Discrepancy in core infarct between non-contrast CT and CT perfusion when selecting for mechanical thrombectomy

Objective: Mechanical thrombectomy (MT) is now an established treatment for acute ischemic stroke (AIS) with large vessel occlusion (LVO) within 6 hours. Since 2018, MT is also recommended from 6-24 hours after selecting with additional mul-timodal imaging including perfusion imaging. We sought to investigate patients with significant discrepancy in core infarct between computed tomography (CT) and CT perfusion (CTP). Methods: In this retrospective study, patients with AIS who were evaluated for MT using the RAPID software (IschemaView, Redwood City, CA, USA) from February 2018 to March 2019 were included. Cases with discrepancy between infarct volume on non-contrast CT and core volume (cerebral blood flow <30%) as analyzed by RAPID on CTP were analyzed. Results: In the study period, 635 patients were evaluated for acute stroke symptoms. Non-contrast head CT was performed in 635 patients, and CTP with RAPID software post processing was performed in 134 patients. Among the 134 patients, 8 (5.9%) patients had gross discrepancy in core infarct between CT and CTP, with underesti-mation of infarct by CTP. Evaluation of these cases shows that the likely reason for this discrepancy is recanalization of a LVO, which then leads to erroneously normal or gross underestimate of the core infarct volume determined from CTP post processing analysis. Conclusions: Recanalization of a LVO can lead to erroneously normal or gross under-estimation of the core infarct as determined by post processing software analysis of CTP data. The whole composite of hyperacute CT imaging should be examined while making decisions. This caveat of perfusion imaging interpretation has not been reported previously.