Astrocytoma pathophysiology

Pathogenesis
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.

Grading
Astrocytomas have great variation in their presentation. The World Health Organization acknowledges the following grading system for astrocytomas:
 * Grade 1 — pilocytic astrocytoma - primarily pediatric tumor, with median age at diagnosis of 12
 * Grade 2 — diffuse astrocytoma
 * Grade 3 — anaplastic (malignant) astrocytoma
 * Grade 4 — glioblastoma multiforme (most common)

In addition to these four tumor grades, astrocytomas may combine with oligodendrocytes to produce oligoastrocytoma. Unique astrocytoma variants have also been known to exist.