Astrocytomas are slowly growing infiltrative tumors that vary greatly in gross and histological appearance. A relatively benign form of astrocytoma is the large, cystic astrocytoma. The solid tumor forms a discrete nodule in the wall of the cyst which contains a yellowish, translucent fluid. Astrocytomas are graded, as depicted in Table 1. The tumor is highly cellular, composed of anaplastic, pleomorphic glial cells.
Mitotic figures are frequent.
Oligodendrogliomas occur mainly in adults. The cerebral hemisphere is a common site. Ependymomas originate in the ependymal lining of the ventricles. Medulloblastoma is a malignant tumor of childhood. It occurs in the midline of the cerebellum and may obliterate the 4th ventricle.