Atypical features of medulloblastoma on magnetic resonance imaging: case report and review of the literature.

Magnetic resonance imaging (MRI) is the radiologic modality of choice used to evaluate suspected lesions in the posterior fossa, given its greater sensitivity compared with other neuroimaging techniques. The case of a 9-year-old girl with progressive ataxia is presented. MRI of the brain demonstrated nonspecific T2-weighted abnormalities involving the cerebellar vermis with minimal mass effect suggested by asymmetric enlargement of the left superior cerebellar peduncle. Postgadolinium studies showed only minimal enhancement of the left superior cerebellar peduncle. After an MRI of the spine demonstrated drop metastases, a cerebellar biopsy was performed, which revealed an infiltrating medulloblastoma confined to the granular layer and leptomeninges. Hence, MRI is an important ancillary tool in the diagnosis of medulloblastoma, but caution needs to be taken when interpreting imaging studies.