Colonic adenomas and serrated lesions
- Lesion
Adenomas are benign gland tumours of the colon that can become cancer; the bigger and more villous they are, the more dangerous.
What it is
Adenomas are neoplastic polyps defined by epithelial dysplasia, and they are the precursors of most colorectal adenocarcinomas. They are found in about three in ten Western adults by age sixty, though most never progress. Sessile serrated lesions resemble hyperplastic polyps but grow in the right colon, lack classic dysplasia, and lead to cancer through the serrated (CpG methylation, BRAF) pathway. Removing a polyp removes its chance of becoming cancer.
Structure
- Pedunculated adenomas have a slender fibromuscular stalk with submucosal vessels, usually covered by normal mucosa.
- Surface texture: velvety or raspberry-like.
- Invasion into the stalk (submucosa) makes it an invasive carcinoma; grade, lymphovascular invasion and margin decide further surgery.
Colorectal polyps that matter
| Polyp | Where | Histology | Malignant potential |
|---|---|---|---|
| Hyperplastic polyp | Left colon, rectum | Serration in the upper crypt only, mature cells | None |
| Sessile serrated lesion | Right colon | Serration to the crypt base, dilated, laterally spreading crypts; no classic dysplasia | Yes (serrated pathway, BRAF, CIMP) |
| Tubular adenoma | Anywhere | Rounded dysplastic glands | Yes; lowest among adenomas |
| Villous adenoma | Often rectum | Long dysplastic villi | Higher; usually larger |
| Traditional serrated adenoma | Left colon | Serrated with eosinophilic dysplastic cells | Yes |
Clinical notes
- Screening colonoscopy is advised from about age forty-five, earlier with a family history.
- Large adenomas can cause occult bleeding and iron deficiency; villous adenomas can rarely secrete enough to cause hypokalaemia.
Test yourself
Think of the answer, then tap the question to see it.
What is the most important predictor of cancer in a colonic adenoma?
Its size; cancer is rare under one centimetre and common in adenomas larger than four centimetres.
How does a sessile serrated lesion differ from a hyperplastic polyp?
Serration extends to the crypt base with dilated, laterally spreading crypts, it favours the right colon, and it has malignant potential.
Why does intramucosal carcinoma of the colon rarely metastasize?
The colonic mucosa lacks functional lymphatics, so spread requires invasion beyond the muscularis mucosae.
Connections
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: Colorectal Cancer Screening (StatPearls (NCBI Bookshelf), 2025); Colorectal cancer: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.