Increased Rate of Successful First Passage Recanalization During Mechanical Thrombectomy for M2 Occlusion

Background Mechanical thrombectomy (MT) is the standard of care for the treatment of acute ischemic stroke (AIS) due to anterior circulation large vessel occlusion. However, the true safety and efficacy of MT in medium size vessel occlusions like the M2 segment of middle cerebral artery has yet to be completely defined. In this study, we analyze the safety and efficacy of MT in M2 occlusions when compared to M1 occlusions. Methods A restrospective analysis was performed on patients with AIS secondary to M1 and M2 occlusions between 2011 and 2018. The inclusion criterias were: 1) AIS secondary to M1 or M2 occlusion, 2) MT performed by stent retrieval technique alone, aspiration technique, or combined stent retrieval-aspiration techniques. Basic patient characteristics, number of passages, first passage recanalization success (≥TICI 2b), total recanalization success, hemorrhagic complications, (including intracerebral hemorrhage[ICH] and subarachnoid hemorrhage [SAH]), and clinical outcomes were compared between both groups. Results Two hundred and sixty patients met inclusion criteria. 171 patients had M1 occlusion versus 89 patients with M2 occlusion. First passage recanalization success rate was significantly higher in the M2 group(55.1% versus 39.2%, p=0.015). Total recanalization success rate was higher in the M2 group but did not reach significance(83% versus 75%, p=0.128). Subarachnoid hemorrhage rate was significantly higher in the M2 group(25% versus 12%, p=0.010) but there was no difference for ICH complications (14.6% versus 16.4%, p=0.711). Conclusion MT for M2 occlusions has similar overall efficacy as M1 occlusions, but with higher first pass successful recanalization rates. MT for M2 occlusions has a higher risk of associated SAH.