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Intracranial and spinal neoplasms may be primary or metastatic; in most autopsy series, metastatic tumors are more common. Primary intracranial neoplasms number about 13,000 new cases per year in the United States and represent about 2% of deaths from malignant neoplasms. They are the second most common group of neoplasms in children, after leukemia and lymphoma if considered as one group. Taken overall, 65% of primary intracranial neoplasms are of glial origin (gliomas), 10% meningiomas, 10% acoustic schwannomas, 5% medulloblastomas, and 10% others. Primary malignant lymphomas of the central nervous system have recently increased in frequency because they are common in patients with acquired immunodeficiency disease (AIDS). Tumors of neurons per se are extremely uncommon except in childhood (eg, medulloblastoma).
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Histogenetic Classification
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Classification on a histogenetic basis has great theoretical value and provides a means of logically remembering all the different kinds of intracranial neoplasms (Table 65-1).
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Topographic Classification
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When a patient presents with an intracranial neoplasm, its location can usually be ascertained by clinical examination and radiologic studies. According to their location, intracranial neoplasms may be classified as supratentorial or infratentorial. Further subdivisions in these main compartments are recognized (Table 65-2), leading to a topographic classification. When the location of the neoplasm is combined with the patient's age, a clinically useful differential diagnosis of the histologic type of the neoplasm can be derived. For example, if a child presents with a neoplasm in a cerebellar hemisphere, it is most likely a juvenile pilocytic astrocytoma (Table 65-2).
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