Introduction
This topic covers necrosis, the death of cells and tissues in a living body, and its advanced form, gangrene, which is necrosis complicated by putrefaction. A good answer defines both, explains their causes and morphology, classifies gangrene, and describes the clinical picture, complications and principles of management of dry and wet gangrene. Most gangrene of the limbs follows arterial occlusion, so this topic links directly to topics 60 and 61.
Necrosis: definition and morphology
Necrosis is irreversible death of cells within living tissue. Under the microscope it is recognised by nuclear changes that appear in sequence: karyolysis (fading of nuclear basophilia), pyknosis (shrinkage and intense staining of the nucleus) and karyorrhexis (fragmentation of the nucleus). The cytoplasm becomes hypereosinophilic and the tissue architecture changes according to the type of necrosis.
- Coagulative necrosis: preserved tissue outline for some days; typical of ischaemic infarcts of solid organs such as the heart and kidney.
- Liquefactive necrosis: digestion of tissue into a liquid mass; typical of brain infarcts and bacterial abscesses.
- Caseous necrosis: cheese-like amorphous material; classic for tuberculosis.
- Fat necrosis: destruction of adipose tissue with calcium soap formation; typical of acute pancreatitis and trauma to breast or abdominal fat.
- Fibrinoid necrosis: deposition of fibrin-like material in vessel walls; seen in severe hypertension and vasculitis.