A patient with metastatic ileal neuroendocrine tumor and diarrhea develops edema and ascites. Autopsy shows white, fibrous endocardial plaques on the ventricular aspects of the tricuspid and pulmonary valves. The aortic and mitral valves are normal. This pattern occurs because:

• A Tumor cells selectively colonize right-sided valves
• B The left-sided valves have thicker endothelium resistant to tumor emboli
• C Venous blood carrying vasoactive amines bathes only the right heart before pulmonary inactivation ✓
• D Left-sided valves are protected by higher oxygen tension

Explanation

In carcinoid heart disease, serotonin and other vasoactive substances secreted by the tumor reach the right-sided valves directly via venous return and stimulate fibroblast proliferation and collagen deposition. The lungs metabolize these amines, protecting the left heart unless there is a patent foramen ovale or bronchial carcinoid. The plaques contain smooth muscle cells and sparse elastic fibers embedded in matrix, not tumor deposits, excluding A.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.