Abstract
A 77-year-old man suffered subarachnoid hemorrhage due to a ruptured aneurysm of the distal anterior inferior cerebellar artery (AICA). He had a history of hearing disturbance in the left ear for more than 3 years. Computed tomography on three separate occasions had found no abnormalities. One month before the hemorrhage, he came to our outpatient service complaining of vertigo. Magnetic resonance (MR) imaging and MR angiography detected no abnormality. Conventional angiography demonstrated an aneurysm of 8 mm diameter in the distal AICA region after the hemorrhage. Filling and wash out of the aneurysm sac by contrast medium was markedly delayed, which suggested that MR imaging had failed to detect the flow void because of the slow blood flow in the dome. The aneurysm was clipped successfully. He was discharged with mild dysarthria on the 33rd postoperative day. MR angiography has limitations in detecting unruptured aneurysms and there is certainly a high risk group of false negatives, including aneurysms located in the distal region of the main trunk.
