Meningiomas.

These tumors arise from the meninges, the fibrous tissues that cover the brain's surface on the spinal cord. These tissues form a protective covering and make up part of the envelope containing the cerebrospinal fluid. Meningioma accounts for 15 percent of all primary brain tumors. It is benign except for a few unusual instances that undergo late malignant transformation. Meningiomas are more common in women than men and their incidence rises steadily with age, beginning in middle adulthood.

Some neurologists have suggested a possible connection between head injury and meningioma, but most experts disagree with this. Meningioma can develop from the meningeal layers anywhere, but the most common locations are over the surface of the brain and near the bone structures at its base.

The tumors, which are grayish and firm, cause displacement of normal brain structures. Seizures are common. Skull X rays may show evidence of erosion of bone, presumably because of pressure from the growth beneath. Meningiomas enlarge slowly and can cause a confusing array of symptoms. Evaluation by spinal tap is generally safe and usually shows elevated protein.

Angiography and CT scanning produce characteristic images that aid in diagnosis. Surgery is the mainstay of therapy, and the neurosurgeon's skill is often crucial because cure depends on total removal. Preoperative radiation may be used to reduce the rich blood supply typical of meningiomas and to reduce the problem of bleeding during surgery. Radiation or repeat surgery are indicated for recurrent growth Chemotherapy is ineffective.