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Necrosis
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types of necrosis coagulative liquefactive caseous fat fibrinoid histology
Here is a comprehensive overview of Necrosis based on Robbins Pathology (Basic Pathology & Pathologic Basis of Disease):
Necrosis
Definition
Necrosis is a pathologic form of cell death resulting from severe, irreversible injury. It is characterized by:
- Denaturation of cellular proteins
- Leakage of cellular contents through damaged membranes
- Local inflammation (distinguishes it from apoptosis)
- Enzymatic digestion of the lethally injured cell
Key causes: ischemia, microbial toxins, burns, chemical/physical injury, pancreatic enzyme leakage (pancreatitis).
Morphological Features
Cytoplasmic Changes
| Feature | Description |
|---|---|
| Increased eosinophilia | Loss of RNA + accumulation of denatured proteins (binds eosin/red dye) |
| Glassy/homogeneous appearance | Loss of glycogen particles |
| Moth-eaten vacuolation | Enzymatic digestion of organelles |
| Myelin figures | Phospholipid precipitates replacing dead cells; may calcify (dystrophic calcification) |
Nuclear Changes (3 Patterns)
| Pattern | Description |
|---|---|
| Pyknosis | Nuclear shrinkage + increased basophilia; dark, shrunken mass |
| Karyorrhexis | Fragmentation of the pyknotic nucleus |
| Karyolysis | Fading of basophilia due to DNase digestion of DNA |
Nuclear changes complete within 1–2 days of necrotic cell death.
Point of No Return (Irreversibility)
Two phenomena mark the transition from reversible → irreversible injury:
- Inability to reverse mitochondrial dysfunction (lost oxidative phosphorylation/ATP)
- Profound membrane dysfunction → lysosomal enzymes enter cytoplasm → autolysis
Clinical Significance: Biomarkers of Necrosis
Necrosis causes leakage of intracellular proteins into circulation — the basis of serum biomarkers:
- Cardiac troponins (cardiac myocyte necrosis) — detectable within 2 hours of MI
- Transaminases (AST/ALT) — hepatocyte necrosis
- Alkaline phosphatase — bile duct epithelium damage
Patterns of Tissue Necrosis
| Pattern | Key Feature | Typical Cause |
|---|---|---|
| Coagulative | Architecture preserved for days; firm, eosinophilic, anucleate cells | Ischemic infarct of solid organs (not brain) |
| Liquefactive | Complete digestion → viscous liquid/pus | Bacterial/fungal infections; CNS hypoxia |
| Gangrenous | Coagulative necrosis of a limb + vascular compromise; "wet" = + bacterial infection → liquefactive | Loss of blood supply to lower extremity |
| Caseous | "Cheese-like" friable yellow-white material; amorphous granular debris on H&E; architecture obliterated | Tuberculosis (surrounded by granuloma) |
| Fat Necrosis | Chalky-white areas (fat saponification); fatty acids + calcium → basophilic deposits | Acute pancreatitis, abdominal trauma |
| Fibrinoid | Bright pink amorphous deposits in vessel walls on H&E | Immune complex deposition (vasculitis, severe hypertension, transplant rejection) |
Necrosis vs. Apoptosis
| Feature | Necrosis | Apoptosis |
|---|---|---|
| Cause | Pathologic (severe injury) | Physiologic or pathologic |
| Membrane integrity | Lost | Maintained |
| Cell swelling | Yes | No (cell shrinkage) |
| Inflammation | Yes | No |
| Nuclear changes | Pyknosis → karyorrhexis/karyolysis | Chromatin condensation → fragmentation |
| Mechanism | Uncontrolled | Tightly regulated (caspases) |
Fate of Necrotic Cells
Most necrotic cells are eliminated by enzymatic digestion + phagocytosis by leukocytes. Uncleared debris serves as a nidus for dystrophic calcification (calcium salt deposition in dead tissue, even with normal serum calcium levels).
Sources: Robbins & Kumar Basic Pathology, 10e; Robbins, Cotran & Kumar Pathologic Basis of Disease, 10e
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