Medulloblastoma

Etiology: small round blue cell tumor
Imaging: well defined / homogenous / enhancing mass, usually arising in midline in roof of 4th ventricle / inferior medullary velum, , can originate off midline such as from Foramen of Lushka, hydrocephalus
CT: well defined and dense
MRI: T1+T2 isointense, homogenous enhancement in 90-95%, calcifications and cyst rare, often restricted diffusion due to high degree of cellularity / high nuclear to cytoplasmic ratio / scant interstitial fluid / decreased extra-cellular space / can be useful for followup / monitoring
DDX:
Complications: systemic metastases in 15%, subarachnoid metastases in 50% – indistinct folia / sulci on T1, leptomeningeal enhancement, sugar coating of cord / drop metastases
Treatment:
Clinical: peaks in childhood and early adult

Radiology Cases of Medulloblastoma

MRI of medulloblastoma in the posterior fossa — Axial (above left), sagittal (above middle) and coronal (above right) T1 MRI with contrast of the brain shows a heterogeneously enhancing mass centered in the fourth ventricle which extends into the right cerebellar hemisphere. Axial T2 MRI (below left) shows the mass to be solid and on diffusion weighted imaging (below right) the mass demonstrates diffusion restriction.

MRI of medulloblastoma — Sagittal T1 MRI without (left) and with (right) contrast of the brain shows a hypointense signal mass filling and distending the fourth ventricle that enhances homogeneously.