There is a mass like focal lesion involving the superior and lateral aspect of the right cerebellar hemisphere and characterised by widening and anatomical distortion of the cerebellar folia with a striated cystic appearance. It does not show enhancement or diffusion restriction. Spectroscopy traces are unremarkable, similar to the contralateral cerebellar hemisphere. There is a local mass effect with an herniated right cerebellar tonsil descending about 7 mm below the foramen magnum and mild distortion of the fourth ventricle. No hydrocephalus. The remainder of the brain parenchyma appears normal.