(Left) Axial NECT shows a

cystic and solid isodense

posterior fossa mass ﬈

causing obstructive

hydrocephalus. The lack of

increased density helps to

differentiate this PA from a

medulloblastoma. (Right)

Coronal T2WI MR shows a

hyperintense

hypothalamic/chiasmatic mass

﬈ with no surrounding

edema. PAs in this location

have variable enhancement.

Optic pathway PAs are highly

associated with

neurofibromatosis 1 (NF1): ≤

1/3 of patients with an optic

pathway PA have NF1.

Cysts, and Disorders

Brain: Pathology-Based Diagnoses: Neoplasms,

131