Early- versus Late-Window Mechanical Thrombectomy for Isolated M2/M3 Middle Cerebral Artery Occlusions: 90-Day Outcomes and Procedural Characteristics in a Single-Center Cohort.

BACKGROUND: Randomized evidence for mechanical thrombectomy (MT) in medium vessel occlusions, particularly beyond 6 h, is heterogeneous. In a secondary analysis of a previously reported single-center cohort, we compared MT for isolated M2/M3 occlusions within versus beyond 6 h from last known well. METHODS: Consecutive patients treated between January 2020 and August 2023 were retrospectively stratified by last-known-well-to-groin-puncture time (≤ 6 h vs. > 6 h). The primary outcome was functional independence (modified Rankin Scale [mRS] 0-2) at 90 days. Because all patients underwent MT, superiority over medical management cannot be addressed. Logistic regression was adjusted for age and baseline NIHSS. RESULTS: Seventy-six patients were analyzed (56 early, 20 late). No significant difference was detected in 90-day functional independence (8/20 [40.0%] vs. 22/56 [39.3%]; absolute risk difference + 0.7%, 95% confidence interval [CI] - 24.3 to + 25.7; p = 1.00), the ordinal 90-day mRS (median 3 vs. 3; p = 0.56), or 90-day mortality (15.0% vs. 10.7%; p = 0.69). After adjustment, late-window treatment was not associated with functional independence (adjusted odds ratio 0.75, 95% CI 0.22-2.56). Late-window procedures required more retrieval maneuvers (median 2 [1-3] vs. 1 [1, 2]; p = 0.017) and rescue therapy (50.0% vs. 14.3%; p = 0.004) and numerically achieved complete first-pass reperfusion less often (20.0% vs. 46.4%; p = 0.070). Symptomatic intracranial hemorrhage was numerically higher in the late group (10.0% vs. 1.8%; p = 0.17). CONCLUSIONS: No statistically significant 90-day outcome difference was detected, although wide confidence intervals do not exclude clinically meaningful differences and a medical-management comparator was absent. Late-window procedures involved greater procedural effort. Findings are descriptive and hypothesis-generating.