Cerebral No‐Reflow after Thrombectomy: International Delphi Consensus on Definition and Imaging Assessment

Abstract

BACKGROUND: The operational definition and imaging assessment of the no-reflow phenomenon, a potential contributor to poor clinical outcome despite successful thrombectomy, remains debated. We aimed to develop expert-based international consensus on the definition, assessment, and reporting standard of cerebral no-reflow post-thrombectomy. METHODS: Three-rounds of a modified Delphi web-based survey was conducted among corresponding authors of peer-reviewed clinical studies on cerebral no-reflow between 2020 and 2025. Responses at each round were used to develop structured questionnaires for subsequent rounds. Consensus was predefined as ≥65% agreement. RESULTS: Among 27 panelists, the response rate was 70%, 74%, and 74% over all rounds. There was broad agreement to conceptualize no-reflow as macrovascular recanalization with impaired microvascular reperfusion. Consensus was reached that macrovascular recanalization is ideally assessed as (1) digital subtraction angiography with expanded thrombolysis in cerebral infarction (eTICI) grades 2c without clear distal vessel occlusions and/or eTICI 3 only, and (2) absence of a wedge-shaped time-to-maximum (Tmax) or time-to-peak (TTP) delay on post-recanalization perfusion computed tomography (CT) or magnetic resonance imaging (MRI). Regarding impaired microvascular reperfusion assessment, cerebral blood flow, and/or volume were preferred over time-based perfusion parameters (Tmax/TTP). The panel expressed a preference that no-reflow should ideally be assessed ≤6 hours post-recanalization. Pending formal validation, histopathological-radiological correlation in animal models would sufficiently validate the use of imaging-based definitions in humans. INTERPRETATION: Based on currently available literature and expert opinions, this Delphi study provides a framework for systematically reporting cerebral no-reflow after endovascular treatment (EVT). The variability in opinions regarding quantitative thresholds highlights priorities for future methodological standardization and validation studies. ANN NEUROL 2026.