Penumbra (medicine)

Penumbra (medicine)

The penumbra in medicine refers to the area surrounding an ischemic event such as a thrombotic or embolic stroke. Immediately following the event, this area is at risk of infarction, but is still salvageable if reperfusion can be achieved.

Definition

The term penumbra is derived from the Latin paene (almost) and umbra (shadow) and was first used in a medical context by Astrup, Siesjö and Symon in 1981 to describe the area of brain tissue that is at risk of infarction following an ischemic event. The penumbra is characterized by two main features: a reduction in cerebral blood flow and a shift in metabolism from aerobic to anaerobic.

Pathophysiology

The penumbra surrounds the ischemic core, the area of brain tissue that is immediately and irreversibly damaged by the ischemic event. The penumbra is at risk of becoming part of the ischemic core if cerebral blood flow is not restored. This is because the penumbra is supplied with blood by collateral circulation, which is insufficient to maintain aerobic metabolism. As a result, cells in the penumbra shift to anaerobic metabolism, leading to a buildup of lactic acid and subsequent acidosis.

Clinical significance

The concept of the penumbra is important in the management of ischemic stroke. The aim of treatment is to restore blood flow to the penumbra before irreversible damage occurs. This can be achieved through thrombolysis or mechanical thrombectomy. The size of the penumbra can be estimated using neuroimaging techniques such as diffusion-weighted magnetic resonance imaging (MRI) and perfusion imaging.

See also

• Ischemia
• Stroke
• Thrombolysis
• Thrombectomy

References

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