Necrosis

The death of tissue cells. Necrosis can occur as a result of ischaemia (inadequate blood supply), which may lead to gangrene; infection, such as tuberculosis; or damage by extreme heat or cold, noxious chemicals, or excessive exposure to X-rays or other radiation. In necrosis due to tuberculosis, the dead tissue is soft, dry, and cheese-like. Fatty tissue beneath the skin that has died as a result of damage or infection develops into tough scar tissue that may form a firm nodule.