WBR0771

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	USMLE Step 1
Main Category	Pathology
Sub Category	Cardiology
Prompt	A 57-year-old man is brought to the emergency department with acute-onset substernal chest pain for the past 2 hours. He explains that his pain radiates to his left shoulder and is associated with nausea and diaphoresis. Following appropriate work-up, he is diagnosed with ST-segment elevation myocardial infarction (STEMI). He undergoes coronary revascularization and is discharged from the hospital the next day. A histopathological analysis of this patient's myocardium will show which of the following findings on light microscopy 12 days following his STEMI?
Answer A	Formation of contraction bands
Answer A Explanation	Contraction bands, necrotic changes, and neutrophil migration starts 12 hours following the onset of myocardial infarction. Neutrophilic migration persists for a few days.
Answer B	Normal pathological specimen
Answer B Explanation	A normal pathological specimen may be observed in 2 cases: Either in a normally perfused myocardium or within very early stages (0 to 4 hours) post-MI.
Answer C	Necrotic cells and neutrophil migration
Answer C Explanation	Contraction bands, necrotic changes, and neutrophil migration starts 12 hours following the onset of myocardial infarction. Neutrophilic migration persists for a few days.
Answer D	Edema, hemorrhage, and formation of wavy fibers
Answer D Explanation	Edema, hemorrhage, and presence of wavy fibers on microscopy are all observed in early coagulative myocardial necrosis during the early stages (4 to 12 hours) post-MI
Answer E	Macrophage infiltration and formation of granulation tissue
Answer E Explanation	Macrophage infiltration and granulation tissue are observed starting 3 days post-MI. These findings persist to approximately 15 days post-MI.
Right Answer	E
Explanation	Following a myocardial infarction, the heart undergoes gross and microscopic changes that are collectively referred to as the evolutionary process of MI: 0 to 4 hours post-MI: Very early following MI, the heart undergoes no gross or microscopic changes. 4 to 12 hours post-MI: The infarcted area starts to demonstrate dark mottling. During that period also, there is edema, coagulative necrosis, and hemorrhage. Wavy fibers are observed microscopically. 12 hours post-MI: Neutrophilic infiltration begins and contraction bands appear, signaling reperfusion injury. Necrotic changes are also observed during that time because cells release their necrotic material. 1 day post-MI: The infarcted area becomes hyperemic, and coagulative necrosis becomes more extensive with more inflammatory changes and neutrophilic migration. These changes persist for 3 days. 3 to 15 days post-MI: The border of the infarcted area becomes hyperemic and shows a soft yellowish infarcted region on gross pathology, and macrophage infiltration followed by granulation tissue is evident on light microscopy. 2 weeks post-MI: The infarcted area turns grayish and a contracted scar is formed. These changes persist for several months post-MI. Educational Objective: At 3 to 15 days post-MI, light microscopy of the heart typically shows infiltration of macrophages and formation of granulation tissue. References:
Approved	Yes
Keyword	Myocardial infarction, STEMI, Chest pain, Inflammation, Neutrophilic infiltration, Granulation tissue, Light microscopy, Post-MI
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