What is the most likely diagnosis?
A left sided predominantly intraventricular mass most likely represents a meningioma.
Why do you think lymphoma and metastases are less likely?
The absence of any interval change over 3 months without treatment makes both most unlikely.
Centred in the left lateral ventricle of the trigone is a brightly enhancing mass which measures 33 x 24 x 41 mm and expands the trigone. It has an intraparenchymal component laterally, with only a very small amount of adjacent vasogenic oedema. There is no evidence of calcification or haemorrhage. The mass is isointense on T1 and on T2 weighted images to grey matter, and demonstrates only minor restricted diffusion. There is no evidence of hydrocephalus and it is an isolated abnormality.
Scattered throughout white matter of both cerebral hemispheres are patchy regions of T2 hyper intensity, which are non-specific but most consistent with chronic small vessel ischaemia. The remainder of the brain is unremarkable with no intra or extra-axial abnormality.