A 55-year-old man dies 4 days after an acute anterior MI. Autopsy shows free wall rupture. Histologically, the infarcted zone at this time would show:
- A Extensive macrophage infiltration with removal of necrotic debris, beginning granulation tissue ✓
- B Coagulative necrosis with early neutrophil infiltration (peak 24–72 h)
- C Dense fibrosis replacing the infarcted zone
- D Contraction band necrosis throughout the infarct zone
Correct answer: A. Extensive macrophage infiltration with removal of necrotic debris, beginning granulation tissue
Explanation
At 4 days post-MI, neutrophils have been largely replaced by macrophages that phagocytose necrotic debris (days 3–7). This macrophage-mediated removal weakens the ventricular wall maximally at days 3–7, explaining the peak risk for free wall rupture and ventricular septal defect. Dense fibrosis forms by 6–8 weeks. Neutrophil infiltration peaks at 24–72 hours. Contraction band necrosis is from reperfusion injury.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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