Bilateral carcinoid heart disease without intracardiac shunt in a patient with advanced functional small bowel neuroendocrine tumour: a clinical conundrum

This case illustrates an atypical presentation of bilateral carcinoid valvulopathy in the absence of intracardiac shunting, likely due to overwhelming systemic serotonin from tumour burden. Although serotonin is typically inactivated in the lungs, extensive exposure may surpass this protective mechanism. The potential role of selective serotonin reuptake inhibitors remains inconclusive. Multidisciplinary coordination is essential for optimizing cardiac and oncologic outcomes, especially when systemic therapy such as PRRT is considered. Left- and right-sided CHD may develop in patients with small bowel NETs even without anatomic shunting. High tumour burden and systemic serotonin exposure may override pulmonary inactivation, leading to left-sided involvement. Early recognition and multidisciplinary care are critical for effective management.