Penumbra (medicine)

Penumbra (medicine)

In pathology and anatomy the penumbra is the area surrounding an ischemic event such as an ischemic, thrombotic or embolic stroke. Immediately following the event, blood flow and therefore oxygen transport is reduced locally, leading to hypoxia of the cells near the location of the original insult. This can lead to hypoxic cell death (infarction) and amplify the original damage from the ischemia; however, the penumbra area may remain viable for several hours after an ischemic event due to the collateral arteries that supply the penumbral zone.

As time elapses after the onset of stroke, the extent of the penumbra tends to decrease; therefore, in the emergency department a major concern is to protect the penumbra by increasing oxygen transport and delivery to cells in the danger zone, thereby limiting cell death. The existence of a penumbra implies that salvage of the cells is possible. There is a high correlation between the extent of spontaneous neurological recovery and the volume of penumbra that escapes infarction; therefore, saving the penumbra should improve the clinical outcome.

One widely accepted definition for penumbra describes the area as "ischemic tissue potentially destined for infarction but not yet irreversibly injured and the target of acute therapies." The original definition of the penumbra referred to areas of the brain that were damaged but not yet dead, and offered promise to rescue the brain tissue with the appropriate therapies.

PET is the gold standard for imaging, but because PET is neither widely available nor rapidly accessible current research focuses on improved MRI techniques. The penumbral area can also be detected based upon an integration of three factors. These factors include: the site of vessel occlusion, the extent of oligaemia (hypoperfused area surrounding the penumbra, but not at risk of infarction ) at that moment, and the mismatch between this perfusion defect and the area of the brain already infarcted