necrosis of a part of the body or an organ, with a characteristic change in its color ranging from bluish to brown or black. Gangrene results when the entry of oxygen into the tissues ceases or is severely restricted. It usually occurs in places that are farthest from the heart (for example, in the toes) or in places with local impairment of blood circulation (for example, in the heart muscle or lung due to infarction). Gangrene may have external or internal causes. External causes include mechanical causes (for example, traumas accompanied by the crushing of tissues with impairment of the integrity of blood vessels and nerves, bedsores), physical causes (burns, frostbite), exposure to ionizing radiation, and chemical causes (exposure of the organism to strong acids and alkalis, arsenic, phosphorus, and so on). Internal causes include states and processes that interfere with tissue nutrition, mainly injuries to blood vessels—wounds, arterial occlusions, and constriction of blood vessels by spasms or anatomical changes, such as those occurring in atherosclerosis, which often causes infarcts, thrombosis, and senile gangrene. Gangrene may occur without microbial action (aseptic gangrene) and with microbial involvement (septic, or putrefactive, gangrene). There are also moist and dry gangrenes and gas gangrene.
Dry gangrene develops when the flow of blood to the tissues ceases abruptly and they dry up, provided that a putrescent infection does not occur. Dry gangrene is characterized by the drying up, wrinkling, and compression of tissues (the affected part decreases in size) due to the coagulation of cell proteins and decomposition of formed blood elements. The necrotic area becomes dark brown or black. The process that results in the development of dry gangrene is called mummification because the affected area outwardly resembles a mummy. The cessation of blood flow is accompanied by sharp pain in the region of impaired circulation; the extremity becomes pale, marmoreal-blue, and"cold. Skin sensitivity and the pulse disappear, although pain persists for a long time in the deep-lying tissues. Necrosis spreads from the periphery to the center. The function of the affected part of the body is impaired. In time a reactive inflammation (demarcation) develops at the boundary between the necrotic and healthy tissue and the necrotic part is sloughed off. Dry gangrene is usually localized in the extremities, tip of the nose, and auricles (especially in cases of frostbite or chemical burn). If putrescent infection occurs in the necrotic tissue, the dry gangrene may change into moist gangrene. In a few months the necrotic tissue may be spontaneously sloughed off. In aseptic necrosis of the internal organs, the necrotic tissue is gradually resorbed and replaced with scar tissue or a cyst (heart muscle, brain). If the reaction of the healthy tissues adjoining the gangrenous area is sluggish, the necrotic process spreads to them as well. Meanwhile the products of putrescent decomposition enter the bloodstream and may cause a severe intoxication.
Moist gangrene is characterized by the grayish brown color of the affected area, tissue edema, and tissue enlargement. The tissues are usually transformed into a soft, dirty-green mass emitting a putrid odor. The tissues eventually liquefy and decompose.
If the course is favorable, there is a distinct boundary between healthy and necrotic tissues. The necrotic tissues are sloughed off, the resulting defect heals, and a scar forms over it. Sometimes (in the absence of infection, and if the focus is limited) moist gangrene may turn into dry gangrene. If the organism is weak and the local tissue reaction sluggish, the process spreads and absorption of the products of putrescent decomposition into the general bloodstream results in the development of sepsis. (This happens frequently in diabetes mellitus patients.) In moist gangrene, sensitivity is lost in the superficial layers of the affected tissues and pain arises in the deeper layers, the body temperature rises, and the patient’s general condition is poor. Treatment and prevention consists in the removal of the factors that might result in the development of gangrene. Other treatment includes blood transfusions, antibiotics, and surgery.
P. B. AVISOV