Distal occlusion and revascularization for microsurgical treatment of ruptured unclippable M1 segment middle cerebral artery aneurysms: Surgical outcomes and complications

Background: Complex, unclippable aneurysms of the pre-bifurcation segment of the M1 middle cerebral artery (pre-bM1) are rare and challenging to treat due to their association with lenticulostriate arteries (LSAs), particularly in ruptured cases. This study evaluates the outcomes and complications of microsurgical treatment employing distal occlusion and revascularization. Methods: Eight patients with ruptured unclippable pre-bM1 aneurysms treated via distal occlusion and revascularization between 2018 and 2024 were retrospectively analyzed for radiographic and clinical outcomes. Results: Complete aneurysm obliteration was achieved in all patients, with seven (87.5 %) out of eight patients attaining this within 7 days post-surgery. No postoperative rebleeding occurred, and all bypass grafts remained patent. Early postoperative LSA infarctions were detected in five patients (62.5 %), with only one (12.5 %) patient experiencing early worsening of hemiparesis. At discharge, good outcomes were observed in five (5/8: 62.5 %) patients overall and four patients (4/4: 100 %) of those with good preoperative grades. Conclusions: Distal occlusion and revascularization proved safe and effective for treating ruptured unclippable M1 aneurysms. The procedure achieved high rates of aneurysm thrombosis with minimal symptomatic complications. Postoperative LSA infarction was the primary complication, although most cases were asymptomatic. Further refinement of microsurgical techniques is warranted to reduce this complication.