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Background: A third of endovascularly treated stroke patients experience incomplete reperfusion (expanded Thrombolysis in Cerebral Infarction, eTICI<3) and the natural evolution of this incomplete reperfusion remains unknown. We systematically reviewed literature and performed a meta-analysis on the natural evolution of incomplete reperfusion after endovascular therapy., Methods: A systematic review of MEDLINE, Embase and PubMed up until March 1, 2024 using a predefined strategy. Only full-text English written articles reporting rates of either favorable (i.e., delayed reperfusion or no new infarct) or unfavorable progression (i.e., persistent perfusion deficit or new infarct) of incompletely reperfused tissue were included. Primary outcome was the rate of delayed reperfusion and its association with functional independence (modified Rankin Scale, mRS 0-2) at 90 days post-intervention. Pooled odds ratios (OR) with 95% confidence intervals (CI) were calculated using a random-effects model., Results: Six studies involving 950 patients (50.7% female; median age 71, IQR 60-79) were included. Four studies assessed the evolution of incomplete reperfusion on MRI perfusion imaging, while two studies used DWI and NCCT imaging, where new infarct was used to denote unfavorable progression. Five studies defined incomplete reperfusion as eTICI2b50 or 2c. Delayed reperfusion occurred in 41% (IQR 33%-51%) of cases 24h post-intervention. Achieving delayed reperfusion was associated with higher likelihood of functional independence at 90 days (OR 2.5, 95%CI 1.9-3.4)., Conclusions: Nearly half of eTICI<3 patients achieve delayed reperfusion, leading to favorable clinical outcome. This subgroup may derive limited or potentially harmful effects from pursuing additional reperfusion strategies (e.g., intra-arterial lytics or secondary thrombectomy). Accurately predicting the evolution of incomplete reperfusion could optimize patient selection for adjunctive reperfusion strategies at the end of an intervention.