Case 015

History/Physical

53-year-old right-handed male.

Impaired sensation on left side of body over past two months.

The axial T2 sequence shows a large complex lesion in the posterior fossa. The solid component (*) arises from the medial right cerebellum. The large cystic component (arrows) expands the 4th ventricle. There is edema in the right cerebellar white matter (arrowheads).

The cyst fluid is slightly hyperintense (*) compared to simple CSF in the enlarged lateral ventricles (arrowheads), indicating proteinaceous debris.

The irregular solid component enhances avidly (arrowheads).

Diagnosis: Pilocytic astrocytoma

Densely fibrillar lesion with microcysts and prominent vessels.

Spindled tumour cells and scattered Rosenthal fibres (arrow).