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Tumors III: Non-glial tumors

Last updated on Monday, April 20 2009 by gliageek

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Meningiomas are the most common extraparenchymal neoplasms affecting the CNS, accounting for approximately 20% of intracranial tumors. They occur predominantly in middle to late adult life, and tend to involve the cerebral convexity, parasagittal region, sphenoid ridge or spinal cord. Meningiomas have been linked to a variety of environmental and genetic factors including trauma, radiation, DNA tumor viruses, and neurofibromatosis type 2, and are associated with a loss of information on chromosome 22. The majority of meningiomas are histologically benign (WHO Grade I), though even these will recur if the patient lives long enough (20% in 10 years after complete resection). About 5% of meningiomas are atypical (WHO grade II) and 2% are anaplastic (WHO grade III), which in this setting primarily indicates more rapid recurrence; extraneural dissemination is rare.

Schwann cells
are the "glia" of the peripheral nervous system, which includes cranial nerves III-XI, as well as the spinal nerve roots. As such, they affect the CNS by compression resulting from growth within the extraparenchymal, intradural compartment. They show a remarkable tendency to arise from sensory nerves, especially the vestibular nerve in the cerebellopontine angle. These tumors used to be called "acoustic neuromas" but are now correctly referred to as vestibular schwannomas. They grow eccentrically from the surface of the nerve root and current surgical treatment attempts to preserve nerve function as much as possible, as recurrence and malignant degeneration are rare.

Epithelial cells do not occur normally within the CNS. They therefore must metastasize from other sites, usually the lung and breast. As non-welcome residents, they tend to be well circumscribed. Solitary metastases occur in approximately half the cases. In addition, about half the patients presenting with a brain metastasis do not have a prior diagnosis of systemic cancer.

Though once a rare tumor, the incidence of Primary Central Nervous System Lymphoma (PCNSL) has markedly increased in recent years. Though this is largely due to its occurrence in AIDS, where it is second to Toxplasmosis as a cause of intraparenchymal mass lesions, there has also been a tripling of the incidence of this tumor in immunocompetent individuals. The reason for this is currently not known, but PCNSL must be considered in the differential diagnosis of intraparenchymal masses in older adults, particularly if the lesions are periventricular or multiple (the latter is seen in about 40% of patients at presentation). Nearly all of these tumors are large B-cell lymphomas. Leptomeningeal involvement by CSF cytology is identified in about 25% of patients. Intra-ocular infiltration is seen in about 20% of patients at presentation. Unlike all of the other tumors discussed above, resection does not play a therapeutic role in the treatment of these patients.