MR shows an intraaxial SOL  involving the cerebellar vermis and left cerebellar parenchyma which contains both solid and cystic components. The solid components are cellular as evidenced by low ADC values.

Originally classified as a glioma, medulloblastoma is referred to now as a primitive neuroectodermal tumor (PNET). This tumor accounts for approximately 7-8% of all intracranial tumors and 30% of pediatric brain tumors.

Medulloblastoma is more common in males than females (1.5:1). Although predominantly a pediatric tumor, medulloblastoma can affect patients of any age from neonates to the elderly. Three quarters of all cases occur in children, with a median age of 9 years.

a. 4th ventricle arises from roof ( superior medullary velum). Distinguishes from ependymoma which arises from floor of 4th ventricle

b. Lateral origin ( cerebellar hemisphere): Adults, more frequently than        children, can have the desmoplastic variant of medulloblastoma. This form of the tumor is situated laterally in the hemisphere with indistinct borders and small cystic or necrotic areas.

a.Prior to administration of intravenous (IV) contrast, the tumor is hyperdense to the brain as a result of its high cellularity. Preoperatively, high density on CT scan can help distinguish medulloblastoma from the hypodense appearance of a cerebellar astrocytoma. Medulloblastoma shows marked contrast enhancement.

b. Ependymoma is another hyperdense tumor that affects the posterior fossa of children. Unlike medulloblastoma, however, it often contains calcifications that can be recognized easily on CT scan. Choroid plexus papilloma usually arises in the trigone of the lateral ventricle in children; however, in adults it is most common in the fourth ventricle. Similar to ependymoma, choroid plexus papilloma commonly contains calcifications

T1WI : Hypointense to gray matter.

90% enhance. Contrast is essential to detect CSF dissemination.

Linear icing- like enhancement over spinal cord; “Zuckerguss”.

T2WI : Near gray matter intensity.

DWI: Restricted diffusion.

Besides identifying the primary lesion, MRI is beneficial in detecting metastatic lesions. To rule out drop metastases, MRI of the spine is obligatory when  medulloblastoma is either considered or diagnosed.