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Background and Purpose: Early and complete recanalization achieved in this new era of endovascular therapy (ET) can result in nearly imperceptible lesions on post-treatment MRI. In this context we have observed a pattern of lesion evolution on MRI that is atypical from that seen following IV tPA alone, including striking reversal of the ischemic core. We sought to determine the frequency of acute lesion reversal following ET, and its association with sustained reversal and clinical outcome.Methods: Patients were included in this study if: 1) ET for anterior territory ischemic stroke from Jan 2015 to July 2016, 2) baseline pre-ET and 24h MRI, and 3) consent for research. Two raters evaluated ADC maps for early “reversal” (defined visually as >50%) by comparing 24h to baseline. FLAIR MRI at 30d were later assessed for reversal from baseline, blinded to 24h scan. Early neurological improvement (ENI) was defined as decrease in NIHSS≥8 at 24h. Good clinical outcome defined as mRS≤2.Results: Twenty-two patients were included: median age 68.5 years, 73% women, median baseline NIHSS 19. Median time from last known well to recanalization 254 min. TICI 2b/3 in 91%. ADC reversal in 12 of 22 (55%) at 24h. Reversal at 30d was associated with 24hr (p=0.002) with two having no visually appreciable infarct at 30d. Baseline NIHSS did not differ for early reversal versus without (18.5 vs. 19.5), however NIHSS differed at discharge (1.5 vs. 8.5, p=0.003); early reversal is significantly associated with ENI (83% vs. 30%, p=0.027), but not with good clinical outcome at 30-90d (50% vs. 30%, p=0.415).Conclusions: In this new era of consistently effective ET, salvageable tissue includes not just penumbra but ischemic core, previously considered irreversibly injured. Despite lesion reversal and ENI, for some patients, independent outcome is not achieved, a finding that reinforces the need for adjunctive treatments to build upon the success of ET.Figure: Example of a patient with early ADC reversal.