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Background: Retrieved clots obtained during intraarterial thrombectomy (IAT) had variable histologic composition containing red (RBC) and white blood cells (WBC), congregated fibrin/platelets. We analyzed histologic composition differences of the retrieved clots by stroke subtypes and recanalization status of the occluded vessels after IAT.Method: We analyzed histologic and angiographic findings of 69 retrieved clots obtained from 26 acute ischemic stroke patients (large-artery atherosclerosis, 6; cardioembolism, 15; undetermined etiology, 5 patients), who received IAT. The individual clot was measured positive pixels of RBC, WBC, and congregated-fibrin/platelet components on Hematoxylin-eosin stained clot using semiautomated quantitative analysis (Aperioscanscope, ver. 12.2, Leica Biosystems). Differences of the three components were compared by the stroke subtypes and by achievement of recanalization status defined as 2 or 3 of the Arterial Occlusive Lesion Scale. Finally, relationship of the recanalization status with clot composition and other risk factors was evaluated using multivariate analysis.Result: RBC component was higher in subtype of cardioembolism (36.04%) than large-artery atherosclerosis (18.18%) and undetermined etiology (24.26%, p=0.019, Kruskal-Wallis test). Instead, congregated-fibrin/platelet component was higher in large-artery atherosclerosis (78.87%) than cardioembolism (59.95%) and undetermined etiology (72.28%, p=0.012). On comparison by the recanalization status, RBC component was higher in retrieved clots achieved recanalization (34.65%) than no-recanalization (13.98%, p=0.003, Mann-Whitney test) of the occluded vessel. Congregated-fibrin/platelet component was lower in the recanalized (61.81%) than the no-recanalized clot (81.63%, p=0.003). On multivariate analysis, RBC component only showed statistical significance as a factor related with recanalization status of the occluded vessels.Conclusion: The present study showed that the high RBC and low fibrin/platelet composition of retrieved clot related with cardioembolic stroke. The RBC-rich clot was related with achievement of recanalization after IAT rather than the platelet/fibrin-rich clot.