On autopsy of a patient who died 5 days after an acute myocardial infarction, the affected myocardium shows yellow-white necrotic tissue with a red-haemorrhagic border. Microscopically, which finding is MOST expected at this stage?
- A Prominent infiltration by neutrophils being replaced by macrophages engulfing necrotic debris ✓
- B Coagulation necrosis with pyknotic nuclei and no inflammatory infiltrate
- C Dense granulation tissue with abundant new capillaries and fibroblasts
- D Complete fibrous scar replacing the infarct zone
Correct answer: A. Prominent infiltration by neutrophils being replaced by macrophages engulfing necrotic debris
Explanation
By days 3–7, the peak of acute inflammatory response (predominantly neutrophils) begins to transition; at day 5, neutrophilic infiltration is maximal and early macrophage recruitment begins to phagocytose dead myocytes. Coagulation necrosis with minimal inflammation is the 0–24 hour pattern; granulation tissue peaks at 1–3 weeks; dense scar forms by 6–8 weeks.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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