Posterior Fossa Tumors in children.

The most important differentials to consider are :

• Medulloblastomas arise from the vermis, are hyperdense on non-contrast CT, and show restricted diffusion on MRI due to high cellularity.

• Ependymomas classically arise from the floor of the fourth ventricle and "squeeze" out through the foramina of Luschka and Magendie.

• Pilocytic astrocytomas are typically cystic with a strongly enhancing mural nodule.