[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Gastrointestinal tract](https://durgical.com/en/general-pathology/areas/gi/) › Gastrointestinal neuroendocrine (carcinoid) tumours

# Gastrointestinal neuroendocrine (carcinoid) tumours

- Lesion

Tumours of the gut's hormone cells grow slowly as firm yellow nodules; some release substances that cause flushing and diarrhoea.

Updated Nov 12, 2026

## Key points

- Gross: firm yellow-tan submucosal nodules; intense desmoplasia can kink and obstruct the small bowel.
- Micro: nests, trabeculae and sheets of uniform cells with salt-and-pepper chromatin; dense-core granules by electron microscopy.
- Immunostains: synaptophysin and chromogranin A positive; Ki-67 sets the grade.
- Carcinoid syndrome (flushing, diarrhoea, bronchospasm, right-sided valve fibrosis) usually means liver metastases, because the liver inactivates serotonin from portal blood.
- Gastric tumours with autoimmune gastritis, MEN1 or Zollinger–Ellison are small and indolent; sporadic gastric ones are more aggressive.
- Urinary 5-hydroxyindoleacetic acid (5-HIAA) is raised in the syndrome.

## What it is

Well-differentiated neuroendocrine tumours, once called carcinoids, arise from the diffuse endocrine cells of the gut, which is their commonest site, with the small intestine leading. They are graded by mitotic rate and Ki-67 index; poorly differentiated, high-grade ones are neuroendocrine carcinomas of small-cell or large-cell type. Behaviour depends strongly on site: appendiceal tumours are almost always benign, while jejunal and ileal tumours are often multiple and aggressive.

## Step by step

- A diffuse endocrine cell of the gut becomes a slow-growing clone.
- The tumour grows in the submucosa and wall, provoking desmoplasia.
- Products released into portal blood are inactivated by the liver.
- Once tumour reaches the liver (or drains outside the portal system), serotonin and kinins reach the systemic circulation.
- Flushing, diarrhoea, bronchospasm and right-heart valve fibrosis follow.

## Behaviour by site

| Site | Typical features | Behaviour |
| --- | --- | --- |
| [Stomach](https://durgical.com/en/conditions/pernicious-anaemia/) | Often multiple, with atrophic gastritis, MEN1 or Zollinger–Ellison | Rarely metastasize; sporadic solitary ones more aggressive |
| [Duodenum](https://durgical.com/en/conditions/zollinger-ellison-syndrome/) | May secrete gastrin (gastrinoma) | Usually cured by resection |
| [Jejunum and ileum](https://durgical.com/en/conditions/carcinoid-syndrome/) | Often multiple; desmoplasia and obstruction | Most aggressive; liver metastases and carcinoid syndrome |
| [Appendix](https://durgical.com/en/conditions/acute-appendicitis/) | Any age; at the tip; usually under two centimetres | Almost always benign |
| Rectum | Found small at endoscopy; produce polypeptide hormones | Metastasis uncommon |

## Markers

- Synaptophysin
- Chromogranin A
- Ki-67 index (grade)
- Somatostatin receptor

## Clinical notes

- Symptoms depend on the hormone made: gastrin causes Zollinger–Ellison syndrome; serotonin causes carcinoid syndrome.
- Somatostatin analogues control symptoms and image the tumour.

## Memory aid

Salt and pepper in a yellow nodule; the liver hides the flush until it is itself invaded.

## Test yourself

Think of the answer, then tap the question to see it.

## Why does carcinoid syndrome usually require liver metastases?

The liver inactivates serotonin and other products carried in portal blood; only tumour in the liver or outside the portal drainage releases them into the systemic circulation.

## Which two immunostains confirm neuroendocrine differentiation?

Synaptophysin and chromogranin A.

## Which site of gastrointestinal neuroendocrine tumour is most aggressive?

The jejunum and ileum, where tumours are often multiple and metastasize.

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## Elsewhere in DurgiPedia

- [Enteroendocrine cells and GALT](https://durgical.com/en/histology/enteroendocrine-cells-and-galt/)
- [Serotonin (5-hydroxytryptamine)](https://durgical.com/en/biochemistry/molecules/serotonin/)

## Connections

## Related 6

- [Autoimmune atrophic gastritis](https://durgical.com/en/general-pathology/autoimmune-atrophic-gastritis/)
- [Hypertrophic gastropathies: Ménétrier, Zollinger–Ellison](https://durgical.com/en/general-pathology/hypertrophic-gastropathies-menetrier-zollinger-ellison/)
- [Tumours of the appendix](https://durgical.com/en/general-pathology/tumours-of-the-appendix/)
- [Gastrointestinal stromal tumour (GIST)](https://durgical.com/en/general-pathology/gastrointestinal-stromal-tumour/)
- [Immunohistochemistry: the principle and the markers to know](https://durgical.com/en/general-pathology/immunohistochemistry-the-principle-and-the-markers-to-know/)
- [Paraneoplastic syndromes: the table to know](https://durgical.com/en/general-pathology/paraneoplastic-syndromes-the-table-to-know/)

## Related conditions 6

- [Carcinoid syndrome](https://durgical.com/en/conditions/carcinoid-syndrome/)
- [Pancreatic neuroendocrine tumours (VIPoma, glucagonoma, somatostatinoma, non-functioning)](https://durgical.com/en/conditions/pancreatic-neuroendocrine-tumours/)
- [Multiple endocrine neoplasia (MEN 1, 2A, 2B)](https://durgical.com/en/conditions/multiple-endocrine-neoplasia/)
- [Pernicious anaemia](https://durgical.com/en/conditions/pernicious-anaemia/)
- [Small bowel obstruction](https://durgical.com/en/conditions/small-bowel-obstruction/)
- [Zollinger-Ellison syndrome (gastrinoma)](https://durgical.com/en/conditions/zollinger-ellison-syndrome/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Gastrointestinal Neuroendocrine Tumors Treatment (PDQ®)–Patient Version](https://www.cancer.gov/types/gi-neuroendocrine-tumors/patient/gi-neuroendocrine-treatment-pdq) (National Cancer Institute, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/gastrointestinal-neuroendocrine-tumours/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/gastrointestinal-neuroendocrine-tumours/