DDX: age? intraventricular or intraparenchymal? supra or infratentorial? 

Ependymoma: 15% of peds post fossa tumor; ages 1-5; 2/3 occur in post fossa (intraventricular floor)& 1/3 in preventricular supratentorial WM, -restricted diffusion; More likely to contain foci of hemorrhage or calcification compared to other pediatric 4th ventricle mass; <20% of pts develop CSF mets; Assoc NF2; surgical resection is primary tx +/- chemorads (never <3 yo)

Medulloblastoma: Age 6-11 yo; hyperdense NECT, classically arises from 4th ventricle roof in midline post fossa; no extension through foramen of Magendie/Luschka; T2WI isointense; intraventricular/roof, +restricted diffusion, >90% enhancement; typically little cyst component

ATRT: <3 yo; off-midline & CPA; 40% are supratentorial; NECT hyperdense; restricted diffusion w/o cystic components dismal prognosis

JPA: MC primary; Peak age 5-15 yo; 60% cerebellum, 25% optic chiasm; variable appearance; solid heterogeneously enhancing mass; off-midline post fossa mass largely composed of a cyst w an enhancing mural nodule arising from cerebellar hemisphere; less frequently includes a centrally necrotic solid mass or a solid mass w/o cyst; no restricted diffusion; Increased enhancement

• Assoc w NF1 (particularly in optic pathway and brainstem)

• Tx w surgery

Brain stem glioma: pons, +restricted diffusion, +/- enhancement (better if NF1)

Choroid plexus carcinoma: hyperenhancing mass arising MC lateral ventricular atria in children & rarely in post fossa(4th ventricle in adults)

Hemangioblastoma: hx of vHL

Acute encephalitis: Neonatal affects any lobe, older children affects inf frontal & temporal lobes; cytotoxic edema w/ GWD loss