The Ischemic Penumbra: Fact or Fiction?

Abstract

Stroke due to occlusion of a middle cerebral artery (MCA), or another major artery in the brain, causes incomplete ischemia which varies from severe to mild (e.g., [19, 26, 34, 35]). A major dividing line is between tissues which are severely ischemic and which, therefore, quickly become infarcted, and tissues which are underperfused but essentially viable. Following experimental MCA occlusion the lateral part of the caudoputamen and some of the overlying neocortex usually belong to the first category, while other neocortical areas and the medial part of the caudoputamen constitute areas “at risk.” In baboons, an ischemic threshold exists at flow rates of about 0.12ml/g per minute, below which ischemic periods of 1–2 h invariably cause infarction [20]. One major problem in stroke research is to assess the revival time of cells existing in the focus, i.e., the longest periods of ischemia which can be tolerated without causing permanent functional deficits, or histological cell damage. Thus, if methods become available to restore flow in an occluded vessel, the revival times are of crucial importance. As we will discuss below, the revival times vary with the actual flow rates. The second major problem is to define ischemia of intermediate degrees, and to assess its functional and histopathological effects. Or, expressed otherwise, it is of crucial importance to explore events in the perifocal tissue (“infarct rim”), as contrasted to those in the focus. This is because the perifocal tissue is potentially salvageable even if the vascular occlusion is permanent.

This study was supported by grants from the Swedish Medical Research Council, and from the United States Public Health Service (via the NIH).