Discrepancy between Angiography and Operative Findings of Small Side Wall Aneurysms in Atherosclerotic Parent Arteries

Preoperative evaluation of precise aneurysmal geometry is important for the treatment of intracranial aneurysms. We present two cases of unclippable side wall aneurysms due to their extremely low dome height, which appeared as saccular in the preoperative image because of a comparatively narrow atherosclerotic parent arterial lumen. In both cases, a calcified vessel wall was noted preoperatively. Lack of a definitive neck and abrupt discrepancy between the fragile aneurysmal wall and the atherosclerotic parent arterial wall was confirmed intraoperatively in both cases. This study describes an illustrative mechanism for the finding with emphasis on the importance of its preoperative diagnosis. Intracranial atherosclerosis associated with small side walled aneurysms may lead to overestimation of aneurysm height on preoperative imaging of the intravascular compartment.