| Define: | A malignant form of astrocytoma histologically characterized by pleomorphism of cells, nuclear atypia, microhemorrhage, and necrosis. They may arise in any region of the central nervous system, with a predilection for the cerebral hemispheres, basal ganglia, and commissural pathways. Clinical presentation most frequently occurs in the fifth or sixth decade of life with focal neurologic signs or seizures. | A malignant astrocytoma characterized by the presence of small areas of necrotizing tissue that is surrounded by anaplastic cells as well as the presence of hyperplastic blood vessels, and that has_material_basis_in abnormally proliferating cells derives_from multiple cell types including astrocytes and oligondroctyes. |