CONCEPTS OF THE ISCHEMIC PENUMBRA

Marc Fisher, MD

Worcester Memorial Hospital, Worcester, MA, USA

The ischemic penumbra represents part of the hypoperfused region associated with focal brain ischemia. Various definitions for the ischemic penumbra have been proposed, but a practical approach is to define this region as that portion of the ischemic territory that can potentially be salvaged by timely intervention. Biochemical and imaging parameters have been used to try to characterize ischemic tissue that defines the existence of the ischemic penumbra. Both approaches can be applied in experimental stroke models, but imaging is the only currently available practical approach for identification of the ischemic penumbra in stroke patients. An approximation of the ischemic penumbra can be made by identifying a mismatch between the perfusion MRI lesion volume and the diffusion MRI lesion volume. This diffusion-perfusion mismatch appears to identify stroke patients more likely to respond to delayed thrombolysis beyond the current 3 hour limit. A more precise identification of the ischemic penumbra will likely encompass quantification of absolute diffusion and perfusion values that will then be related to ultimate tissue outcome after therapy is given. Hopefully, in the near future, imaging identification of the ischemic penumbra will guide acute stroke therapy to target those patients most likely to respond to treatment.