What does the ischemic penumbra refer to on imaging?

• A. Irreversibly damaged core
• B. Normal brain tissue
• C. Bleeding tissue
• D. Tissue at risk but potentially salvageable

Answer: (D)

In imaging, the ischemic penumbra is tissue that has reduced blood flow due to a blockage but is not yet irreversibly damaged, meaning it could still be saved with timely restoration of circulation. On perfusion imaging, this shows up as a region with delayed blood arrival and reduced flow that extends beyond the area where diffusion has already become abnormal. The diffusion-restricted area represents the irreversibly damaged core, while the surrounding hypoperfused tissue without diffusion restriction is the penumbra. The key takeaway is the mismatch: tissue at risk but potentially salvageable if reperfusion occurs promptly. This is not normal tissue and it is not bleeding tissue; it’s the battlefield where rapid treatment can make a difference.