Related Experiment Video
Updated: Jun 13, 2026
The Stroke Preclinical Assessment Network Multi-Laboratory Model of Thromboembolic Stroke with Thrombolysis: TE-MCAo
Published on: December 19, 2025
Mechanical Thrombectomy for M2 versus M1 Occlusions: A Propensity-Matched Analysis With Severity-Stratified
Matthew M Zidan1, Hanna Zimmermann2, Helge Kniep2
1From the Department of Diagnostic and Interventional Neuroradiology (M.M.Z., S.O., C.G., A.R., F.D.), Bonn University Hospital, Bonn, Germany; Department of Neuroradiology (H.Z., F.D.), LMU-Klinikum der Universität München Medizinische Klinik und Poliklinik IV, Munich, Germany and Department of Diagnostic and Interventional Neuroradiology (H.K., J.F.), University Medical Center Hamburg- Eppendorf, Germany. mousa.zidan@ukbonn.de.
Background And Purpose:
Recent randomized controlled trials of endovascular therapy (EVT) for medium-vessel occlusions yielded neutral results, partly attributed to enrollment of patients with mild deficits and exclusive reliance on the 90-day mRS. Using propensity score matching (PSM), we compared mechanical thrombectomy (MT) outcomes between M1 and M2 occlusions.
Methods:
This retrospective cohort study used data from the Top-Gear imaging repository. Patients with isolated M1 or M2 occlusions who underwent EVT were included. PSM was performed on age, sex, pre-stroke mRS, admission NIHSS, IV tPA administration, and number of recanalization passes (>3). Primary outcome was 90-day mRS ≤2. Secondary outcomes included ENI and 90-day mRS distribution.
Results:
Of 419 screened patients, 171 met eligibility criteria (M1: n=98, M2: n=73). After PSM (n=52 per group), M2 occlusions were associated with significantly higher rates of good outcome (51.9% vs. 30.8%, p=0.04) and lower mortality (19.3% vs. 38.5%, p=0.05). In multivariable logistic regression, M2 occlusion was independently associated with favorable outcome (OR 2.32, 95% CI 1.01-5.3, p=0.04). Stratified analysis by baseline NIHSS after PSM showed that ENI was uncommon in mild strokes (NIHSS ≤5) but occurred in 75% and 65.6% of patients with moderate and severe M2 strokes, respectively. Among M2 patients with ENI, 64.5% achieved mRS ≤2 at 90 days, compared to 33.3% of M1 patients with ENI.
Conclusions:
The M2 occlusion location was independently associated with favorable outcome following MT, with a particularly pronounced benefit among patients with moderate-to-severe baseline deficits. ENI was associated with good functional outcome in M2 occlusions, not in M1 occlusions. These findings suggest that the benefit of MT in M2 occlusions may be concentrated in patients with NIHSS ≥6, a population potentially underrepresented in recent RCTs.
Insights
Mechanical thrombectomy (MT) for M2 occlusions shows better outcomes than M1, especially in severe strokes. Early neurological improvement (ENI) predicts good results in M2 occlusions, suggesting MT benefits may be concentrated in specific patient groups.
Area of Science:
- Neurology
- Interventional Neurology
- Stroke Medicine
Background:
- Recent trials on endovascular therapy (EVT) for medium-vessel occlusions had neutral results.
- This may be due to including patients with mild deficits and relying solely on the 90-day modified Rankin Scale (mRS).
- Propensity score matching (PSM) can help compare outcomes between different occlusion types.
Purpose of the Study:
- To compare mechanical thrombectomy (MT) outcomes between M1 and M2 medium-vessel occlusions using PSM.
- To investigate the association of early neurological improvement (ENI) with functional outcomes in M1 versus M2 occlusions.
- To identify patient subgroups that may benefit most from MT in medium-vessel occlusions.
Main Methods:
- Retrospective cohort study using the Top-Gear imaging repository.
- Included patients with isolated M1 or M2 occlusions undergoing EVT.
- Used PSM based on age, sex, pre-stroke mRS, NIHSS, IV tPA, and recanalization passes; primary outcome was 90-day mRS ≤2.
Main Results:
- After PSM, M2 occlusions showed significantly higher rates of good outcomes (51.9% vs. 30.8%, p=0.04) and lower mortality (19.3% vs. 38.5%, p=0.05).
- M2 occlusion was independently associated with favorable outcomes (OR 2.32, p=0.04).
- ENI was common in moderate-to-severe M2 strokes (65.6%-75%) and associated with good outcomes (64.5% mRS ≤2), unlike in M1 occlusions (33.3% mRS ≤2).
Conclusions:
- M2 occlusion location is independently associated with favorable outcomes after MT, particularly in patients with moderate-to-severe deficits (NIHSS ≥6).
- ENI predicts good functional outcomes in M2 occlusions but not M1 occlusions.
- MT benefit in M2 occlusions may be concentrated in patients with NIHSS ≥6, a group potentially underrepresented in prior RCTs.
