Which imaging before reperfusion strategy?

The ischemic penumbra is a transient and potentially reversible condition. Therefore, infarct progression and its counterpart penumbral salvage are highly variable and result from the interaction of 3 major factors: collateral flow, revascularization delay and success. Multimodal brain imaging now offers in clinical practice an exhaustive characterization of the acute ischemic injury: vessel site occlusion, infarction/critical hypoperfusion volume, and collateral flow. From 1995 to 2015, IV alteplase administered within 4.5hours after the onset of acute BI diagnosed by the absence of hemorrhage on a non-contrast head CT scan has been the only approved revascularization treatment. Over the past 2years, 6 randomized trials have confirmed the benefit of a thrombectomy performed within 6-8 hours after the onset of an acute anterior BI downstream of an ICA/M1 occlusion. The recommended imaging modality for such patients remains a NCCT to exclude an hemorrhage and a CTA to confirm the proximal vessel occlusion. As a consequence, in the absence of collateral or penumbral imaging, studies and meta-analyses, have emphasized the importance of treatment delay on the outcome of patient after a revascularisation treatment (tPA/thrombectomy). These findings have supported the development of mobile stroke unit for tPA administration and the direct transfer of the patients eligible to thrombectomy to a comprehensive stroke center, bypassing primary stroke unit and sometimes conventional neuro imaging. In addition randomized controlled trial that did enroll patients based on the presence of a target mismatch on multimodal imaging demonstrated a higher benefit of revascularisation treatment by comparison with those who did not.This year the results of the randomized trial, Diffusion-weighted Imaging or Computerized Tomography Perfusion Assessment with Clinical Mismatch in the Triage of Wake-up and Late Presenting Strokes Undergoing Neurointervention with Trevo (DAWN)demonstrated for the first time that revascularization treatment for BI complicating an ICA or a proximal MCA M1 was still beneficial from 6 to 24hours after onset among patient who did have per their clinical exam and the multimodal brain imaging have a persistent penumbra. With this as a background we will discuss the yield of imaging for the selection of patients for a revascularization therapy.