- adenomatous colon polyps
- hamartomatous colon polyp
- hyperplastic colon polyps
- inflammatory colon polyps
- lymphoid colon polyps
Adenomatous colon polyps are thought to progress histologically from adenoma to dysplasia, to carcinoma; thus screening detection of precancerous polyps is considered useful. The individual risk for a polyp progressing to cancer is low, in the order of 3% and it is thought that it takes 10-15 years for a polyp to devolve into carcinoma.
Patients with familial adenomatous polyposis (FAP) have a markedly increased number of colon polyps, often numbering in the hundreds, with a corresponding increased risk of malignant degeneration.
Current imaging modalities cannot differentiate between different polyp histologies, which is defined at pathology.
Colon polyps are most often detected during colonoscopy, which is considered the gold standard for detection. Colonoscopy also has the added benefit of being able to snare and remove any polyps encountered. Flexible sigmoidoscopy may also be used, although the entire colon is not visualised.
Non-invasive radiologic imaging can also detect polyps. In the past, this was traditionally accomplished with a barium enema (usually double contrast for polyp detection), however, CT colonography is playing an increasing role in polyp detection. Barium enema has a significantly decreased sensitivity and specificity for polyp detection (~50% of polyps >1 cm detected on colonoscopy were seen on double contrast barium enema) 4.
Treatment and prognosis
Because of the benefits of screening, screening studies (usually colonoscopy) are recommended at age 50 for men and women. The actual screening program depends on the patient's region and risk factors, however. Screening at age 40 years or younger is recommended for patients at higher risk (e.g. FAP). Patients with FAP often receive prophylactic total colectomy.
The risk of malignancy of a colon polyp varies with its size
- <5 mm: <1% risk of cancer
- 5-9 mm: <1-2% chance of cancer
- 10-20 mm: ~10% chance of cancer
- >20 mm: 40-50% chance of cancer
Other features may indicate that a polyp is higher risk
- ≥3 adenomas
- high-grade dysplasia
- villous features
These high-risk patients should receive a follow-up screening study sooner than the general population (currently, 3-year follow-up with colonoscopy is suggested). Lower risk patients may follow up in 5-10 years, and patients with only hyperplastic polyps need only a 10-year follow-up evaluation, like the general population.
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- 2. Pickhardt PJ, Hassan C, Halligan S et-al. Colorectal cancer: CT colonography and colonoscopy for detection-systematic review and meta-analysis. Radiology. 2011;259 (2): 393-405. doi:10.1148/radiol.11101887 - Free text at pubmed - Pubmed citation
- 3. Winawer SJ, Zauber AG, Fletcher RH et-al. Guidelines for colonoscopy surveillance after polypectomy: a consensus update by the US Multi-Society Task Force on Colorectal Cancer and the American Cancer Society. Gastroenterology. 2006;130 (6): 1872-85. doi:10.1053/j.gastro.2006.03.012 - Pubmed citation