What is the differential diagnosis for this lesion, in an elderly patient?
Abscess, cystic metastasis, cystic primary brain tumour.
Which do you favour and why?
Both the morphology (regular thin peripheral enhancement) and more importantly restricted diffusion on DWI strongly favour an abscess.
Selected MRI images demonstrate a left cerebellar hemisphere lesion, which has high T2 signal centrally, and a thin relatively regular rim of contrast enhancement peripherally. Centrally restricted diffusion is present, confirmed on ADC (not shown). Note the presence of dilatation of the occipital horns, consistent with hydrocephalus.