A 60-year-old man dies 3 days after an acute MI. Autopsy shows a large area of necrosis in the left ventricular wall with surrounding hyperemia. Histology shows loss of nuclei, wavy myofibers with cytoplasmic eosinophilia, and prominent neutrophilic infiltration. No macrophages are seen. This time-course of histological changes corresponds to:

• A 1-3 hours: irreversible injury onset
• B 5-7 days: macrophage infiltration and granulation tissue formation
• C 2 weeks: scar formation with dense collagen deposition
• D 1-3 days: neutrophilic infiltration phase with beginning of coagulation necrosis ✓

Explanation

The histological sequence of MI is well-defined: at 1-3 hours, electron microscopy shows changes but H&E is normal; at 4-12 hours, early coagulation necrosis with wavy fibers and cytoplasmic eosinophilia begin; at 1-3 days, dense acute neutrophilic infiltration predominates (pyknotic nuclei, beginning myocyte disintegration) — this is the highest risk period for rupture. Macrophages replace neutrophils by day 3-5 and peak at 5-7 days. Granulation tissue appears at 1-2 weeks; mature scar completes by 6-8 weeks.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.