Background Mechanical thrombectomy (MT) is standard of care for treatment of acute ischemic stroke due to proximal anterior circulation large vessel occlusion, such as the M1 segment of the middle cerebral artery (MCA). The effectiveness and complication profile in more distal vessels such as the M2 segment, however, remains to be completely defined.

Methods All MT treatments for acute M1 or M2 occlusion between 2011 and 2018 were retrospectively reviewed. Patients with thrombectomy using Merci device, intra-arterial pharmacological thrombolysis, mechanical wire maceration, or only using a balloon were excluded. Patient characteristics (age, NIHSS), number of passages, first passage recanalization success (TICI 2b or higher), total recanalization success, and hemorrhagic complications (ICH and SAH) were compared between M1 and M2 groups.

Results Two hundred sixty cases, including 171 M1 and 89 M2 occlusions, were analyzed. The mean age of patients and median of NIHSS were 70.7 ± 15.0 (SD) years and 15 (1–33), respectively. There was no significant difference between M1 and M2 groups for age and NIHSS (p=0.727 and p = 0.065, respectively). The total number of passages in M2 group was significantly less than M1 group (Median of 1 and range of 1 to 5 versus median of 2 and range of 1 to 7, p=0.023). First passage recanalization success rate was significantly higher in the M2 group than the M1 group (55.1% versus 39.2%, p=0.015). The total recanalization success rate also trended higher in the M2 group, but it did not reach statistical significance (83% versus 74.7%, p=0.132). Subarachnoid hemorrhage rate was significantly higher in the M2 group than the M1 group (24.7% versus 12.3%, p=0.010), but there was no difference for ICH between the two groups (p=0.862).

Conclusion Mechanical thrombectomy for M2 occlusions is effective, has a higher rate of first pass recanalization, and has lower total pass number than M1 thrombectomy. However, mechanical thrombectomy in the M2 using recent generations of stent retriever technology is associated with higher rates of SAH, likely related to tension on the vessels when pulling through a more tortuous MCA segment.

Disclosures H. Baharvahdat: None. A. Mowla: None. J. Jones: None. Y. Ooi: None. N. Kaneko: None. R. Jahan: None. S. Tateshima: None. V. Szeder: None. M. Nour: None. F. Vinuela: None. G. Duckwiler: None. G. Colby: 2; C; Stryker Neurovascular, Medtronic.