Acute Ischemic Stroke
Time, Penumbra, and Reperfusion
Current guidelines advocate intravenous thrombolysis for patients with ischemic stroke <4.5 hours from onset without additional imaging beyond noncontrast computed tomography (CT) of the brain.1 Rapid administration of intravenous tissue-type plasminogen activator (IV-tPA) will reduce disability. Treatment of patients within 3 hours has an odds ratio of 1.53 (95% confidence interval, 1.26–1.86) for a favorable outcome (modified Rankin scale [mRS], 0–2) at 3 months.2 However, this represents an absolute increase of 9% compared with placebo and is available to a minority of patients with ischemic stroke because of the rigid time constraints.3 Modern stroke imaging grants unprecedented access to the pathophysiology in individual patients with stroke. Time remains of key importance with respect to patient outcomes. However, it is now possible to not only routinely visualize the causative occlusion, but also estimate the ischemic core, the penumbral tissue at risk if reperfusion does not occur, and the state of the collateral blood supply. The current focus of Acute Ischemic Stroke (AIS) intervention should be to achieve reperfusion of the penumbra. Recent trials point to potential avenues to improve patient access by imaging-based patient selection and the importance of rapid and complete reperfusion of the penumbra.
Penumbral Imaging for Patient Selection
Three parenchymal vascular states exist in varying proportions in each AIS patient. These are the ischemic core, the penumbra, and a region of benign oligemia.4,5 Separating the penumbra from the ischemic core is of critical importance in guiding stroke therapy. So too is separating the penumbra from the region of benign oligemia. By definition, the penumbra is the region of tissue that is at risk of being recruited into the ischemic core. Thus, the penumbra is the principal target for reperfusion and, therefore, should dictate patient selection. Given the progressive nature of ischemic stroke, establishing the continued existence of …