What we know and don’t know about MeVOs

We know that the natural history of M2 occlusions is poor. Despite the relatively distal occlusion site, only half of patients with M2 occlusions achieve a good functional outcome at 90 days.3 The clinical course of M3 occlusions and occlusions of the A2/3 and P2/3 segments is unknown, partly because vascular imaging was not routinely performed for AIS in the pre-EVT era, and even if it was, detecting MeVOs can be challenging, particularly for physicians with little imaging experience. Technically, imaging tools to detect MeVOs, such as perfusion imaging and multiphase CT angiography,4 have been available for many years, even before devices that render safe and responsible EVT in MeVOs possible. However, it is only recently that innovative postprocessing methods, such as time variant multiphase CT angiography color maps,5 which further facilitate MeVO detection for unexperienced readers, have become available. Since MeVO patients were underrepresented in previous EVT trials (the MulticenterRandomized Clinical trial of Endovascular treatment for Acute ischemic stroke in the Netherlands (MR CLEAN) trialwas the only trial that included patients with M2 occlusions, and they constituted only 8% of the trial’s patient population),6 there is no clear guideline based EVT recommendation for MeVO strokes.2 7 We have …