Fibrinoid necrosis is a type of connective tissue necrosis seen paicularly in autoimmune diseases (eg, rheumatic fever, polyaeritis nodosa, and systemic lupus erythematosus). Collagen and smooth muscle in the media of blood vessels are especially involved. Fibrinoid necrosis of aerioles also occurs in accelerated (malignant) hypeension. Fibrinoid necrosis is characterized by loss of normal structure and replacement by a homogeneous, bright pink-staining necrotic material that resembles fibrin microscopically. Areas of fibrinoid necrosis contain various amounts of immunoglobulins and complement, albumin, breakdown products of collagen, and fibrin. Also Know: Fat Necrosis: Fat necrosis most characteristically occurs in acute pancreatitis when pancreatic enzymes are liberated from the ducts into surrounding tissue. Pancreatic lipase acts on the triglycerides in fat cells, breaking these down into glycerol and fatty acids, which complex with plasma calcium ions to form calcium soaps. Liquefactive Necrosis: Liquefaction of necrotic cells results when lysosomal enzymes released by the necrotic cells cause rapid liquefaction. Lysis of a cell as a result of the action of its own enzymes is autolysis. Liquefactive necrosis is typically seen in the brain following ischemia. Coagulative Necrosis: In this type of necrosis, the necrotic cell retains its cellular outline, often for several days. The cell, devoid of its nucleus, appears as a mass of coagulated, pink-staining, homogeneous cytoplasm. Coagulative necrosis typically occurs in solid organs, such as the kidney, hea (myocardium), and adrenal gland, usually as a result of deficient blood supply and anoxia. It is also seen with other types of injury, eg, coagulative necrosis of liver cells due to viruses or toxic chemicals, and coagulative necrosis of skin in burns. Ref: Chandrasoma P., Taylor C.R. (1998). Chapter 1. Cell Degeneration & Necrosis. In P. Chandrasoma, C.R. Taylor (Eds), Concise Pathology, 3e