A well circumscribed rounded FLAIR hyperintense lesion is centred just to the right of midline in the cerebellar vermis involving the roof of the fourth ventricle. The T2 signal is slightly high, higher than grey matter. Prominent vessel traverses the right lateral aspect of the lesion and demonstrating intrinsic high T1 signal/low T2 signal within the lesion but normally enhancing outside the lesion. No intralesional enhancement. No cystic changes. No intralesional signal loss on gradient-echo sequence to suggest calcification or haemorrhage. There are patchy areas of mildly elevated/intermediate CBV within the mass. MR spectroscopy demonstrates elevated choline and depressed NAA, but no large lactate peak.
Conclusion: Vermian non-enhancing solid lesion is unusual in appearance. The differential is primarily between a medulloblastoma (lack of enhancement suggests genetic group 4) and pilocytic astrocytoma (lack of enhancement is unusual).