Does the MRI confirm the diagnosis? Explain the low T2 signal.
Yes, appearances are consistent with a giant, mostly thrombosed, aneurysm. Very low T2 signal due to a combination of flow void centrally and thrombus (blood product induced signal drop out) peripherally.
In the suprasellar region, anterior to the pituitary is a 19 x 21 x 18mm rounded mass with heterogeneous lamellated internal signal (predominantly high T1 and very low T2) consistent with a thrombosed aneurysm. Posterosuperiorly flow void is noted consistent with a patent aneurysm 8 x 6 x 6mm arising from the ACA / Acom complex. The dome of the thrombosed aneurysm presses down on both optic nerves, more so on the left. Oedema is present in gyrus rectus on the right. Chronic small vessel ischaemic change is seen elsewhere.