Figure 14c. Medulloblastoma in a 33-year-old man with a 6-month history of headache and 2-week history of ataxia, vertigo, and vomiting. (a) Axial T1-weighted MR image shows predominantly hypointense masses that involve both cerebellar hemispheres. There is an ill-defined area (arrows) of nearly isointense signal along the posterior margin of the left cerebellar mass. Linear areas that are isointense (arrowheads) relative to normal cerebellar tissue are noted along the ventral margin of the left hemispheric mass. These areas bear some resemblance to the "striated" pattern seen in dysplastic cerebellar gangliocytoma (Lhermitte-Duclos disease), with the exception that the axis is perpendicular to that typically seen in the latter disease. (b) Axial T2-weighted MR image reveals predominant hyperintensity of the masses. An area of mild hypointensity suggestive of soft tissue can be seen along posterior margin of left hemispheric mass. (c) Contrast-enhanced axial T1-weighted MR image demonstrates intense enhancement of the soft-tissue portion.