Necrosis

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1. 1 Necrosis

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3. NECROSIS localised area of death of tissue degradation of tissue by hydrolytic enzymes liberated from dead cells invariably accompanied by inflammatory reaction. Causes : various agents such as hypoxia chemical and physical agents microbial agents Immunological injury, etc. 3

4. Characterise 2 Essential change characterize Irreversible cell injury in necrosis of all types 1.cell digestion – Lytic enzymes 2.Denaturation -Proteins 4

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6. Types of necrosis Based on etiology and morphologic appearance 5 types of necrosis Coagulative Liquefaction Caseous Fat & fibrinoid necrosis. 6

7. 1.Coagulative necrosis most common type of necrosis caused by irreversible focal injury Mostly from sudden cessation of blood flow -( ischaemic necrosis) less often from bacterial and chemical agents Grossly Early stage - pale, firm, slightly swollen - infarc t. (tissue death due to inadequate blood supply) With progression, the affected -more yellowish, softer, and shrunken 7

8. Coagulative necrosis Microscopically hallmark - conversion of normal cells into their ‘tomb stones’ (outlines of the cells are retained and the cell type can still be recognized but their cytoplasmic and nuclear details are lost. ) necrosed cells are swollen , more eosinophilic cytoplasm than the normal. nuclear changes of pyknosis , karyorrhexis and karyolysis 8

9. Coagulative necrosis Infiltrated by inflammatory cells the dead cells are phagocytosed leaving granular debris and fragments of cells 9

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11. 2.Liquefactive necrosis commonly due to ischemic injury bacterial or fungal infections But hydrolytic enzymes in tissue degradation have a dominant role in causing semi-fluid material. common examples - infarct (tissue death )brain and abscess cavity Grossly affected area -soft with liquefied center containing necrotic debris. Later - cyst wall is formed 11

12. Liquefactive necrosis Microscopically the cystic space contains necrotic cell debris & macrophages filled with phagocytosed material. cyst wall -proliferating capillaries, inflammatory cells, and gliosis - case of brain proliferating fibroblasts( that synthesizes the extracellular matrix & collagen) - case of abscess cavity 12

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14. 3.Caseous necrosis –cheese like necrosis is found in the centre of foci of tuberculous infections. combines features of both coagulative and liquefactive necrosis. Grossly resemble dry cheese and are soft, granular and yellowish. present in the capsule of the tubercle bacilli, Mycobacterium tuberculosis . 14

15. Caseous necrosis –cheese like Microscopically centre of the necrosed focus contain structureless eosinophilic material having scattered granular debris of disintegrated nuclei. surrounding tissue shows characteristic granulomatous inflammatory reaction consisting of epithelioid cells (modified macro phages having slipper-shaped vesicular nuclei), interspersed giant cells of Langhans ’ foreign body type peripheral mantle of lymphocytes 15

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18. Caseous necrosis –cheese like 18

19. 4.Fat necrosis special form of cell death occurring at mainly fat-rich anatomic locations in the body. examples are: traumatic fat necrosis of the breast, especially in heavy and pendulous breasts, mesenteric ( wrapping around the circumference of the intestine – creeping fat )fat necrosis due to acute pancreatitis. 19

20. Fat necrosis Acute pancreatitis - there is liberation of pancreatic lipases from injured or inflamed tissue results in necrosis of the pancreas as well as of the fat depots throughout the peritoneal cavity sometimes, even affecting the extraabdominal adipose tissue. fat necrosis - there is hydrolysis and rupture of adipocytes causing release of neutral fat which changes into glycerol and free fatty acids. leaked out free fatty acids complex with calcium to form calcium soaps (saponification) 20

21. Fat necrosis Grossly - appears as yellowish-white and firm deposits. Formation of calcium soaps imparts the necrosed foci firmer chalky white appearance. Microscopically - the necrosed fat cells have cloudy appearance surrounded by an inflammatory reaction. Formation of calcium soaps is identified in the tissue sections as amorphous, granular and basophilic material 21

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23. Fat necrosis 23

24. 5.Fibrinoid necrosis characterised by deposition of fibrin-like material staining properties of fibrin such phosphotungistic acid haematoxylin (PTAH) stain. examples - peptic ulcer etc 24

25. 5.Fibrinoid necrosis Microscopically Identified by brightly eosinophilic hyaline-like deposition in the vessel wall. Necrotic focus is surrounded by nuclear debris of neutrophils ( leucocytoclasis ) Local haemorrhage may occur due to rupture of the blood vessel 25

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