Introduction Necrosis

Necrosis is defined as a localized area of death of tissue followed later by degradation of tissue by hydrolytic enzymes liberated from dead cells, it is invariably accompanied by an inflammatory reaction. Necrosis can be caused by various agents such as hypoxia, chemical, and physical agents, microbial agents, immunological injury, etc.

TYPES OF NECROSIS

Based on etiology and morphologic appearance, there are 5 types of necrosis: three major forms are coagulative, liquefaction (colliquative), and caseous necrosis; others are fat and fibrinoid necrosis.

COAGULATIVE NECROSIS

Coagulative necrosis is the most common type of necrosis caused by irreversible facal injury ,mostly from sudden cessation of blood flow (ischaemic necrosis),and less often from bacterial and chemical agent. The organs commonly affected are heart, kidney, and spleen.

Gross: pale, firm, slightly swollen, yellow, softer, shrunken, etc.

LIQUEFACTION NECROSIS

Liquefaction or colliquative necrosis also occurs commonly due to ischaemic injury and bacterial and fungal infections but hydrolytic enzymes in tissue degradation have a dominant role in causing semi-fluid material. the common example are infarct brain and abscess cavity .

Gross: affected area is soft with the liquefied center containing necrotic debris .later, a cyst wall is formed.

CASEOUS NECROSIS

Caseous (caseous=cheese-like) necrosis is found in the center of the foci of tuberculous infection. It’s combines features of both coagulative and liquefactive necrosis.

Gross: foci of caseous necrosis resemble dry cheese and are soft, granular, and yellowish. this appearance is partly attributed to the cytotoxic effects of lipopolysaccharides present in the capsule of the tubercle bacilli,  Mycobacterium tuberculosis.

FAT NECROSIS

Fat necrosis is a special form of cell death occurring at mainly fat-rich anatomic locations in body. Examples are traumatic fat necrosis of breast, especially in heavy and pendulous breasts, and mesenteric fat necrosis due to acute pancreatitis.

In the case of acute pancreatitis, there is liberation of pancreatic lipase from injured or inflamed tissue that results in necrosis of the pancreas as well as of the fat depots throughout peritoneal cavity and sometimes, even affecting the extra-abdominal adipose tissue.

Gross: fat necrosis appears as a yellowish-white and firm deposit. formation of calcium soaps imparts the necrosis foci firmer and chalky white appearance.