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PH-GI15

Benign tumours of the small and large intestine

The tumours beneath the intestinal lining: lipoma, leiomyoma, haemangioma and lymphangioma, low-risk GIST and neuroendocrine tumours (carcinoids) of the ileum and appendix, how they bleed, obstruct or telescope the bowel, and the carcinoid syndrome.

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  • 5 steps · 10 questions
  • 3D normal anatomy

By the end, you can

  • Relate each layer of the intestinal wall to the tumours that arise from it.
  • Describe the gross and microscopic appearance of lipoma, leiomyoma, haemangioma and lymphangioma.
  • Explain why neuroendocrine tumours and GISTs are graded or given a risk by size, site and proliferation rather than simply called benign.
  • Explain how serotonin from a neuroendocrine tumour causes the carcinoid syndrome only when it bypasses the liver.
  • Relate bleeding, obstruction and intussusception to the way submucosal tumours grow.
  • Recognise the classic appearances, grades and tests of benign intestinal tumours and neuroendocrine tumours, and explain how resection, somatostatin analogues, radionuclide therapy and liver-directed treatment act on them.

What it is

Benign intestinal tumours are slow-growing neoplasms of the small and large intestine that do not invade or spread. Besides the epithelial polyps (adenomas and hamartomas), most arise beneath the lining: lipoma (fat), leiomyoma (smooth muscle), haemangioma and lymphangioma (vessels). Neuroendocrine tumours and gastrointestinal stromal tumours range from indolent to malignant; small ones often behave benignly.

4 types to tell apart
Mesenchymal tumours
Lipoma, leiomyoma, haemangioma and lymphangioma, from fat, smooth muscle and vessels of the wall, usually under intact mucosa.
Neuroendocrine tumours (carcinoids)
From neuroendocrine cells of the crypts; small appendiceal and rectal tumours usually behave benignly, ileal ones often spread.
Gastrointestinal stromal tumour
From the interstitial cells of Cajal; small tumours with few mitoses carry very low risk.
Epithelial polyps
Adenomas, serrated lesions and hamartomas of the lining, taught in the polyps and polyposis lesson.

US spelling: tumours → tumors, haemangioma → hemangioma, tumour → tumor.

Normal function

Layers of the wall and the cells in each

The intestine has the same layered wall along its length. The mucosa, with its in the small intestine and its , renews its epithelium every few days. Scattered among the crypt cells are neuroendocrine cells (enterochromaffin cells), which release serotonin and other signals into the wall when the lumen is stretched or chemically stimulated. A thin borders the mucosa.

The is loose connective tissue with fat cells, blood vessels and lymphatics. Beyond it, the and smooth muscle layers propel the contents; between them lies the with the interstitial cells of Cajal, the pacemaker cells that set the rhythm of contraction.

Each tissue has its own tumour: fat gives lipoma, smooth muscle leiomyoma, vessels haemangioma and lymphangioma, interstitial cells of Cajal GIST, and neuroendocrine cells NETs. Most grow beneath the epithelium, so they form smooth bulges covered by normal mucosa, unlike the epithelial polyps.

Point to it on the model