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FIGURE 27-5 A: Anterior–posterior cerebral angiogram, right-sided internal carotid artery injection, demonstrating anterior communicating artery aneurysm. B: Oblique image, cerebral angiogram, delineating anterior communicating artery aneurysm.

Internal carotid–posterior communicating artery aneurysm typically presents with third nerve palsy with a dilated ipsilateral pupil.

Anterior communicating aneurysm is occasionally associated with chiasmal compression. Usually, CT scan shows a thick SAH in the frontal interhemispheric fissure.

Internal carotid–ophthalmic artery aneurysm is often bilateral and is more common in female than male patients.

Basilar artery aneurysms are the most frequent posterior circulation aneurysm. They are often associated with multiple cranial nerve deficits and brain stem dysfunction.

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Uncommon aneurysms. There are a variety of other aneurysms besides the berry type. These aneurysms include:

Inflammatory aneurysms , which arise secondary to infection of a cerebral artery (“mycotic aneurysm” technically refers only to fungal infection)

Atherosclerotic aneurysms , which form ectatic or fusiform aneurysms (these seldom hemorrhage but are more likely to make their presence known by pressing on eloquent structures or by leading to thromboembolic infarcts)

C Treatment

Surgical clipping with a small metallic clip placed around the aneurysm neck denies flow to the weakened, dilated dome of the aneurysm and is the standard treatment.

Interventional radiology, the obliteration of the aneurysmal sac by placement of thin metal coils by using angiographic technique, is rapidly gaining ground as the treatment of choice for aneurysms with well-defined necks. The obvious risk of the technique is vessel perforation with catastrophic consequences. However, in experienced hands, the procedure is safe and greatly simplifies patient care.

Some types of aneurysms in the internal carotid artery can be treated with gradual occlusion of the carotid artery in the neck to diminish the flow and induce thrombosis in the aneurysm.

SAH patients require extensive and often complex care in the intensive care unit to address a host of problems, such as hypertension, hyponatremia, cardiac arrhythmias, vasospasm, stroke, and hydrocephalus.

Inflammatory aneurysms frequently resolve with antibiotic or antifungal therapy.

D Prognosis

The rate of bleeding from unruptured aneurysms is 2%–3% per year. Approximately one third of patients die from an SAH before they reach hospital care; another one third die during their acute hospitalization, either from rebleed before definitive clipping or from complications; and one third survive. Of the surviving one third, approximately 50% are able to return to their former lifestyle or line of work. The rest survive with impairment.

VIII Tumors of the Central Nervous System

A Overview

The overall incidence of brain tumors in the United States is approximately 10,000–13,000 new cases per year; 4,000 cases are spinal cord tumors.

CNS tumors are the most common solid tumor encountered among young patients, and they account for approximately 20% of all pediatric neoplasms.

Bimodal distribution for the frequency of brain tumors

First frequency age peak occurs in childhood (3–10 years of age).

Among children, 50% of brain tumors occur in the posterior fossa, and 50% occur in the supratentorial compartment.

Common brain tumors occurring among children are cerebellar astrocytoma, medulloblastoma, craniopharyngioma, and brain stem glioma.

Second frequency peak occurs in the sixth decade.

Most common brain tumors occurring among adults are metastatic carcinoma, malignant glioma, meningioma, and pituitary adenoma.

Incidence of brain tumor according to gender

There are significant genetic issues with respect to brain tumors and sex ratio. Neurofibromatosis types I and II have also been associated with chromosomal abnormalities.

Most brain tumors show a preponderance among males.

Medulloblastomas exhibit a 5:2 male:female ratio.

Meningiomas reveal a 4:1 ratio favoring females over males; meningiomas also have been found to be associated with abnormalities of monosomy of chromosome 22.

B Classification of brain tumors

The nomenclature for brain tumors is often confusing. In general, there has been an increasing trend to classify tumors based on their histologic characteristics. This is broadly based on the cell origin.

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Cells derived from astrocyte cell lines

Glial tumors (gliomas) constitute nearly 50% of brain tumors.

The histology of the tumor is graded by increasing malignancy from low -grade astrocytoma to anaplastic astrocytoma to glioblastoma multiforme.

Glial tumors can include oligodendrogliomas and ependymomas.

Adults tend to get malignant tumors, whereas children are more prone to low -grade, midline astrocytomas in the posterior fossa.

Nonglial cell tumors. Tumors in this group include meningiomas (which arise from arachnoidal cells), schwannomas (which arise from Schwann's cells), medulloblastomas (which arise from primitive neuroectodermal remnants during embryologic development), pituitary tumors (which arise from hormonal cells in the pituitary gland), pineal tumors (which often arise from germ cells), and tumors arising from the blood vessels (e.g., hemangioblastomas and metastatic tumors).

C Diagnosis

Tumors make themselves apparent by symptoms that are related to several mechanisms.

Mass effect

The brain and spinal cord are relatively intolerant of space -occupying lesions, which compete with normal tissue for space within the rigid skull or vertebral canal.

As a general principle, CNS tissues are much more tolerant of slow -growing lesions than of rapid volume change.

Eloquence

Tumors in eloquent areas of the brain become symptomatic while relatively small as opposed to lesions in relatively “silent” areas of the brain, where the tumor becomes symptomatic first when the mass effect is great enough to affect eloquent structures at some distance.

As a general rule, the more eloquent the region in which the lesion arises, the more dramatic the patient's symptoms.

CNS dysfunction can occur because of blood flow impairment. Tumors can impede blood flow by several methods.

Compression of normal blood vessels, depriving normal brain tissue of sufficient blood flow

Tumors can produce brain dysfunction by a “steal phenomenon.” As tumor metabolism increases, blood flow is diverted from normal areas of the brain, causing dysfunction.

Tumors can produce metabolic impairment by growth factors and chemical messengers and interfere with normal “host” brain function.

Tumors can cause seizures, either by direct mechanical irritation or by affecting normal brain metabolism through parts a, b or c above.

Tumors can obstruct CSF outflow, which can lead to gradual enlargement of the ventricles and hydrocephalus.

D Neurologic evaluation

A history of either acute onset or progressive neurologic deficits should be elicited.

The presence of asymmetry upon examination may indicate upper motor neuron dysfunction.

An examination that indicates specific lobar dysfunction is highly suspicious for a focal lesion, such as a brain tumor.

Additional studies are required to pinpoint the lesion. It is important that CT and MRI scans be obtained with contrast to demonstrate disruption of the blood–brain barrier (a frequent manifestation in the vicinity of a tumor). Studies include:

CT scan

MRI scan

Skull films

Angiography

PET scan

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E Specific tumors (supratentorial)

Astrocytomas of the cerebrum are generally slow -growing, infiltrating tumors with poorly defined borders.

Peak incidence is during the fourth decade of life.

Clinical presentation. Astrocytomas often present with seizures, headaches, increased ICP, and focal neurologic deficits. CT and MRI scans show irregular nonhomogenous enhancement with a zone of edema around the tumor.

Treatment includes:

Aggressive surgical resection with an attempt to completely resect the tumor

Radiation therapy

An additional focal radiation boost to the bed of the tumor (with brachytherapy or stereotactic radiosurgery)

Chemotherapy

Prognosis is often related to several factors, including age of the patient, neurologic condition, and histology of the tumor.

Patients with low -grade astrocytomas have a median survival of approximately 5 years.

Patients with anaplastic astrocytomas have a median survival rate of 2 years.

Patients with glioblastomas have a median survival rate of 1 year.

Ependymomas are generally well-circumscribed tumors that occur in the vicinity of ventricles; they often metastasize through CSF pathways.

Clinical presentation often includes increased ICP and symptoms secondary to increased ICP. MRI or CT scan shows an irregularly enhancing lesion with a well-defined border in the vicinity of the ventricle.

Treatment includes:

Aggressive surgical resection

Radiation therapy

Prognosis. The median survival for patients with ependymomas is 5 years.

Oligodendrogliomas are slow -growing gliomas that often have calcification in them.

Clinical presentation. The most common presentation is seizures, and there is often a focal neurologic deficit. CT and MRI scans reveal calcified areas in nearly 40%–50% of tumors.

Treatment includes surgical resection, with or without radiation therapy.

Prognosis. The median survival rate is 10 years for a patient with oligodendrogliomas.

Meningiomas account for 15% of intracranial neoplasms, with a clear predilection for females. Lesions are usually adjacent to the dura with a well-defined border. Meningiomas often have variable amounts of calcium within them and are often associated with extensive edema in the adjacent brain, which is often badly compressed.

Clinical presentation includes headache, focal neurologic deficits, and seizures. CT and MRI scans often reveal homogenous, intensely enhancing mass and well-demarcated border with normal brain.

Treatment includes surgical excision; it can include radiation therapy. New modalities include chemotherapy for malignant meningiomas.

Prognosis is variable, depending on factors such as location and extent of resection.

Metastatic tumors. Approximately one fifth of cancer patients will develop intracranial metastases. Metastases from lung, breast, prostate, kidney, and malignant melanomas represent the most frequent source of intracranial metastases.

Clinical presentation includes increased ICP, obstructive hydrocephalus, focal neurologic deficit, and spontaneous intracerebral hemorrhage. CT and MRI scans often reveal well-circumscribed, enhancing masses surrounded by a ring of cerebral edema. Often, there are multiple lesions typically distributed at the junction of the gray and white matter.

Treatment includes surgical resection if the lesion is solitary or the histology is in question. Treatment also includes steroid and whole -brain radiation therapy followed by focal radiosurgical boost.

Prognosis. Approximately 50% of patients with a single intracranial metastasis will live for 1 year after diagnosis. Survival is increasing with more aggressive therapy, including stereotactic radiosurgery and chemotherapy.

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Meningiocarcinomatosis is a special case of metastatic tumor in which the tumor spreads diffusely throughout the subarachnoid space. Typically, these patients present with evidence of meningismus and ventricular obstruction and may require shunting. Cranial nerves II, VII, and VIII are most commonly involved. Meningiocarcinomatosis is most commonly associated with leukemia, lymphoma, or breast cancer. Often, this type of tumor requires radiation therapy and intrathecal chemotherapy.

F Specific tumors (infratentorial)

Posterior fossa tumors. Approximately 50% of brain tumors in children are located in the posterior fossa. By contrast, only 25% of tumors in adults are in the posterior fossa.

Types. These tumors include midline cystic cerebellar astrocytomas of the cerebellum and brain stem, medulloblastomas, ependymomas, choroid -plexus papillomas, and epidermoid tumors. Most common are acoustic neuromas, epidermoid cysts, meningiomas, and hemangioblastomas.

Clinical presentation. Tumors of the posterior fossa can present with a headache secondary to ventricular obstruction. They can also present with ipsilateral ataxia and lack of coordination from lesions in the cerebellum as well as unsteady gait and truncal ataxia. In addition, loss of equilibrium and nystagmus may be present.

Treatment and prognosis depend on tumor type and location.

Medulloblastomas are malignant tumors of the vermis and the fourth ventricle from arrest of neuroectodermal cells during embryologic development. These tumors are most frequently encountered during the first and second decades of life, with a male predominance.

Clinical presentation. These tumors most commonly occur in the midline or lateral cerebellar hemisphere. Patients with a medulloblastoma present with cerebellar and brain stem dysfunction and increased ICP. CT and MRI scans demonstrate a nonhomogenous, enhancing mass usually adjacent to or in the fourth ventricle.

Treatment is extensive surgical resection and radiation therapy to the site as well as the rest of the entire neuraxis to prevent CSF seeding. Radiation therapy cannot always be used in young children, and chemotherapy remains the treatment of choice after surgery.

Prognosis. Thirty-three percent of patients survive 10 years. Survival is increased by total resection and radiation therapy.

Ependymomas arise from the floor of the fourth ventricle and are most common during childhood.

Clinical presentation. Ependymomas usually present with obstruction of CSF pathways. There is increased ICP and disequilibrium. CT and MRI scans show a modular, multilobulated, enhancing tumor in the fourth ventricle.

Treatment. Ependymomas are surgically resected, but often the floor of the fourth ventricle cannot be invaded to remove the tumor. Radiation therapy is usually required after removal.

Prognosis. Median survival for patients with an ependymoma is 2.5 years.

Brain stem gliomas. These tumors occur most frequently in the first decade of life.

Clinical presentation

Typically, this tumor presents with cranial palsies of the brain stem with gait unsteadiness and evolving myelopathy.

Hydrocephalus can occur secondary to fourth ventricular obstruction.

CT and MRI scans often demonstrate diffuse and poor enhancement of an intra -axial lesion within the brain stem.

Classic MRI appearance is sufficient for diagnosis, obviating the need for biopsy.

Treatment. Tumors are often largely unresectable. Radiation therapy remains the mainstay of treatment.

Prognosis. Median survival for a child with a brain stem glioma is 2 years.

Cerebellar astrocytomas have a much more benign history than astrocytomas occurring elsewhere. Like brain stem gliomas, their peak incidence is in the first decade of life, but they are generally restricted to the cerebellum. Cerebellar astrocytomas are often cystic.

Clinical presentation. Patients typically present with cerebellar dysfunction and ipsilateral dysmetria. With progressive growth, obstructive hydrocephalus can develop. CT and MRI

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scans usually reveal a multicystic or cyst -associated enhancing nodule. The nodule may be low density and is often located in the lateral cerebellar hemisphere.

Treatment and prognosis. Tumors can be completely resected in up to 80%–90% of patients, which usually results in cure. Even patients who undergo partial resections have a median survival of 8 years.

Hemangioblastomas are the most common primary intra -axial tumor in the posterior fossa in adults.

Clinical presentation. Patients present with cerebellar dysfunction.

Hemangioblastomas can be a part of von Hippel–Lindau disease with hemangioblastomas of the cerebellum and retina, in association with congenital cysts of the kidneys, pancreas, liver, and renal cell carcinoma. Approximately 10% of these patients have erythrocytosis secondary to tumor secretion of erythropoietin.

CT and MRI scans usually reveal a mural nodule within a cyst; the nodule is intensely enhancing.

Angiography reveals an intense vascular blush on this lesion.

Treatment. Surgical resection is the treatment of choice but may be extremely difficult due to the vascularity of the tumor.

Tumors of the cerebellopontile angle. Typically, these tumors involve the cerebellopontile angle with differential involvement of cranial nerves V, VII, and VIII as well as the adjacent cerebellum. Several tumors may be involved in this location, including acoustic neuromas, meningiomas, and epidermoid cysts.

Acoustic neuromas arise from the vestibular portion of cranial nerve VIII.

Clinical presentation. These are benign tumors that usually present with tinnitus, hearing loss, and evolving unsteadiness. Commonly, the patient first notices problems with speech discrimination followed by a gradual loss of hearing. With large tumors, there is often loss of the corneal reflex as well as facial weakness. If the tumor is quite large, it compresses the cerebellum and leads to nystagmus and gait ataxia.

Enhanced CT and MRI scans often demonstrate acoustic neuroma in the internal auditory meatus. Often, the internal auditory meatus is expanded or trumpet-shaped from the lesion.

MRI has now become the method of choice for evaluating the posterior fossa and cerebellopontile angle because these structures are better seen on MRI. With CT, bony artifacts from the petrous ridge often hide important radiographic features.

Brain stem auditory evoked potentials and audiometric testing are very useful for lesions affecting the VIII nerve or a brain stem.

Treatment involves resection or stereotactic radiosurgery.

Prognosis is related to tumor size and extent of resection.

Meningiomas may also present in the cerebellopontile angle with precisely the same signs and symptoms as acoustic neuroma.

Epidermoid cysts also commonly occur in the cerebellopontile angle and again can present with cerebellopontile angle syndrome. Progressive dysfunction of cranial nerves V, VII, VIII, and the lower cranial nerves, along with progressive cerebellar compression, are typical.

G Pituitary tumors

Clinical presentation. Pituitary tumors tend to present in one of three ways.

The first way is with headache and compression of the optic chiasm. Frequently, the patient presents with bitemporal hemianopsia.

The second presentation is with endocrinopathy. Often, endocrinopathies consist of Cushing's syndrome (secondary to excess adrenocorticotropic hormone secretion), acromegaly (secondary to excessive growth hormone secretion), hyperprolactinema, or hypopituitarism.

The third presentation is the occasional presentation of a tumor with pituitary apoplexy. This is an acute massive hemorrhage into a pituitary tumor, which may mimic the onset of a ruptured berry aneurysm. Frequently, these patients will have headache, impaired vision, extraocular muscle dysfunction, stiff neck, and endocrinopathy.

In approximately 30% of the cases, the patients do not have endocrinopathy (so-called nonsecreting pituitary adenomas).

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Diagnostic tests

Radioimmunoassays are used to document the level of specific hormones in situations of endocrinopathy.

CT and MRI scans are useful for demonstrating the erosion of the sella as well as sellar and suprasellar tumors.

Angiography is still occasionally used in the event that there is some question about whether an intrasellar or suprasellar aneurysm may be present.

MRI with and without contrast has now become the method of choice for diagnosis. With modern MRI techniques, flow voids associated with aneurysms are usually detectable.

Treatment

Medical therapy in the form of bromocriptine (a dopaminergic agonist) can often be used successfully for prolactin -secreting adenomas. Bromocriptine has also proved useful for other kinds of endocrinopathies, such as in some selected patients with acromegaly.

Surgical resection is the treatment of choice for most nonprolactin -secreting tumors and prolactinomas that are progressively symptomatic despite medical therapy. This is especially true for tumors that are impinging on the optic chiasm.

A trans-sphenoidal route can be used for small tumors with little suprasellar extension.

For tumors with extensive suprasellar mass, a frontal or pterional craniotomy may be required.

Radiation therapy (usually in the range of 4,000–5,000 Cgy) is frequently used as an adjunct after partial surgical resection and is effective in controlling approximately 90% of pituitary adenomas that remain after surgery.

IX Congenital Lesions of the Nervous System

A Dysraphism

Usually, defective fusion of a raphe is associated with some findings on general physical examination. For example, examination of the back may reveal a tuft of hair, a nevus, a lipoma, abnormal blood vessels, a dimple, or a sinus tract. All of these are highly suggestive of an underlying dysraphic state.

Spina bifida results from failure of fusion of the vertebral arches.

It may be totally asymptomatic and be found incidentally on spinal radiograph (spina bifida occulta), or it may be symptomatic.

Spina bifida can be associated with other congenital anomalies, such as dermal sinus, diastematomyelia (splitting of the cord into halves), or neuroenteric cysts.

Meningocele. This rare lesion is a saclike posterior midline herniation of the dura mater and is usually not associated with any neurologic deficits. Repair is indicated primarily for cosmetic reasons.

Myelomeningocele is herniation of the dura mater and neural elements posteriorly as a result of incomplete closure of the spine. This lesion may be associated with hydrocephalus secondary to a Chiari malformation (i.e., an abnormally low position of the cerebellar tonsils).

Surgical treatment is aimed at closure of the defect.

Neurologic defects are common, and their severity is related to the location of the lesion. Patients with high lesions have a worse prognosis.

B

Hydrocephalus literally means “water head,” and the abnormality may be congenital or acquired. It is caused by an obstruction to the flow (obstructive hydrocephalus) or reabsorption (communicating hydrocephalus) of CSF.

Etiology. The most common causes are:

Sequelae of intraventricular hemorrhage in the premature baby

Aqueductal stenosis

Chiari malformation

Type I. The fourth ventricle is above the foramen magnum, but the upper part of the cervical cord is displaced caudally.

Type II (most commonly seen). There is a downward herniation of the fourth ventricle and the cerebellar tonsils.

Types III and IV. There is progressive caudal displacement of the cerebellar vermis, pons, and medulla below the foramen magnum.

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Dandy-Walker syndrome , in which there is probable agenesis of the foramina of Magendie and Luschka, resulting in the filling of the posterior fossa with a large cyst and enlargement of the lateral and third ventricles

Clinical findings. Patients may present with bulging fontanelles, scalp vein dilatation, a rapidly increasing head circumference, decreased upward gaze (Parinaud's syndrome), papilledema, lethargy, irritability, nausea, ataxia, and vomiting.

Treatment. A CT or MRI scan is done to confirm the diagnosis, and then a shunt is placed to divert the ventricular fluid.

A ventriculoperitoneal shunt is most commonly used.