Ischemic core and penumbra in human stroke

Background and Purpose-The ischemic core and penumbra have not been thoroug hly characterized after acute cerebral thromboembolic occlusion in humans. Differentiation between areas of potentially viable and irreversibly injure d ischemic tissue may facilitate assessment and treatment of stroke patient s. Methods-Cerebral blood flow (CBF) was measured in 20 patients with acute mi ddle cerebral artery (MCA) occlusion between 60 and 360 minutes after strok e onset, with the stable xenon computerized tomography (CT) technique. Thre shold displays were generated at a single level, and the percentages of hem isphere with CBF less than or equal to 6, less than or equal to 10, 11 to 2 0, 21 to 30, and >30 cm(3) . 100 g(-1) . min(-1) were measured. The corresp onding images on 12 available follow-up CT scans were similarly assessed to determine the area of final infarct. Comparisons were analyzed with a pair ed Student's t test and Pearson's correlation coefficient. Results-Discrete and confluent areas of CBF less than or equal to 20 cm(3) . 100 g(-1) . min(-1) were identified in all patients, ipsilateral to the s ymptomatic MCA territory. The average area of CBF less than or equal to 20 cm(3) . 100 g(-1) . min(-1) within the ipsilateral hemisphere was 66+/-17% compared with 36+/-12% contralaterally (P<0.001), A difference in the exten t of low CBF was due primarily to areas with CBF less than or equal to 10 c m(3) . 100 g(-1) . min(-1) (48+/-18% versus 16+/-7%, P<0.001), The area of most severe ipsilateral ischemia (less than or equal to 6 cm(3) . 100 g(-1) . min(-1)) best corresponded to the final area of infarction (37+/-18% ver sus 40+/-24%; correlation coefficient, 0.866; P<0.01). The acute ischemic c ore destined to infarction was not surrounded by a widened rim of moderate ischemia because the area with CBF 11 to 20 cm(3) . 100 g(-1) . min(-1) was similar bilaterally (19+/-4% versus 20+/-7%, P=0.792, thus not significant ). Conclusions-Our study in acute human stroke involving MCA occlusion indicat es that a severely ischemic core (CBF less than or equal to 6 cm(3) . 100 g (-1) . min(-1)), observed between 1 to 6 hours after stroke onset, correspo nds to the cerebral tissue destined to infarction. The ischemic penumbra wi th now values between 7 and 20 cm(3) . 100 g(-1) . min(-1) surrounding the ischemic core is very narrow. Therefore, strategies to improve the outcome of many patients with acute MCA occlusion must either include interventions to reverse the ischemic process within a few minutes of onset or increase the cerebral tolerance of ischemia and thereby prolong the potential therap eutic window.