Abstract TP40: Does The Middle Cerebral Artery Territory Have An Anatomically Defined Ischemic Core?

Abstract

Background: In this study, we sought to determine whether an anatomically-defined ischemic core exists in patients with complete MCA territory ischemia; and whether the depth of ischemia, probability of timely reperfusion, or differential tissue vulnerability contributes to its anatomic location. Methods: Mean transit time (MTT) and FLAIR maps were obtained from stroke patients at 3.0 (tp1), 6.2 (tp2) hours, and 1 month after onset. 14 patients (11 received IV tPA) with complete MCA ischemia (visually identified using tp1 MTT) were included. MTT prolongation (pMTT) was computed as: MTT- (median MTT of the non-ischemic hemisphere). All images were aligned to the automated anatomic labeling (AAL) atlas using a B-Spline non-linear registration. To merge data with either left or right MCA ischemia, images with R MCA were flipped right to left prior to image registration. Four aggregate maps were generated as: infarct probability (IP=# of patients with infarction/total # of patients); average pMTT; reperfusion probability (RP=# of patients with reperfusion/total # of patients); and IP normalized to the severity of hypoperfusion (vulnerability index=IP/average pMTT). Pearson correlation was performed between IP and pMTT. Results: IP in patients with complete MCA ischemia is highest in the putamen, insula and internal capsule (>80%, Fig. A). This region of high IP co-localized to areas of the largest prolonged MTT-deepest ischemia (pMTT>12 sec, Fig B), but did not complement regions of high RP (Fig C). The vulnerability index did not show a “hot-spot” in the high IP regions (Fig. D). Moreover, IP and pMTT were highly correlated (r=0.75). Conclusions: The ischemic core for the MCA territory corresponds to regions with greatest pMTT but not to those with low reperfusion probability. Moreover, the relatively uniform vulnerability index suggests that depth of ischemia rather than differential tissue vulnerability accounts for this region having the highest infarct probability.