A 26-year-old intravenous heroin user presents with fever, night sweats, and progressive dyspnea. Blood cultures grow Staphylococcus aureus. Transoesophageal echocardiography shows a large mobile vegetation on the tricuspid valve with severe regurgitation. The excised valve at pathology shows the structure marked **A** — bulky, friable vegetations on the tricuspid leaflets. Which of the following best describes the microscopic composition of these vegetations?
A. Hyalinized collagen and smooth muscle proliferation with sparse inflammatory cells
B. Granulation tissue with giant cells and caseating necrosis characteristic of chronic infection
C. Fibrin, platelets, neutrophils, and bacterial colonies embedded in a meshwork of inflammatory cells
D. Lipid-laden macrophages and cholesterol crystals with minimal bacterial infiltration
Explanation
Why "Fibrin, platelets, neutrophils, and bacterial colonies embedded in a meshwork of inflammatory cells" is right
The clinical anchor explicitly states that histology of the vegetations marked A confirms "colonies of gram-positive cocci embedded in a meshwork of fibrin, platelets and neutrophils with leaflet myonecrosis." This is the pathognomonic microscopic appearance of acute infective endocarditis on the tricuspid valve in an intravenous drug user. The vegetations are friable and crumbling because they lack the organized structural support of normal valve tissue—they are essentially bacterial colonies held together by platelets and fibrin in a loosely organized inflammatory matrix. This composition explains why septic emboli readily break off and lodge in the pulmonary circulation, as occurred in this patient's clinical course.
Why each distractor is wrong
Lipid-laden macrophages and cholesterol crystals with minimal bacterial infiltration: This describes atherosclerotic plaque or lipid-rich lesions, not infective endocarditis. Acute IE is characterized by abundant bacteria and acute inflammation, not lipid accumulation.
Hyalinized collagen and smooth muscle proliferation with sparse inflammatory cells: This pattern is seen in chronic, healed or fibrotic valve disease (e.g., rheumatic heart disease or healed endocarditis), not acute active IE. Acute IE shows active inflammation and bacterial invasion, not collagen remodeling.
Granulation tissue with giant cells and caseating necrosis characteristic of chronic infection: Caseating granulomas are pathognomonic for tuberculosis or fungal infections, not bacterial endocarditis. Acute staphylococcal IE does not produce caseating necrosis; it produces acute suppurative inflammation with abscess formation.
High-YieldNEET PG
Acute infective endocarditis vegetations are friable, crumbling masses of bacteria, fibrin, and platelets—not organized tissue—which is why they embolize readily and are difficult to sterilize with antibiotics alone.
Robbins and Cotran Pathologic Basis of Disease, 10th ed., Ch. Cardiac Valvular Disease
Practice similar questions
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.
