Within the fourth ventricle has an enhancing tumour extending inferiorly posterior to the upper cervical cord. It moulds to the contours of the surrounding brainstem and cerebellum. On some of the lower images there appears to be a component arising from the dorsal aspect of the medulla. The mass demonstrates only intermediate diffusion restriction, prominent susceptibility induced signal loss suggesting blood product, without frank haemorrhage.
On the right side of the lesion a more focal region demonstrates signal loss and increased density on CT and may represent calcification or more acute blood. The PICAs are embedded with thin the mass without obvious large additional flow voids. The outlet to the fourth ventricle is occluded with resultant obstructive hydrocephalous and minor transependymal oedema. The remainder of the brain is unremarkable in appearance,
Conclusion: Fourth ventricular mass almost certainly represents an ependymoma. Choroid plexus papilloma and haemangioblastoma are much less likely differentials.