Third Cerebellar Hemisphere: An Unusual New Cerebellar Anomaly

Sagittal T2-weighted MR image reveals a mildly dysplastic third cerebellar hemisphere located within a bony outpouching connected to the medulla, with a thin band of soft tissue of signal intensity similar to that of the cortex. In addition, it also reveals a low-lying torcular herophilli and mild basilar invagination. The visualized supratentorial parenchyma appears normal.