Almost all tumors that originate in the nervous system are tumors of nonconducting support cells, the neuroglia. These growths are termed gliomas and may be named for the specific type of cell involved, such as astrocytoma, oligodendroglioma, or schwannoma (neurilemoma). Because they tend not to metastasize, these tumors may be described as benign. However, they do harm by compressing brain tissue. The symptoms they cause depend on their size and location. There may be seizures, headache, vomiting, muscle weakness, or interference with a special sense, such as vision or hearing. If present, edema and hydrocephalus add to the effects of the tumor. A meningioma is a tumor of the meninges. Because a meningioma does not spread and is localized at the surface, it can usually be removed completely by surgery.
Tumors of neural tissue generally occur in childhood, and may even originate before birth, when nervous tissue is actively multiplying. Also, cancer may metastasize to the brain from elsewhere in the body. For unknown reasons, certain forms of cancer, especially melanoma, breast cancer, and lung cancer, tend to spread to the brain.
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