A 52-year-old man has episodic facial flushing and watery diarrhea for 8 months. Examination reveals a pansystolic murmur at the left sternal edge increasing on inspiration. CT shows multiple liver lesions and an ileal mass. Which finding best explains why he has carcinoid syndrome?

• A The primary tumor secretes serotonin directly into the systemic circulation
• B The ileal tumor obstructs the portal vein
• C Liver metastases allow vasoactive mediators to reach the systemic circulation ✓
• D Ectopic production of ACTH by the tumor

Explanation

Carcinoid syndrome occurs when vasoactive substances such as serotonin escape hepatic first-pass metabolism. This happens almost exclusively with liver metastases or with tumors draining into the systemic veins (bronchus, gonad). The murmur described is tricuspid regurgitation from right-sided endocardial fibrosis, caused by serotonin exposure on the venous side of the circulation. A purely ileal primary without metastases does not produce the syndrome because the liver metabolizes serotonin.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.