Mechanical thrombectomy in M1 and M2 segments of middle cerebral arteries: A meta-analysis of prospective cohort studies

Background: Recent studies indicate that endovascular therapy is superior to intravenous thrombolysis in treating M1 segment MCA occlusions, however, the effectiveness of mechanical thrombectomy in MI vs. M2 segment occlusions is unclear. Methods: The meta-analysis was conducted by searching databases from January 2016 to January 2023, without language constraints. The quality of the studies was assessed using the Newcastle-Ottawa Scale. Pooled data analysis of outcomes, pre-existing medical comorbidities, and baseline scores were performed. Results: Six prospective cohort studies with 6356 patients were included (4405 vs. 1638). Patients with M2 occlusion had a significantly lower mean baseline NIHSS at admission (MD: -2.14; 95 %CI: -3.48 to -0.81; p = 0.002). Conversely, patients with M1 occlusion had a lower ASPECTS at admission score (MD: 0.29; 95 %CI: 0.00-0.59; p = 0.05). No significant difference was found between segments in terms of pre-existing medical comorbidities (OR: 0.96; 95 %CI: 0.87-1.05; p = 0.36), mortality rate at 90 days (OR: 0.88; 95 %CI: 0.76-1.02; p = 0.10), and hemorrhage occurrence within 24-hours (OR: 1.06; 95 %CI: 0.89-1.25; p = 0.53). Patients with M2 occlusion were more likely to have good outcomes after therapy (OR: 1.18; 95 %CI: 1.05-1.32; p = 0.006). Successful recanalization rates were comparatively higher among patients with an M1 occlusion (OR: 0.79; 95 % CI: 0.68-0.92; p = 0.003). Functional outcomes at 90 days are better in M2 occlusion patients, while successful recanalization rates are higher in M1 occlusion patients. No significant differences were found in mortality rates or hemorrhage incidence. Conclusions: These results suggest that mechanical thrombectomy is a safe and effective treatment for MCA occlusions in both M1 and M2 segments.