PILOCYTIC ASTROCYTOMA.

A large well defined lesion (measuring ~ 58 x 48 x 42 mm) is seen in the posterior fossa in midline. The lesion appears hypointense on T1W and hyperintense on T2W / FLAIR. Few peripheral foci of GRE blooming are seen - likely calcification / hemorrhage. No obvious diffuse restriction is seen. The lesion shows thin peripheral enhancement with eccentric nodular enhancement. Mild edema is seen in the adjacent cerebellar parenchyma. The lesion is causing mass effect on the brainstem and fourth ventricle. There is dilatation of third and bilateral lateral ventricles with periventricular ooze. D/D: Pilocytic astrocytoma.