Primary Sonic Hedgehog-activated dorsal brainstem medulloblastoma and ipsilateral cerebellar atrophy in an adult.

Medulloblastoma (MB) that arises outside the cerebellum from cells of the dorsal brainstem is rare. The most common subtype of MB in the dorsal brainstem is the Wingless (WNT) subtype that contains activating mutations in the WNT pathway effector CTNNB1. Ipsilateral cerebellar hemi-atrophy with a brainstem tumour is a finding that is usually documented with brainstem gangliogliomas as a possible specific imaging sign.