glioma
n. a form of brain tumor that develops from support cells (glia) of the central nervous system. There are three main types, grouped according to the form of support cell involved: astrocytoma (from astrocytes), ependymoma (from ependymal cells), and oligodendroglioma (from oligodendrocytes). Astrocytomas are classified from Grade I to Grade IV by severity and rate of growth: Grade I tumors (also called pilocytic astrocytomas), Grade II astroblastomas, Grade III anaplastic astrocytomas, and Grade IV glioblastomas. Glioma is the most common type of brain cancer and accounts for about a quarter of spinal cord tumors. Also called neuroglioma.