NECROSIS-Dr Sowmya Srinivas

DEFINITION NECROSISIts an irriversible injury produced by enzymatic digestion of dead cellular elements

APOPTOSISIts a vital process that helps eliminate unwanted cells-an internally programmed series of events causing cell death

MECHANISM

MORPHOLOGY OF NECROSIS :

1.Cellular swelling or rupture2.Denaturation  and coagulation of cytoplasmic proteins3.Breakdown of cell organelles4.Breakdown of nuclear DNA

PATTERNS OF NECROSIS IN TISSUES OR ORGANS

As a result of cell death the tissues or organs display one of these six macroscopic changes:

1.Coagulative necrosis2.Liquefactive necrosis3.Caseous necrosis4.Fat necrosis5.Gangrenous necrosis6.Fibrinoid necrosis

PATTERNS OF NECROSIS IN TISSUES OR ORGANS

1.Coagulative necrosis: the outline of the dead cells are maintained and the

tissue is somewhat firm. Example: Myocardial infarction, liver, kidney, thermal burns  

2.Liquefactive necrosis: the dead cells undergo disintegration and affected

tissue is liquefied. Example: Brain

GROSS - NECROSIS

• Affected areas look white, grey or yellow in colour. • Have a cooked meat appearance. • Sharply demarcated (by red zone) from healthy tissue.• In case of gangrene the area is green, orange or black

(iron sulphide)

MICROSCOPY - NECROSIS

The microscopic changes of necrosis vary with the type of necrosis. Some general changes of necrosis in the cytoplasm are: Eosinophilia: The cytoplasm stains darker red in colour.Swelling and vacuolation: The cells are swollen and

contain different types of vacuoles. Changes in the nucleus: The nucleus may show

condensation (Pyknosis), fragmentation (karyorrhexis) and may disappear (karyolysis).

COAGULATIVE NECROSIS

Most common type of necrosis. Architectural outlines persist but cellular details are

lost. Type of tissue can be recognized. Denaturation (coagulation) of structural and enzymic

proteins blocks proteolysis.

CAUSES OF COAGULATIVE NECROSIS

• Ischemia due to thrombosis/ embolism as in infarcts.• Bacterial toxins e.g. Fusobacterium necrophorum in

livers in cattle.• Muscular dystrophy due to deficiency of selenium and

vit. E in cattle and sheep. • Necrosis of renal epithelium due to poisoning from

mercuric salts.

Gross appearance: • Necrotic area is firm, opaque with cooked meat appearance.• It is sharply demarcated from the healthy areas.Microscopic appearance: • Architectural outlines are present; cellular details are

lacking.Result: • Dead tissues remain in the body for a long period, ultimately

removed by macrophages.

GROSS – COAGULATIVE NECROSIS

NORMAL CARDIAC MUSCLE

MICROSCOPIC VIEW

COAGULATIVE NECROSIS

MICROSCOPIC VIEW

CASEOUS NECROSIS

Dead tissue is converted into a homogenous, granular mass resembling cottage cheese.

Cause: Associated with lesions of Mycobacterium tuberculosis, the cause of caseous lymphadinitis.

Gross appearance: The area of necrosis is amorphous, granular, friable, white-grey resembling cottage cheese. The caseous mass is enclosed within a connective tissue capsule.

Microscopic appearance: The necrotic tissue is amorphous, granular mass enclosed inside a zone of granulomatous inflammation, containing macrophages. No architectural or cellular details are seen. Calcification commonly occurs in the necrotic areas.

GROSS – CASEOUS NECROSIS

MICROSCOPY – CASEOUS NECROSIS

LIQUEFACTIVE NECROSIS• Rate of dissolution of the necrotic cells is faster than

the rate of repair. Usually results in an abscess secondary to bacterial infection.• Hydrolysis of dead tissues or cells rapidly destroyed by

lysosomal enzymes from neutrophilic leukocytes (i.e., bacterial infections), or clostridia or snake poison. • Liquefactive necrosis that is caused by neutrophilic

leukocytes is called pus.

LIQUEFACTIVE NECROSIS