Infarction Types

Mnemonic

Red or white, and the difference is the blood supply:

• White (pale, anaemic) infarcts occur in solid organs with a single end-arterial supply: heart, kidney, spleen. No collateral flow, so the area is pale
• Red (haemorrhagic) infarcts occur where blood can re-enter: dual blood supply (lung, liver), loose tissue (bowel), venous occlusion (testicular torsion, ovarian torsion), or after reperfusion

“Lung and liver bleed into their infarcts; heart, kidney and spleen go pale.”

Infarcts are typically wedge shaped with the apex at the occluded vessel and the base at the organ surface, and they undergo coagulative necrosis everywhere except the brain, which liquefies.

Watershed areas are the most vulnerable to hypoperfusion rather than occlusion: the splenic flexure and rectosigmoid in the bowel, and the cortical border zones in the brain, which is why global hypotension produces a characteristic pattern of damage.

Expansion

White (anaemic, pale) infarcts

• Solid organs with a single end-arterial supply
• Heart, kidney, spleen
• Typically wedge shaped with the apex at the occluded vessel

Red (haemorrhagic) infarcts

• Loose tissue that allows blood to collect, or tissues with a dual blood supply, or venous occlusion, or after reperfusion of a previously infarcted area
• Lung (dual supply from bronchial arteries), bowel (rich anastomoses), testis and ovary (torsion causing venous occlusion), brain after reperfusion

Factors determining severity

• Nature of the supply: dual supply protects, which is why pulmonary embolism causes infarction in only 10 to 15 per cent
• Rate of occlusion: gradual occlusion allows collaterals to develop
• Tissue vulnerability to hypoxia: neurones die within 3 to 5 minutes, myocardium in 20 to 30, fibroblasts survive hours
• Oxygen content of blood: anaemia and hypoxaemia worsen the outcome

Infarcts show coagulative necrosis everywhere except the brain, where liquefactive necrosis leaves a cyst.