WBR0771

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Cardiology
Prompt	[[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	AnswerA::Formation of contraction bands
Answer A Explanation	AnswerAExp::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	AnswerB::Normal pathological specimen
Answer B Explanation	AnswerBExp::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	AnswerC::Necrotic cells and neutrophil migration
Answer C Explanation	AnswerCExp::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	AnswerD::Edema, hemorrhage, and formation of wavy fibers
Answer D Explanation	AnswerDExp::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	AnswerE::Macrophage infiltration and formation of granulation tissue
Answer E Explanation	AnswerEExp::Macrophage infiltration and granulation tissue are observed starting 3 days post-MI. These findings persist to approximately 15 days post-MI.
Right Answer	RightAnswer::E
Explanation	[[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	Approved::Yes
Keyword	WBRKeyword::Myocardial infarction, WBRKeyword::STEMI, WBRKeyword::Chest pain, WBRKeyword::Inflammation, WBRKeyword::Neutrophilic infiltration, WBRKeyword::Granulation tissue, WBRKeyword::Light microscopy, WBRKeyword::Post-MI
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