Background and Purpose- The introduction of stent retrievers allows for a complete extraction and histological analysis of human clots. Initial studies describe an impact of preinterventional clot migration on technical and clinical success of thrombectomy and an association with worse clinical outcome. We, therefore, performed a large study of consecutive patients whose clots have been histologically analyzed and tried to determine whether clot composition influences the rates of clot migration and thereby interventional and clinical outcome. Methods- We retrospectively evaluated data of a prospectively collected cohort of 198 consecutive patients with occlusion of the middle cerebral artery. We investigated the relationship between clot histology expressed as percentage of the main components (fibrin, erythrocytes [red blood cell], and white blood cells), the preinterventional computed tomography attenuation of the emboli, embolus length, and clot migration. We defined a binary outcome (clot migration versus no clot migration). The impact of embolus composition and computed tomography features was assessed in univariable and multivariable logistic regression models. Results- One hundred sixty-three patients fulfilled the inclusion criteria, of which 36 (22.1%) showed a clot migration. Patients with proven clot migration had significantly higher levels of red blood cells than patients without clot migration (median 50% versus 26%, P<0.001). Lower amounts of fibrin were significantly more often observed in patients in the clot migration group as compared to the no clot migration group (43.5% versus 62.0%, P<0.001). Stroke cause did not differ between migrated and stable emboli. Multivariable analysis identified a higher amount of erythrocytes (adjusted odds ratio, 1.03 per median percentage, P<0.001) and a shorter embolus length (adjusted odds ratio, 0.90 per mm, P<0.008) as independent predictors of clot migration. Conclusions- Erythrocyte-rich clots and a shorter embolus length are independent reliable predictors for clot migration. This finding is clinically important as clot migration might have a negative impact on technical and clinical outcomes of patients suffering from emergent vessel occlusions of the middle cerebral artery undergoing endovascular therapy.
