Red (haemorrhagic) versus white (pale) infarcts
An infarct (an area of tissue death from loss of blood supply) is red (haemorrhagic) if blood floods into the dead tissue and white if little blood leaks in.
Remember
When an artery is blocked, a solid organ with a single blood supply typically gives a white infarct. If there is a second blood supply, soft tissue that bleeds easily, or blood that cannot drain away through the veins, blood can still reach the dead tissue and the infarct is red, classically in the lung.
Memory aid
Ask where blood could still come from. Nowhere means pale; somewhere means red.
Use it by asking, for any blocked vessel, whether blood has another route into the dead tissue.
An infarct is an area of tissue death (necrosis) caused by loss of blood supply (ischaemia). Its colour depends on how much blood leaks into the dead tissue.
A white infarct forms when there is little bleeding (haemorrhage) into the dead area. It occurs in solid organs with a single blood supply, such as the heart, kidneys and spleen. In the kidney, for example, the arterial branches are end arteries, which means they do not communicate with neighbouring branches, so a blocked branch leaves the tissue with no alternative supply.
A red infarct forms when blood floods into the dead tissue, which happens in soft tissue (tissue that is soft and bleeds easily) or in tissue with more than one blood supply. The lung is the classic example. It has a dual circulation: the pulmonary arteries, plus the bronchial arteries, which are small vessels from the aorta that nourish the airways and supporting tissue. If an embolus (a clot or other lump of material carried in the blood until it lodges) blocks a branch of the pulmonary artery, the bronchial arteries stay open and keep delivering blood, which leaks into the dead tissue.
Other tissues also give red infarcts. In the colon, numerous anastomoses (connections between blood vessels) mean that blood can still enter the area when one vessel is blocked. In the brain, red infarcts occur after reperfusion (blood flowing again) of damaged vessels, and the tissue is soft, so when it dies it collapses and injures the surrounding blood vessels, causing bleeding.
A red infarct is also linked with impaired venous outflow, meaning that blood can enter the organ but cannot drain away.
Key facts
- White infarct
- little bleeding into the dead tissue, in solid organs with a single blood supply such as the heart, kidney and spleen.
- Red infarct
- blood haemorrhages into dead tissue, in soft tissue or tissue with more than one blood supply, such as the lung, colon and brain.
- Lung
- the pulmonary and bronchial circulations mean that the unblocked supply bleeds into the dead tissue.
- Kidney
- the branches of the renal artery do not communicate with each other, so a blocked branch gives a white infarct.
- Colon
- numerous anastomoses mean blood can still enter the area when one vessel is blocked, so the tissue can bleed into the dead area and the infarct is red.
- Brain
- red infarcts occur after reperfusion of damaged vessels, and the soft tissue collapses as it dies and injures surrounding blood vessels, causing bleeding.
Exam traps
- A heart infarct is typically white even though it is the best-known infarct, because the heart is a solid organ with a single supply and little blood leaks into the dead tissue.
- A dual supply does not make the liver the textbook example of a red infarct, because about 75% of its blood comes from the portal vein, which keeps supplying the tissue, so infarction of the liver is uncommon.
- A dual arterial supply does not limit bleeding into dead tissue, because the unblocked artery bleeds into it and so favours a red infarct.
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