Fig. 2.

a Preoperative sagittal T1-weighted MR image demonstrating marked hydrocephalus with bulging third ventricular floor, downward bending mammillary bodies, and an open aqueduct. The cerebellum is not rotated. A thin vertical line between dilated fourth ventricle and cisterna magna indicates a Blake’s pouch cyst. The inferior lobules of the vermis are flattened. b Preoperative axial T2-weighted MR image demonstrating a bilateral indentation on the caudomedial cerebellar surface similar to Fig 1b. c Preoperative axial T2-weighted MR image demonstrating enlarged lateral ventricles without periventricular hyperintensities