High-Flow Bypass for Ruptured Aneurysms at Non-branching Sites of the Middle Cerebral Artery: A Case Report

Small cerebral aneurysms that occur at non-branching sites are generally considered to have extremely weak aneurysm walls or a pseudoaneurysm formed by a thrombus. Since conventional clipping and coil embolization are difficult and high-risk, trapping with bypass has been considered the preferred treatment method. The aim of this study is to investigate a case of trapping with high-flow bypass for a ruptured aneurysm at non-branching sites of the middle cerebral artery (MCA). In this study, the CT results indicated subarachnoid hemorrhage, while the CT angiography (CTA) results showed a small aneurysm at the non-branching site of the MCA M1 segment. Moreover, the intraoperative digital subtraction angiography (DSA) results strongly suggested a pseudoaneurysm. The aneurysm was judged to be a pseudoaneurysm over the rupture site of the true aneurysm sac. Coil embolization was performed, but the treatment was interrupted as the aneurysm completely disappeared during the procedure. However, based on the magnetic resonance angiography findings, the aneurysm reappeared on day five and became enlarged. Thus, trapping with high-flow bypass was performed on day 15 and the patient was cured. Owing to the unusual and noteworthy course of this case, trapping with high-flow bypass was considered to be the safest and most reliable first-choice treatment procedure for pseudoaneurysm at non-branching sites of the MCA.