The ischaemic penumbra

The concept of an ischaemic penumbra, surrounding a focal cerebral lesion, is now widely accepted, although no universal definition of the 'penumbra' exists. In the present review, we consider the penumbra as that volume of b rain tissue at the periphery of a focal, irreversibly damaged area that is threatened by recruitment into necrosis. Implicit to such a definition are several secondary concepts. First, the penumbra is both spatial, in that it surrounds the densely ischaemic core, but it is also temporal, in that its evolution toward infarction is a relatively progressive phenomenon. The pe rtinent literature is summarized. Second, penumbral tissue is potentially s alvageable; the most recent animal studies are reviewed. Third, because ele ctrically silent and pathologically damaged tissues have identical function al characteristics, it is evident that most clinical rating scales, be they neurological, behavioural, or psychological, are poorly adapted to address the problem of the penumbra. Finally, the penumbral tissue is remarkably a nd intensively 'active': multiple processes of cell death and repair occur and involve molecular mechanisms, electrophysiology and the vasculature, Cu rr Opin Neurol 14:83-88. (C) 2001 Lippincott Williams & Wilkins.