Definition of Astrocytoma

Astrocytomas are primary intracranial tumors derived from astrocytes cells of the brain. They may arise in the cerebral hemispheres, in the posterior fossa, in the optic nerve, and rarely, the spinal cord. The WHO has given a four point scale depending on the histologic grade of the tumor (see below). This article focuses on the well-differentiated (Grade 2) astrocytoma. For grade 1 and 4 astrocytomas, see respective article headings:

Well-differentiated astrocytomas constitute about 25 to 30% of cerebral gliomas. They have a predilection for the cerebrum, cerebellum, hypothalamus, pons, and optic nerve and chiasm. Although astrocytomas have many different histological characteristics, the most common type is the well-differentiated fibrillary astrocytoma. These tumors express glial fibrillary acidic protein (GFAP), which possibly functions as a tumor suppressor, and is a useful diagnostic marker in a tissue biopsy.