Myocardial Infarction - Introduction (II) - Gross Pathology and Microscopic Pathology
Gross pathology:
Upon examination an MI appear grossly as pale yellow areas in the myocardium
• If reperfusion has occurred, the infarcted areas may appear red
• May be either subendocardial, transmural or multifocal
• In the first 6 to 12 hours, usually no grossly detectable changes unless using tetrazolium incubation
• After 18 to 24 hours, there may be either myocardial pallor or mottling
• In 2 to 3 days, the infarcted zone begins to appear yellow as polymorphonuclear leukocytes infiltrate the tissue, the pallor increases as more polymorphonuclear leukocytes continue to infiltrate the infarcted myocardium
• At 7 days, distinct gelatinous early scar with red borders and depression on cut surface is present
• At 14 days, gelatinous change transitions to early white scar
• By 7 to 8 weeks, cicatrization may be complete
• Complications with structural changes after myocardial infarction include rupture of papillary muscle , ventricular rupture , ventricular aneurysm or pseudoaneurysm
Myocardial necrosis in an acute MI appear grossly as pale yellow areas in the myocardium
• If reperfusion has occurred, the infarcted areas may appear red
• May be either subendocardial, transmural or multifocal
• In the first 6 to 12 hours, usually no grossly detectable changes unless using tetrazolium incubation
• After 18 to 24 hours, there may be either myocardial pallor or mottling
• In 2 to 3 days, the infarcted zone begins to appear yellow as polymorphonuclear leukocytes infiltrate the tissue, the pallor increases as more polymorphonuclear leukocytes continue to infiltrate the infarcted myocardium
• At 7 days, distinct gelatinous early scar with red borders and depression on cut surface is present
• At 14 days, gelatinous change transitions to early white scar
• By 7 to 8 weeks, cicatrization may be complete
• Complications with structural changes after myocardial infarction include rupture of papillary muscle, ventricular rupture, ventricular aneurysm or pseudoaneurysm
Microscopic examination:
• Hypereosinophilia of myocyte sarcoplasm (myofibers, myocytes), nuclear pyknosis and karyolysis
• Coagulation necrosis - hypereosinophilia with blurring or loss of the striated pattern of the myocyte sarcoplasm
• Colliquative myocytolysis (hydropic change of myocytes) in subendocardial location
• Contraction band necrosis (which may be part of reperfusion injury including interstitial hemorrhage) is frequently present
• Wavy and thinned myocytes (fibers) can also be seen, however wavy myocytes without thinning should not be interpreted as infarcted myocardium
• Inflammatory response starts at around 4 hours with margination and progresses as shown in the sequential histopathologic changes table
• If reperfusion occurs, contraction band necrosis is prominent with interstitial hemorrhages
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