Tolga Daniel Dittrich, MD
Computed tomography perfusion (CTP) has become widely accepted as the imaging modality for the estimation of the infarct core and subsequent selection for endovascular treatment (EVT) in ischemic stroke due to large vessel occlusion (LVO), especially in the late time window. The radiological correlate for the core in CTP is usually the volume of tissue with a (compared with the contralateral hemisphere) reduction in cerebral blood flow (CBF) <30%. Overestimation of the core in CTP is thought to be time-dependent and may be a concern, especially with rapid imaging after symptom onset and fast reperfusion after imaging.
García-Tornel et al. addressed the question of the influence of time and collateral status on ischemic core overestimation. They retrospectively evaluated patients with anterior circulation LVO strokes with successful reperfusion after EVT. The core was considered to be the tissue with CBF <30% in CTP. Collateral status was assessed by the hypoperfusion intensity ratio (time to maximum of tissue residue function >6 seconds/time to maximum of tissue residue function >10 seconds). The reference for the final infarct volume was the non-contrast CT after 24 to 48 hours.
Among the 407 patients included, the median core volume was 7 ml (IQR 0-27), and the final infarct volume was 20 ml (IQR 5-55). Ischemic core overestimation was present in 83 patients (20%) (median 12 ml, IQR 5-41). Poor collateral status (aOR 1.41 [95% CI 1.20-1.65]; per 0.1 hypoperfusion intensity ratio increase) and earlier onset to imaging time (aOR 1.14 [95% CI 1.04-1.25]; per 60 minutes earlier) were independently associated with core overestimation. The impact of poor collateral status on core overestimation was more substantial in early (≤ 240 minutes) imaging patients (p<0.01).
Although the results have limited impact on patient selection for EVT in the early time window and infarct core overestimation may be less of a problem at late time window presentation, the role of collateral status as an important factor in assessing infarct core in CTP is highlighted: Severely hypoperfused tissue does not necessarily correspond to already infarcted tissue in patients with poor collateral status.
