Carcinoid syndrome — SCE Endocrinology MCQ

Correct answer: B — Systemic release of vasoactive mediators from hepatic metastases

The best answer is “Systemic release of vasoactive mediators from hepatic metastases”. A midgut neuroendocrine tumour may remain clinically silent while portal drainage permits hepatic metabolism of vasoactive mediators. Hepatic metastases can release serotonin and other mediators into the systemic circulation, bypassing effective first-pass clearance and producing carcinoid syndrome. “Reduced intestinal serotonin synthesis after ileal obstruction” is less appropriate because ileal obstruction does not explain raised 5-HIAA or the emergence of systemic mediator symptoms “Increased hepatic first-pass metabolism of tumour-derived serotonin” is less appropriate because increased first-pass metabolism would reduce rather than precipitate systemic symptoms “Calcitonin secretion from metastatic thyroid C cells” is less appropriate because the established ileal primary and serotonin biochemistry do not support metastatic medullary thyroid carcinoma “Histamine release caused by a primary clonal mast-cell disorder” is less appropriate because mast-cell histamine release can cause flushing but does not explain the timing after hepatic neuroendocrine metastases

Reference: ENETS guidance paper for carcinoid syndrome. https://pmc.ncbi.nlm.nih.gov/articles/PMC9539661/