Colonic Polyps and Colorectal Screening
On this page
Direct answer
Colonic polyps are mucosal growths, and adenomas are the neoplastic type with malignant potential, following the adenoma-carcinoma sequence. Tubular adenomas are the most common, while villous histology and high-grade dysplasia carry the greatest cancer risk; hyperplastic polyps are generally benign. Colonoscopy with polypectomy is both diagnostic and therapeutic, and faecal immunochemical testing serves as a non-invasive screen whose positive result leads to colonoscopy.
What you must remember
- Adenoma: neoplastic polyp with malignant potential, classified as tubular, tubulovillous or villous in increasing order of risk.
- Advanced adenoma: 10 mm or larger, or with high-grade dysplasia or a villous component, and the main target of surveillance.
- Hyperplastic polyp: usually small, benign and found in the rectosigmoid.
- Sessile serrated lesion: a serrated polyp with malignant potential, typically in the right colon, and easily missed.
- Familial adenomatous polyposis: APC mutation producing hundreds of adenomas, usually from adolescence, with colectomy needed.
- Lynch syndrome: mismatch repair defect causing early colorectal cancer, managed with altered surveillance.
- FIT: detects human haemoglobin in stool, so a positive result requires colonoscopy.
Where the exam tests the screening trap
Screening questions reward attention to histology, hereditary risk and the limits of non-invasive tests.
- Trap: treating all polyps as equally dangerous Correct: hyperplastic polyps are benign, while adenomas and sessile serrated lesions carry malignant potential.
- Trap: accepting a negative FIT as clearance in an adenoma-prone patient Correct: FIT detects bleeding, not every adenoma, so symptomatic or high-risk patients still need colonoscopy.
- Trap: missing a hereditary cause in a young patient Correct: multiple adenomas or early-onset cancer suggest FAP or Lynch syndrome, which need genetic counselling.
Colorectal cancer is not part of the national screening programme, which covers oral, breast and cervical cancers, so screening in India relies on symptoms and family history.
Frequently asked questions
What defines an advanced colorectal adenoma?
An advanced adenoma is one 10 mm or larger, or one with high-grade dysplasia or a villous component on histology. Advanced adenomas carry the greatest risk of progression to colorectal cancer and largely determine the surveillance interval after polypectomy.
Why is a faecal immunochemical test not enough after a positive result?
Faecal immunochemical testing detects human haemoglobin in stool, so a positive result signals bleeding that needs colonoscopy to locate the source. The test does not reliably detect every adenoma, so colonoscopy with polypectomy remains the definitive investigation.
Which hereditary syndrome causes hundreds of colonic adenomas?
Familial adenomatous polyposis, caused by an APC gene mutation, produces hundreds of colonic adenomas, usually beginning in adolescence. Colectomy is generally needed before cancer develops, and genetic testing is offered to relatives.
Which polyp type belongs to the serrated pathway of colorectal cancer?
A sessile serrated lesion belongs to the serrated pathway of colorectal cancer and typically arises in the right colon. Such lesions are easily missed on colonoscopy and need careful removal with specialist follow-up because they can progress to cancer.