Abstract WP69: Does CBF Below 30% Actually Represent Infarct Core in Acute Ischemic Stroke? Proof of Mis-Concept

Abstract

On CT perfusion (CTP), cerebral blood flow < 30% than the contralateral hemisphere (CBF<30) is considered a marker of infarct core. Our hypothesis is that CBF<30 defines a reversible poor hemodynamic area rather than core and aimed to study CBF<30 evolution over time, its relationship with leptomeningeal collateral circulation (CC) and outcome parameters. Methods: Retrospective analysis of a prospective database of acute ischemic strokes who underwent CTP on admission and immediately after endovascular thrombectomy (EVT). CC was graded on CT angiography (CTA) by the modified Tan scale (good CC: 2-3 grades). Complete recanalization was defined by modified Thrombolysis in Cerebral Ischemia ≥ 2B. Final infarct volume (FIV) was semi-automatically measured on 48-72h CT; ghost core was defined as: admission CBF<30 - FIV > 10cc. Results: We included 494 patients; median time from onset to CT: 137 min (IQR 68-238). Median CBF<30 volume on admission: 8 cc (0-28). With longer onset-to-CT times ischemic changes progressively increased on non-contrast CT (ASPECTS decay r=-0.21, p<0.01), however CBF<30 progressively decreased (r=-0.13, p<0.01). 294 patients (60.6%) presented good CC. Good CC was associated with lower admission CBF<30 (median CBF<30 on good CC: 0 cc (0-12) vs 28.5 (7-57) on poor CC, p<0.01). In recanalized patients (419, 84.8%), CBF<30 virtually disappeared in CTP post-EVT (n=103) (median CBF<30: 0ml (IQR 0) (88%= 0 cc) despite that most patients developed established infarcts (median FIV 16 (4-50), 59% FIV>10cc)). Even in recanalized patients, baseline CBF<30 only moderately correlates with FIV (r=0.55, p<0.01). A ghost core was identified in 13.7% (34.5% if CT was performed <90min from onset). 46.6% patients had good functional outcome (mRS<3 at 3 months). A multivariate analysis of recanalized patients showed that CC (OR 0.43, CI 0.27-0.69, p<0.01) but not CBF<30 was an independent predictor of functional outcome. Conclusion: CBF<30 represents an hemodynamic state rather than established infarct core, evolving over time inversely as it should physiologically (increase of infarct core over time). CBF<30 should be considered as an outcome predictor but not used as exclusion criterion for EVT, especially in early time-windows.