What is the most likely diagnosis? What is the differential?
Left posterior fossa mass demonstrates features typical of an haemangioblastoma and considering the patient's age this is the most likely diagnosis, with cystic metastasis and pilocytic astrocytoma far less likely.
Left intra-axial posterior fossa mass measuring 14 x 28 mm characterised by large cyst with enhancing nodule measuring 13 x 10 mm. The nodule abuts pia inferiorly and a small superficial vessel is seen entering the nodule (best seen on T2 weighted images). No evidence of abnormal susceptibility or diffusion restriction.
Associated surrounding oedema and mass effect causes effacement of the adjacent sulci and compression of the fourth ventricle. Dilated lateral ventricles and third ventricle with transependymal oedema present consistent with hydrocephalus. Tonsillar herniation, presumed secondary to mass effect from the tumour is also noted.
No further lesions are identified.