A 65-year-old man dies 4 days after acute myocardial infarction. At autopsy, the infarcted zone of the left ventricle shows yellow-tan softening. Histologically, which finding is most characteristic at this stage?

• A Coagulation necrosis with preserved ghost outlines and no inflammatory infiltrate
• B Abundant macrophage infiltration replacing neutrophils with granulation tissue formation ✓
• C Dense neutrophilic infiltrate with early removal of necrotic debris
• D Dense fibrous scar replacing all myocardium with no residual inflammatory cells

Explanation

The temporal sequence of MI histology: 0–4h — no change (wavy fibers at periphery); 4–24h — coagulative necrosis begins, neutrophil marginalization; 1–3 days — extensive neutrophilic infiltrate; Day 3–7 (4 days falls here) — neutrophils diminishing, macrophages appearing, beginning of granulation tissue formation (ingrowth of capillaries and fibroblasts); Day 7–14 — abundant granulation tissue; Weeks 2–8 — fibrous scar formation. Yellow-tan softening represents early enzymatic digestion and beginning of repair.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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