadrantanopia is commonly encountered. It may involve part or all of the quadrant, depending on the extent of resection. In patients with temporal lobe gliomas, this deficit may already be present before surgery.

Original printed pages 624–625

2.3 Occipital lobectomy

This procedure is suitable for gliomas in the occipital lobe. It may be performed with the patient sitting or recumbent. In the recumbent position, place the patient semiprone or on the side, with the operative side uppermost, the face directed toward the floor, and the occiput uppermost. After skin preparation, make an inverted U-shaped incision to preserve the occipital artery and nerve. Make a craniotomy with its medial edge approximately 1.5 cm from the midline. At its lower edge, make 2 burr holes approximately 1.5 cm above the transverse sinus, then cut the bone obliquely downward toward each other, crossing the transverse sinus. The remaining bone is fractured when the bone flap is elevated. Open the dura approximately 1.5 cm above the transverse sinus, with the flap based beside the superior sagittal sinus.

In the non-dominant hemisphere, occipital lobe resection may begin approximately 6 cm from the occipital pole. In the dominant hemisphere, no more than 4 cm should be removed to avoid damaging the angular gyrus, which forms part of the sensory speech center. Resect the brain in the same manner as for frontal lobectomy, using suction and bipolar coagulation. Medially, branches of the posterior cerebral artery supplying the occipital lobe will be encountered; coagulate or clip and divide them. After completing the parenchymal resection, coagulate or clip the cortical veins draining into the transverse sinus, torcula Herophili, and superior sagittal sinus. The occipital pole can then be removed. As with lobectomy elsewhere, take care not to enter the occipital horn.

Functional loss after occipital lobectomy. If occipital lobectomy is performed correctly, the only visual field loss will be contralateral homonymous hemianopia. However, if resection in the dominant hemisphere extends too far anteriorly, nearly to the junction of the occipital, parietal, and temporal lobes, it will impair reading (dyslexia), writing (dysgraphia), and calculation (dyscalculia). If Wernicke's area is resected, the patient will have sensory dysphasia.

Original printed pages 625–626

Method 3: Biopsy

Biopsy obtains tumor tissue for identification of its type, helping guide the use of additional treatments such as radiotherapy. It is suitable for deep tumors in critical locations, such as the thalamus, basal ganglia, or near the third ventricle. Attempting to remove an entire tumor in these areas would be dangerous and cause further functional loss. Either needle biopsy or open biopsy may be used. CT and stereotaxis are now used to guide the needle accurately into the tumor^(30,31) A needle biopsy from only one site may not reliably establish the nature of the tumor, because different parts of a glioma may show different degrees of malignancy. The periphery is usually less malignant than the central region. CT guidance overcomes this problem by allowing samples to be taken from several sites. Nevertheless, the procedure can cause intratumoral hemorrhage that cannot be controlled immediately, and the patient may deteriorate.

Open biopsy involves craniotomy and exposure of the tumor, followed by removal of a portion large enough for histological examination. This allows the surgeon to inspect the tumor directly and, in some cases, recognize its type. It also permits control of bleeding caused by the biopsy.

None of the 3 surgical methods for gliomas described above is ideal, because they cannot yet cure the disease. Additional treatment, including radiotherapy and chemotherapy, which remains experimental, is still needed to prolong survival. Treatment of gliomas must therefore be individualized to determine the best method for each patient, considering the location and natural history of the particular tumor type, as discussed below. An account of the natural history of each tumor is consequently needed to explain its treatment.

Original printed pages 626–629

ASTROCYTOMA

Astrocytoma is a brain tumor arising from astrocytic cells. It grows by infiltration and lacks a clearly defined boundary. It accounts for approximately half of all gliomas. Within the cerebral hemispheres, astrocytomas occur most frequently in the frontal lobe, followed by the temporal and parietal lobes; the occipital lobe is rarely affected. Most occur in middle age, with a peak incidence at approximately 34–45 years⁽³²⁾

Astrocytomas may also arise in the thalamus, hypothalamus, optic nerve, chiasm, brain stem, and cerebellum. Tumors at the last 5 sites are common in children and will be discussed separately by location. Cerebellar astrocytoma has a better prognosis than cerebral hemispheric astrocytoma because it often consists of a large cyst with a small mural nodule in its wall. Removal of the mural nodule may cure the patient.

Some astrocytomas arise near the genu of the corpus callosum and extend into the frontal lobe and cingulate gyrus on the same side or on both sides. Psychiatric symptoms may be the initial presentation.

Astrocytomas may be subdivided according to the predominant tumor cell type into fibrillary, protoplasmic, and gemistocytic astrocytomas. Each has characteristic cell shape, cytoplasm, and astrocytic fibrils (see the pathology chapter). They have also been classified by degree of malignancy. Kernohan⁽³³⁾ divided astrocytomas into 4 grades: grade 1 is the most benign; grade 2 corresponds to anaplastic astrocytoma in the WHO classification⁽³⁴⁾ and has greater malignancy; grades 3 and 4 are the most malignant, termed glioblastoma multiforme or poorly differentiated glioma.

Fibrillary astrocytoma is the most common benign form among tumors of the various astrocytic cell types. In the cerebral hemispheres, however, it is less common than glioblastoma multiforme⁽³⁵⁾ Hemispheric astrocytomas may sometimes develop a cyst (Figure 7.23). The cyst contains straw-colored fluid and contributes substantially to raised intracranial pressure and focal neurological deficits. Surgical drainage of the cyst can greatly improve neurological symptoms. It is a palliative treatment for tumors in locations where complete removal is not possible.

Because astrocytoma is a benign tumor, metastasis or spread through the cerebrospinal fluid pathways has not been observed. Recurrence after the first operation is nevertheless common because the tumor infiltrates critical brain regions, such as the motor area, thalamus, and hypothalamus. Extensive resection along this infiltration is not possible without loss of brain function or life. The tumor may therefore be considered malignant by location, since it cannot be completely removed.

Symptoms and signs. Regardless of its cell type, astrocytoma produces the 2 main groups of symptoms described above: general symptoms of raised intracranial pressure and focal symptoms corresponding to its location in the brain. These symptoms do not identify the tumor type. However, the speed with which symptoms and signs develop may help indicate whether the tumor is malignant or benign.

Focal symptoms may be irritative, destructive, or a combination of both. Astrocytoma most often presents with seizures, which may be focal, Jacksonian, or generalized. Temporal lobe tumors may cause uncinate fits or psychomotor epilepsy. Seizures are common when the tumor is in or near the motor cortex, and a history of seizures often precedes diagnosis by years, generally 1–2 years. Diagnosis is now made earlier because CT and MRI are highly effective investigations, prompting physicians to refer patients with these symptoms for imaging at an early stage. Deficits such as limb weakness do not develop as rapidly as in glioblastoma multiforme, because the benign tumor grows slowly by infiltration. In some cases CT clearly shows an extensive area of low density due to astrocytoma, yet with very little mass effect.

Symptoms of raised intracranial pressure—headache, vomiting, and blurred vision—are less common than in malignant glioma or glioblastoma multiforme. This is illustrated by CT showing a large low-density astrocytoma without midline shift (Figure 6.96).

Cerebellar astrocytoma is benign, occurs predominantly in children, and commonly involves a cerebellar hemisphere. Patients therefore have ipsilateral cerebellar signs: ipsilateral ataxia, dysmetria, dysdiadochokinesia, hypotonia, and nystagmus. Symptoms of raised intracranial pressure subsequently develop as the fourth ventricle is compressed and obstructed.

Astrocytomas of the brain stem, hypothalamus, optic nerve, and chiasm will be discussed under their respective headings.

Original printed page 629

Diagnosis

In addition to taking the history and examining for the signs described above, special radiological investigations help establish an accurate diagnosis.

1. MRI is currently the best investigation, clearly demonstrating the extent of the tumor even when it is poorly visualized on CT. For example, if the tumor is only slightly hypodense or nearly isodense with brain tissue on CT, MRI demonstrates it better.

2. CT scanning is another accurate diagnostic method, but is inferior to MRI for low-grade astrocytoma. The tumor appears as a low-density area and is not better visualized after contrast enhancement, whereas MRI shows it more clearly.

3. Skull radiographs may show small clusters of calcification scattered throughout the tumor. Raised intracranial pressure may cause changes in the sella turcica or separation of the cranial sutures; these latter changes are not specific to astrocytoma.

4. Cerebral angiography shows an avascular region at the tumor site, without a tumor blood supply; only displacement of nearby vessels is seen. This differs from glioblastoma multiforme, which has numerous newly formed, abnormal vessels supplying the tumor.

Original printed pages 629–630

Treatment

As already stated, astrocytomas or gliomas are treatable, but most cannot be cured because there is still no ideal method of removing all the tumor without destroying function in the brain it has infiltrated. Treatment is therefore directed toward relieving symptoms and providing a period of better quality of life or minimal disability. Attempts at complete removal are generally difficult to accomplish and often cause immediate deficits such as hemiplegia, aphasia, or hemianesthesia, imposing suffering on both the patient and family. The surgeon should bear this in mind and exercise judgment during the operation about when to stop, so as to avoid further loss of brain function, and then use other treatments.

Original printed pages 630–639

Surgical treatment of cerebral hemispheric astrocytoma

The method of tumor removal must be planned according to its location, size, and characteristics (solid, cystic, anaplastic, and vascularity). In general, the 3 surgical options for glioma are those described above. At present, the author prefers direct tumor resection because excellent surgical instruments are available. Lobectomy is now very rarely performed, except when the tumor lies at the pole of a lobe, cannot be completely removed, and raised intracranial pressure persists. In that situation, a lobectomy is needed to reduce intracranial pressure and prolong survival.

Osteoplastic craniotomy for this tumor is performed in the usual manner described at the beginning of the chapter. The opening should be wide enough to show the cortical anatomy. Before opening the dura, assess whether it is tense from raised intracranial pressure. If so, first reduce the pressure by hyperventilation or 20% mannitol at 1 g/kg body weight, approximately 200–300 cc for an adult. Wait until the dura relaxes before opening it. Opening the dura while the pressure is high causes cerebral herniation and may rupture or tear the brain.

After opening the dura, inspect the cortex for changes. In some cases the tumor is clearly visible at the surface (Figure 7.21). The affected gyri are enlarged and pale yellowish, unlike normal cortex. Displacement of vessels and normal cortex is readily apparent. In some cases a cyst containing straw-colored fluid is visible at the brain surface (Figure 7.23)

When a glioma lies beneath the cortex (subcortically), cortical changes may or may not be apparent, depending on the size and depth of the tumor. A superficial tumor broadens and pales the overlying cortex. Also inspect the cortical veins. In glioblastoma multiforme or malignant glioma, some cortical veins may be enlarged and contain arterialized blood (Figure 7.28A). This indicates shunting of arterial blood within the malignant tumor. Gently palpating the cortex with a wet index finger (never a dry finger, which may cause subpial hemorrhage), together with reviewing the CT and angiogram, helps localize the tumor. A non-cystic tumor may feel firm, whereas a cystic tumor feels soft. Seek the softest area, corresponding to the part of the cyst nearest the brain surface. Make a small cortical incision of approximately 2–3 mm and pass a cannula through the cortex toward the tumor. Resistance will be felt when the cannula enters solid tumor. If it enters a cyst, resistance disappears and straw-colored fluid is obtained.

Real-time ultrasonography is now used during brain surgery to identify the location and extent of a tumor^(36,37,38), enabling accurate access to subcortical tumors and increasing the surgeon's confidence.

When opening the cortex to reach the tumor, choose the point where it lies closest to the surface, guided by cortical changes and the feel of the cannula as it reaches the tumor. Avoid incising clinically important cortex, such as the motor and speech areas. However, if the tumor is at the surface of the motor cortex and that cortex is very thin, an incision may be made there because its function has already been lost. The important point is to make the incision transverse to the length of the precentral gyrus or motor cortex. Do not incise longitudinally along the motor cortex, as this would extend the loss of motor function (Figure 7.20)

Since the introduction of loupes and microscopes for brain tumor surgery, a long cortical incision has become unnecessary; 2–3 cm is sufficient. Illumination from a coaxial headlight and the microscope gives a clear, broad view at depth and permits tumor removal. Once the cortex has been opened to the tumor, use a self-retaining brain retractor on both sides to improve the view and free both of the surgeon's hands. Resect only tissue that looks different from normal brain: tumor is grayish with a pink tinge and is usually easily removed by suction. The following cases illustrate the method of removal.

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Case 1: Parasagittal glioma of the posterior frontal lobe adjacent to the motor cortex. A 36-year-old patient first had clonic seizures of the left leg approximately 1 year earlier and received anticonvulsants at a provincial hospital. There were another 3–4 seizures over the next 6 months. Six months before admission, the patient began to have headaches without vomiting or blurred vision; analgesics relieved the pain. Three months before admission, mild left leg weakness appeared and gradually progressed. On the day of admission, a seizure began in the left leg and became generalized. Afterwards, the patient could not move the left leg for several hours. Examination showed mild spastic monoparesis of the left leg. A brain tumor in the leg area of the right motor cortex was diagnosed. Right carotid angiography showed an avascular parasagittal tumor in the posterior frontal lobe. At surgery, opening the dura revealed a tumor on the surface of the posterior superior frontal convolution, adjacent to the motor cortex (Figure 7.21). The cortex was widened and pale yellowish. The tumor had a very sparse blood supply compared with the vessels of the normal cortex, a characteristic appearance of astrocytoma. Displacement of the cortical vein was obvious. From its surface the tumor appeared circumscribed, but its deep portion might lack a defined boundary. The motor cortex was clearly infiltrated in some areas and compressed in others, explaining the seizures and weakness of the left leg.

In this patient, surgery had to be planned to remove only the tumor and protect 3 structures: 1) the motor cortex; 2) the cortical vein, which is particularly important in this region, as tearing it may cause cerebral swelling and death; and 3) the anterior cerebral artery and its branches above the corpus callosum and cingulate gyrus, which also supply the tumor.

Tumor resection. This portion of the superior frontal gyrus had been destroyed by the tumor and had lost all function; its removal would therefore cause no further deficit. Begin by coagulating and dividing small vessels at the tumor margin. Then use suction and bipolar coagulating forceps to remove the tumor, working outward from its center. Send a large specimen for histological identification. Coagulate or clip and divide branches of the anterior cerebral artery supplying the tumor, taking care not to injure the callosomarginal or pericallosal arteries. Initially use a large suction tube, working from anterior to posterior. Near normal brain, change to a smaller tube and reduce suction to avoid injury. Removing the tumor over a broad area provides a view in all directions without a retractor (Figure 7.22). Do not retract the motor cortex, as this may cause ischemia or tearing with hemorrhage. Once part of the tumor has been removed, the cortical vein relaxes. Cut the arachnoid membrane beside and parallel to the vein to separate it from the tumor. Cover the vein completely with cotton to protect it, then remove the adjacent tumor with a small suction tube at low pressure. In this location, the tumor can be removed widely anteriorly, laterally, and medially. Posteriorly, however, some tumor attached to the motor cortex may have to remain; attempting complete removal could increase motor deficits.

After tumor removal, obtain meticulous hemostasis, especially where residual tumor remains, since it may bleed later. Close the dura tightly, followed by the skull and skin in layers.

Histological examination in this case showed a grade 2 protoplasmic astrocytoma. This tumor is soft and gelatinous and can be aspirated more easily than fibrillary astrocytoma. The patient received postoperative radiotherapy.

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Case 2: Temporal lobe cystic astrocytoma. A 26-year-old Thai man had intermittent headaches for more than 1 year, relieved by analgesics. In the 2–3 months before admission the headaches progressively worsened and no longer responded to analgesics. Vision in both eyes became blurred, with occasional diplopia. The left arm and leg became progressively weaker, without numbness. He sometimes felt slightly unsteady when walking. One day before admission, clonic seizures began in the left side of the face and the left arm and then became generalized. Initial examination showed papilledema, left homonymous quadrantanopia, and mild weakness of the left arm and leg.

Right carotid angiography demonstrated a large avascular temporal lobe tumor with a patch of small vessels supplied by the middle cerebral artery. Exploratory craniotomy and opening of the dura revealed a cystic tumor at the surface of the posterior half of the temporal lobe, containing straw-colored fluid (Figure 7.23). The posterior portions of the superior and middle temporal gyri had been completely destroyed. Arterialized blood in the cortical vein over the cyst suggested malignancy, although the presence of such a large cyst made malignancy less likely.

Tumor resection. In this case the tumor was in the right hemisphere, so the sensory speech center was not a concern; only the distal middle cerebral artery required particular care. Such cystic tumors often contain a solid component, or mural nodule, with a relatively clear boundary. This appearance is common in cerebellar astrocytoma. In some cases, however, there is no discrete mural nodule, and the solid component usually lies on the inner side, deep to the brain surface. First open and drain the cyst to reduce intracranial pressure. Coagulate and divide the vessels and cyst wall around its margin to expose the interior. In this case a distinct pinkish-gray mural nodule projected into the cavity. A branch of the middle cerebral artery supplied it from above and medially. Begin separating the tumor by incising the cyst wall at a distance of approximately 1–2 cm around the nodule (Figure 7.24). In fact, there is no fixed rule for how close to or far from the nodule the incision should be. Observe how far tumor-like tissue extends around it and incise slightly beyond that area. Dissect along the tumor margin, trying to remain outside its boundary. When a branch of the middle cerebral artery is seen, follow it to the small branches supplying the tumor, then coagulate and divide them to disconnect its blood supply. Use suction and bipolar coagulating forceps to separate the tumor from the surrounding normal brain; the nodule should then come away easily. When the dissection reaches the temporal horn of the lateral ventricle, try to avoid entering it. If it is entered, prevent blood from falling inside by covering the opening with cotton. Remove the cotton once tumor resection and hemostasis are complete, then plug and cover the opening with Gelfoam. Finally, close the dura tightly.

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In this case, the clearly demarcated solid tumor was completely removed (Figure 7.25). Histology showed fibrillary astrocytoma. The cyst wall need not be removed if it shows degeneration and gliosis and is therefore not growing. This can be recognized while incising the wall at the cyst margin away from the mural nodule: it is yellowish-white, without the pinkish-gray areas characteristic of glioma. At 13 years of follow-up, this patient remained well, without symptoms of recurrence. This case illustrates a cystic astrocytoma of the cerebral hemisphere in which, fortunately, the tumor formed a discrete mass, unlike most other cases, which are infiltrative. Complete removal of the mass cured the patient. Thus, a cystic astrocytoma of the cerebral hemisphere with a mural nodule can have a favorable prognosis, like a cystic astrocytoma of the cerebellar hemisphere. A degenerated cyst wall does not cause tumor recurrence. However, if tumor spreads within the cyst wall without forming a nodule, it must be carefully aspirated, resected, and separated from normal brain. The principle is always to remain within the tumor boundary and avoid damage to normal brain, especially clinically important areas. Meticulous hemostasis is essential because residual tumor may cause postoperative hemorrhage.

Original pages 639–640

Case 3: Cystic astrocytoma in the motor area of the dominant hemisphere

A 43-year-old man employed by the electricity authority had seizures involving the right arm and right side of the face, with inability to speak during the seizures. He subsequently developed headache, difficulty speaking, and weakness of the right arm and leg. Examination showed motor dysphasia and mild weakness of the facial muscles and right arm; the arm was weaker than the leg. C.T. demonstrated a cystic tumor in the left frontal lobe adjacent to the motor and speech areas.

A craniotomy was performed. After the dura was opened, the premotor and motor gyri appeared pale and broadened, and felt cystic on palpation. A cannula inserted only 1 cm through the cortex entered the cyst and yielded straw-colored fluid. The brain subsided as the fluid was aspirated. A cortical opening approximately 2 cm long exposed a tumor spreading along the cyst wall and infiltrating toward the motor area and Broca's speech area. It was therefore decided to perform only a biopsy and marsupialization to provide an opening for drainage. Histological examination showed a grade 2 astrocytoma.

The tumor was not dissected out because removing a lesion of this kind often immediately worsens speech impairment and hemiparesis through additional surgical damage to the brain, while still failing to remove the entire tumor. The patient should therefore be given a period of life without disability together with radiotherapy. This patient completed a course of irradiation. Immediately after surgery he could speak fluently and had good strength in the right arm, indicating that the preoperative speech difficulty and limb weakness had resulted from compression by the enlarging cyst. He returned to a normal working life for 1 1/2 years before the same symptoms recurred. Repeat C.T. showed a recurrent cyst and a slight increase in tumor size. A second craniotomy revealed adhesions at the opening that had obstructed drainage from the cyst. The cyst fluid was removed as before, and a wider marsupialization was performed. The tissue removed on this occasion was a grade 3 astrocytoma. This operation relieved headache and vomiting only temporarily. The hemiparesis subsequently progressed, and the patient died 6 months later.

Original pages 640–641

Results of treatment of astrocytoma

In general, patients with astrocytoma survive an average of approximately 3–5 years after surgery. The prognosis is much better than for glioblastoma multiforme, in which average survival is approximately 5–12 months. Among the cases described, cystic astrocytomas with a mural nodule have the best prognosis, with a long period free of tumor recurrence. Astrocytomas commonly recur after surgery, especially when they are near or within clinically important areas of the brain, a major obstacle to extensive excision. After the first operation, clinical and radiological examinations must be repeated periodically. Renewed tumor growth indicates failure of the first operation, and repeat surgery is necessary to determine the tumor histology and reduce the mass effect and intracranial pressure. In general, indications for reoperation for recurrent gliomas include a young patient in good health, no loss of brain function, and a tumor location accessible to surgery without causing functional loss. A further indication is a long interval between the first operation and the return of tumor symptoms. From experience with recurrent gliomas, the results of a second operation are often poor, as the period of improvement is usually shorter than after the first. Astrocytoma is frequently found to have changed into malignant astrocytoma. Nevertheless, surgery combined with radiotherapy has been found to prolong survival compared with surgery alone. In grade 1 and 2 astrocytomas treated by incomplete excision, the 5-year survival rate is 19%; adding postoperative irradiation increases 5-year survival to 45%.⁽⁴⁰⁾ Efforts at radical excision nevertheless prolong survival more than partial excision or biopsy alone. The use of an operating microscope, CO₂ laser, and ultrasonic aspirator to assist tumor removal has now increased surgical success and reduced neurological morbidity and mortality.⁽³⁹⁾

Original pages 641–642

GLIOBLASTOMA MULTIFORME

This is the most highly malignant tumor of neuroglial cells, corresponding to astrocytoma grades 3 and 4 in Kernohan's classification. It grows rapidly and infiltrates and destroys brain tissue, producing symptoms and signs within 1–2 months. In addition to rapid tumor growth, there is extensive surrounding cerebral edema. Together these two factors cause signs of raised intracranial pressure in almost every patient.

This tumor usually occurs in a cerebral hemisphere and is uncommon in the posterior fossa. The frontal lobe is the most frequent site and the occipital lobe the least frequent. In some cases it spreads through the corpus callosum to the opposite hemisphere, producing the so-called butterfly appearance (Figure 3.30).

Most of these tumors are poorly demarcated, although portions of the mass may be clearly defined in some cases. At surgery the tumor is usually gray-pink or gray-red because of its rich blood supply, an important cause of operative blood loss. Newly formed tumor vessels are abnormal, with endothelial proliferation (Figure 3.39) and shunting, as demonstrated on angiograms and during surgery by arterial blood in cortical veins draining the tumor. These new vessels are fragile and bleed easily, and hemostasis during surgery is often difficult. Rapid tumor growth can cause central necrosis and hemorrhage because the blood supply is inadequate. Endothelial proliferation causes vascular occlusion and necrosis, which can lead to hemorrhage. At surgery or in the specimen, patches of necrosis and hemorrhage can be seen (Figures 3.31 and 3.33).

The surrounding cerebral edema may give the impression that the tumor can be separated from the edematous brain. In reality, the swollen tissue adjacent to the tumor is usually infiltrated by tumor cells that can subsequently proliferate. When a glioblastoma reaches the cortical surface, gray-pink tissue can be seen spreading along the cortex. Dissemination into the subarachnoid space may be visible. In some cases the tumor reaches and adheres to the dura, with increased vascularity in this region and possible bleeding when the dura is opened. The author, however, has never found tumor cells within the dura itself.

Original pages 642

Symptoms and signs

Patients develop focal symptoms and signs according to the tumor location, together with general symptoms of raised intracranial pressure, as in astrocytoma and other tumors discussed in Chapter 5. The important distinction is that symptoms and signs develop more rapidly than in astrocytoma. Within approximately 1–2 months, patients become severely symptomatic even if the tumor is not particularly large, because extensive edema spreads into the surrounding brain. Headache due to raised intracranial pressure is therefore commonly the presenting symptom. Seizures and hemiplegia depend on the location of the tumor. Extension into the corpus callosum causes relatively rapid development of dementia, followed by progressively deteriorating consciousness. In a small minority of cases, symptoms begin suddenly, usually because of intratumoral hemorrhage, necessitating urgent surgery.

Original pages 642–644

Diagnosis

A history of symptoms and signs developing and deteriorating relatively rapidly first suggests malignancy, such as glioblastoma. Radiological investigation helps establish the correct diagnosis, especially C.T. or MRI combined with angiography.

1. Skull radiographs. Changes due to raised intracranial pressure, such as demineralization of the dorsum sellae, are uncommon because glioblastoma grows rapidly and causes symptoms within a short time, before skull changes develop. Most skull radiographs are therefore normal. If the pineal gland is calcified, it may be seen displaced to the opposite side. As these changes are not specific to brain tumors, this method has now been abandoned in favor of C.T. and MRI, which give more reliable results.

2. Computerized tomography (C.T.). This investigation provides a definite diagnosis. On C.T., glioblastoma appears as a high-density lesion that enhances well with contrast medium. The center may contain low-density areas of necrosis. Another important finding is low-density cerebral edema surrounding the mass, extending over a wide area even when the glioblastoma itself is not large. This is an important cause of relatively rapid deterioration, reflected by the mass effect on C.T. (Figure 6.93).

3. Magnetic resonance imaging (MRI). This is the newest investigative method and demonstrates tumors very clearly, particularly neuroepithelial tumors. MRI has high sensitivity and specificity, is free from bone-related artifacts, distinguishes the brain's white and gray matter, and clearly delineates tumor margins. Most of these tumors, together with the edematous brain, show high intensity on T₂-weighted images (Figure 6.120).

4. Cerebral angiography. Before C.T. became available, angiography was the best investigation for identifying glioblastoma multiforme. The important features are (Figure 6.82): i) tumor vessels of varying caliber with a beaded appearance, caused by newly formed vessels and endothelial cell proliferation; ii) staining beginning in the arterial phase and disappearing before the venous phase, with an uneven pattern because parts of the tumor are necrotic; and iii) early venous drainage.

The abnormal vessels in glioblastoma multiforme sometimes need to be distinguished from those of an arteriovenous malformation (AVM) or meningioma. The distinction is not difficult, because an AVM produces no mass effect or vascular displacement unless it has ruptured and formed a hematoma. Glioblastoma, in contrast, produces mass effect and displaces cerebral vessels. Venous drainage in an AVM appears early in the arterial phase and disappears earlier than in glioblastoma, because the shunts are larger and there is no raised intracranial pressure. Glioblastoma is a mass that raises intracranial pressure and slows blood flow; early venous drainage begins in the late arterial or early capillary phase. In the author's observations, most AVMs consistently have several large draining veins, whereas glioblastomas usually have only one large vein, or at most two, one large and one small. To distinguish a meningioma, examine its feeding vessels and tumor staining. Meningiomas receive blood from both the external and internal carotid systems and show homogeneous staining that persists into the venous phase. Early venous drainage is uncommon except in angiomatous meningiomas. Glioblastoma receives blood only from the internal carotid artery, lacks homogeneous staining, and loses its staining earlier than meningioma. The clinical course is also important in differentiation: meningioma progresses slowly, whereas glioblastoma causes rapid deterioration.

Original pages 644–645

Treatment

Glioblastoma multiforme is accepted as an incurable tumor that causes death in every case within a short period. In general, survival is approximately 5–8 months after diagnosis. This is because the tumor grows rapidly and provokes a reaction in the surrounding brain, with extensive cerebral edema. These changes lead to brain herniation and progressive deterioration. If a patient survives more than a year and a half or two years, this tumor is unlikely, and the histology should be reviewed. Nevertheless, treatment should be attempted to prolong life and reduce suffering.

Steroid therapy. From experience using steroids or dexamethasone at 20 mg/day in patients with glioblastoma and metastatic brain tumors, improvement begins on the second day of treatment and is most marked around days 3–4. Headache, drowsiness, and limb weakness diminish. The precise mechanism is unknown, but steroids are generally believed to reduce cerebral edema and intracranial pressure.⁽⁴¹⁾ Steroids should therefore be given before and after surgery in every case to help lower intracranial pressure during surgery and facilitate access to the tumor.

Treatment of glioblastoma consists of removing as much tumor as possible without increasing disability, followed by irradiation. Chemotherapy remains under investigation.

Original pages 645–646

Surgical treatment of glioblastoma multiforme

The surgical principles are the same as those for astrocytoma: remove as much tumor as possible without increasing disability, and achieve internal decompression to lower intracranial pressure and provide a period of symptomatic improvement. During this interval the patient can receive irradiation without severe neurological symptoms. For tumors in the frontal, temporal, or occipital lobe of the nondominant hemisphere, normal brain may be removed together with the tumor, or a lobectomy may be performed, to increase decompression. For tumors in the parietal lobe or in areas of the dominant hemisphere concerned with speech, limb movement, or other important functions, removal should be confined to the tumor. Brain tissue should not be excised, to avoid disability. If tumor extending into an important brain region is necrotic, cautious aspiration may be attempted. If it is infiltrative and the brain retains its structure, however, it should be left untouched.

At some institutions, when C.T. or angiography suggests glioblastoma multiforme, only a biopsy is performed to establish the diagnosis, followed directly by irradiation. The rationale is that tumor excision and biopsy alone, each combined with irradiation, do not differ in survival.

External decompression by craniotomy with removal of the bone flap is strongly discouraged. Although it can immediately improve neurological symptoms, the benefit is brief. As the tumor enlarges and expands outward, further problems arise. The scalp over the surgical site becomes tense and bulges outward (Figure 7.26), distressing the patient, and the wound may sometimes break down.

The following cases illustrate tumor removal techniques.

Original pages 646–648

Case 1: Frontal pole glioblastoma multiforme

A 45-year-old soldier had developed headache 4 months before admission, followed by blurred vision and vomiting. Two months later he became inactive and poorly responsive to his surroundings, neglected personal hygiene, and no longer dressed as neatly as he previously had in uniform. His memory became confused and his intellectual ability declined markedly. One week before admission he became slightly unsteady on standing and walking. On admission he was slow, seldom answered questions, and showed impaired intellectual function. Fundoscopy revealed papilledema, and a grasp reflex was present in the left hand. A frontal lobe tumor was diagnosed. Right carotid angiography demonstrated a large, anteriorly situated frontal lobe tumor, richly supplied by the anterior cerebral artery and to a lesser extent by the middle cerebral artery (Figure 7.27). The AP view showed considerable midline displacement of the anterior cerebral artery, with early venous drainage in the late arterial phase. These angiographic features, together with the relatively rapid clinical deterioration, suggested malignancy, particularly glioblastoma multiforme.

Operative technique. For such a highly vascular tumor in the frontal pole, planned removal by frontal lobectomy is safer than cutting directly into the tumor, which would certainly cause substantial blood loss. The feeding vessels should therefore be divided before the tumor is removed. The frontal craniotomy must be large enough, with its anterior edge next to the orbital ridge, its posterior edge approximately 1 cm behind the coronal suture, its medial edge approximately 1–1.5 cm from the midline, and its inferior edge extending down to the pterion. Intracranial pressure must always be lowered before opening the dura, using hyperventilation or mannitol. After dural opening, frontal lobe resection begins at the superior frontal gyrus, with the line of section behind the tumor margin but anterior to the genu of the corpus callosum and the anterior cerebral artery coursing around the genu and over the corpus callosum. Beware of displacement of the anterior cerebral artery by midline shift, which can cause disorientation or misidentification. Brain section should proceed both deeply and inferiorly through the middle and inferior frontal gyri together, creating a broad exposure rather than working in a narrow channel. As the brain is aspirated, branches of the anterior cerebral artery supplying the tumor will be seen medially in the frontal lobe; these are coagulated or clipped and divided. Cortical veins on the surface draining into the superior sagittal sinus are initially preserved and divided last, when the tumor is to be removed. During section through the inferior and middle frontal gyri, tumor-feeding branches of the middle cerebral artery are likewise encountered, coagulated or clipped, and divided. In this way the section gradually deepens toward the base of the frontal lobe, allowing the frontal lobe and tumor to be removed together. If the olfactory nerve has already been destroyed, it may be divided while leaving the olfactory bulb in place to prevent CSF rhinorrhea. The dura, skull, and scalp are then closed in layers.

Original pages 648–651

Case 2: Glioblastoma multiforme in the motor area

A 40-year-old woman had a 3-month history of headache. Two months before admission she developed right-sided limb weakness, greater in the arm than the leg, but could still walk. Two weeks before admission she had one generalized convulsion, beginning in the face, spreading to the limbs, and then involving the whole body. Thereafter, the right-sided weakness became so severe that she could no longer walk unaided and needed support. She also developed diplopia. On the day of admission she vomited and became drowsy. Examination showed drowsiness; she could still answer questions but was reluctant to do so, and appeared to have a continuous headache. Fundoscopy showed papilledema. There was a left sixth nerve palsy, definite right upper motor neuron facial weakness, and right hemiplegia affecting the arm more than the leg. Pinprick sensation was normal, with bilateral positive Babinski signs. Left-sided angiography demonstrated a frontoparietal tumor.

Operative technique. The angiographic appearance together with complete hemiplegia indicated that the motor cortex and fibers had already been destroyed. Removing the tumor was therefore unlikely to cause much additional loss of limb motor function. The tumor was also distant from Broca's and Wernicke's centers. Direct removal of the tumor alone was undertaken to provide a period of improvement during which irradiation could be given.

After dural opening, the tumor was visible on the brain surface in the face and arm regions of the motor cortex. It was gray-pink, and had destroyed the cortex. The cortical vein draining the tumor was enlarged and contained arterialized blood (Figure 7.28 A). Palpation showed the inferior part of the tumor to be cystic. Puncture with a cannula yielded pale, blood-stained fluid, resembling water used to wash meat (Figure 7.28 B). Aspiration allowed the brain to subside slightly. Tumor removal began at the margin facing the Sylvian fissure, followed by dissection along the anterior and posterior borders toward the superior part, initially preserving the large cortical draining vein. Dividing this vein too early could cause hemorrhage and brain swelling. Deeper dissection exposed branches of the middle cerebral artery entering the tumor from below; these were coagulated or clipped and divided, interrupting its blood supply and reducing bleeding during subsequent dissection. The cystic component made it easier to identify tumor margins without much brain retraction. Once enough feeding vessels had been divided, as indicated by the cortical vein becoming less red or turning dark, the tumor was aspirated and excised from within toward its periphery. This reduced the chance of injuring surrounding normal brain. Eventually all visible tumor was removed. The brain relaxed well, indicating relief of pressure (Figure 7.28 C). The ultrasonic aspirator now greatly facilitates tumor aspiration.

Postoperatively the patient recovered well, without symptoms of raised intracranial pressure. Right leg strength gradually improved and she could walk, although right arm and facial weakness remained unchanged. Speech was unaffected, and she completed irradiation.

Surgery thus improved neurological function without increasing deficits and allowed a period of comfortable life. Correct surgical technique enabled effective tumor removal with little blood loss. Histology confirmed glioblastoma multiforme. Eight months after surgery the tumor recurred, and the patient eventually died.

Original pages 651–653

Case 3: Glioblastoma multiforme of the parieto-occipital lobe

A 35-year-old patient had begun to experience mild headaches approximately 5 months before admission, relieved by analgesics. Two months later the headaches gradually increased and were sometimes accompanied by vomiting. Vision became blurred, and the patient occasionally walked into furniture on the left, without arm or leg weakness. Neurological examination revealed bilateral papilledema with retinal hemorrhages, left inferior homonymous quadrantanopia, left astereognosia, and a left Babinski sign and ankle clonus. A right parietal lobe tumor was diagnosed. Right carotid angiography showed a large parieto-occipital tumor with extensive abnormal intratumoral vessels supplied by terminal branches of the middle cerebral artery (Figure 7.29 A, B). Parts of the tumor were avascular, indicating necrosis or hemorrhage. Later films showed early venous drainage. This angiographic appearance strongly suggested either glioblastoma multiforme or a metastatic brain tumor.

Tumor removal. Two large vessels from the middle cerebral artery supplied the tumor in this case; any contribution from the posterior cerebral artery was not visible. The first principle of removal was to interrupt the tumor's blood supply. The cortex was first incised along the anterior tumor margin to approach the terminal middle cerebral artery branches. Once identified, they were coagulated and divided from the tumor. The tumor was then reduced by aspiration and excision from within toward its margins, beginning in the necrotic or avascular area identified on the angiogram. If aspiration and excision reached a vascular region without bleeding, this indicated that the blood supply had been completely interrupted. Removal was continued in this way to the normal brain. If the tumor was difficult to aspirate, it could instead be dissected along its external boundary with normal brain. At this stage, the reduced mass could readily be retracted to expose the operative space. Dissection was continued posteriorly and medially around the entire lesion, allowing complete removal. The deep portion might lie against the occipital horn, which should not be opened. If an opening occurred, it was plugged with Gelfoam and carefully sealed.

Postoperatively, homonymous quadrantanopia persisted, but symptoms of raised intracranial pressure disappeared. Histology showed glioblastoma multiforme. The key to successful surgery in this case was complete interruption of the blood supply before removing the tumor from its center toward its periphery.

Original pages 653–655

Case 4: Parietotemporal glioblastoma multiforme in the dominant hemisphere

A 52-year-old patient presented with progressively increasing headache for 6 months. Ten days before admission the headache became severe, with vomiting and inability to understand speech and reading. On admission the patient was drowsy and slept continuously. Examination showed mild sensory dysphasia, papilledema, right homonymous hemianopia, and parietal lobe signs: astereognosis, acalculia, finger agnosia, inability to identify parts of the right side of the body, inability to read or write, and inability to draw simple figures. A left parietotemporal tumor was diagnosed.

C.T. showed a mass in the posterior parietotemporal region, extending deep from the lateral cortex toward the midline. Marked cerebral edema was visible lateral to the tumor (Figure 7.30) and was thought likely to account for the speech disturbance.

Tumor removal. Because the tumor was in the dominant hemisphere containing Wernicke's sensory speech center, care was required to avoid damaging this area with a cortical incision and causing a permanent, physician-induced deficit. In this patient, impaired speech might have been due solely to edema extending into the speech center and could be expected to improve as edema subsided after tumor removal. The cortical incision should therefore be made in the posterior parietal parasagittal region to avoid injury to the speech center.

The principles of tumor removal were as described above. In this case the blood supply had to be considered from three directions: branches of the anterior, middle, and posterior cerebral arteries. These feeding vessels were to be interrupted before aspirating and excising the tumor. Complete removal was not possible because of its depth and proximity to the cerebral midline; attempts to remove it all might have endangered the patient, so the deep portion was left. Nevertheless, the tumor was greatly reduced and the brain relaxed. Postoperatively the patient recovered well, and speech and the various parietal lobe signs returned almost to normal. This showed that some symptoms had arisen from compression by the mass and edema; after mass removal and resolution of edema, brain function could return. This example also illustrates an approach to tumor removal that avoids damaging important brain regions.

Original pages 655

OLIGODENDROGLIOMA

Oligodendroglioma arises from oligodendrocytes and is a relatively benign, very slowly growing tumor found in adults approximately 30–50 years of age. It occurs most commonly in the cerebral hemispheres, particularly the frontotemporal region rather than other lobes. Growth is infiltrative, although a distinct margin may sometimes be visible, and multiple areas of cystic degeneration may occur. Calcification is frequent, occurring in 40–50% of oligodendrogliomas, and can be seen radiologically and histologically. The characteristic microscopic appearance consists of uniformly sized cells with dark-staining central nuclei, absent or scant cytoplasm, and sharply defined cell borders, giving a fried-egg appearance. The cells are tightly packed in a honeycomb pattern (Figure 3.40).

Original pages 655–656

Symptoms and signs

Because oligodendroglioma grows very slowly, symptoms usually develop gradually over a long period before correct diagnosis and treatment, generally approximately 3–5 years. When raised intracranial pressure develops, the symptomatic interval is shorter. Seizures are the most common initial symptom and may be the only symptom, so patients may receive anticonvulsant medication for a long time. Other accompanying symptoms may include headache, psychiatric symptoms, limb weakness, and unclear speech, depending on the brain region damaged by the tumor (see Chapter 5). In the past, diagnosis was often made only after loss of brain function and raised intracranial pressure had developed. The author now believes that earlier diagnosis should be possible because C.T. and MRI are excellent diagnostic aids. In an adult presenting with a first seizure, an organic lesion must always be considered. Brain tumors are a common such lesion, so C.T. or MRI should be obtained directly, as these are safe and painless. Some oligodendrogliomas can nevertheless cause rapid deterioration if the tumor extends toward a ventricle and causes hydrocephalus, or if intratumoral hemorrhage occurs.

Original pages 656

Diagnosis

Several radiological investigations can suggest oligodendroglioma.

1. Skull radiographs. The important finding on plain skull films is calcification in small fragments of varying sizes scattered throughout the tumor. It occurs in approximately 50% of oligodendrogliomas⁽⁴²⁾ (Figure 7.31 D).

2. C.T. Oligodendroglioma generally has two components. One is hypodense or isodense and may or may not enhance after contrast injection. The other consists of calcification, appearing as scattered bone-density hyperdensities, especially near the tumor margins. There is usually no visible surrounding cerebral edema, or very little (Figure 7.32).

3. MRI. The tumor may appear hypointense on T₁-weighted images and hyperintense on T₂-weighted images, but MRI does not show calcification as C.T. does.

4. Cerebral angiography shows an avascular mass.

Original pages 656–657

Treatment

The principles of treating oligodendroglioma are the same as for other gliomas: craniotomy and complete tumor removal without damaging important brain functions. Some tumors form a clearly demarcated mass that can be completely removed as judged by the naked eye, particularly when located at a lobar pole. Others lack a distinct mass and infiltrate the insula, basal ganglia, motor or speech areas, or a ventricle. In these cases only as much partial removal as is feasible should be attempted. Complete excision should not be pursued at the cost of function in important brain regions. This consideration is always essential because oligodendroglioma grows very slowly and the patient may live for many years; disability should therefore not be inflicted.

Indications for surgery. Because oligodendroglioma grows very slowly, a frequent question is whether a patient whose only symptom is seizures well controlled by anticonvulsants, with no other neurological symptoms or raised intracranial pressure, should undergo immediate surgery or wait until neurological deficits or raised pressure develop. There are two schools of thought: operate immediately, or wait. Surgeons favoring delay believe that several years may elapse before this slow-growing tumor causes functional deterioration, and fear that surgery might immediately cause limb weakness or other disability. The author favors immediate surgery, without waiting for further loss of function. Operating while the tumor is small and has not yet damaged important structures is easier and less dangerous than operating on a large tumor that has already caused neurological deficits. Furthermore, radiological diagnosis can be mistaken. Tissue should therefore be removed and examined to establish the exact diagnosis and guide subsequent treatment. C.T. and MRI now assist diagnosis and clearly show the tumor's location and extent, allowing surgeons to operate more confidently while avoiding important brain structures.

Radiotherapy. Because oligodendroglioma is a benign tumor, postoperative irradiation has been considered ineffective.^(43,44) Some institutions nevertheless administer it and report a higher proportion of patients surviving beyond 5 years. Sheline G.F. et al.⁽⁴⁵⁾ studied postoperative irradiation and found an increase in 5-year survival from 31% to 85%, in 10-year survival from 25% to 55%, and in median survival from 2.8 to 8 years. Chin, H.W. et al. reported 24 patients treated with surgery and irradiation, with a 5-year survival rate of 100%.⁽⁴³⁾

Original pages 657–658

Results of treatment

Gross total removal leads to longer survival than partial excision. Most patients survive more than 5 years. The prognosis is particularly good for a clearly defined mass that can be completely removed. In Case 1, follow-up has continued for 8 years without recurrent symptoms.

Original pages 658–660

Case 1: A discrete frontal lobe oligodendroglioma

A 40-year-old patient presented with generalized seizures and a change in personality. Previously active and talkative, the patient had become slow at work and less communicative. More recently there were headaches, impaired memory, and occasional confusion. The patient appeared indifferent and reluctant to answer questions, spoke slowly, had impaired recent memory, right-sided anosmia, bilateral papilledema, and frontal lobe signs. Skull radiographs showed calcification in the right frontal lobe. Carotid angiography demonstrated a mass at the base of the right frontal lobe (Figure 7.31 A, B).

Operative removal. A transcoronal incision and right frontal craniotomy are performed. The anterior edge of the craniotomy is placed close to the orbital ridge to expose the frontal pole readily; the posterior edge lies just behind the coronal suture, the superior edge 1.5 cm from the midline, and the inferior edge as low as possible to facilitate exposure of the frontal base. Because intracranial pressure is raised, hyperventilation and mannitol are used to lower it before dural opening. A lateral approach gives easier access to this tumor than a frontal pole approach or a cortical incision through the middle frontal convolution. From the side, the posterior and inferior portions of the tumor can be lifted away from the internal carotid and anterior cerebral arteries. As this is the nondominant hemisphere, part of the inferior frontal convolution can be excised to expose the tumor without excessive retraction (Figure 7.31 C). Once the tumor is reached, dissection follows its posterior and inferior margins toward the midline. Some tumor in this region is removed to open a corridor to the anterior cerebral artery and its anteriorly directed tumor-feeding branches. These branches are coagulated and divided. The entire tumor can then be dissected out easily and without blood loss.

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In this case the tumor was removed as a whole. Radiography of the specimen clearly showed the intratumoral calcifications commonly seen in oligodendroglioma (Figure 7.31 D). Histology confirmed oligodendroglioma. Nowadays, gradual aspiration from the center toward the margins with an ultrasonic aspirator greatly facilitates removal.

Original pages 660–661

Case 2: Infiltrative oligodendroglioma

A 36-year-old male bank employee had a 1-year history of generalized seizures and progressively slower work performance. Neurological examination revealed no other abnormalities.

C.T. showed a hypodense frontotemporal lesion infiltrating toward the basal ganglia. Calcified portions appeared hyperdense (Figure 7.32).

Surgery. Complete removal in such a case would be impossible without damaging the basal ganglia. The aim should be partial resection of tumor in the temporal and frontal lobes while leaving the part near the basal ganglia. A frontotemporal craniotomy is performed, followed by cortical incisions in the anterior superior temporal gyrus and inferior frontal convolution at the sites of visible cortical abnormality. Suction and coagulation are used to remove tumor progressively inward as extensively as feasible, without damaging the insula, middle cerebral artery, or Sylvian fissure with its veins and arteries. Resection must stop at the basal ganglia. This reduces tumor size and intracranial pressure and establishes the tumor type.

After surgery, no additional neurological deficit was present. Histology showed oligodendroglioma, and irradiation was not given. The patient returned to his previous bank work. Three years later symptoms recurred: slow speech, inactivity, loss of sexual desire, and mild headache, but still no limb weakness. Repeat C.T. showed expansion of the hypodense region, and further tumor removal was undertaken. As after the first operation, he initially recovered well without limb weakness. Twenty-four hours later, however, he developed left-sided limb weakness and drowsiness. Repeat C.T. showed hemorrhage extending into the basal ganglia. It was decided not to reopen and evacuate the hematoma, because surgery might further damage the basal ganglia; the hemorrhage had already destroyed part of the basal ganglia and tumor. Medical treatment would be continued provided consciousness did not progressively deteriorate. Fortunately, the patient recovered with medical treatment, although left hemiparesis persisted.

This case shows that infiltration into important brain structures such as the basal ganglia limits complete tumor removal. Residual tumor can regrow sooner than a discrete mass such as that in Case 1. Postoperative hemorrhage also occurs more readily, a risk that should always be remembered.

Original pages 661–662

OPTIC GLIOMAS

These gliomas arise in the anterior visual pathway: the optic nerve, chiasm, and optic tract. Most are benign, very slowly growing astrocytomas composed of elongated, hair-like astrocytic cells, hence the name pilocytic astrocytoma.^(46,47) The author has never personally encountered malignant optic gliomas, although they have been reported in both children and adults.^(48,49)

Reports indicate that 75% of optic gliomas occur in children under 12 years and are more frequent in patients with von Recklinghausen's disease, or neurofibromatosis. Some occur in patients with café-au-lait spots. Thus, when optic glioma is suspected, cutaneous abnormalities support the diagnosis. Conversely, deteriorating vision in a patient with von Recklinghausen's disease requires thorough investigation for an optic pathway glioma.

The tumor may arise at different sites. In the optic nerve it is termed optic nerve glioma and may be unilateral or bilateral. Optic chiasmal glioma refers to a tumor arising in the chiasm. These two entities differ somewhat in symptoms and signs, treatment, and prognosis. An optic nerve tumor may extend into the chiasm; conversely, a chiasmal tumor may extend into an optic nerve, the optic tract, hypothalamus, or interpeduncular fossa.

Original pages 662–665

Symptoms and signs

The principal symptom is visual loss, the pattern depending on tumor location.

OPTIC NERVE GLIOMA. This causes progressively worsening vision in the affected eye. Visual field loss usually begins as a central or paracentral scotoma, followed by peripheral visual loss. Because most patients are children and the tumor grows slowly, a history of visual deterioration is often difficult to obtain. Fundoscopy shows a pale optic disc (optic atrophy). Optic nerve gliomas commonly arise within the orbit; later enlargement therefore produces forward protrusion of the eye (proptosis) (Figure 7.33 A). This is nonpulsatile, and ocular movement is generally preserved unless the mass becomes very large, when motility is impaired and strabismus develops. Tumor may grow through the optic foramen and form a mass on the intracranial optic nerve, giving a dumbbell configuration with enlargement of the optic foramen. Extension into the chiasm causes bilateral visual field loss without a consistent specific pattern.

CHIASMAL GLIOMA. Vision deteriorates progressively in both eyes. Bilateral visual field defects have no characteristic pattern; their borders may be regular or irregular depending on tumor infiltration. A chiasmal glioma may extend into one or both optic nerves. The eye whose optic nerve is destroyed becomes blind first. Fundoscopy shows primary optic atrophy. Nystagmus in the absence of cerebellar signs is an important indicator of chiasmal disease,⁽⁵⁰⁾ arising as the eyes search for objects. In some cases the tumor enlarges to compress the anterior third ventricle and hypothalamus and obstruct the foramen of Monro, causing hydrocephalus and raised intracranial pressure with papilledema. Thus, either optic atrophy or papilledema may be found in chiasmal glioma. Hypothalamic dysfunction may manifest as diabetes insipidus, diencephalic syndrome, or precocious puberty.^(51,52,53)

The author has also encountered a patient with an intraorbital optic nerve glioma, chiasmal glioma, and large frontal lobe astrocytoma, without hypothalamic dysfunction. This 24-year-old woman had developed blurred vision at age 12, with bilateral visual field loss and optic atrophy. Angiography at that time showed a suprasellar mass. Frontal craniotomy revealed a large chiasmal tumor (Figure 7.34); biopsy showed pilocytic astrocytoma. Twelve years later, the left eye was proptotic and blind, the right eye had visual field loss, and headache and personality changes had developed. C.T. demonstrated tumor in the left intraorbital optic nerve, chiasm, and frontal lobe (Figure 7.35 A, B). The frontal tumor was removed and was found to have grown from the optic chiasm. At the same operation, the intraorbital optic nerve glioma on the left side was excised from behind the globe to its junction with the chiasm. Histology showed astrocytoma in all specimens.

Original pages 665–666

Investigations

Before C.T. and MRI became available, skull radiography was an important investigation for diagnosing optic nerve glioma.

Skull radiographs. In optic nerve glioma, lateral skull films often show a change in the sella turcica termed a J-shaped or pear-shaped sella (Figure 6.23), caused by tumor pressure eroding the anterior clinoid process and tuberculum sellae. This change, however, is not specific to optic nerve glioma. The optic foramen view is also very important.⁽⁵⁴⁾ It shows enlargement of the foramen on the affected side (Figure 6.22). Normally the optic foramen is oval, with an average diameter of 5 mm. A round foramen wider than 6 mm, or a difference of more than 1 mm between sides, is abnormal. Both foramina may be enlarged if a chiasmal glioma extends into both optic nerves. A normal-sized foramen does not exclude optic nerve glioma, however, because some tumors do not grow through the optic canal.

C.T. and MRI. These are the best methods and have replaced the other radiological investigations. They clearly demonstrate the optic nerve and intraorbital tumor. Low-density orbital fat provides good contrast with the isodense optic nerve. They also show the location, size, shape, and extension into neighboring structures. Because optic nerve glioma is isodense, intravenous contrast does not make the tumor more clearly visible.⁽⁵⁵⁾ The optic canal is clearly seen on C.T. sections through it. For an intracranial tumor at the sella turcica, MRI depicts the lesion more clearly than C.T., in axial, sagittal, and coronal views. The midsagittal view best shows a chiasmal tumor.

PNEUMOENCEPHALOGRAPHY, VENTRICULOGRAPHY, CAROTID ANGIOGRAPHY. These demonstrate a suprasellar mass when it is fairly large but cannot determine its type. They are no longer used for this investigation. In some cases, however, carotid angiography may be necessary to exclude vascular disease and assist surgical planning.

Original pages 666–667

Diagnosis

Optic gliomas can be diagnosed from the clinical signs described above: a child, usually under 12 years, with progressively deteriorating vision leading to blindness and proptosis on the affected side, sometimes accompanied by strabismus, with optic atrophy on fundoscopy. Chiasmal gliomas impair acuity and visual fields in both eyes, with no fixed pattern of field loss. Hypothalamic dysfunction, including diabetes insipidus, diencephalic syndrome, or precocious puberty, or symptoms of raised intracranial pressure such as headache and vomiting, may accompany the visual changes. If features of von Recklinghausen's disease are also present and skull radiographs show an abnormally enlarged optic foramen and a J-shaped sella, the diagnosis of optic glioma is fairly certain. C.T. and MRI best support the diagnosis and demonstrate compression of neighboring structures.

Original pages 667–669

Treatment

There are two methods of treating optic glioma: surgery and radiotherapy. The choice depends principally on the patient's vision and the tumor's location, according to the following principles.

1. When an intraorbital optic nerve glioma causes severe loss of vision or blindness in that eye together with proptosis, the best treatment is excision of the optic nerve and tumor from behind the globe to close to the optic nerve–chiasm junction. If the proximal optic nerve is free of tumor, postoperative radiation is unnecessary. Removal of only the intraorbital tumor should be avoided because it may extend into the intracranial optic nerve. The globe need not be removed, thereby preserving appearance, unless tumor is also present within it.

2. When an optic nerve tumor extends into the chiasm but both eyes retain vision, even if vision on the affected side is worse, and there is no proptosis, the involved optic nerve should not be divided. Biopsy followed by radiotherapy is preferable. For example, a 3-year-old girl presented with oscillation of both eyes when looking at objects. Examination showed searching nystagmus. Both eyes retained vision, but detailed acuity and field testing was impossible because she did not cooperate. C.T. showed sausage-shaped enlargement of the right optic nerve (Figure 7.36A). Frontal craniotomy and orbital exploration disclosed an optic nerve tumor extending into the chiasm. Biopsy of the proximal optic nerve showed glioma. Postoperative radiotherapy gave a good result: she retained vision in both eyes without deterioration and performed well at school. C.T. 10 years after treatment showed that the optic nerve glioma had become slightly smaller rather than enlarged (Figure 7.36B), indicating that radiotherapy could arrest its growth. At follow-up 10 years after surgery, visual acuity, visual fields, and optic nerve size remained unchanged. Menstruation was normal. Continued follow-up is necessary to determine whether the tumor will grow again. Had the involved optic nerve been excised, she would immediately have lost vision in one eye.

3. In chiasmal glioma, tumor excision should not be attempted because it would further impair vision in both eyes and could cause blindness. Moreover, because the tumor infiltrates, there is no way to determine whether removal from the chiasm is complete. Biopsy followed by radiotherapy is appropriate.

Original pages 669–674

Surgical Techniques for Optic Gliomas

Several approaches are available:

1. Transcranial (transfrontal) approach.
1.1 Extradural orbitotomy.
1.2 Intradural approach.
1.3 Combined extradural and intradural approach.

2. Lateral orbital wall resection is an unsatisfactory approach. It requires division of the zygomatic arch to reach and resect the lateral orbital wall, and may damage the frontal branch of the facial nerve. The author therefore usually uses frontal craniotomy.

TRANSFRONTAL APPROACH. This is a good approach and the only one that exposes both the intraorbital optic nerve glioma and its intracranial extension, including the optic chiasm and the opposite optic nerve.

Technique. Position the patient supine with the face turned approximately 15° to the opposite side. Make a transcoronal incision and frontal craniotomy on the tumor side. The craniotomy resembles that used for pituitary-region tumors: its anteroinferior edge must lie close to the orbital ridge and its medial edge at the midline.

C.T. and MRI now show the location and extent of these tumors fairly clearly. Previously, pneumoencephalography and angiography gave less precise localization, making it necessary always to open the dura and inspect the intracranial optic pathway before opening the orbit. Although this remains a sound practice, it is unnecessary in some cases, in which extradural orbitotomy alone suffices. For example, when an optic nerve glioma lies at the distal end of the nerve beside the globe and the proximal nerve is normal in appearance and size, extradural orbitotomy avoids the frontal lobe and olfactory nerve damage from retraction that often accompanies an intradural approach. Frozen section of the proximal intraorbital optic nerve also helps determine whether the dura must be opened. If no tumor is present in the nerve near the orbital apex, opening the dura is unnecessary.

For extradural orbitotomy, gently separate the dura from the orbital roof posteriorly to the anterior clinoid process, and retract the dura and frontal lobe with a spatula. Open the orbit using a small chisel on its thin roof, which is easily penetrated, then enlarge the bony opening with rongeurs. Unroof the optic canal to expose the dural sheath. The orbital fascia, which is the orbital periosteum and joins the dura at the optic foramen, will bulge through the opening. Incise it along the optic nerve and transversely, then place retraction sutures to expose the orbital structures. Use a microscope at this stage: the nerves and other structures are small in children and still harder to recognize when flattened by the tumor. From above, the frontal branch of the ophthalmic division of the trigeminal nerve can be seen on the levator palpebrae superioris and superior rectus muscles. The small trochlear nerve crosses the levator tendon from lateral to medial to supply the superior oblique. All these nerves and muscles must be identified and preserved. To approach the optic nerve, divide the tendon at the origin of the levator near the annulus of Zinn (Figure 7.37) and reflect it anterolaterally with its supplying nerves. Open the annulus of Zinn and optic canal dura by a transverse incision parallel to the superior rectus margin. Retract the superior rectus laterally with the levator and separate the fat to expose the whole optic nerve and tumor. Protect the oculomotor nerve, which lies lateral to the optic nerve and sends branches beneath it to the inferior rectus and medial rectus muscles. The small trochlear nerve is sometimes difficult to find and may be divided during dissection. Loss of superior oblique function is not considered particularly important here because that eye is blind and the abnormal eye movement is difficult to notice.

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Divide the optic nerve near the globe first, where the other nerves are farther apart because they have already branched to their destinations. Lift and reflect it posteriorly to separate it from posterior and lateral structures. Divide its proximal end at the optic canal.

After removing the tumor and securing hemostasis with bipolar coagulation, close the orbital fascia. To prevent postoperative pulsation of the globe, the author covers the orbital roof defect with a thin acrylic sheet. It need not be sutured to the skull: projections engaging the bony margin hold it in place.

TRANSFRONTAL INTRADURAL APPROACH. Perform frontal craniotomy, open the dura, and retract the frontal lobe from the orbital roof to expose the optic nerve, chiasm, and internal carotid artery. This approach suits tumors extending intracranially or arising in the chiasm. Incise the arachnoid around the chiasm and internal carotid artery to allow greater frontal lobe retraction and better visualization of the chiasm. If only one optic nerve contains tumor and vision is already lost, divide that nerve close to the chiasm. Leave no optic nerve remnant, even if it appears normal, because tumor cells may remain. If vision persists in that eye, however, do not divide the optic nerve; perform biopsy alone followed by radiotherapy.

For a tumor arising in the chiasm, with or without extension into the optic nerve or hypothalamus, take a biopsy from the region most evidently occupied by tumor, where the nerve fibers have already been destroyed. Do not attempt complete removal. A mass projecting beyond the chiasm may be excised while avoiding further chiasmal damage, as in the example above. Attempting to remove tumor from within the chiasm only increases visual loss.

TRANSFRONTAL COMBINED APPROACH. There are two methods:

1. After transfrontal craniotomy, separate the dura from the orbital roof and perform extradural orbitotomy as described above to expose the optic nerve and tumor. If inspection of the chiasm and optic nerve is necessary, open the dura and retract the frontal lobe. The nerve can then be divided both within the orbit and at its proximal end.

2. After transfrontal craniotomy, open the dura and retract the frontal lobe to expose the chiasm and optic nerve. Incise the dura over the orbital roof along the orbital margin and lift it from the bone. Then perform orbitotomy and unroof the optic canal to expose the entire optic nerve (Figure 7.38).

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Radiotherapy. Optic glioma responds to radiotherapy. In the example above, 10 years after irradiation the tumor had become slightly smaller rather than enlarged. The author therefore considers radiotherapy suitable for optic nerve glioma when vision remains and proptosis is not marked, and also for chiasmal glioma.

Original pages 674

Treatment Results and Prognosis

Surgery gives very good results only for optic nerve glioma confined to the orbit without extension into the chiasm. Excision of the optic nerve and tumor cures the disease. Prognosis depends on whether the tumor extends into the chiasm or originates there. Surgery is ineffective in these cases; radiotherapy is the best treatment, arresting or slowing growth and sometimes shrinking the tumor. The patient's condition may remain unchanged for nearly 10 years. Nevertheless, renewed growth remains possible over long follow-up. Most patients survive for a long time because these tumors grow very slowly.

Original pages 674–675

Brain Stem Gliomas

Brain stem gliomas are the third most common tumors in children, after cerebellar astrocytoma and medulloblastoma.^(56,57,58) They occur most often between 3 and 10 years of age.^(59,60) Most are benign gliomas, with very few malignant gliomas. Even a benign glioma must, however, be regarded as malignant because its location prevents surgical removal. The tumor usually starts in the pons and extends into the medulla, midbrain, or both. The true incidence is difficult to establish because histology is often unknown. In many patients the symptoms, signs, and radiological investigations such as C.T. and MRI establish the diagnosis clearly; surgery to obtain tissue is therefore not performed, given the poor prognosis and risk of further functional loss.

These patients consequently receive radiotherapy without a tissue diagnosis, and the brain may not be examined after death. Furthermore, a small biopsy specimen may not establish the tumor type and malignancy reliably; taking a larger specimen risks further brain stem dysfunction. Reported incidence therefore does not accurately reflect the true frequency.

The pathological changes in the brain stem and histological features are described in Chapter 3.

Original pages 675–676

Symptoms and Signs

These tumors occur predominantly in children and do not produce raised intracranial pressure until late in the disease. Diagnosis is therefore often delayed until symptoms are advanced.

Symptoms generally develop gradually and reflect dysfunction of the following important structures: i) cranial nerves, their nuclei, and other special nuclei; ii) corticospinal and sensory tracts; iii) cerebellar peduncles; iv) the reticular activating system; and v) the ventricular system, late in the disease. Details appear in Chapter 5.

In summary, cranial nerve dysfunction accompanied by long tract signs and cerebellar dysfunction indicates a brain stem lesion. The affected cranial nerve level localizes the tumor. Several nerves may be involved unilaterally or bilaterally, depending on its extension. Because brain stem gliomas occur most often in the pons and next in the medulla, manifestations include diplopia, convergent squint, unilateral or bilateral lower motor neuron facial weakness, facial numbness, choking on swallowing, altered voice, and vomiting from compression of the medullary vomiting center. Horizontal or vertical nystagmus is commonly found. Lateral gaze palsy may also result from damage to the pontine lateral gaze center.

Abnormal walking is also common. Truncal or gait ataxia may result from damage to the cerebellar peduncles. Spastic hemiparesis or quadriparesis with extensor plantar responses is frequently found. Advanced disease produces decerebration (Figure 7.39) and declining alertness. Most patients have no symptoms or signs of raised intracranial pressure early because the tumor does not obstruct cerebrospinal fluid pathways. Late in the disease, a large brain stem tumor may obstruct the fourth ventricle, basal cistern, and tentorial notch. Tumors originating in the midbrain or extending there from the pons may produce raised intracranial pressure from hydrocephalus relatively early by obstructing the aqueduct of Sylvius (Figure 3.24). Patients then develop headache, vomiting, papilledema, and drowsiness.

Reported mental and personality changes in children with brain stem glioma commonly include apathy, emotional unrest, declining school performance, and deterioration in writing and speech (see Case 1).

Original pages 676

Diagnosis

The diagnosis can be made with considerable certainty from age, history, and examination. Most patients are children in their first decade, with progressively increasing brain stem dysfunction involving several cranial nerves, corticospinal and sensory tracts, cerebellar peduncles, and the reticular activating system, as described above. Raised intracranial pressure is absent except late in the disease. Radiological investigations provide strong support for the diagnosis.

Original pages 676–678

Investigations

C.T. and MRI are currently the best methods. C.T. shows enlargement of the brain stem with obliteration of the posterior fossa cisterns. The tumor is hypodense or isodense; after contrast injection its density may remain unchanged or become hyperdense. Extension into the cerebellar peduncle and the floor of the fourth ventricle may flatten and displace the fourth ventricle posteriorly (Figure 6.97). C.T. may also show hydrocephalus, an exophytic mass extending from the brain stem into the fourth ventricle or cerebellopontine angle, and intratumoral cysts. These findings guide the choice between partial tumor resection and shunting alone. Its limitations are poor depiction of medullary tumors and poor sagittal visualization. Before MRI, C.T. combined with metrizamide cisternography depicted exophytic and medullary tumors very well. This method has been used very little since MRI became available.

MRI excellently demonstrates the location, size, shape, and extent of brain stem tumors, both intrinsic and exophytic. Unlike C.T., it clearly shows tumors in the medulla and those extending into the upper spinal cord, making it especially useful in these locations. Axial, coronal, and sagittal views are available. These tumors show decreased signal intensity on T1-weighted images and increased signal intensity on T2-weighted images (Figure 6.121).

Previously, pneumoencephalography (PEG), ventriculography, and vertebral angiography were useful diagnostic investigations. All were invasive and hazardous, and demonstrated a mass without clearly defining its extent. PEG and ventriculography showed posterior bowing of the fourth ventricle and aqueduct of Sylvius, with greater separation from the clivus, and no hydrocephalus (Figure 6.134). On anteroposterior vertebral angiography, both posterior cerebral and superior cerebellar arteries bowed laterally. Lateral views showed the basilar artery displaced against the clivus. In some tumors growing anteriorly out of the brain stem against the clivus, however, the basilar artery could be displaced posteriorly away from the clivus. These had to be distinguished from other lesions arising near the clivus outside the brain stem. The posterior cerebral artery was elevated.

Original pages 678–679

Treatment

Because these tumors arise within the brain stem, a vital part of the brain, complete surgical removal is impossible. Treatment usually consists of biopsy to determine tumor type, followed by radiotherapy. Brain stem tumor biopsy presents two problems: i) obtaining tissue sufficient for histological diagnosis is difficult because surgeons fear that a large biopsy will worsen brain stem function and therefore take only a small specimen. Diffuse enlargement may make selection of the biopsy site difficult. C.T. and MRI now localize the tumor precisely, facilitating biopsy and definite tissue sampling.⁽⁶¹⁾ ii) Histology may differ within different parts of a tumor; a biopsy from one site may not reveal its true malignancy,⁽⁶²⁾ making prognosis less reliable.

Whether to biopsy patients whose clinical and radiological findings clearly indicate brain stem glioma remains controversial. Some give radiotherapy without biopsy, arguing that biopsy risks further brain stem damage and may not establish the precise tumor type or malignancy. The author believes that biopsy should be performed whenever possible in every patient to determine the tumor type first. However detailed C.T. or MRI may be about appearance and location, they cannot establish the type with certainty. Biopsy identifies benign or malignant tumor type, helps predict its course, and guides further treatment. This not only helps parents understand the prognosis but also improves knowledge of incidence and treatment results for each tumor type with radiotherapy or effective chemotherapy currently under investigation. Such knowledge will help improve future treatment of brain stem glioma.

C.T. and MRI distinguish tumors outside the brain stem from intrinsic tumors fairly clearly. They greatly improve surgical planning by showing tumor characteristics and location, cerebrospinal fluid obstruction or hydrocephalus, and extension outside the brain stem or into the fourth ventricle. The indications for surgery are as follows:

1. If diagnosis remains uncertain after C.T. or MRI and histology is needed for further treatment, perform surgical exploration and biopsy.

2. If C.T. and MRI show an intratumoral cyst close to the brain stem surface, open and evacuate the cyst and obtain tissue. Precise imaging localization makes this relatively straightforward, and surgery generally causes no further brain stem damage. Although not curative, it can produce temporary improvement and prolong survival. Before C.T. and MRI, diagnosis relied on pneumoencephalography (PEG), ventriculography, and angiography, which could not identify an intratumoral cyst. Exploration was needed to look for a surface suggesting a cyst within the brain stem tumor. Finding one was fortunate because draining it improved the patient's condition. If none was evident, searching further was inadvisable because it would damage the brain stem; biopsy of an evident tumor area was sufficient. The following example illustrates the effect of draining a cyst in a brain stem glioma.

Original pages 679–683

Case 1: Brain Stem Glioma with a Cyst

A 6-year-old boy had experienced frequent near-fainting episodes for a year before admission. He subsequently bumped into objects, fell frequently, and often dropped things. His speech and school performance deteriorated. He sometimes cried, became easily angry, and behaved aggressively. Two months before admission, he developed incomplete eyelid closure and weakness of both sides, worse on the left. Increasing unsteadiness left him unable to walk or sit unaided. His speech became indistinct, with projectile vomiting and drowsiness. On examination he answered questions poorly, was irritable, and spoke slowly with a drawl. There were sixth nerve palsy, bilateral facial palsy, bilateral extensor rigidity with occasional flexion of the left arm, increased deep tendon reflexes, and bilateral positive Babinski signs (Figure 7.39). The history and examination suggested a brain stem tumor. Vertebral angiography and ventriculography showed posterior bowing of the fourth ventricle and aqueduct of Sylvius without hydrocephalus (Figure 7.40), characteristic of a brain stem tumor. Exploratory suboccipital craniectomy was performed.

Operative technique. Open the posterior fossa as described for other tumors. After opening the dura, before inspecting the fourth ventricle, elevate each cerebellar tonsil and hemisphere to inspect the outside of the brain stem and the cerebellopontine angles, ensuring that there is no extrinsic lesion. Then separate the tonsils to inspect the floor and cavity of the fourth ventricle. To expose its anterior portion, divide the inferior vermis in the midline, preserving the vessels on either side, and separate the vermis and tonsils. A pale or light-yellow area on the ventricular floor indicates the cyst wall, which can be opened to drain the cyst without further functional loss. In this case the wall lay in the midline anterior to the striae medullares. Before opening it, a needle inserted in the midline of the ventricular floor aspirated pale tea-colored fluid (Figure 7.41A). The wall was then opened in the midline or at its thinnest point to expose the tumor and establish drainage, or marsupialization (Figure 7.41B). A microscope or loupe should be used at this stage to visualize the tumor clearly and remove a small portion safely for histology. Extensive or complete removal should not be attempted because it would damage the brain stem.

Histology showed astrocytoma. The patient was very drowsy for the first 2 postoperative days and became alert on the third. The striking change was almost complete disappearance of bilateral limb extensor rigidity. Only bilateral hyperreflexia remained, greater on the left. He was discharged on postoperative day 17 and returned for radiotherapy.

3. When tumor projects into the fourth ventricle or outside the brain stem and obstructs cerebrospinal fluid pathways, remove the extrinsic portion without damaging the brain stem. This reopens cerebrospinal fluid pathways, relieves brain stem compression, lowers raised intracranial pressure, and prolongs survival.^(63,64) There is now increasing support for resecting such tumors, whereas these patients were formerly considered beyond surgical help.^(65,66)

4. In a tumor with intratumoral hemorrhage, evacuation of the hematoma may allow recovery.

5. In hydrocephalus, a ventriculoperitoneal or ventriculoatrial shunt relieves raised intracranial pressure.

Radiotherapy. Because these tumors arise within the brain stem and cannot be removed completely, radiotherapy is necessary. The accepted dose is 5000–5500 rad, divided over 5–6 weeks. Improvement is generally apparent early during irradiation, with little further change later. Results depend on several factors, including location, tumor type, and early response. Patients who improve early during radiotherapy survive longer than those who show no change afterward.⁽⁶⁷⁾ After irradiation, patients with low-grade astrocytoma survive approximately 2–4 years, whereas those with glioblastoma survive no longer than 1 year.

Original pages 683–684

Thalamic Gliomas

Thalamic tumors are uncommon, accounting for approximately 3% of childhood brain tumors.⁽⁶⁸⁾ Most are astrocytomas, either benign or malignant, and usually arise in childhood or young adulthood. Oligodendroglioma and ependymoma are still less common.

Symptoms and signs. Manifestations vary with extension into structures adjacent to the thalamus: the basal ganglia, internal capsule, third ventricle, midbrain, corpus callosum, and hypothalamus. Details appear in Chapter 5. The commonest presentation is raised intracranial pressure with unilateral weakness and sensory loss, caused by damage to sensory fibers, thalamic nuclei, and internal capsule, together with tumor compression of the posterior third ventricle producing obstructive hydrocephalus. Headache, vomiting, blurred vision, and papilledema result. Experience shows that hemiparesis or hemiplegia is generally more prominent than sensory loss, although anatomically one might expect sensory disturbance first because the thalamus is a sensory center. Limb weakness results from internal capsule compression and progressively becomes hemiplegia when the capsule is destroyed. Patients complain of numbness in the weak limbs; this progresses to loss of every sensory modality when the tumor destroys the ventral posterolateral thalamic nucleus.⁽⁶⁹⁾

Homonymous hemianopsia may result from compression of the lateral geniculate body, optic tract, or optic radiation. Some patients develop upward conjugate gaze palsy and anisocoria when the quadrigeminal plate and pretectal midbrain are compressed from above. Large tumors may produce cerebellar dysfunction—ataxia, incoordination, and nystagmus—through damage to the cerebellorubrothalamic system.⁽⁷⁰⁾ Confusion, memory impairment, excessive sleep, and emotional lability may also occur through destruction of the dorsomedial thalamic nucleus and its fibers to the frontal cortex.⁽⁷¹⁾

In summary, a child with progressive hemiparesis and hemisensory deficit together with raised intracranial pressure should be suspected of having a thalamic tumor, usually a thalamic glioma.

Original pages 684–685

Investigations

C.T. or MRI currently demonstrates thalamic tumors best, showing their characteristics and extension into neighboring brain structures and thus better explaining the patient's symptoms and signs. They also show hydrocephalus and other mass effects, aiding treatment planning. The tumor may be hypodense, isodense, or hyperdense, with or without calcification. When calcification is present, the tumor is a benign glioma. Most tumors become hyperdense after contrast injection.

Previously, the main investigations were carotid angiography and PEG or ventriculography. Angiographic changes usually appeared late, when the mass was large, whereas PEG or ventriculography showed the tumor while still relatively small because the thalamus adjoins the ventricles. Important angiographic changes involve the lenticulostriate, anterior choroidal, and lateral posterior choroidal arteries and the internal cerebral and thalamostriate veins. The anterior and middle cerebral arteries show no changes specific to tumors in this region. On anteroposterior views, the lenticulostriate arteries are displaced laterally and downward (Figure 6.61). The anterior cerebral artery generally remains in the midline. Upward tumor expansion may separate the pericallosal arteries. Middle cerebral branches and the angiographic point are stretched laterally. Venous changes indicating a thalamic tumor are elevation and medial inclination of the thalamostriate vein and displacement of the internal cerebral vein across the midline, while the anterior cerebral artery remains central. On lateral views, the anterior choroidal artery enlarges; its proximal part is compressed and straightened and its distal part bows posteriorly (Figures 6.60, 6.61). The lateral posterior choroidal artery forms a wider arch, and elevation of the thalamostriate vein widens the venous angle.

PEG and ventriculography are reliable investigations. A characteristic, consistently observed feature is elevation of the central and posterior floor of the lateral ventricle on the tumor side, outlining the mass. The third ventricle bows toward the opposite side, especially posteriorly. This curvature indicates a deep tumor extending into the third ventricle. Its anterior part and the lateral ventricle enlarge because of obstruction in the posterior third ventricle.

Original pages 685–687

Treatment

The thalamus is a vital, deep brain structure, and these tumors infiltrate without a clear boundary. Resection in this region is therefore considered contraindicated: it increases functional loss without allowing complete removal or cure. Most treatment consequently relies on radiotherapy. Surgery chiefly aims to obtain tissue for diagnosis and establish a ventriculoatrial or ventriculoperitoneal shunt to lower intracranial pressure from cerebrospinal fluid obstruction at the posterior third ventricle. Radiotherapy without biopsy to establish tumor type is inappropriate because the lesion may not respond, exposing the patient to irradiation without benefit. Treatment results would also be impossible to interpret. Biopsy methods are:

1. Craniotomy: transcallosal approach or transventricular approach.

2. C.T.-guided stereotactic biopsy.

The transcallosal approach enters the lateral ventricle through the corpus callosum and exposes the thalamus well whether the ventricle is small or large. Perform a posterior parietal craniotomy near the midline and separate the medial parietal surface from the falx cerebri, as in pineal tumor surgery. Incise the corpus callosum anteroposteriorly to enter the lateral ventricle and expose the thalamic tumor for straightforward biopsy.

For the transventricular approach, make a cortical incision in the posterior parietal lobe approximately 4 cm from the midline. Separate the white matter deeply toward the lateral ventricle, expose the thalamus, and take a biopsy. Hydrocephalus makes ventricular access easier.

The author has not performed C.T.-guided stereotactic biopsy but considers it suitable for deep thalamic tumors. Caution is necessary because vascular injury may cause intrathalamic hemorrhage, which cannot be controlled immediately as it can during open biopsy.

In summary, thalamic glioma is treated with radiotherapy and, when obstructive hydrocephalus is present, a shunt. Improvement may last months or years, depending on tumor malignancy.

Original pages 687–688

Ependymoma

Ependymoma is a benign tumor arising from ependymal cells, which belong to the neuroglial group. It occurs mainly in children and adolescents and originates in the ventricular walls, most often in the fourth ventricle, followed by the lateral ventricles, third ventricle, and aqueduct of Sylvius. It may grow into the ventricle or brain substance, producing symptoms according to location. It can occur in either the cerebrum or posterior fossa.

Cerebral ependymomas commonly occur in the parietal lobe and expand into the brain. Some grow to the cortical surface and extend into several lobes, as in Figure 7.42.

Fourth ventricular ependymomas usually adhere to the posterior ventricular floor near the obex and extend anteriorly within the ventricle or posteriorly into the cisterna magna. They may pass through the foramen magnum into the spinal canal. At surgery, opening the dura reveals tumor filling the cisterna magna. This portion is usually well defined and easily removed. Adherence to the fourth ventricular floor is the main obstacle to complete excision because this region contains vital respiratory and cardiac centers and cranial nerve nuclei. Attempted dissection may be fatal, while the residual attachment allows tumor regrowth.

Original pages 688

Symptoms and Signs

Most manifestations are those of raised intracranial pressure because the tumor obstructs cerebrospinal fluid flow before producing localizing signs. Tumors arising in the cerebrum and expanding within brain tissue produce focal symptoms according to their location.

Fourth ventricular tumors likewise present first with raised intracranial pressure, often early because cerebrospinal fluid pathways are readily obstructed. In young children, the head frequently becomes abnormally large. Cerebellar and brain stem signs usually appear later. Extension into the spinal canal may also cause neck stiffness and spasm of the neck and shoulder muscles, producing a tilted neck with limited movement.

Original pages 688–689

Diagnosis

Before C.T. and MRI, carotid angiography was used for suspected supratentorial lesions and vertebral angiography for suspected posterior fossa tumors. If localization remained unclear, air ventriculography (Figure 6.133) or contrast ventriculography (Figure 7.43) was performed.

C.T. and MRI now provide excellent investigation, clearly showing tumor boundaries, location, size, and hydrocephalus. Angiography and ventriculography are therefore no longer performed for this purpose.

Original pages 689–690

Treatment

Because the tumor is benign, surgery aims at complete removal to prevent recurrence. Its location and size must nevertheless be considered. Sites such as the fourth ventricular floor, aqueduct of Sylvius, and third ventricle are dangerous: attempting complete removal may cause postoperative death. Establishing the diagnosis, inserting a cerebrospinal fluid shunt, and giving radiotherapy is preferable. Cerebral tumors may be very large and involve several lobes, likewise making attempted total removal highly dangerous.

The following example illustrates successful surgery for a fourth ventricular ependymoma.

Original pages 690–692

Case 1: Ependymoma of the Posterior Fourth Ventricle

A 21-year-old woman presented with headache, vomiting, and blurred vision for 3 months. More recently she had slight unsteadiness to either side but could still work. Two weeks before admission she developed diplopia and worsening headache. Examination showed bilateral papilledema, right sixth nerve palsy, good limb strength, a slightly ataxic gait without consistent deviation to either side, and bilateral corticospinal tract signs. A posterior fossa tumor was diagnosed. Angiography showed hydrocephalus, and contrast ventriculography demonstrated a mass in the posterior fourth ventricle obstructing cerebrospinal fluid flow and causing marked ventricular enlargement (Figure 7.43A, B).

Tumor removal. Suboccipital craniectomy was performed. Opening the dura revealed a well-defined grayish-pink tumor filling the cisterna magna, with part extending into the spinal canal and part spreading alongside the medulla (Figure 7.44A). Structures requiring protection were i) the medulla; ii) lower cranial nerves; iii) the posterior inferior cerebellar artery; and iv) the fourth ventricular floor. Starting dissection from below was inconvenient because the mass had to be elevated with a spatula to expose the spinal cord and medulla; removing the spatula allowed it to fall back and obscure the field. Suction within the tumor was particularly inadvisable because deeper aspiration could injure the spinal cord, medulla, or ventricular floor. The author considered removal from above easier: with the patient sitting, the tumor's weight drew it downward and clearly exposed its upper margin. Complete removal was achieved without damage to the medulla or fourth ventricle (Figure 7.44B). The ventriculogram showed enlargement of the anterior half of the fourth ventricle and a clear tumor boundary. Dissection therefore began along the tumor margin adjacent to the posterior vermis to enter the ventricle. This clearly exposed the tumor boundary and ventricular floor, which was completely covered with cotton for protection. The covering was extended progressively downward as dissection proceeded inferiorly. The tumor descended under its own weight, revealing its origin at the side of the fourth ventricle. Dividing this attachment freed the mass without dissection near the spinal cord or beside the medulla (Figure 7.45).

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When the tumor lies high in the fourth ventricle, removal requires the method illustrated in Case 2.

Original pages 692–694

Case 2

The patient presented with raised intracranial pressure. Investigation disclosed a fourth ventricular tumor. Opening the posterior fossa revealed tonsillar herniation down to C2–3 (Figure 7.46), with no tumor visible on the cerebellar surface. Separating the tonsils exposed tumor at the foramen of Magendie. Because this opening was too small for easy access to the tumor's sides and anterior portion, the posterior vermis was divided in the midline while preserving vessels on either side (Figure 7.47). Retraction improved anterior and lateral exposure, allowing access to the anterior fourth ventricle and identification of its floor. After separating tumor from the floor, the floor must always be protected with cottonoid before suction and cutting. Proceeding gradually inferiorly and laterally permits complete removal. Tumor adherent to the ventricular floor must not be stripped off, because doing so endangers cranial nerve nuclei and the respiratory and cardiac centers. A thin adherent layer should be left in place (Figure 7.48).

Tumor extending into the cerebellar hemisphere should also be removed. Extension through the foramen of Luschka into the cerebellopontine angle should not be removed because it commonly adheres to the brain stem and cranial nerves. Tumor extending into the aqueduct of Sylvius and obstructing cerebrospinal fluid flow may, however, be removed because it does not infiltrate the aqueductal gray matter. In this second case, removal exposed a large aqueduct through which the third ventricle could be seen.

Original pages 694–695

Choroid Plexus Papilloma

Choroid plexus papilloma is a benign, slowly growing tumor arising in the choroid plexus. It is therefore intraventricular and well circumscribed, and complete surgical removal cures the disease. Its ventricular location commonly causes hydrocephalus. Despite being benign, it can be fatal if diagnosis and removal do not precede complications such as severe hydrocephalus or intraventricular hemorrhage.

Hydrocephalus may result from three factors: I) excessive cerebrospinal fluid production by the tumor; II) obstruction of cerebrospinal fluid pathways by the tumor; and III) repeated bleeding into the cerebrospinal fluid, increasing protein and causing adhesions.

Excess cerebrospinal fluid production is supported by resolution of hydrocephalus after removal of a nonobstructing intraventricular tumor.^{(72,73,74,75)} Obstruction occurs early in the narrow third and fourth ventricles. A tumor at the lateral ventricular trigone may enlarge the temporal or occipital horn disproportionately to the rest of the ventricle. Removal restores normal cerebrospinal fluid pathways and resolves the hydrocephalus.

Some patients present with subarachnoid and intraventricular hemorrhage. If they survive the bleeding, increased cerebrospinal fluid protein, adhesions, or leptomeningeal fibrosis impair circulation and absorption, producing hydrocephalus.

Choroid plexus papilloma accounts for approximately 0.5–0.6% of all brain tumors. Most occur in children within the first 2 years of life, predominantly in the lateral ventricle. In adults they usually occur in the fourth or third ventricle.

Some lateral ventricular papillomas contain calcification, making the highly vascular mass firmer. At surgery they may resemble intraventricular meningiomas; both have a choroid plexus pedicle and receive blood from choroidal arteries. They may nevertheless be distinguished because a meningioma has a smooth rather than papillary or cauliflower-like surface, although it may be nodular, and is firmer.

Original pages 695–696

Symptoms and Signs

The commonest initial manifestation is raised intracranial pressure or hydrocephalus. Because the tumor occurs in young children, an infant may initially develop normally and later develop an enlarged head, possibly with vomiting, restlessness, or drowsiness. Older children may complain of headache. In the author's experience, all children presented with head enlargement and no focal signs. A large papilloma in one lateral ventricle may cause hemiparesis through marked enlargement of that ventricle or direct compression of the corticospinal tract. Fourth ventricular papillomas likewise present with raised intracranial pressure; cerebellar signs are uncommon until the mass is large enough to produce cerebellar and cranial nerve signs.

Intraventricular or subarachnoid hemorrhage from the tumor may cause sudden severe deterioration, followed by drowsiness or death from very high intracranial pressure.

Original pages 696–697

Diagnosis

Raised intracranial pressure, an enlarged head in a child, absence of focal neurological deficits, and increased cerebrospinal fluid protein or xanthochromia should always suggest an intraventricular tumor.

Sampling cerebrospinal fluid in choroid plexus papilloma is hazardous by either lumbar or ventricular puncture; neither is now necessary for this purpose. Lumbar puncture in raised intracranial pressure may cause tonsillar herniation. Another observed phenomenon is a rapid rise in cerebrospinal fluid pressure after fluid removal for examination or pressure relief, even when hydrocephalus had previously progressed slowly. The patient may become unconscious or die rapidly. Lowering cerebrospinal fluid pressure stimulates massive new fluid production and often causes subependymal and paraventricular petechial hemorrhages.⁽⁷⁶⁾

C.T. and MRI now clearly demonstrate intraventricular tumors, displacing older investigations. Before C.T., the investigative sequence was as follows:

1. Skull radiographs show changes from raised intracranial pressure: sutural separation, head enlargement, and sometimes calcification. These are not specific to choroid plexus papilloma.

2. AIR CONTRAST STUDIES. Air introduced into the ventricle outlines the white tumor against the dark air. This demonstrates its boundaries fairly clearly (Figure 6.133) and was considered a specific investigation for intraventricular tumors, but is now rarely performed.

3. CEREBRAL ANGIOGRAPHY. This is not particularly helpful for precise tumor boundaries or localization. It shows hydrocephalus and the feeding vessels, helping surgical removal with less blood loss. Tumor staining may be visible. Angiography is difficult and hazardous in small children and is therefore seldom performed.

4. C.T. The tumor is clearly seen both before and after contrast because its intraventricular density differs from cerebrospinal fluid. It is isodense on unenhanced C.T. and becomes strikingly hyperdense with enhancement.⁽⁷⁷⁾ (Figure 7.52.) C.T. shows the boundaries, size, location, and hydrocephalus and is therefore the best diagnostic method.

5. MRI demonstrates location, boundaries, size, and hydrocephalus as well as C.T.

Original pages 697–698

Treatment

The best treatment for choroid plexus papilloma is complete surgical removal with minimal injury to neighboring brain tissue. Because the tumor is benign, complete removal is curative. Partial removal followed by radiotherapy is ineffective.

Tumor removal. Operative techniques and complications differ somewhat with the tumor's location, as follows.

Original pages 698–699

1) Choroid Plexus Papilloma of the Fourth Ventricle

For a fourth ventricular choroid plexus papilloma, perform suboccipital craniectomy without extensive lateral exposure because the tumor is within the ventricle. Before opening the dura, release cerebrospinal fluid through a ventriculostomy to lower intracranial pressure. Tumor seldom protrudes externally when the dura is opened because it obstructs cerebrospinal fluid pathways before becoming very large. The key to removal without major blood loss is division of the vessels supplying the choroid plexus. These arise from the posterior inferior cerebellar artery (PICA). The choroid plexus lies at the posterior velum of the fourth ventricle. Separate and elevate the cerebellar tonsils to expose PICA medially between the tonsil and medulla. Following the arteries distally brings the two PICAs close together. Divide the uvula and nodulus of the vermis in the midline to expose the posterior velum. Here the choroidal artery branches from PICA before PICA turns laterally to supply the vermis and cerebellar hemisphere (Figure 7.49); PICA must be preserved during surgery. In choroid plexus papilloma, the choroidal arteries are enlarged and prominent and form the tumor pedicle. Coagulate them with bipolar forceps and divide them on both sides. The tumor immediately shrinks. It can then be removed easily without blood loss. This method permits complete removal in every case because the papilloma has a choroid plexus pedicle and a clearly defined boundary all around. Direct suction and cutting to debulk the tumor before dividing its feeding vessels is particularly inadvisable: it causes substantial bleeding and obscures vital structures, including the medulla, cranial nerves, and fourth ventricular floor.

Original pages 699

2. Choroid Plexus Papilloma of the Lateral Ventricle

Tumors in this ventricle can be subdivided by location: the frontal horn adjacent to the foramen of Monro, the body of the lateral ventricle, and the trigone. The trigone is the most frequent site. Each location requires knowledge of the relevant cerebral anatomy and a somewhat different operative technique. The approaches may therefore be classified by tumor location as follows.

Original pages 699–700

2.1 Papilloma of the Trigone

The two common tumors in the trigone are choroid plexus papilloma and meningioma. Other tumors, including ependymoma, astrocytoma, and epidermoid tumors, may also occur here. Meningioma is more common than papilloma. These tumors are supplied chiefly by the anterior choroidal artery and sometimes also by the posterior choroidal artery, as demonstrated by carotid and vertebral angiography. These vessels are usually not greatly enlarged and are tortuous.

Important anatomical structures that must always be considered when operating here are the sensory speech center (Wernicke's or perceptive speech center) in the dominant hemisphere, the optic radiation, the tail of the caudate nucleus, and the pulvinar of the thalamus. Any approach must account for their functions and minimize functional loss. Several routes are available. However, these tumors are often large because the ventricular location is a silent area, producing no focal symptoms, and surgery is therefore difficult. Except for small tumors, no approach is completely satisfactory for exposing every part of the tumor and its feeding vessels through a single cortical incision.

Operative technique. Three approaches to trigonal tumors are commonly used (Figure 7.50).

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Original pages 700–701

2.1.1 Lateral Parietotemporal Approach

This provides easy access to a trigonal tumor because only a thin layer of brain separates the cortex from the tumor. It has three disadvantages.

First, in the dominant hemisphere it causes postoperative dysphasia through damage to the angular and supramarginal gyri of the temporoparietal lobe, the location of the sensory speech center.

Second, part of the optic radiation is damaged because the incision crosses its fibers perpendicularly as they run toward the occipital lobe, causing a homonymous quadrantanopia.

Third, a large tumor obscures the anterior and posterior choroidal arteries. Early division of these vessels to reduce the tumor's blood supply is difficult. Piecemeal removal may therefore cause heavy, uncontrollable, and potentially fatal blood loss.

Original pages 701–702

2.1.2 Posterior Middle Temporal Gyrus Incision

The incision is made in the posterior portion of the middle temporal gyrus (Figures 7.50 and 7.51). This gives good access to the tumor and anterior choroidal artery, allowing easy interruption of the tumor's blood supply. Removal is therefore safe, with little blood loss and no injury to neighboring structures. Possible disadvantages include postoperative homonymous quadrantanopia, probably less extensive than with the first approach because the incision runs parallel to the optic radiation fibers. In the dominant hemisphere, some speech disturbance may still occur.

Original pages 702–704

2.1.3 Parieto-occipital Paramedial Incision

This is the safest approach, particularly for a tumor in the dominant hemisphere, because it avoids the optic radiation, which runs inferolaterally in the parietal lobe, and the sensory speech center. The cortical incision is made at the level of the parieto-occipital fissure, approximately 3–4 cm from the midline, and extends about 4 cm anteriorly (Figures 7.50 and 7.51). It provides access to feeding vessels, especially the posterior choroidal artery approaching medially. However, the anterior choroidal artery is less accessible than with the first two approaches because it lies lateral and inferior to the tumor. Ventricular enlargement from hydrocephalus permits the tumor to be turned to expose the vessels.

Thus, no single approach is best for removing a trigonal papilloma. The surgeon should be skilled in all the approaches described and thoroughly understand the anatomy and functions of this region. The operation must be individualized according to tumor location, size, feeding vessels, and vascularization demonstrated by C.T. and angiography. If necessary, more than one approach may be combined to interrupt both the anterior and posterior choroidal arterial supply completely. Complete, safe removal without blood loss is then possible. Nevertheless, even an easily removed tumor may be followed by fatal complications, which require careful attention and prevention, as the following case illustrates.

Case example. An 18-month-old child had progressive head enlargement for approximately six months and a right squint for one month. Examination showed hydrocephalus and a right sixth nerve palsy, without other focal signs. C.T. showed a mass at the trigone of the left lateral ventricle and marked hydrocephalus (Figure 7.52).

The tumor was within the left lateral ventricle of the dominant hemisphere, clearly circumscribed, and extended into the occipital horn. The images suggested that the glomus of the choroid plexus, or tumor pedicle, would be readily visible through a parieto-occipital paramedial incision. A parieto-occipital craniotomy was therefore performed, and the dura was opened after partial cerebrospinal fluid drainage. The cortical incision was placed as described above. On entering the ventricle, a pink-red tumor was seen. Slight rotation exposed the choroid plexus and feeding vessels. Cottonoids covered the ventricular passage toward the frontal horn to prevent blood entering the horn and obstructing the foramen of Monro. The vessels passing from the choroid plexus into the tumor were coagulated with bipolar forceps and divided. The tumor immediately shrank and was removed without any blood loss. After complete removal and partial suction of cerebrospinal fluid, the brain collapsed markedly because the ventricle was very large. Multiple bridging veins tore, causing sudden, widespread subdural hemorrhage. The bleeding sites could not be found. The child went into shock and died.

This case shows that selecting the correct approach can make tumor removal straightforward. However, choroid plexus papilloma may cause hydrocephalus with extreme ventricular enlargement, as in this child. Excessive cerebrospinal fluid drainage should therefore be avoided. Saline should be maintained within the ventricle to prevent excessive collapse. This error regrettably cost the child's life.

Original pages 704

2.2 Choroid Plexus Papilloma of the Body of the Lateral Ventricle

The tumor may arise in the middle of the ventricular body or near the foramen of Monro and extend into the frontal horn. Papillomas in the body are difficult to remove because nearby motor and sensory fibers place these functions at risk. The choroid plexus and papilloma are usually supplied by the posterior choroidal artery. As the tumor grows, it obstructs cerebrospinal fluid flow from the temporal and occipital horns, which consequently tend to enlarge more than the other ventricular portions.

Tumor removal. A cortical incision directly through the motor or sensory cortex should be avoided because it causes disability. Either of the following two approaches may be used.

Original pages 704–706

2.2.1 Middle Frontal Gyrus Incision

An incision is made in the posterior middle frontal gyrus, anterior to the motor cortex, toward the ventricle (Figure 7.53). This is suitable for a tumor in the anterior ventricular body, adjacent to the foramen of Monro, or extending into the frontal horn. Make a 3–4 cm incision along the gyrus and separate the white matter toward the ventricle. If C.T. shows marked ventricular enlargement, proceed straight inward; with less enlargement, direct the approach slightly medially. Within the ventricle, the septum pellucidum forms the medial wall, the caudate nucleus lies laterally, and the thalamus lies below, with the thalamostriate vein between the latter two structures. The interventricular foramen of Monro lies inferiorly and leads into the third ventricle. Its anterior border is the fornix and its posterior border is the thalamus. The choroid plexus runs into the foramen. As elsewhere, gently rotate the tumor to expose the choroid plexus at the foramen of Monro, then follow it posteriorly along the floor of the lateral ventricle. Coagulate with bipolar forceps and divide the tumor's feeding vessels within the choroid plexus. Usually the very large ventricle permits the tumor to be rotated or displaced sufficiently to expose the plexus. In a very large tumor, such as the papilloma at the foramen of Monro shown in Figure 7.54, the ventricle is markedly enlarged, yet entry through a posterior middle frontal gyrus incision may reveal neither the choroid plexus nor its tumor-feeding vessels. In this situation, use bipolar coagulation and remove small portions of tumor until the choroidal vessels can be seen; this is sufficient. Blood loss is relatively slight with this method. Direct suction of the tumor should be avoided because it causes substantial bleeding. After coagulation and division of the choroidal vessels, the remaining papilloma immediately shrinks and can easily be removed as a whole. Ensure that the choroid plexus attached to the tumor has been completely divided, since traction on an undivided attachment may cause further bleeding.

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Original pages 706–707

2.2.2 Transcallosal Approach

This approach is suitable for tumors in the middle of the lateral ventricular body because it avoids incisions through motor and sensory cortex and the resulting loss of function. It is also suitable for tumors extending into both ventricles (Figure 7.55). Preoperative cerebral angiography should include the venous phase to locate the large veins draining into the superior sagittal sinus. This helps position the craniotomy so that brain retraction does not damage these veins.

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Technique. Position the patient supine with the head facing straight ahead. Place the posterior craniotomy margin approximately 3 cm behind the coronal suture and the anterior margin 5 cm in front of it. Extend the medial margin slightly across the midline to the opposite side. After draining ventricular cerebrospinal fluid, open the dura with its flap based on the superior sagittal sinus. Approach the corpus callosum at a site without a large bridging vein entering the sinus. Occasionally a less important bridging vein must be divided to allow greater lateral retraction of the medial frontal lobe. Gently separate the frontal lobe from the falx cerebri with a self-retaining retractor. The cingulate gyrus and pericallosal artery will be seen over the corpus callosum; protect them carefully. Bring in the microscope at this point. After adequately retracting these structures laterally, incise the corpus callosum approximately 3 cm from the genu and extend the incision posteriorly for about 3 cm. Keep it 0.5–1 cm off the midline to avoid the bodies of the fornices, which lie close together beneath the middle of the corpus callosum. Injury to the fornix may impair memory. Passing through the corpus callosum enters the ventricle. Tumor removal follows the principles already described: expose, coagulate, and divide the feeding vessels first, then remove the tumor completely in pieces. The thalamostriate and septal veins must also be preserved.

Original pages 707–708

Results of Treatment of Choroid Plexus Papilloma

If the tumor is completely removed before the brain is damaged by hydrocephalus, a very large mass, or spontaneous hemorrhage, the results are excellent. The patient is cured, with normal cerebral development and function, because the tumor is benign and well circumscribed. Hydrocephalus due to excess cerebrospinal fluid production by the papilloma or obstruction of cerebrospinal fluid pathways resolves after tumor removal. However, when spontaneous tumor hemorrhage also contributes to hydrocephalus, adhesive obstruction of the basal cisterns and subarachnoid space may leave persistent hydrocephalus after removal. Some patients require a cerebrospinal fluid shunt for its resolution.

Results are poor for malignant papilloma because it infiltrates without clear boundaries and is difficult to remove completely. Surgery therefore cannot cure it, and radiotherapy does not change the outcome.

Postoperative radiotherapy is unnecessary for papilloma because it is benign and can be completely removed.

Original pages 708

MEDULLOBLASTOMA

Medulloblastoma is a malignant cerebellar tumor accounting for approximately 20% of intracranial tumors in children. It occurs most often between ages 3 and 8 years.⁽⁷⁸⁾ It is occasionally seen in older children and very rarely in adults.

Location. As described in the pathology chapter, medulloblastoma arises in the cerebellar midline, the vermis, originating in the roof of the fourth ventricle at the posterior medullary velum. Its growth compresses and destroys the vermis, which appears broadened and pale at operation (Figure 7.57). Larger tumors extend into the cerebellar hemispheres. Most commonly, the tumor grows into and fills the fourth ventricle. It frequently extends downward into the cisterna magna and upper cervical spinal canal.

Medulloblastoma grows rapidly and tends to disseminate tumor cells through the cerebrospinal fluid pathways. After its removal, tumor deposits are frequently found throughout the central nervous system, including the spinal subarachnoid space, cauda equina, cisterns, and surfaces of the cerebellum and cerebrum. It is therefore a highly malignant posterior fossa tumor.

Original pages 708–709

Symptoms and Signs

The symptoms and signs of vermian tumors described in Chapter 5 may occur with a large medulloblastoma. Because it arises in the roof of the fourth ventricle, its characteristic clinical features are truncal ataxia and relatively rapid development of raised intracranial pressure from obstruction of cerebrospinal fluid flow at the fourth ventricle or aqueduct. Patients tend to fall forward or backward while sitting or standing, although limb incoordination may be absent or slight when examined lying down. Horizontal nystagmus may be absent but can appear when the tumor extends into a cerebellar hemisphere. Sudden deterioration sometimes follows hemorrhage or hydrocephalus with herniation.

Vomiting and headache are common. Vomiting results from raised intracranial pressure and pressure on the vomiting center in the floor of the fourth ventricle. It often occurs on waking in the morning: during sleep, respiration slows, PCO₂ rises, and cerebral venous return is less efficient than in the upright position, raising intracranial pressure. Patients feel better after vomiting because subsequent hyperventilation lowers the pressure. The same explanation applies to headache that is worst on waking or late at night, sometimes severe enough to awaken the patient, and disappears or improves after vomiting. Headache progressively worsens as the mass enlarges or cerebrospinal fluid obstruction increases. Young children may develop head enlargement, usually not very marked because the rapidly growing medulloblastoma produces symptoms before substantial enlargement occurs.

Original pages 709

Diagnosis

Accurate diagnosis from the history and clinical signs alone may be difficult. Nevertheless, the patient's age, signs localizing the lesion to the vermis, relatively rapid symptom development, and raised intracranial pressure should suggest medulloblastoma before other tumor types. Definitive diagnosis requires examination of removed tumor tissue.

Original pages 709–710

Investigations

C.T. is important for suggesting the diagnosis. Medulloblastoma usually appears as a large, round, well-circumscribed hyperdense mass in the middle of the cerebellum, filling the fourth ventricle (Figure 6.102a). Contrast produces marked, uniform enhancement throughout the tumor.⁽⁷⁹⁾ On C.T., the absence of cysts and calcification distinguishes medulloblastoma from ependymoma, astrocytoma, and hemangioblastoma,⁽⁷⁹⁾ although very large tumors may contain multiple cysts (Figure 7.56).

MRI also shows the tumor very clearly. It is hypointense relative to brain on T₁-weighted images and hyperintense and homogeneous on T₂-weighted images.⁽⁸⁰⁾

Angiography shows displacement of PICA and its branches and sometimes faint tumor staining, together with features of hydrocephalus. Skull radiographs show changes from raised intracranial pressure, such as separation of the sutures. Neither angiography nor skull radiography is now performed for this purpose, because they fail to show the mass clearly; C.T. or MRI gives much better results.

For dissemination into the spinal subarachnoid space, MRI is the best method of visualizing tumor deposits. If MRI is unavailable, myelography can also demonstrate spinal tumors.

Original pages 710–714

Treatment

The current standard treatment for medulloblastoma is surgical removal followed by irradiation of the entire neuraxis, because the tumor spreads through cerebrospinal fluid and is radiosensitive. Surgery establishes the tumor type and reopens cerebrospinal fluid pathways, allowing obstructive hydrocephalus to resolve without shunting. Shunting in medulloblastoma carries a risk of disseminating tumor cells to other parts of the body. Removal also relieves pressure on the brainstem and cerebellum. The operative options currently used are:

1. Removal of all visible tumor (radical resection), followed by radiotherapy.

2. Partial resection to relieve pressure on surrounding brain and reopen cerebrospinal fluid pathways, followed by radiotherapy.

3. Biopsy and ventriculoperitoneal shunting, followed by radiotherapy.

All three methods have advantages and disadvantages.

Total resection. Attempting complete removal in the fourth ventricle is very hazardous and has high mortality. Survivors, however, live longer and remain symptom-free longer than after other operations. Comparing total with partial resection, Raimondi and Tomita⁽⁸¹⁾ reported one-year survival of 92% and five-year survival of 42% after total removal. After partial removal, survival was shorter: 65% at one year and only 30% at five years.

Technique. The author most often uses the sitting position, although lateral, semiprone, or prone positioning is also possible. Sitting offers good exposure at eye level but has the disadvantages and potential complications already described. Make a midline incision and a moderately wide suboccipital craniectomy. Extensive lateral exposure is unnecessary because the tumor is in the cerebellar midline. After opening the dura, tumor may protrude through the foramen of Magendie, or it may remain hidden behind a bulging, broadened vermis. Sometimes gray-pink sheets of disseminated tumor cover the cerebellar hemispheres and tonsils (Figure 3.51). This is characteristic of medulloblastoma; tumor cells may already have disseminated into the cisternal and spinal cerebrospinal fluid. For this reason, postoperative irradiation of the entire neuraxis is advisable.

To expose the tumor, divide the inferior vermis in the midline while preserving PICA branches and veins, and separate the two sides. The length of the vermian incision depends on tumor size. Before resection, cover the subarachnoid space around the medulla with cotton to prevent tumor cells entering the spinal subarachnoid space. If the tumor can be lifted from the fourth ventricular floor, cover the floor with cotton before cutting the tumor to protect this part of the brain. The tumor is gray-pink, soft, and easily aspirated. Suction combined with bipolar coagulating forceps permits complete removal. Begin internally to reduce tumor bulk and make its margins clearer, then remove the remainder. Where tumor involves important structures such as the dentate nucleus or cerebellar peduncles, complete removal may be dangerous or disabling. If frozen section confirms medulloblastoma, these portions may be left for destruction by radiotherapy. Highly vascular residual tumor, however, may bleed postoperatively and cause death. In such cases, only complete removal ensures that no postoperative hemorrhage arises from residual tumor.

Complete removal of a very large medulloblastoma, or any other large tumor, may itself cause fatal complications. A two-year-old child presented with a one-year history of head enlargement. During the preceding three months, gait had become unsteady, progressing to inability to sit or stand without falling forward or backward. Examination and C.T. showed a very large vermian tumor with hydrocephalus. The tumor was completely removed. Both cerebellar hemispheres then collapsed downward; the operation was being performed in the sitting position. All the bridging veins draining into the transverse sinus became stretched and eventually tore, causing a subdural hematoma and cerebellar swelling. The child died from brain swelling. This experience led the author subsequently to operate with the patient lying down rather than sitting and to favor partial rather than attempted complete resection when frozen section identifies medulloblastoma.

Partial resection. Its aims are: i) to reduce tumor bulk and brain compression; ii) to establish the tumor type; and iii) to reopen cerebrospinal fluid pathways. It is appropriate for very large medulloblastomas such as the example on C.T. (Figure 7.56), filling the vermis and fourth ventricle and compressing the cerebellar hemispheres.

Technique. Expose the posterior fossa as in the first method, but remove bone widely around the exposure and also remove the atlas arch to aid decompression. After opening the dura, tumor is seen on the vermian surface, spreading widely and severely compressing the cerebellar hemispheres. It extends into the cisterna magna as far as C₁ (Figure 7.57). Attempted complete removal would be very dangerous, so only partial resection is performed. First coagulate and divide surface vessels, then open a moderately wide window into the tumor. Use suction and bipolar coagulation to remove it from within toward its margins. This reduces fourth ventricular compression and may restore a passage for cerebrospinal fluid. Tumor in the cisterna magna may be an extension of the mass above; if separable from the medulla, remove it to open the foramen of Magendie and permit cerebrospinal fluid flow. In other cases, disseminated cells have grown to cover the entire medulla. Do not attempt to remove this portion because of the extreme danger; use radiotherapy. Biopsy alone may suffice in such a case, followed by radiotherapy once medulloblastoma is confirmed. Even with biopsy alone, a wide craniectomy and dural opening decompress the posterior fossa and reduce brainstem compression. Some patients require a ventriculoperitoneal shunt to relieve obstructive hydrocephalus and improve comfort during radiotherapy.

Original pages 714–715

Radiotherapy

Medulloblastoma is particularly radiosensitive. Every patient should therefore receive radiotherapy after surgery and histological confirmation. Irradiation without a tissue diagnosis should not be performed, because some cerebellar tumors can be cured by surgery alone.

Radiotherapy should follow surgical relief of posterior fossa pressure and hydrocephalus. Irradiation before decompression may be dangerous because the resulting reactive brain swelling further increases intracranial pressure. Starting irradiation without first relieving pressure also loses valuable time for preventing pressure-related optic nerve damage. If raised pressure persists during almost a month of radiotherapy, the patient may become blind. Because medulloblastoma tends to disseminate through cerebrospinal fluid, particularly after surgery, irradiation must encompass both the head and spine along the entire neuraxis.

The current neuraxis irradiation schedule gives 5400 rads to the posterior fossa, 4000 rads to the rest of the brain, and 3500 rads to the spinal cord.⁽⁸²⁾

Original pages 715

Results of Treatment

Patients with medulloblastoma improve immediately after surgery and radiotherapy. If neither the tumor nor the operation has impaired brain function, they can return to work. Nevertheless, even after complete removal and full radiotherapy, the tumor invariably recurs. A review of recent reports covering patients of all ages treated with surgery and irradiation gives a five-year survival rate of approximately 60%. Following complete resection and a full course of radiotherapy, five-year survival reaches 77%.⁽⁸²⁾ It is generally accepted that postoperative radiotherapy prolongs survival by approximately 1–2 years compared with surgery alone.

Original pages 715–716

Treatment of Recurrent Tumor

Recurrent medulloblastoma has three treatment options: I) repeat surgical removal; II) radiotherapy; or III) surgery followed by radiotherapy. The choice depends on the patient's general condition and neurological impairment, the location and size of recurrence, the radiation dose already given, and the interval since initial treatment. Recurrent symptoms always require repeat C.T. or MRI to guide treatment. If there is a localized mass and the patient can tolerate surgery, repeat removal is advisable. If the patient's condition precludes surgery, radiotherapy is preferable and often improves symptoms.

Original pages 716

PINEAL GLAND TUMORS

Tumors in the pineal region include those arising from the pineal gland itself—pineocytoma, pineoblastoma, pinealoma (germinoma), teratoma, and carcinoma—and tumors of nearby structures. These include the quadrigeminal plate, upper midbrain, posterior third ventricle, and splenium of the corpus callosum, usually astrocytomas, ependymomas, or choroid plexus papillomas. These tumors are appropriately considered together because they produce similar symptoms, signs, and treatment problems.

Original pages 716–717

Symptoms and Signs

Patients with pineal gland tumors have three groups of symptoms and signs:

1. Raised intracranial pressure from hydrocephalus: headache, vomiting, papilledema, and head enlargement in young children.

2. Compression of the quadrigeminal plate produces important localizing signs, including Parinaud's syndrome: paralysis of upward conjugate gaze, dilated pupils unreactive to light (reflex iridoplegia), deafness, and an ataxic gait.

3. Hypothalamic dysfunction results from hypothalamic destruction by an ectopic suprasellar pinealoma or from hydrocephalus. Manifestations include diabetes insipidus, hyperthermia, cachexia, and precocious puberty.

These manifestations were described in detail in Chapter 5.

Original pages 717–718

Diagnosis

A pineal gland tumor can be diagnosed confidently when focal signs indicate damage to the quadrigeminal plate. Most patients present with raised intracranial pressure, and examination reveals Parinaud's phenomenon. Hypothalamic symptoms may or may not coexist. If hypothalamic symptoms are the presenting complaint, suprasellar disease must first be excluded.

Other investigations supporting diagnosis include skull radiographs, contrast ventriculography, and angiography. These methods are now obsolete for this purpose, with C.T. and MRI remaining in use.

1. Skull radiographs show two important changes: signs of raised intracranial pressure and calcification in the pineal region. A calcified pineal gland is not normally found in children, so calcification here should suggest a pineal tumor. It does not, however, identify the tumor type.

2. VENTRICULOGRAPHY establishes the diagnosis by demonstrating hydrocephalus and outlining the tumor in the posterior-superior third ventricle. The aqueduct of Sylvius is usually not seen; if visible, it is displaced downward.

3. VERTEBRAL ANGIOGRAPHY shows characteristic elevation of the posterior choroidal artery, best seen in the lateral view (Figure 6.63). As the tumor grows upward, the great vein of Galen, normally bowed downward, is displaced upward (Figure 6.62). Tumor staining is sometimes visible. Angiography also helps distinguish an aneurysm of the great vein of Galen, which must be recognized before surgery.

4. C.T. is excellent for diagnosing pineal-region tumors. Marked contrast enhancement clearly demonstrates their size and margins, as well as hydrocephalus and calcification (Figure 6.114). It may show ventricular dissemination or simultaneous ectopic pinealoma and a pineal-gland pinealoma (Figure 6.115).

5. MRI also clearly demonstrates tumor margins and hydrocephalus. The tumor is isointense on both T₁- and T₂-weighted images. Sagittal images are particularly useful in pineal-region disease, showing the relationships to the quadrigeminal plate, splenium, third ventricle, and vein of Galen.⁽⁸³⁾ Unlike C.T., MRI does not demonstrate calcification.

Original pages 718–719

Treatment

Several treatments are available for pineal gland tumors, depending on tumor type and size. Germinoma, pineocytoma, and pineoblastoma are radiosensitive. If tissue examination identifies one of these types, radiotherapy gives good results. Teratomas are radioresistant; irradiation is ineffective, and surgical removal is required. Complete removal of a large tumor, however, is difficult and highly dangerous.

The treatment options are:

1. Complete surgical removal, particularly for a benign, well-circumscribed teratoma, which is curable by total excision.

2. Biopsy or partial resection to reduce the mass and obtain a histological diagnosis, followed by a ventriculoatrial or ventriculoperitoneal shunt for hydrocephalus. Germinoma or pineoblastoma is then treated with radiotherapy; radioresistant tumors are not irradiated.

3. Ventriculoatrial or ventriculoperitoneal shunting followed by radiotherapy without surgical tissue diagnosis, relying instead on the location, common tumor types in this region, and appearances on C.T. and MRI, with subsequent C.T. monitoring. This approach is not particularly well justified, since it may expose the patient to irradiation without benefit.

Original pages 719–720

Surgical Removal of PINEAL GLAND Tumors

Complete removal of a pineal gland tumor is extremely difficult, hazardous, and associated with high mortality. Postoperative disability is frequent because the tumor adheres closely to the internal cerebral veins, great vein of Galen, basal veins of Rosenthal, quadrigeminal plate, aqueduct of Sylvius, third ventricle, and superior cerebellum, while the operative corridor is narrow. Consequently, complete removal has been possible in very few patients. The microscope and microsurgical instruments now permit total excision in a higher proportion. Several approaches are available; selection depends on the tumor's character, size, and location. Sagittal MRI clearly shows its position, size, and direction of growth and helps choose the approach. Three principal routes are used (Figure 7.58).

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