Necrosis is irreversible cell injury that can occur through several mechanisms and patterns. It involves severe damage to cell membranes leading to loss of integrity and contents leaking out. Morphological changes include nuclear changes like pyknosis, karyorrhexis, and karyolysis as well as cytoplasmic changes like dense eosinophilic cytoplasm and vacuolization. The main patterns discussed are coagulative necrosis, where architecture is preserved; liquefactive necrosis, where tissues digest into pus; and caseous necrosis, seen in tuberculosis as cheesy white areas.

1. Necrosis
Dr. S Poude, MD
Department of Pathology

2. Irreversible changes
•Necrosis and
•Apoptosis

3. Irreversible injury
• Severe injury or persistent injury causes irreversible damage.
• Extensive damage to cell membrane
• Vacuolisation of mitochondria
• Reduced capacity to generate ATP
• Necrosis
Morphogical changes are :
• Nuclear changes and cytoplasmic changes

4. Nuclear changes:
• Are pathognomonic of necrosis and are of 3 types:
• Pyknosis – shrunken,small and hyperchromatic nuclei.
• Karyorrhexis – pyknotic nucleus breaks up into fragments
• Karyolysis – with time the nuclear fragments slowly fade and
ultimately disappear(enzymatic degradation by endonucleases)

7. Cytoplasmic changes:
• Dense pink cytoplasm ( eosinophilic cytoplasm)
• Glassy and homogeneous
• Becomes vacuolated and motheaten in appearance
• Dead cells may be replaced by large, whorled phospholipid masses
called myelin figures

8. Necrosis
• Is the result of denaturation of intracellular proteins and enzymatic
digestion of the lethally injured cell
• unable to maintain membrane integrity
• their contents often leak out, a process that may elicit inflammation
in the surrounding tissue.

9. Patterns of Tissue Necrosis
• Coagulative necrosis
• Liquefactive necrosis
• Gangrenous necrosis
• Caseous necrosis
• Fat necrosis
• Fibrinoid necrosis

10. Coagulative necrosis
• the architecture of dead tissues is preserved
for a span of at least some days
• the injury denatures enzymes also and so
blocks the proteolysis of the dead cells
• as a result, eosinophilic, anucleate cells may
persist for days or weeks
• E.g Renal infarction, Myocardial infarction
• Caused by obstruction of blood supply
• A localized area of coagulative necrosis is
called an infarct

11. Coagulative necrosis

12. Coagulative necrosis

13. Coagulative necrosis

14. Liquefactive necrosis
• is characterized by digestion of the dead cells,
resulting in transformation of the tissue into a
liquid viscous mass.
• No structural detail can be made out
• The necrotic material is frequently creamy
yellow because of the presence of dead
leukocytes and is called pus
• CNS often manifests as liquefactive necrosis
• E.g., Bacterial, fungal and ischemic injury of
CNS

15. Liquefactive necrosis

16. Liquefactive necrosis

17. Gangrenous necrosis
• not a specific pattern of cell death
• usually applied to a limb, generally the lower leg, that has lost its
blood supply and has undergone necrosis (typically coagulative
necrosis) involving multiple tissue planes.

18. Caseous necrosis
• Most often in foci of tuberculous infection
• The term “caseous” (cheeselike) is derived from the friable white
appearance of the area of necrosis
• microscopic examination, the necrotic area appears as a collection
of fragmented or lysed cells and amorphous granular debris

19. Caseous necrosis

20. Caseous necrosis

21. Fat necrosis
• The focal areas of fat destruction, typically resulting from release of
activated pancreatic lipases into the substance of the pancreas and
the peritoneal cavity
• The fatty acids, so derived, combine with calcium to produce grossly
visible chalky-white areas (fat saponification)

22. Fat necrosis

23. Fat necrosis

24. Fibrinoid necrosis
• Special form of necrosis usually seen in immune reactions involving
blood vessels
• Deposits of these “immune complexes,” together with fibrin that
has leaked out of vessels, result in a bright pink and amorphous
appearance in H&E stains, called “fibrinoid” (fibrin-like) by
pathologists

25. Fibrinoid necrosis

26. Take home message

28. • Thank You