A patient dies 5 days after transmural myocardial infarction. Autopsy shows yellow softening of the necrotic myocardium with a neutrophilic infiltrate and early macrophage invasion. This corresponds to which phase of MI healing?
- A Intermediate phase (3-7 days) — maximal neutrophil infiltration transitioning to macrophage phagocytosis ✓
- B Hyperacute phase (0-6 hours) — no histological change
- C Early phase (1-3 days) — coagulative necrosis with nuclear pyknosis and neutrophil influx
- D Late phase (7-14 days) — granulation tissue and beginning scar formation
Correct answer: A. Intermediate phase (3-7 days) — maximal neutrophil infiltration transitioning to macrophage phagocytosis
Explanation
At 3-7 days post-MI, the zone of coagulative necrosis is maximally infiltrated by neutrophils (peak at ~48 hours) followed by monocyte-derived macrophages that begin phagocytosing necrotic debris, producing the gross yellow soft appearance. This is the most vulnerable period for mechanical complications (free wall rupture, papillary muscle rupture causing acute MR, ventricular septal defect) because macrophage-mediated proteolysis weakens the wall before fibroblast-derived collagen is deposited.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.