Medulloblastomas are primarily childhood tumors, where they account for one third of all posterior fossa neoplasms. Medulloblastomas most commonly occur in the cerebellar vermis. In older children and adults they may occur laterally in the cerebellar hemisphere. Imaging studies depict the typical location in the cerebellar vermis, with filling and enlargement of the fourth ventricle. Typically the mass is solid, but cystic changes are not uncommon, especially in the laterally located tumors.
Enhancement is variable, but usually moderate and heterogeneous.
Medulloblastomas tend to metastasize widely through CSF spread, with CSF dissemination present in up to half the cases at initial surgery.