Pilocytic astrocytoma: 

- well circumscribed, often cyst with mural nodule 

- Usually peds 

- Cerebellum, hypothalamus, optic nerve (in NF-1) 

- WHO grade I 

- Prognosis varies greatly depending on resectability, which depends on location
- Biologically distinct from the diffuse/infiltrating astrocytomas (grade II, III, IV)
- 17q loss, BRAF mutations

- Path 

- variation between loose pale areas, dense pink areas. 

- bipolar spindled cells with hair-like processes. fibrillary background 

- Rosenthal fibers - glassy pink deposits of GFAP, a protein produced by astrocytes 

Imaging: 

hypothalamus

optic nerve 

classic cerebellar