Necrosis : Definition, Types and Examples

Q. Define Necrosis. Enlist its types with an example of each.

Ans: Necrosis is the type of cell death that is associated with loss of membrane integrity and leakage of cellular contents culminating in dissolution of cells, largely resulting from the degradative action of enzymes on lethally injured cells.

Types of Necrosis:
i) Coagulative Necrosis
- underlying tissue architecture is preserved,

- affected tissues take on a firm texture

- characteristic of infarcts in all of the solid organs except the brain

ii) Liquefactive Necrosis
- seen in focal bacterial or fungal (occasionally) infections

- the dead cells are digested completely, transforming the tissue into a liquid viscous mass

- seen often in hypoxic death of cells within CNS

iii) Caseous Necrosis (Caseous = Cheese like)
- Encountered most often in foci of tubercular infection

- friable yellow white appearance of the necrotic region

- area of caseous necrosis is often enclosed within a distinctive inflammatory border; this appearance is characteristic of a focus of inflammation known as a granuloma

iv) Fat Necrosis
- focal areas of fat destruction

- seen in Acute Pancreatitis

- grossly visible chalky white areas can be seen

v) Fibrinoid Necrosis
- special form of necrosis visible by light microscopy

- usually in immune reactions in which complexes of antigens and antibodies are deposited in the walls of arteries.

- a bright pink and amorphous appearance on H&E preparations called fibrinoid (fibrin-like) by pathologists

- seen in  immunologically mediated diseases (e.g. polyarteritis nodosa)

vi) Gangrenous Necrosis
- mostly the affected organ has lost its blood supply and has undergone coagulative necrosis involving multiple tissue layers

- When bacterial infection is superimposed, coagulative necrosis is modified by the liquefactive action of the bacteria and the attracted leukocytes (resulting in so-called wet gangrene)

- e.g. necrosis of a limb (mostly lower)

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