What is the diagnosis?
Features are those of a tectal plate glioma with compensated longstanding obstructive hydrocephalus, suggesting that this tumour is indolent and has been present for many years.
The right side of the tectal plate is expanded by a nodular mass which measures 15 x 14 x 11 millimetres in size. It is hyperintense on T2, isointense on T1, and demonstrates no contrast enhancement or restricted diffusion. The aqueduct is compressed with prominent obstructive hydrocephalus of the third and lateral ventricles. There is no transependymal oedema, marked thinning of the corpus callosum, and fenestration of the septum pellucidum, which is cavum and demonstrates prominent flow artefact anteriorly.
The cerebellar tonsils are low lying, protruding 8 mm below foramen magnum in keeping with an acquired Chiari one malformation.
The remainder of the brain is unremarkable with no intra or extra-axial abnormality.