## Morphologic Features of Necrosis in Acute MI **Key Point:** Necrosis is characterized by loss of cell membrane integrity, uncontrolled protein denaturation, and a vigorous inflammatory response. The infarcted myocardium at 24 hours shows classic coagulation necrosis. ### Morphologic Changes in Necrotic Tissue (Coagulation Necrosis) | Feature | Necrosis | Apoptosis | |---------|----------|----------| | **Cell membrane** | **Disrupted early** | Intact initially | | **Nuclear changes** | Karyorrhexis, pyknosis, karyolysis | Pyknosis, fragmentation into bodies | | **Cytoplasm** | Hypereosinophilic, denatured proteins | Normal or slightly pale | | **Inflammatory response** | Severe (neutrophils, macrophages) | Minimal (macrophages only) | | **Cell boundaries** | Lost due to membrane rupture | Maintained in apoptotic bodies | | **Contents** | Spilled into tissue | Contained in apoptotic bodies | **High-Yield:** In coagulation necrosis (the pattern seen in MI), the tissue architecture is preserved initially, but the cells are dead — the nucleus undergoes karyorrhexis (fragmentation) and karyolysis (dissolution), and the cytoplasm becomes hypereosinophilic due to loss of ribosomes and denaturation of structural proteins. ### Why Option 1 (Intact cell membrane) is WRONG **Warning:** An intact cell membrane is a feature of **apoptosis** in its early stages, NOT necrosis. In necrosis, the cell membrane is disrupted early, allowing leakage of cell contents (including enzymes, ions, and proteins) into the surrounding tissue. This triggers the inflammatory cascade. ### Correct Features of Necrosis (Options 0, 2, 3) 1. **Karyorrhexis and loss of nuclear chromatin** — The nucleus fragments into irregular pieces, and chromatin is lost as DNA is degraded by non-specific nucleases (not caspase-activated, as in apoptosis). 2. **Hypereosinophilia of the cytoplasm** — Loss of basophilic ribosomes and denaturation of proteins causes the cytoplasm to stain intensely pink (eosinophilic) on H&E. 3. **Infiltration by inflammatory cells** — Neutrophils arrive within hours, followed by macrophages. This inflammatory response is absent in apoptosis and is a key distinguishing feature. **Clinical Pearl:** In acute MI, the infarcted myocardium at 24 hours shows coagulation necrosis with a dense neutrophilic infiltrate at the border zone. By 3–7 days, macrophages predominate and begin clearing the necrotic debris. This inflammatory response contributes to ventricular remodeling and scar formation. **Mnemonic:** **NERD** for Necrosis: - **N**uclear fragmentation (karyorrhexis) - **E**osinophilic cytoplasm - **R**uptured membrane - **D**amage to surrounding tissue (inflammation) [cite:Robbins 10e Ch 2]
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