Bowel polyps (colorectal polyps)
A bowel polyp is a growth projecting from the lining of the colon or rectum. Polyps are common — they are found in a large proportion of people over fifty undergoing colonoscopy — and the great majority are harmless in themselves. Their importance is entirely about the future: almost every colorectal cancer begins as a polyp, and the process takes ten to fifteen years. Removing polyps interrupts that process. This is the reason bowel screening works, and it is one of the few instances in medicine where a simple intervention demonstrably prevents a common cancer.
The types, and how they form
Adenomas
The classical precancerous polyp, accounting for most polyps removed. They form when the APC gene — the brake on the Wnt signalling pathway that regulates how often the bowel lining renews itself — is lost. β-catenin accumulates, cells proliferate without restraint, and a small adenoma appears. Further genetic faults (KRAS, SMAD4, ultimately TP53) accumulate over years and may eventually produce invasive cancer.
Not all adenomas progress; most never do. Risk of progression rises with:
- size — above 10mm is the important threshold
- architecture — villous or tubulovillous carry more risk than tubular
- high-grade dysplasia
- number — multiple adenomas indicate a field at risk
Serrated lesions
Increasingly recognised as the origin of a substantial minority of colorectal cancers, and clinically the most troublesome group.
- Hyperplastic polyps — small, usually in the rectum and sigmoid, and generally harmless.
- Sessile serrated lesions — flat, pale, often covered by a mucus cap, typically in the right colon, and easily missed. They progress through BRAF mutation and widespread methylation of gene promoters, which silences genes including the mismatch repair gene MLH1. They progress faster than conventional adenomas, which is why they account for a disproportionate share of cancers appearing between scheduled colonoscopies.
- Traditional serrated adenomas — uncommon, with a clear malignant potential.
Because these lesions are subtle, the quality of the colonoscopy matters as much as the fact that one was performed: thorough bowel preparation, careful withdrawal technique, adequate withdrawal time, and high-definition imaging all materially affect how many are found.
Other types
- Inflammatory pseudopolyps — in ulcerative colitis and Crohn's disease; regenerative, not premalignant, but they make surveillance harder.
- Hamartomatous polyps — juvenile polyps, and those of Peutz-Jeghers syndrome. Individually benign, but multiple ones point to a syndrome.
- Lipomas and other submucosal lesions — benign, requiring no treatment.
Symptoms
Most polyps cause none at all, which is the entire rationale for screening. Larger polyps may cause:
- rectal bleeding, or blood detected only on a faecal immunochemical test
- iron-deficiency anaemia
- mucus discharge — a large villous adenoma of the rectum can secrete enough mucus to cause electrolyte disturbance, though this is rare
- change in bowel habit, with large lesions
- rarely, intussusception from a large pedunculated polyp
How they are found
- Colonoscopy — both diagnostic and therapeutic, and the definitive investigation.
- Faecal immunochemical test (FIT) — the basis of most population screening programmes. It detects human haemoglobin in stool and identifies those needing colonoscopy. It is good at detecting cancers and large polyps, less so small ones, and a normal result does not exclude a polyp.
- CT colonography — where colonoscopy is incomplete or unsuitable; any polyp found still requires colonoscopy for removal.
Treatment
Polyps are removed at colonoscopy, and complete removal is the objective. Technique depends on size and shape:
- Cold snare polypectomy — now the preferred method for small polyps under 10mm, with lower risk of delayed bleeding and perforation than diathermy.
- Hot snare polypectomy — for larger pedunculated polyps.
- Endoscopic mucosal resection — fluid is injected beneath a flat lesion to lift it from the muscle layer, and it is then snared, in one piece where possible.
- Endoscopic submucosal dissection — for large flat lesions where an intact single specimen is needed to assess depth and margins accurately, particularly where early cancer is suspected.
- Transanal endoscopic surgery — for large rectal lesions unsuitable for endoscopic removal.
- Surgical resection — now rarely needed for a benign polyp. Advanced endoscopic techniques in specialist hands have made segmental colectomy for a benign lesion largely avoidable, and a patient advised to have a bowel resection for a benign polyp is entitled to ask whether endoscopic removal has been considered by someone who performs these regularly.
Lesions are tattooed if they may need later surgery or careful re-inspection.
When a polyp contains cancer
A proportion of polyps prove on examination to contain invasive cancer. Whether the polypectomy alone suffices depends on defined criteria: depth of invasion into the submucosa, clearance of the resection margin, differentiation, and the presence of lymphovascular invasion or tumour budding. Favourable features mean the polypectomy is likely curative; unfavourable features indicate a risk of lymph node involvement and formal resection is recommended. This decision is made in a multidisciplinary meeting, and it is a genuine balance rather than an automatic rule.
Recovery
Polypectomy is performed at the time of colonoscopy, usually as a day case. Most patients resume normal activity the next day. After removal of large polyps, advice is given to avoid heavy exertion and to stop or adjust blood-thinning medication for a defined period.
Recognised complications are uncommon but should be known: bleeding, which may occur up to two weeks afterwards, and perforation, which is rare. Significant rectal bleeding, severe abdominal pain or fever after polypectomy requires prompt assessment.
Follow-up
Surveillance intervals are determined by what was found — the number, size and histology of the polyps — and by the quality and completeness of the examination. In broad terms:
- one or two small tubular adenomas, completely removed — return to routine screening, with no need for early repeat colonoscopy. This is a change from older practice, and over-surveillance carries its own costs and risks.
- multiple adenomas, or any adenoma 10mm or larger, or with high-grade dysplasia or villous architecture — surveillance colonoscopy at a defined interval, typically three years.
- large lesions removed in pieces — early check of the resection site, within months.
- serrated lesions — surveillance according to size, number and site.
- suspected polyposis syndrome — genetic assessment and a protocol-driven programme.
When to seek an opinion
Rectal bleeding, a change in bowel habit lasting more than a few weeks, iron-deficiency anaemia, or a positive screening test. A family history of bowel cancer or of multiple polyps is a reason to ask about starting screening earlier than the general population.
Common questions
Does having a polyp mean I will get bowel cancer?
No. Most polyps never become cancer, and removing them removes the risk from those that might have. Having polyps does mean you are more likely to form others, which is why a repeat examination is arranged at an interval appropriate to what was found.
How long does a polyp take to become cancer?
Typically ten to fifteen years, and many never do. That slow pace is exactly why screening works: there is a long window in which a polyp can be found and removed before it ever becomes dangerous.
Was it painful? Will removal hurt?
No. The bowel lining has no pain sensation of the kind skin has, so polyps are removed painlessly during the colonoscopy, usually with sedation. Most people are unaware it has happened.
Do I need an operation?
Almost never for a benign polyp. Even large flat polyps can usually be removed through the colonoscope using specialised techniques. If you have been advised to have part of your bowel removed for a polyp that is not cancer, it is reasonable to ask whether an advanced endoscopic removal has been considered first.
The polyp contained cancer. What now?
Not necessarily anything further. Where the cancer is confined to the surface layers, the polyp was completely removed with a clear margin, and the microscopic features are favourable, the removal itself may be all the treatment needed. Where the features are less favourable, a bowel resection is advised to remove the nearby lymph glands. This is decided by a team reviewing the microscope findings in detail.
When do I need another colonoscopy?
It depends on the number, size and type of polyps found. One or two small ones completely removed often means simply returning to routine screening rather than an early repeat. Larger or multiple polyps mean a check at a defined interval, usually about three years. You should be told your interval and the reason for it.
Can I stop polyps forming?
Not entirely, but risk is reduced by not smoking, keeping weight down, staying active, limiting alcohol and red and processed meat, and eating more fibre. None of this replaces having the examinations, which remain the reliable way of preventing bowel cancer.
Should my family have colonoscopies?
Having had a few polyps is not in itself a reason for relatives to be screened early. Where polyps are very numerous, occur at a young age, or there is a family history of bowel cancer, genetic assessment and earlier screening for relatives are recommended.
Related conditions
Other conditions of the colon & rectum covered on this site:
- Colon cancer
- Rectal cancer
- Diverticular disease and diverticulitis
- Crohn's disease — the surgical perspective
- Ulcerative colitis — the surgical perspective
- Large bowel obstruction and volvulus
- Appendicitis
- Hereditary bowel cancer syndromes (Lynch syndrome and FAP)
This page provides general information and does not replace an individual medical consultation. Assessment and treatment are decided for each patient after review of their history, examination and investigations.