The document provides information on pilocytic astrocytomas including: - Pilocytic astrocytomas most commonly occur in the cerebellum in children between 5-15 years old. They present as well-circumscribed yet non-encapsulated masses that are often cystic with a projecting nodule. - Microscopically, they have a biphasic pattern of dense, elongated astrocytes alternating with loose, microcystic regions. They frequently contain Rosenthal fibers and abnormal, thick-walled blood vessels. - Pilocytic astrocytomas are considered low-grade tumors that grow slowly by expansion rather than infiltration. They have a benign