Normal Epithelium → Dysplastic Epithelium → Adenoma → Adenocarcinoma
- A protuberance of colorectal mucosa into the lumen
- Importance is in identifying those with malignant potential
- These are Adenomas that can become adenocarcinomas. At post mortem one third had an adenomatous polyp. Most occur beyond the splenic flexure. The worry is the adenoma-carcinoma sequence.
Adenomatous polyps : malignancy risk
- ↑ Degree of dysplasia - ↑ mitotic figures ↑pleomorphism of nuclei, loss of polarity, formation of layers
- ↑ Number of polyps , ↑ Size of polyps e.g. > 2 cm
- Villous adenomas - highest risk
- Tubulovillous or Tubular adenomas - lower risk
- Carcinoma in situ - severe dysplasia confined to the mucosa
- Malignant transformation - when there is invasion of the muscularis mucosa
- Adenomatous polyps should be removed once detected. If adenomatous then a complete colonoscopy for other polyps needed. Metaplastic polyps need no follow up.
Genetic syndromes with Adenomatous polyps
- Familial adenomatous polyposis (AD mutation in adenomatous polyposis coli (APC) gene)
- Turcot's syndrome (FAP + glioblastomas or medulloblastomas)
- Gardner's syndrome (FAP + Osteomas + soft tissue tumours and sebaceous cysts
Non Neoplastic: No malignant potential. Various types of polyps found.
- Metaplastic polyps (hyperplastic) seen in the rectum and are small (2-5 mm) and flat and do not become dysplastic or malignant and may be biopsied at endoscopy
- Inflammatory Pseudopolyps seen with inflammatory bowel disease (UC/CD)
- Hamartomatous polyps - there are two forms, those due to Peutz-Jegher's syndrome seen below and Juvenile polyps seen in children under 10 often in rectum and may cause bleeding or prolapse through anus and are easily resected.
Genetic syndromes with hamartomatous polyps
- Peutz-Jegher's syndrome - AD mucocutaneous pigmentation of lips and gums. Small bowel and colonic polyps. Childhood intussusception or bleeding.
- Cronkhite-Canada syndrome - alopecia, nail atrophy, skin hyperpigmentation and watery diarrhoea