Impact of the Recanalization Level and the First-Pass Effect on Functional Outcomes in Patients After M2 MCA Occlusion Thrombectomy

<b>Objective</b>: Acute ischemic stroke (AIS) remains one of the most common causes of death and disability in the world. Mechanical thrombectomy (MT) is the modality of choice in the treatment of AIS and large vessel occlusion (LVO). The endovascular treatment of medium and distal vessel occlusions (DMVO) is currently under intensive scientific investigation. The aim of our study was to prove the feasibility, effectiveness and safety of MT in patients with a primary, isolated occlusion of the M2 segment of the middle cerebral artery (MCA), with a focus on the recanalization level and the first-pass effect (FPE) as predictors. <b>Methods</b>: We prospectively assessed patients after MT for primary isolated occlusion of the M2 MCA segment that were treated at our center during a three-year period between July 2021 and June 2024. Our final cohort included 137 patients who met the inclusion criteria. Epidemiological, clinical and technical data, as well as the clinical and safety outcomes of MT procedures, were recorded and analyzed. The primary outcome was defined as a modified Rankin scale (mRS) score of 0-2. Secondary outcomes included excellent functional independence (mRS 0-1) and successful recanalization, defined by a modified thrombolysis in cerebral infarction (mTICI) score of 2c-3. Safety outcomes included symptomatic intracerebral hemorrhage (sICH), any intracerebral (IC) hemorrhage and 90-day mortality. <b>Results</b>: The mean age of our cohort was 71.8 ± 12.5 years; 59 were men (43.1%). The primary outcome (mRS 0-2) was achieved in 89 (65%) patients. An excellent functional outcome (mRS 0-1) was reached in 58 (42.3%) and successful recanalization (mTICI 2c-3) in 118 (86.1%) patients. sICH was present in 5 cases (3.7%), any IC hemorrhage in 42 (30.7%) and 90-day mortality in 28 (20.4%). We found a statistically significant correlation between the primary outcome (mRS 0-2) and a successful recanalization mTICI of 2c-3 (<i>p</i>-0.024). This correlation was even stronger between excellent functional outcomes and a recanalization mTICI of 2c-3 (<i>p</i> < 0.001). The study did not confirm the importance of the first-pass effect (FPE) during MT of the M2 segment (<i>p</i>-0.489). We also noticed a significant 31.3% mortality increase in the group of patients in which recanalization of the occluded M2 branch was insufficient. <b>Conclusions</b>: MT is a powerful and effective treatment method for AIS caused by an occlusion of the M2 segment in real-life conditions. Patients have a higher probability of a long-term good functional outcome when complete or near-complete reperfusion is achieved.