Thrombus Migration in the Middle Cerebral Artery: Incidence, Imaging Signs, and Impact on Success of Endovascular Thrombectomy

BACKGROUND Thrombus migration (TM) in intracranial vessels during ischemic stroke has been reported in the form of case reports, but its incidence, impact on the technical success of subsequent endovascular thrombectomy and patients' outcome have never been studied systematically. METHODS AND RESULTS Retrospective analysis was done of 409 patients with isolated middle cerebral artery occlusions treated with endovascular thrombectomy. TM was observed (1) by analyzing discrepancies between computed tomographic angiography and digital subtraction angiography and (2) by comparing infarct pattern in the striatocapsular region with exact, angiographically assessed thrombus location within the M1-segment and the involvement of the middle cerebral artery perforators. Preinterventional infarction of discrepant regions (infarction in regions supplied by more proximal vessels than those occluded by the clot) was ensured by carefully reviewing available preinterventional multimodal imaging. Adequate imaging inclusion criteria were met by 325 patients. Ninety-seven patients showed signs of TM (26 with direct evidence, 71 with indirect evidence). There was no difference in the frequency of preinterventional intravenous recombinant tissue plasminogen activator administration between patients with TM and those without (63.9% vs 64.9%, P=0.899). TM was associated with lower rates of complete reperfusion (Thrombolysis in Cerebral Infarction score 3) (adjusted odds ratio 0.400, 95% CI 0.226-0.707). Subsequently, preinterventional TM was associated with lower rates of substantial neurologic improvement (adjusted odds ratio 0.541, 95% CI 0.309-0.946). CONCLUSIONS Preinterventional TM does not seem to be facilitated by intravenous recombinant tissue plasminogen activator and often occurs spontaneously. However, TM is associated with the risk of incomplete reperfusion in subsequent thrombectomy, suggesting increased clot fragility. Occurrence of TM may thereby have a substantial impact on the outcome of endovascularly treated stroke patients.