necroses

Necrosis is a form of cell and tissue death that results from irreversible injury and occurs in localized areas of tissue. It is characterized by loss of plasma membrane integrity, swelling of cells, and the uncontrolled release of intracellular contents, which often triggers an inflammatory response in the surrounding tissue.

Causes of necrosis include ischemia and hypoxia due to disrupted blood supply, exposure to toxins, infections, physical trauma, chemical injury, and autoimmune processes. The mechanism varies with the type of necrosis, but a common feature is the failure of cellular homeostasis leading to rapid cellular rupture and tissue destruction.

Major forms of necrosis include coagulative necrosis, liquefactive necrosis, caseous necrosis, fat necrosis, and fibrinoid necrosis. Coagulative necrosis typically follows ischemia in solid organs and preserves tissue architecture for a time due to protein denaturation. Liquefactive necrosis is dominated by enzymatic digestion of tissue, as seen in the brain or abscesses, resulting in a liquid mass. Caseous necrosis has a cheese-like appearance and is associated with granulomatous inflammation, notably tuberculosis. Fat necrosis arises from lipase activity in adipose tissue, with saponification and chalky deposits. Fibrinoid necrosis involves immune complex–mediated damage to vessel walls, with deposition of fibrin.

Morphologically, necrosis shows cellular swelling, membrane rupture, and breakdown of organelles, with characteristic nuclear changes such as karyolysis, pyknosis, and karyorrhexis. The surrounding inflammation and subsequent healing processes influence clinical outcomes and potential fibrosis or scarring.

Clinically, necrosis signals irreversible tissue injury and can lead to organ dysfunction or sepsis. Management targets the underlying cause, maintains perfusion when possible, and may require debridement or removal of necrotic tissue. Necrosis is distinct from apoptosis, a programmed, typically non-inflammatory form of cell death; programmed necrosis (necroptosis) shares features of both processes. See also apoptosis, necroptosis, gangrene.