[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Conditions](https://durgical.com/en/conditions/) › Carcinoid syndrome [Conditions](https://durgical.com/en/conditions/) · [Metabolism: amino acids and the urea cycle](https://durgical.com/en/conditions/) # Carcinoid syndrome A neuroendocrine tumour releases serotonin into the blood, causing flushing, diarrhoea and damage to the right-sided heart valves. Updated 2026-11-01 ## Structures involved Tap one to see what it is and open it in 3D. - [Ileum](https://durgical.com/en/anatomy/ileum/) - [Liver](https://durgical.com/en/anatomy/liver/) - [Tricuspid anterior leaflet](https://durgical.com/en/anatomy/superior-leaflet-of-right-atrioventricular-valve/) - [Tricuspid septal leaflet](https://durgical.com/en/anatomy/septal-leaflet-of-right-atrioventricular-valve/) - [Tricuspid posterior leaflet](https://durgical.com/en/anatomy/inferior-leaflet-of-right-atrioventricular-valve/) - [Pulmonary anterior cusp](https://durgical.com/en/anatomy/anterior-semilunar-leaflet-of-pulmonary-valve/) - [Pulmonary right cusp](https://durgical.com/en/anatomy/right-semilunar-leaflet-of-pulmonary-valve/) - [Pulmonary left cusp](https://durgical.com/en/anatomy/left-semilunar-leaflet-of-pulmonary-valve/) - [Right ventricle](https://durgical.com/en/anatomy/right-ventricle/) - [Skin](https://durgical.com/en/anatomy/skin/) ## In biochemistry - [Serotonin and melatonin synthesis: Step 2 · Aromatic L-amino acid decarboxylase (AADC)](https://durgical.com/en/biochemistry/pathways/serotonin-and-melatonin-synthesis/#paso-2) - [Tryptophan](https://durgical.com/en/biochemistry/molecules/tryptophan/) - [Molecules derived from amino acids](https://durgical.com/en/biochemistry/topics/molecules-derived-from-amino-acids/) - [Serotonin (5-hydroxytryptamine)](https://durgical.com/en/biochemistry/molecules/serotonin/) ## In histology - [Enteroendocrine cells and GALT](https://durgical.com/en/histology/enteroendocrine-cells-and-galt/) - [Pineal gland and the diffuse endocrine system](https://durgical.com/en/histology/pineal-gland-and-the-diffuse-endocrine-system/) ## Why it happens - [Histamine, serotonin, bradykinin and the plasma protein cascades](https://durgical.com/en/general-pathology/histamine-serotonin-bradykinin-and-the-plasma-protein-cascades/) - [Mediators of inflammation: the table to know](https://durgical.com/en/general-pathology/mediators-of-inflammation-the-table-to-know/) - [Paraneoplastic syndromes: the table to know](https://durgical.com/en/general-pathology/paraneoplastic-syndromes-the-table-to-know/) ## What it is A set of symptoms from substances (mainly serotonin) released by a well-differentiated neuroendocrine tumour, almost always of the small bowel with liver metastases. ## Who gets it A minority of people with neuroendocrine tumours develop it, almost always middle-aged or older adults. ## Causes - Neuroendocrine tumour of the [ileum](https://durgical.com/en/anatomy/ileum/) with liver metastases (most common) - Bronchial or ovarian tumours, which drain straight into the systemic circulation ## Risk factors - Midgut neuroendocrine tumour - Liver metastases ## Pathophysiology Tumour cells turn much of the tryptophan into serotonin. While the tumour drains to the [portal vein](https://durgical.com/en/anatomy/hepatic-portal-vein/), the liver inactivates serotonin with monoamine oxidase; liver metastases release it into the [hepatic veins](https://durgical.com/en/anatomy/hepatic-veins/). Serotonin causes diarrhoea and fibrosis of the tricuspid and pulmonary valves (the lung breaks it down before the left heart). Bradykinins and histamine cause flushing. Spending tryptophan lowers niacin synthesis. ## Symptoms and signs - Sudden flushing of face and neck - Watery diarrhoea - Wheezing - Abdominal pain - Oedema and signs of right heart failure ## Red flags - Carcinoid crisis: hypotension, bronchospasm and intense flushing, sometimes during anaesthesia or procedures - Right heart failure ## Diagnosis **Clinical** Flushing with diarrhoea in a patient with a [liver](https://durgical.com/en/anatomy/liver/) mass or bowel tumour. **Tests** 5-Hydroxyindoleacetic acid (5-HIAA) in 24-hour urine or plasma; chromogranin A; biopsy with neuroendocrine markers. **Imaging** Abdominal CT or MRI; PET with labelled somatostatin analogues; echocardiography for the valves. ## Treatment **Medical** Somatostatin analogues (octreotide, lanreotide) to control symptoms and growth **Medical** Telotristat, which inhibits tryptophan hydroxylase, for diarrhoea that does not respond **Surgical** Resection of the primary tumour and liver metastases when possible; valve replacement for advanced heart disease **Procedure** Embolisation or ablation of liver metastases **Acute** Prevention of carcinoid crisis with somatostatin analogues before surgery ## Drugs for this condition - [Octreotide](https://durgical.com/en/pharmacology/octreotide/) ## Complications - Carcinoid heart disease (tricuspid regurgitation and pulmonary stenosis) - Carcinoid crisis - Pellagra from niacin deficiency - Mesenteric fibrosis ## Prognosis The tumours usually grow slowly; carcinoid heart disease is the main cause of death and worsens the outlook. ## Test yourself Think of the answer, then tap the question to see it. ## Why does carcinoid syndrome usually appear only with liver metastases? The liver inactivates serotonin arriving by the portal vein; metastases release it straight into the hepatic veins. ## Which valves does it damage, and why those? Tricuspid and pulmonary, because the lung breaks serotonin down before it reaches the left heart. ## Which urinary metabolite is measured for diagnosis? 5-HIAA, the breakdown product of serotonin. ## Why can pellagra appear? The tumour spends tryptophan on serotonin, leaving little to make niacin. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/conditions/carcinoid-syndrome/) ## Related conditions - [Hartnup disease](https://durgical.com/en/conditions/hartnup-disease/) - [Heart failure](https://durgical.com/en/conditions/heart-failure/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [Carcinoid syndrome: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000347.htm) (MedlinePlus, US National Library of Medicine, 2026); [5-HIAA urine test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003612.htm) (MedlinePlus, US National Library of Medicine, 2026); [Serotonin and melatonin biosynthesis](https://reactome.org/PathwayBrowser/#/R-HSA-209931) (Reactome, 2026). [← All conditions](https://durgical.com/en/conditions/) ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/conditions/carcinoid-syndrome/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/carcinoid-syndrome/