Ischemic penumbra

Ischemic penumbra denotes the part of an acute ischemic stroke that is at risk of progressing to infarction but is still salvageable if reperfused. It is usually located around an infarct core which represents the tissue which has already infarcted or is going to infarct regardless of reperfusion.

The primary aim of current acute stroke intervention is to prevent the penumbra from proceeding to established infarct.

CT perfusion

On CT perfusion the ischemic penumbra has been variably defined using a combination of parameters. Generally, it should be conceptually thought of as "the area of the brain with reduced perfusion" minus the "infarct core".  In practice, which parameters are used to define each component has varied. A fairly common definition for penumbra is the area of brain with :

  • prolonged (increased) T-max, typically >6 seconds (or other measures of delayed arrival of contrast such as mean transit time (MTT) or time to peak (TTP)), and...
  • normal or increased cerebral blood volume (CBV) due to autoregulation
  • This region will have only a moderate decreased cerebral blood flow (CBF). This is in contrast to the infarct core which will have a marked decrease in cerebral blood flow and also a decrease in cerebral blood volume.


    On MRI, the ischemic penumbra is also determined by the area of the brain with reduced perfusion :

    • penumbra: shows perfusion changes same as that with CT
    • infarcted core: shows restricted diffusion (established infarct) apart from decreased cerebral blood volume and cerebral blood flow
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