A patient with myocardial infarction dies 72 hours after onset. Autopsy shows a yellow-tan soft area with a rim of hyperemia. Microscopically, the area shows coagulative necrosis with ghost cell outlines and prominent neutrophilic infiltration. Which specific landmark microscopic finding distinguishes this stage from the 1-week appearance?

• A Wavy myofiber change — seen at 72 hours but not at 1 week
• B Granulation tissue with ingrowth of capillaries and macrophages replacing neutrophils
• C Dense neutrophilic infiltration — distinguishes day 3 from the macrophage-dominated day 7-10 stage ✓
• D Contraction band necrosis exclusively seen at 72 hours

Explanation

At 72 hours (3 days) post-MI, the infarct zone shows maximal neutrophilic infiltration with coagulative necrosis preserving cell outlines. By day 7-10, neutrophils are replaced by macrophages (mononuclear phagocytes) that begin removing necrotic debris; granulation tissue ingrowth begins at the periphery by day 7-14. Wavy fiber change is an early (hours 1-12) finding. Contraction bands indicate reperfusion injury, not specific timing. This neutrophil-to-macrophage transition is the key histological landmark differentiating the acute versus early subacute stages.

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

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