A 50-year-old man dies 8 hours after the onset of crushing chest pain. Autopsy reveals occlusive coronary thrombus over an atherosclerotic plaque. Which of the following accurately describes the earliest detectable histological change versus the first macroscopic change in the infarcted myocardium at this time point?
- A By 8 hours: histology shows coagulative necrosis with nuclear pyknosis; gross examination shows a pale yellow area with hyperemic border
- B At 8 hours: dense neutrophil infiltrate is the predominant histologic finding, visible on H&E stain; gross specimen shows a well-demarcated yellow soft area
- C At 8 hours: no reliable light microscopic changes are yet visible; electron microscopy may show mitochondrial swelling and amorphous densities; grossly the area may show slight pallor, but definitive pallor appears only at 24–72 hours ✓
- D At 8 hours: contraction bands and hemorrhage indicate reperfusion; macroscopic pallor with soft consistency is evident
Explanation
The timing of histological and gross changes in MI is a classic examination topic. At 8 hours, light microscopy is often unremarkable or shows only early wavy fiber change and early coagulative changes (loss of cross-striations, eosinophilia). Reliable histologic changes (coagulative necrosis, nuclear pyknosis/karyolysis, early neutrophil margination) appear by 12–24 hours. Electron microscopy is the first to show mitochondrial swelling and dense amorphous calcium precipitates (ischemic densities) within 30–60 minutes. Gross pallor (pale/soft area with hyperemic border) appears at 24–72 hours; before 24 hours, the gross changes are often subtle or absent. Neutrophilic infiltration peaks at 24–72 hours.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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