Clinical Features

Tumors of the nervous system are distinguished by their preference for particular age groups (Table 11.1) and gender and predilection for particular anatomic sites. Brain tumors occur at all ages, but the incidence is higher in childhood and late adulthood. With few exceptions, a male prevalence is noted. In children, they are more common in the infratentorial, and in adults, in the supratentorial compartment. Brain tumors can present with seizures, focal neurologic deficits, psychiatric symptoms, and symptoms and signs of raised intracra-nial pressure (ICP) (see Chapter 2).

Diagnosing brain tumors relies on their clinical presentation, supplemented with ancillary tests. Standard diagnostic aids are neuroimaging using computed tomography (CT) scan, magnetic resonance imaging (MRI), and angiography. Emerging new MRI techniques (such as fast fluid-attenuated inversion recovery [FLAIR] imaging, magnetization transfer imaging, diffusion/

table 11.1.

Age-Related Distribution of Common Intracranial Tumors

Tumors

Optic nerve/chiasma astrocytoma" Brainstem glioma Choroid plexus papilloma -Cerebellar astrocytoma Medulloblastoma Craniopharyngioma Ependymoma Cerebral atrocytoma Oligodendroglioma Pituitary adenoma Hemangioblastoma Meningioma Schwannoma Metastases

Average range of age (yrs)

5-20

perfusion-weighted imaging, and MR spectroscopy) better define the neural tumors by distinguishing between benign and malignant features, outlining their metabolic activities and vascular supply, and differentiating between recurrence and radiation effect. Biochemical assays identify tumor-secreted hormones and circulating tumor markers. A cytologic study of the cerebrospinal fluid is indicated when subarachnoid dissemination of a tumor is suspected. Biopsy is valuable to confirm the neoplastic nature of a lesion and to determine its histology.

Pathologic Features

Brain tumors are graded on the basis of their histologic characteristics from 1 to 4, providing an approximate prognostic guide. Grade 1, a benign tumor, grows slowly. Grossly, it is circumscribed or encapsulated. Histologically, the tumor cells are well differentiated, resembling the cell of origin; mitosis is absent or very rare; blood vessels are scanty and normal.

By contrast, grade 4, a malignant tumor, grows fast, invading and destroying the local tissue. Grossly, it is ill-defined and is surrounded by edema. (The pathologic effects of edema are presented in Chapter 2 and summarized here in Table 11.2.) Histologically, the tumor cells are anaplastic (undifferentiated); pleomorphic, (varied in shape, size, and pattern); mitosis is common, often atypical; blood supply is rich with abnormal vessels; and hemorrhage and necrosis are common. Grade 2 tumors have one, and grade 3 tumors, three or four criteria of malignancy. Brain tumors are prone to disseminate and seed along the cerebrospinal fluid (CNF) pathways. A few metastasize outside the nervous system to lymph nodes, viscera, and bone marrow. Tumorous invasion of the veins and dural sinuses and shunting procedures are potential routes for extracra-nial metastases.

A correlation between the histologic appearance and biologic behavior of the tumors varies and often is poor. The biologic behavior takes into account the speed and pattern of growth, tendency to malignant transformation and recurrence, dissemination via CSF, and responsiveness to therapy. Estimated mean-survival with grade 2 tumors is 5 to 10 years; with grade 3, 2 to 3 years; and with grade 4, 1 to 1.5 years.

Diagnosing nervous system tumors in surgical or autopsy specimens requires a supplementation of standard histologic stains with immunohistologic techniques using antibodies to tumor-specific antigens (Table 11.3). The proliferative capacity of the tumor cells can be assessed by using monoclonal antibodies MIB-1 to the Ki-67 proliferation related nuclear antigen. A Ki-67/ MIB-1 labeling index (LI) of greater than 7% to 8% indicates a higher grade of malignancy and poorer prognosis. Immunohistologic stain can be applied to detect mutations in the p53 suppressor gene. Electron microscopic examination is helpful in diagnostically doubtful cases.

table 1 1.2.

Pathologic Changes

Produced by Expanding

Intracranial Lesions

Edema

Hydrocephalus

Herniations

Pituitary necrosis

Vascular lesions

Bony erosions

Major Tumor-Related Immunohistologic

Stains

GFAP

S-100 protein

Synaptophysin

Astrocytic tumors

Astrocytic tumors

Neuronal/glial tumors

Ependymoma

Ependymoma

Medulloblastoma

Oligodendroglioma

Oligodendroglioma

Pineal gland tumor

Neuronal/glial tumors

Neuronal/glial tumors

Choroid plexus papilloma

Neurinoma

Neurofibroma

Vimentin

EMA

Cytokeratin

Meningioma

Meningioma

Craniopharyngioma

Hemangioblstoma

Choroid plexus papilloma

Choroid plexus papilloma

Hemangiopericytoma

Choroid plexus papilloma

Chromogranin

AFP

PLAP

Neuroendocrine tumor

Embryonal carcinoma

Germinoma

GFAP, glial fibrillary acidic protein; EMA, epithelial membrane antigen; PLAP, placental alkaline phosphatase; AFP, a-fetoprotein.

Classification

The first valid classification of brain tumors based on their histogenesis was published by Bailey and Cushing in 1929, and served as the basis for further classification. A newly revised classification of tumors of the nervous system was published by the World Health Organization (WHO) in 2000. Cytogenetic and molecular genetic features have become important in tumor characterization. It is anticipated that genetic profiling of the tumors will provide an improved prognostic guide and help in selecting appropriate therapy.

The tumors presented here are divided into 11 categories and graded according to the WHO. An overview of childhood tumors and hereditary tumor syndromes, harmful effects of tumor therapies, and paraneoplastic diseases complete the chapter.

TUMORS OF THE NEUROEPITHELIUM

During brain development, the primitive cells of the neuroepithelium proliferate and differentiate into neu-roblasts and glioblasts, which then mature into neurons and glial cells. Tumors with neuroepithelial cell lineage constitute the largest group of intracranial tumors. The group includes gliomas, neuronal and mixed neuronal/ glial tumors, embryonal tumors, and tumors of the pineal gland parenchyma. Their preferential sites are listed in Table 11.4.

Gliomas

This largest group of neuroepithelial tumors comprises the astrocytic, oligodendroglial, and ependymal tumors derived from the three types of glial cells: astrocyte, oligodendroglia, and ependymal glia, respectively.

0 0

Post a comment