Embryonal tumors/ Primitive Neuroectodermal Tumors (PNET)

Question 1

Atypical Teratoid/Rhabdoid Tumor (ATRT)

Answer 1

Infant with destructive tumor of CPA cistern, IAC, & petrous apex

assoicated with rhabdoid tumor of kidney

CT: lytic bony destruction

T2: isointense (high cellularity)
C+: varies
Restricted diffusion

Question 2

Medulloblastoma

Answer 2

Best diagnostic clue: Round, dense 4th ventricle mass

Midline in peds and eccentric in adults

CT: hyperattentuatiing (high cellularity), enhances

T1: hypointense to gray matter 
T2: isointense to gray matter
FLAIR: hyperintense
C+ enhances avidly but may be heterogeneous  
Restricted diffusion 

look for leptomeningeal spread (sugar coating) and drop mets.

ddx: ependymoma and pilocytic astrocytoma does not have restricted diffusion.