Microcirculatory Collaterals Modulate Ischemic Core Heterogeneity on Diffusion-Weighted Imaging

Endovascular thrombectomy (EVT) is an effective treatment for acute ischemic stroke due to large vessel occlusion (AIS-LVO). The ischemic core is best determined on DWI, which is commonly thresholded for automated analysis using ADC maps. However, there may be substantial heterogeneity in ADC values within the ischemic core. We determined how tissue-level collaterals, measured by hypoperfusion intensity ratio (HIR) on cerebral perfusion imaging, influences ischemic core heterogeneity.

We performed a post hoc analysis of the CT Perfusion to Predict Response to Recanalization in Ischemic Stroke Project 2 (CRISP 2) study of patients with AIS-LVO who underwent baseline CT/CTP and follow-up MRI/MR perfusion (MRP) prior to EVT. Patients were dichotomized into favorable (HIR ≤0.5) and unfavorable (HIR >0.5) groups, and variability in ADC reduction was determined across an ischemic core defined by standard thresholds of ADC ≤620 × 10-6 mm²/s.

One hundred ninety-seven CRISP 2 patients met criteria: 113 (57%) favorable HIR and 84 (43%) unfavorable HIR. Favorable HIR patients had lower baseline NIHSS scores (median 14 versus 16; P = .012), smaller hypoperfusion volumes (time-to-maximum >6 seconds and >10 seconds), smaller ischemic core volumes (27 mL versus 50 mL; P < .001), and were less frequently treated with IV thrombolysis (29% versus 45%; P = .016). ADC heterogeneity was lower in favorable HIR (standard deviation: 167.2 versus 193.5; P = .01), but the mean ADC was similar between groups. Clinical outcomes were not different between favorable and unfavorable HIR groups. Multivariable analysis showed HIR was independently associated with ADC standard deviation (P = .002) and coefficient of variation (P = .003) at the comprehensive stroke center.

Favorable tissue-level collaterals (low HIR) are associated with reduced ischemic core ADC heterogeneity.