Polyps in the colon (large bowel)

- Juvenile polyps: these are usually solitary polyps called hamartomas that affect 1 to 2 per cent of older children or adolescents. A single polyp carries no significant cancer risk but when these polyps are inherited and usually multiple (about one third of patients), the colon cancer risk is about 10 per cent. In this case, regular surveillance after excision (cutting out) of all polyps is required.
- Peutz-Jeghers polyps: found in Peutz-Jeghers syndrome, in association with freckling of the lips, are also of the hamartomatous type. These usually present in early adult life and carry a low but definite risk of malignancy, probably around five per cent per polyp, so they need excision. The number of polyps per individual is very variable and ranges, from as few as one or two to as many as 20 or more. Peutz-Jeghers polyps can also occur in the small intestine and can then be difficult to diagnose because they are beyond the reach of conventional fibre-optic endoscopes (internal telescope instruments). Such polyps tend to present with symptoms of obstruction (bowel blockage) or abdominal pain. Diagnosis is usually made with barium X-rays (taken after the patient swallows barium liquid to show up the inside of the intestine). Treatment will usually be an operation that opens up the abdomen.
- Inflammatory pseudopolyps: can occur as a complication of ulcerative colitis or Crohn's disease of the colon. They are completely harmless and carry no risk of cancer but they can be confused with adenomatous polyps on examination.
- Cronkhite-Canada syndrome: an exceptionally rare condition, involves multiple colon polyps, hyperpigmentation (darkening of the skin) and nail atrophy (wasting away). The syndrome is not inherited and affects middle-aged or older individuals. It is linked with malabsorption and has been reported to respond to vitamin E therapy.

What causes polyps?

Most polyps, with the exception of the inflammatory pseudopolyps, result from some form of genetic (DNA) mutation in one of the colon lining cells. Fortunately, several, probably at least five, mutations are needed in the same cell before cancer occurs and most benign polyps probably only have one gene mutated. DNA damage occurs surprisingly often.

Even in a healthy adult's colon, about 10 per cent of the lining cells, on average, contain major abnormalities of the chromosomes (packages of DNA that contain many genes). Fortunately, almost all these cells seem to undergo a form of programmed death called apoptosis, and then fall off harmlessly into the bowel lumen (cavity).

Adenomatous polyps, even those from individuals who do not have familial polyposis, commonly contain mutations that stop the gene working in both copies of the adenomatous polyposis coli (APC) gene, the gene that is mutated in familial polyposis coli.

What symptoms do polyps cause?

Polyps usually cause no symptoms until they grow to 2cm or more in diameter. Then the most common symptom is rectal bleeding. If a polyp is large enough, say 2cm in diameter, it can simulate faeces so the colon undergoes vigorous muscular movements (peristalsis) in a futile attempt to expel the polyp. This can lead to severe colicky pains.

Occasionally, large polyps with a characteristic villous (frondy) appearance will cause profuse watery diarrhoea, which can then result in severe potassium deficiency causing muscle weakness.

How is the diagnosis made?

Polyps can be seen directly during colonoscopy (telescope examination of the whole large bowel starting at the rectum). An experienced doctor can often differentiate metaplastic polyps from the pre-malignant adenomatous polyp by appearance alone.

Nevertheless, most doctors prefer not to take the risk of getting it wrong and either take biopsy samples (small bites of tissue) or cut out the entire polyp (polypectomy). In this case, checking the polyp's cells under the microscope (histology) is not essential providing that the doctor is certain that the polyp has been completely removed.

Symptomless polyps are often found at barium enema examination (an X-ray test done after barium liquid is poured into the rectum) in a patient with bowel symptoms that could be due to irritable bowel syndrome. They are also commonly found by chance when screening is performed using flexible sigmoidoscopy (examination of the lowest part of the bowel using a bendy telescope) or colonoscopy.

What is the treatment?

Polypectomy Most polyps can be removed during colonoscopy while the patient is sedated. This is done by passing a wire snare down the colonoscope, looping and tightening the snare around the stalk of the polyp, then passing an electric current through the wire. This coagulates the blood vessels and then cuts through the stalk. The polyp is then usually sent to the pathology laboratory for microscopic examination.

The polypectomy is painless because the colon nerves are only sensitive to stretching. Polypectomy is very safe but carries a risk of perforation (going through the bowel wall) in about one case in 300 and bleeding in one case per 100. Bleeding usually stops by itself and only rarely needs treatment with blood transfusion.

Surgery

Occasionally, a polyp is too large to be removed endoscopically, usually when the diameter is more than about 4cm and, particularly, if the base of the polyp is broad with no well-defined stalk. In these cases, endoscopic removal can carry an unacceptably high risk of bleeding or perforation. Such polyps are also more likely to already contain cancer and removal by surgery that opens up the abdomen can be the safest option to ensure cure.

Large, rectal polyps can sometimes be removed through the anus under general anaesthetic without the need to cut open the abdomen.

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