Colon polyps

What are colon polyps?

A colon polyp is an outgrowth of tissue from the wall of the large bowel or colon. Polyps can vary in size. A polyp can look like a pea or a wart, sometimes a small mushroom on a stalk, or even resemble an area of raised carpet with many finger-like projections. There are many types of colon polyps, some of which carry no potential for developing into cancer and some that do.

Colon polyps may be single or multiple, very small in size or they may grow to 2 centimetres in diameter or larger. They are most common in Western countries.

Adenomas and hyperplastic polyps

The 2 most common types of polyps are adenomas and hyperplastic polyps.

Colonic adenomas are more common as people get older. Doctors believe they may represent an increased risk for colorectal cancer, although they believe only a small number of adenomas develop into cancer and those that do take many years to do so. Hyperplastic polyps, although they do not involve a risk for colorectal cancer in themselves, can sometimes contain adenomas, especially if the hyperplastic polyps are large.

What causes colon polyps?

The cause of colon polyps is unclear. Some evidence suggests that they may be related to unhealthy lifestyle factors. Smoking, being overweight, having a sedentary lifestyle, eating a diet that is high in fat and low in fibre, and drinking excess alcohol can increase your risk of colon polyps and colon cancer.

Genetic factors may also play a part, especially in people with a family history of colon polyps or colorectal cancer.

In a condition called familial polyposis, a hundred or more small polyps develop on the colon, so that it looks like a carpet of small raised lumps. Several members of a family may suffer from this condition, and there is a high risk that one or more of the polyps may turn malignant. For this reason, people who have a relative who has had polyps should have regular examinations and sometimes may need to have their colon removed to prevent cancer from developing. Usually people with familial polyposis who aren't treated go on to develop cancer by the age of 40.

Doctors estimate that adenomas of the colon occur in about 20 per cent of middle-aged and older adults, but it may be the case that only people with certain genetic profiles, or those who have large polyps, go on to develop colorectal cancer.

What are the symptoms of colon polyps?

In most cases, polyps do not cause any symptoms and may only be discovered during a routine screening by your doctor. They may, however, bleed and you may see blood on your stool or from your rectum, or they will result in excessive mucus in your bowel motions. Sometimes (although this is rare), a large polyp may obstruct or block your bowel, which leads to constipation or diarrhoea, abdominal pain or vomiting.

How are colon polyps diagnosed?

Because there are often no readily apparent symptoms, the diagnosis of colon polyps is usually made only after certain investigations are carried out, including:

  • sigmoidoscopy or colonoscopy, which are both forms of endoscopy, in which a flexible lighted instrument (an endoscope) is inserted into the rectum to view part or all of the colon; and
  • X-ray barium studies of the large bowel, also called a barium enema. In this test a small tube is placed in the rectum, and barium and air are gently introduced. The barium will highlight the bowel so that any abnormalities will show up on X-ray.

Because polyps and early bowel cancer commonly have no symptoms, screening for bowel cancer is recommended. For the majority of people, a test known as a faecal occult blood test (FOBT) should be done once every 1-2 years after you turn 50. If the FOBT detects traces of blood in the bowel movements (faeces) your doctor will recommend another test – usually a colonoscopy. For people with a family history of bowel cancer or those with inflammatory bowel disease, screening may need to be more intensive, so consult your doctor.

What can be done to prevent colon polyps?

  • A diet that's high in fibre and calcium, and low in dietary fat may help protect against the development of colon polyps. Stopping smoking, keeping physically active and cutting down on alcohol may also help.
  • When an adenoma has been identified and removed, your doctor may recommend periodic screening by colonoscopy. Because this type of polyp can recur and does carry some risk of developing into colorectal cancer, regular checks are important.
  • There is some evidence that aspirin and similar drugs, known as non-steroidal anti-inflammatory drugs (NSAIDs), may protect against colonic adenomas, however, the evidence is not conclusive at present. Do not start taking aspirin without first asking the advice of your doctor.

How are colon polyps treated?

Rectal or colon polyps are generally removed because it has been shown that doing this significantly reduces a person's risk of getting colon cancer. Usually, they are removed during a colonoscopy. In the procedure, doctors manoeuvre a long wire loop through the colonoscope and around the base of the polyp. The loop is pulled tight, and then an electrical current is passed through the wire. This cauterizes the base of the polyp so that it can be removed without bleeding. This causes only minimal discomfort and the person can usually go home on the same day as the procedure. In rare cases where the polyp is very large, traditional surgery may be needed to remove it.

Last Reviewed: 10 May 2009
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