Specific Indications

Categories of CNS disease amenable to diagnosis by brain biopsy or mimicking types of disease normally presenting as neurosurgical conditions are summarized in Table 25-8 . This disorder can be grouped into conditions that present with mass lesions, focal or multifocal nonmass

TABLE 25-8 -- BRAIN AND MENINGEAL BIOPSY DIAGNOSES

Category

Examples

Neoplasms

Gliomas, metastatic tumors, CNS lymphoma

Infections (inflammatory)

HIV encephalitis, opportunistic infections (toxoplasma, cytomegalovirus, herpes simplex, cryptococcus), bacterial abscess, cysticereosis, tuberculosis, sarcoidosis

Degenerative diseases

Creutzfeldt-Jakob disease, Alzheimer's disease, Picks disease

Vascular diseases

Vasculitis, amyloid angiopathy, vascular malformations

Epilepsy

Mesial temporal sclerosis, dysplasias and malformations, Rasmussen's encephalitis

Metabolic diseases

LeukodystrophiesX storage diseases, mitochondrial diseases

CNS, central nervous system; HIV, human immunodeficiency virus.

lesion abnormalities, and diffuse abnormalities. Mass lesions include most neoplasms and neoplastic or non-neoplastic cysts, some forms of infection (abscesses, cerebritis, tuberculomas, some encephalitides), specific vascular disorders (hemorrhages, early infarcts), malformations or developmental lesions (hamartomas, some migrational abnormalities), and a variety of miscellaneous conditions (sarcoidosis, acute multiple sclerosis, and adrenoleukodystrophy). Conditions that produce imaging study abnormalities that are not necessarily mass lesions include (1) forms of neoplasia (infiltrating gliomas, gliomatosis, lymphomas); (2) cerebrovascular disorders (vasculitides, vasculopathies); (3) infections (viral encephalitis, progressive multifocal leukoencephalopathy, CNS syphilis); (4) degenerative diseases (Creutzfeldt-Jakob disease, Huntington's disease); (5) inflammatory and immunologic disorders (acute disseminated encephalomyelitis, limbic encephalitis, Rasmussen's encephalitis); (6) developmental and malformative disorders (cortical migrational disorders and dysplasias); (7) toxic and metabolic disorders (leukodystrophies, central pontine myelinolysis, mitochondrial encephalopathies); and (8) some forms of epilepsy (mesial temporal sclerosis, malformations). Finally, some conditions show either no imaging study abnormalities or show only atrophy without focal findings, e.g., degenerative diseases (Alzheimer's disease, Parkinson's disease), toxic and metabolic diseases (hepatic encephalopathy, many storage diseases), and most cases of idiopathic epilepsy.

Tumors. The differential diagnosis of a mass lesion presumed to be neoplastic can be limited by considering the age of the patient and the location of the tumor. Table.,25-1Q. lists examples of tumors encountered in certain nervous system locations in the pediatric and adult age groups. Diagnostic biopsy is usually directed toward the mass lesion. As noted earlier, the possibilities of tissue heterogeneity and central necrosis should be taken into account by adequate sampling of different areas including the interface between tumor and adjacent brain. A preliminary intraoperative assessment by frozen section is useful

TABLE 25-9 -- DIFFERENTIAL DIAGNOSIS OF SPACE-OCCUPYING CENTRAL NERVOUS SYSTEM LESIONS

Neoplasms

Infections Cerebrovascular Demyelinating Cysts

Intra-axial: gliomas, metastatic tumors, lymphoma Extra-axial: meningiomas, neuromas

Abscesses (bacterial, fungal, parasite), granulomas (tuberculosis, sarcoidosis), necrotizing lesions (toxoplasma, some focal viral encephalitides )

Hemorrhages, acute infarctions

Acute multiple sclerosis, adrenoleukodystrophy

Metastatic neoplasms, primary neoplasms (glioma), primary developmental disorders (meningeal, neuroepithelial, colloid, enterogenous)

to gauge the adequacy of the specimen for diagnosis and to predict how tissues should be handled for ancillary studies. Neoplasms that may present without evidence of a mass lesion and mimic other forms of neurological disease include neoplasms disseminated in the subarachnoid space (metastatic carcinoma, glioma, lymphoma), infiltrating gliomas (low-grade astrocytomas or oligodendrogliomas), and some forms of mixed neuronal and glial neoplasms (dysembryoplastic neuroepithelial tumor, gliomatosis cerebri) and lymphomas. Non-neoplastic mass lesions such as infections can be suspected on intraoperative frozen section evaluation, and appropriate ancillary studies can be done.

Radiation Necrosis. Following therapeutic radiation therapy for intracerebral neoplasms, the distinction between recurrent neoplasm and radiation necrosis is often difficult. Diagnostic brain biopsy is often useful in demonstrating residual or recurrent neoplasm and may show the coagulative tissue necrosis and vasculopathic changes characteristic of radiation necrosis in adjacent brain parenchyma, with or without evident tumor. Diagnostic brain biopsy can be performed as part of the therapeutic removal of necrotic tissue as well.

Non-neoplastic Cysts. Diagnostic biopsy of a cyst wall can be performed as part of cyst fenestration or drainage and may be useful in distinguishing between neoplastic and non-neoplastic cystic mass lesions.

Infections. Infectious diseases of the central nervous system are diagnosed by a variety of means, including assessment of clinical history, standard laboratory studies, serological and microbiologic evaluation of blood and cerebrospinal fluid, and imaging studies. Diagnostic brain biopsy plays a limited role in this setting. In the case of mass lesions or focal brain lesions, diagnostic brain biopsy may be useful in distinguishing between neoplasms and infections. Diagnostic brain biopsy evaluated by morphological and microbiological studies may also be useful in identifying an organism that has failed to be diagnosed by blood or cerebrospinal fluid studies. Diagnostic brain biopsy is also performed when a suspected infectious lesion fails to respond to a trial of antimicrobial therapy. Diagnostic brain biopsy is also performed in some patients with HIV infection and certain CNS complications. The spectrum of possible infectious complications in these patients is large and varied. Common CNS infections include toxoplasma cerebritis, cryptococcal and other fungal infections of the meninges or brain parenchyma, herpes simplex and cytomegalovirus encephalitis, and progressive multifocal leukoencephalopathy (JC virus). Although these infections often present with characteristic clinical and imaging features, a considerable overlap among these infections and primary CNS lymphoma can occur. In HIV patients who fail a trial of antimicrobial agents for a suspected infection, diagnostic brain biopsy may also be useful.

DEGENERATIVE DISEASES

Many degenerative diseases are characterized by neuronal loss and gliosis in various brain structures without distinctive features. Diagnosis by brain biopsy remains inconclusive in many cases. In patients with a rapidly progressive dementia, a distinction can be made between Creutzfeldt-Jakob disease and degenerative disorders by

TABLE 25-10 -- DIFFERENTIAL DIAGNOSIS OF NEOPLASTIC CENTRAL NERVOL

S SYSTEM TLMORS

Adulthood Childhood

Cerebral Hemispheres

Astrocytoma, glioblastoma, oligodendroglioma, metastatic tumor, lymphoma

Astrocytoma, ependymoma, choroid plexus tumor, primitive neuroectodermal tumor

Diencephalon

Astrocytoma, glioblastoma, colloid cyst, pituitary adenoma

Germ cell tumors, craniopharyngioma

Posterior Fossa

Metastatic tumor, hemangioblastoma

Medulloblastoma, ependymoma, cerebellar pilocytic astrocytomas, brain stem astrocytoma, choroid plexus tumor

Cerebral Meninges

Meningioma, CN VIII schwannoma, metastatic carcinoma, lymphoma

Meningioma, nerve sheath tumors, astrocytoma, ependymoma

Nerve sheath tumors, astrocytoma

CN, Cranial nerve.

the presence of spongiform changes or prion proteins in the former. In addition, the demonstration of senile plaques and neurofibrillary tangles in a random biopsy of cerebral cortex, while suggestive of Alzheimer's disease, does not exclude the possibility of other forms of neurodegenerative disease or the presence of other concomitant disease. Because of the variability of distribution of the pathological changes in most degenerative disorders, random biopsies may be nondiagnostic. For adequate evaluation, a piece of cerebral cortex with overlying leptomeninges and underlying white matter that can be oriented is desirable. Tissue should be considered potentially infectious, and precautions for Creutzfeldt-Jakob disease should be taken according to local institutional guidelines. The tissue should be fixed and reserved for possible electron microscopy or other studies.

VASCULAR DISEASES ( Tab!e25-11 )

Surgical resection of tissue is occasionally performed in the setting of cerebrovascular disease. Diagnostic brain or meningeal tissue biopsy is usually performed when CNS vasculitis is suspected. Resection of brain tissue is usually performed for the diagnosis and treatment of vascular malformations. Symptomatic treatment of acute cerebrovascular diseases, usually hemorrhages and traumatic lesions, by evacuation of hematoma with removal of damaged brain tissue, may provide histological evidence of specific etiologies such as amyloid angiopathy or hypertensive vasculopathy. Some cases of cerebrovascular disease, such as

TABLE 25-11

-- TISS

JE DIAGNOSES IN CEREBROVASCULAR DISEASE

Vasculitis

Primary CNS vasculitis, CNS involvement in systemic vasculitis, infectious vasculitis

Vascular malformations

Arteriovenous malformation, cavemous angioma, venous angioma

Vasculopathies and diseases presenting as intracranial hemorrhages

Amyloid angiopathy, hypertensive vasculopathy, vasculitis, primary or metastatic neoplasms, infections

Cerebrovascular diseases mimicking mass lesions

Recent infarction

infarcts, present as mass lesions and may be clinically mistaken for neoplasms.

METABOLIC DISEASES

Diagnosis of metabolic and storage disorders by brain biopsy has been superseded in many conditions by biochemical and molecular genetic analysis of more readily obtainable non-CNS cells and tissues. In cases in which metabolic or storage disease involving the CNS is suspected but no metabolic defect can be identified by other means, random biopsy of cerebral cortex and white matter may provide either positive or useful negative information. Reserved frozen or properly fixed tissues may prove useful later when subsequent clinical clues or testing techniques become available.

EPILEPSY

Some patients with intractable epilepsy may benefit from surgical resection of brain tissue (see Chapter s? ). In patients with complex partial seizures originating in the temporal lobe, temporal lobectomy with partial hippocampectomy may be beneficial. Examination of medial temporal lobe structures may disclose evidence of neuronal loss and gliosis in the hippocampus, amygdala, or adjacent gray matter structures (mesial temporal sclerosis). In occasional cases, other pathological findings (neoplasm, vascular malformation, cicatrix) may account for an epileptogenic focus. In some patients with intractable epilepsy with focal abnormalities demonstrated by electrophysiological, conventional neuroimaging modalities, or physiological imaging modalities such as positron-emission tomography scanning, removal of the focus is indicated. Pathological findings may include cortical migrational abnormalities, dysplasias, vascular malformations, glial scars, neoplasms, or focal infections. More widespread resections such as lobectomy or even hemispherectomy are occasionally performed with patients with established neurological deficits and more extensive malformations or with progressive lesions such as Rasmussen's encephalitis. Despite the finding of a focal lesion on one or more studies, no specific pathology is found in a large percentage of cases.

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