What is the differential diagnosis of T1 hyperintense foci in the subarachnoid space?
Subarachnoid hemorrhage and ruptured dermoid cyst.
The patient had a history of hydrocephalus and underwent a VP shunt insertion.
Complex right temporal intra-axial lesion. On T1 weighted images it displays heterogeneous intensity predominantly low signal in the centre of the lesion with peripheral hyperintensity. On T2 weighted axial images the lesion is predominantly hyperintense in the centre and periphery. There is prominent chemical shift artefact at the anterior margin of the T1 hyperintense components confirming that this is fatty material. Furthermore, the peripheral component demonstrates signal loss on fat-suppressed T2 gradient echo sequences. Scattered rounded droplets of hyperintense signal in T1 and FLAIR are seen disseminated within the subarachnoid space.