Carcinoid tumors are rare. They arise from enterochro-maffin cells typically located in the gastrointestinal tract. At the time of diagnosis, more than 30% of patients have disseminated disease characterized by cutaneous vasomotor flushing, secretory diarrhea, and mild bronchospasm.
In carcinoid heart disease, 5-hydroxytryptamine is meta¬bolized to 5-hydroxyindoleacetic acid (5-HIAA). Elevated levels of 5-HIAA in the urine confirm the diagnosis. Echocardiography confirms thickening of the tricuspid and pulmonary valves with tricuspid and pulmonary valve regurgitation and in some cases, pulmonary valve stenosis. The lesions in the heart may cause right-sided heart failure. Because the blood cannot be ejected adequately through the pulmonary valve, the right ventricle work is increased. Because the tricuspid valve leaks, blood regurgitates into the veins of the neck and back toward the liver, which becomes pulsatile with each heartbeat.
The malignant tumor may spread to involve the muscle of the heart. These metastatic carcinoid tumors of the heart are about 2 cm and can be detected by echocardiography.