MRI of a 35-year-old female with dysplastic gangliocytoma of the cerebellum (Lhermitte-Duclos disease), which is a rare posterior fossa disease that results in an expansive appearance of the cerebellum with thickened folia. The lesion is isointense in T1 and hyperintense in T2, without enhancement. There is posterior fossa mass effect with fourth ventricle shift and effacement.  A ventricular diversion was performed before the MRI scan.