1. What is the most frequent malignant primary neoplasm in adults?

Glioblastoma multiforme

(Medulloblastoma is the most frequent malignant brain tumor in children.)

2. In adults what histologic features differentiate an astrocytoma, an anaplastic astrocytoma, and a glioblastoma multiforme?

A low grade astrocytoma has only slight hypercellularity and slight pleomorphism, no vascular proliferation and no necrosis.

An anaplastic astrocytoma is moderately cellular and pleomorphic with no necrosis but vascular proliferation may be present.

A glioblastoma multiforme has moderate to marked hypercellularity and pleomorphism, and necrosis. Vascular proliferation may be present (but is not required).

3. Compare childhood cerebellar astrocytoma, and third ventricle astrocytomas. Both are usually pilocytic astrocytomas.

Pilocytic astrocytomas typically occur in children and young adults and are usually located in the cerebellum or in the floor or wall of the third ventricle or optic nerve (or less often in the cerebral hemispheres.) The tumors are often cystic grossly and microscopically are composed of fusiform astrocytes which possess unusually long wavy fibrillary processes. Rosenthal fibers, intracellular mass of amorphous material contained within filament-rich glial processes, and microcysts are often present and in these tumors endothelial proliferation does not imply a poor prognosis. Both types grow slowly and removal often results in cure in the cerebellum.