Necrotic tissue
Also known as: dead tissue, devitalized tissue
Necrotic tissue is tissue that has died as a result of injury, ischemia, or infection. Unlike programmed cell death, necrosis involves cell rupture and release of intracellular contents, which provokes an inflammatory response in the surrounding tissue.
Necrosis is unregulated cell death caused by an external insult — loss of blood supply, infection, trauma, toxins, extremes of temperature, or radiation. Injured cells swell, their membranes fail, and their contents spill into the surrounding tissue. Because those contents are recognized as danger signals, necrosis is accompanied by inflammation. This distinguishes it from apoptosis, an energy-dependent, tightly regulated form of cell death in which the cell shrinks, fragments into membrane-bound bodies, and is cleared without inflammation.
Pathologists classify necrosis by its appearance and cause. Coagulative necrosis, the most common pattern, follows ischemia in most solid organs and preserves tissue architecture for a time. Liquefactive necrosis, typical of the brain and of bacterial abscesses, digests tissue into a viscous mass. Caseous necrosis produces a cheese-like appearance and is characteristic of tuberculosis. Fat necrosis follows pancreatic enzyme release or trauma to fatty tissue, and fibrinoid necrosis affects vessel walls in immune-mediated vasculitis. Gangrenous necrosis is a clinical term for necrosis of a limb, dry when purely ischemic and wet when superinfected.
In wound care the same tissue is described by how it looks in the wound bed. Eschar is thick, dry, leathery, tan-to-black devitalized tissue; slough is soft, moist, yellow or gray stringy material. Necrotic tissue provides no barrier function, supports bacterial growth, and physically obstructs the migration of new tissue across the wound, so wounds do not progress through the healing phases until it is removed. Debridement — sharp, enzymatic, autolytic, mechanical, or biological — is the intervention, and the presence of eschar or slough also prevents accurate staging of a pressure injury.
The topic spans several exams. The NPTE and NPTE-PTA test necrotic tissue within integumentary system content, where recognizing eschar and slough and understanding their effect on wound healing and pressure injury staging is expected. USMLE Step 1 tests the pathology side — the patterns of necrosis, their causes, and the contrast with apoptosis — including in organism-specific contexts such as the black eschar of cutaneous anthrax caused by *Bacillus anthracis*.
Key takeaways
- Necrotic tissue is dead tissue resulting from ischemia, infection, trauma, or toxic injury.
- Necrosis causes cell rupture and inflammation; apoptosis is regulated and does not.
- Major patterns include coagulative, liquefactive, caseous, fat, fibrinoid, and gangrenous necrosis.
- In wounds, necrotic tissue appears as dry black eschar or moist yellow slough.
- Wounds do not heal until necrotic tissue is debrided, and eschar prevents accurate pressure injury staging.