On the MRI sequences, the vermian mass appears iso-to hypointense to the cortical grey matter on T1, iso-to hyperintense on T2/FLAIR, containing areas of cystic change/necrosis with heterogeneous enhancement following IV contrast and restricted diffusion within the solid component (the ADC value of the tumour is around 554 x 10-6 mm2/s, lower than normal cerebellum. No calcification or haemorrhagic component is seen.
Moderate surrounding vasogenic oedema with a mass effect on the brainstem and fourth ventricle with tonsillar herniation. Dilated third and lateral ventricles with transependymal oedema (obstructive hydrocephalus).
The MRS shows elevated choline and decreased NAA.