What is the ischemic penumbra, and how is it identified on imaging studies in the context of acute ischemic stroke?

The ischemic penumbra refers to brain tissue that is ischemic but not yet infarcted, making it potentially salvageable with timely intervention. It is often identified on imaging by a mismatch between diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) on MRI, or by CT perfusion showing regions of reduced cerebral blood flow but preserved cerebral blood volume. Clinically, recognizing the penumbra is crucial for determining eligibility for reperfusion therapies. A common pitfall is mistaking the penumbra for infarcted tissue, which can lead to inappropriate management decisions.