Abstract WP138: Collateral Status Measured by Hypoperfusion Intensity Ratio Correlates With Infarct Core Size and Growth Rate in MCA Medium Vessel Occlusions <6 Hours and 6-24 Hours Post Onset

Abstract

Purpose: Hypoperfusion intensity ratio (HIR) derived from CT perfusion (CTP) has shown to be a useful surrogate marker of collateral status, but prior studies focused on ICA/M1 large vessel occlusions (LVO). We aimed to determine: associations between HIR and clinical/imaging metrics of stroke severity for M2 and M3 medium vessel occlusions (MVO), any differences between <6h and 6-24h from onset as MVO often present later than LVO, and what optimal HIR threshold describes infarct growth rate (IGR) >10mL/h (fast progressor). Methods: We retrospectively analyzed consecutive patients arriving within 24h from onset, with M2 or M3 occlusion on CTA, and had concurrent CTP. RAPID generated maps of infarct core defined as rCBF<30% and HIR defined as Tmax>10s/Tmax>6s. IGR was defined as core size/onset-to-CTP time. ASPECTS and NIHSS data were also collected. Correlations were tested using Spearman's rank analysis, for the cohort and separately for <6h and 6-24h subgroups. Difference in HIR between subgroups was tested using Mann-Whitney U. Optimal threshold for IGR>10mL/h was determined by ROC analysis. Results: 78 patients included with median (IQR) age of 79 (64-84), onset of 7.5h (2.5-14.5), NIHSS of 12 (7-18), ASPECTS of 7 (9-10), core size of 4 mL (0-22), and IGR of 0.57 mL/h (0-2.8). 63 M2 and 15 M3 occlusions identified with median HIR of 0.35 (0.06-0.52). For the cohort, HIR was highly correlated to core size r=0.740 and IGR r=0.710, moderately correlated to NIHSS r=0.474 and ASPECTS r=-0.331 (all p<0.003). 28 and 50 patients presented <6h and 6-24h, respectively, without significant difference in HIR, median 0.31 vs 0.36 (p=0.543). For <6h, HIR was moderately correlated to core size r=0.672, IGR r=0.639, NIHSS r=0.435, and ASPECTS r=-0.496 (all p<0.021). For 6-24h, HIR was highly correlated to core size r=0.791 and IGR r=0.777, moderately correlated to NIHSS r=0.502 and ASPECTS r=-0.376 (all p<0.007). ROC analysis showed AUC of 0.860 (p<0.001) for IGR>10mL/h, with optimal HIR threshold at 0.43 for sensitivity of 100% [95% CI: 59.0-100], specificity of 64.8% [95% CI: 52.5-75.5]. Conclusion: In acute MCA MVO strokes <6h and 6-24h, HIR as marker of collateral status is moderate to highly correlated to stroke severity, especially size and growth rate of the infarct core.