There is a lobulated mass in the midline of the posterior fossa measuring 24 x 32 x 30 mm (trans, AP, CC). It is intimately related in the inferior vermis and extends into the left cerebellar hemisphere. It abuts the floor of the fourth ventricle and partially effaces it and it extends through the foramen magnum and displaces the medulla anteriorly.
The mass has homogenous enhancement with no diffusion restriction. There are prominent flow voids within the tumour. I note that the tumour is hyperdense on a non-contrast CT.
Right frontal approach ventricular drain with tip in the right lateral ventricle. Mild hydrocephalus persists. The cisternal magna is enlarged.The remainder of the brain is unremarkable with no evidence of CSF seeding.
IMPRESSION: Vascular appearing posterior fossa mass centred in the inferior cerebellar with MRI appearances not pathognomonic of any one particular entity. The differential diagnosis is between choroid plexus papilloma, haemangioblastoma, ependymoma and pilocytic astrocytoma. Medulloblastoma is unlikely due to facilitated diffusion.