This case was initially thought to represent Lhermitte-Duclos disease (LDD) also termed dysplastic cerebellar gangliocytoma, is a rare tumor of cerebellum.  Multiple radiologists with varying degrees of sub-speciality on 3 continents thought this is the most likely diagnosis.

In Lhermitte-Duclos the abnormal tissue involves the cerebellar cortex, and is usually confined to one hemisphere.  It can atypically, as in this case, have a cystic component. Enhancement is not a typically a feature, although in the case mild enhancement is present. The dysplastic ''mass'' grows slowly with patient presentation usually related to the symptomatology resulting from obstructive hydrocephalus. The extent of the mass varies, with this case being particularly profound such the degree of the resultant mass effect.

The chief differential for the appearances in this age group is an atypical medulloblastoma - one with extensive nodularity.² 

Surgical resection was undertaken, at which time the surgeon stated it didnt seem at all like a medulloblastoma.

It was histopathological confirmation was of a medulloblastoma.