Bowel (colonic) polyps are small non-cancerous (benign) growths on the inside lining of the bowel (colon and rectum).
How common are they?
Bowel polyps are really common in older people. About 1 in 4 people over the age of 50 years develop at least one colonic polyp. Bowel polyps are much less common in younger people.
Some people develop just one bowel polyp. It is not uncommon to have two or more. However, having more than five polyps is unusual.
What are the symptoms?
Most people with one or more bowel polyps do not have any symptoms. Most people who have a bowel polyp will never know they have one. Sometimes a polyp will be found when you have a faecal occult blood test to see whether you have any bleeding from your bowel.
However, some people with bowel polyps will get symptoms. These symptoms include blood in the stools (faeces). There may also be mucus in the stools.
A bowel polyp may cause diarrhoea or constipation but this is much less likely than blood in the stools. Diarrhoea or constipation is much more likely to have a cause other than a bowel polyp.
What are the causes of bowel polyps?
The lining of the bowel constantly renews itself throughout our lives. New cells are made in the lining of the bowel and these cells eventually die to be replaced by more new cells. Each of these cells contains genes which control how the cell works.
If the gene doesn't work properly then some cells may grow more quickly. This may eventually cause a polyp to develop. Some faulty genes which cause a tendency for the lining of the bowel to develop polyps or bowel cancer may be inherited from our parents.
What are the types of bowel polyp?
Most bowel (colonic) polyps develop in the part of the colon called the descending colon, which leads down to the rectum. However, they can occur anywhere in the colon or rectum. Bowel polyps can be divided into three types: hyperplastic polyps, adenomas and polyposis syndromes.
These are common. They are small - usually less than half a centimetre in diameter. They are generally regarded as harmless and only very rarely develop into a cancerous (malignant) growth.
These too are common. Most are small (usually less than a centimetre in diameter) but they can be bigger. There is a small risk that an adenoma may, in time, become cancerous. If one does turn cancerous, the change usually takes place after a number of years. Most bowel cancers (colorectal cancers) develop from a polyp that has been present for 5-15 years. In other words, although most adenomas do not become cancerous, the vast majority of cancers in the bowel initially develop from an adenoma that has been present for a number of years.
It is difficult to be certain of the exact risk of developing cancer from an adenoma. One study suggested that for a single 1 cm adenoma, the risk of it turning cancerous was about 1 in 12 after 10 years, and about a 1 in 4 after 20 years. However, the risk seems to vary depending on factors such as the size of the adenoma and the exact type of adenoma. There are different types of adenoma and some types are more likely than others to develop into bowel cancer.
Polyposis syndromes are a group of inherited conditions. They include:
- Familial adenomatous polyposis (FAP).
- Hereditary nonpolyposis colorectal cancer (HNPCC)/Lynch's syndrome.
- Gardner's syndrome.
- Turcot's syndrome.
- Peutz-Jeghers syndrome.
- Cowden's disease.
- Familial juvenile polyposis.
- Hyperplastic polyposis.
These are rare syndromes. They cause polyps in young people and often cause multiple bowel polyps that have a high chance of developing into bowel cancer.
How are bowel polyps diagnosed?
Most bowel (colonic) polyps do not cause symptoms. So, most people with bowel polyps will not be diagnosed. Tests may be done if you have symptoms that indicate a bowel problem, or for various other reasons. For example, if you have seen blood in your stools (faeces) or if you are found to have blood in your stools following a routine screening test which is now offered to older people.
What is a colonoscopy?
Most bowel polyps are diagnosed by this procedure. Colonoscopy is a test where an operator - a doctor or a nurse - looks into your colon. A colonoscope is a thin, flexible telescope. It is about as thick as a little finger. It is passed through the anus and into the colon. It can be pushed all the way around the colon as far as the caecum (where the small and large intestine meet). The colonoscope contains fibre-optic channels which allow light to shine down so the operator can see inside your colon.
A sample (biopsy) will be taken at the time of the colonoscopy. This is very important so that it can be checked whether the polyp is cancerous (malignant).
What about other tests?
Sometimes a bowel polyp is diagnosed by other tests:
- A special X-ray test of the bowel - this procedure is called a barium enema.
- A test procedure called sigmoidoscopy - this enables a doctor or nurse to use an instrument called a sigmoidoscope to look into the rectum and sigmoid colon. The procedure is similar to a colonoscopy but it uses a shorter telescope.
If a polyp is seen on a barium enema you will still need a colonoscopy to remove the polyp and to take a sample (biopsy) of it for further investigation.
You will also need a colonoscopy if a polyp is found when you have a sigmoidoscopy. This is to make sure there are no more polyps beyond the reach of sigmoidoscopy.
How are bowel polyps treated?
If you are diagnosed with a bowel (colonic) polyp, you will usually be advised to have it removed, even if it is not causing any symptoms. This is because there is a small risk of the polyp developing into a cancerous (malignant) growth at some time in the future.
Most bowel polyps can be removed during a colonoscopy. The colonoscope has a side channel down which a grabbing device can be passed. This device can be manipulated by the operator. The operator can therefore see and also remove a polyp during a colonoscopy. The removal of the polyp is usually painless. Once removed, the polyp is sent to the laboratory to be looked at under a microscope. This is done to check:
- That it has been completely removed.
- The type of polyp.
- Whether it is non-cancerous (benign) or showing signs of cancerous (malignant) change.
Most removed polyps will show full removal and be totally benign.
Your doctor will advise on the need for follow-up. This may depend on factors such as the size of the polyp, the exact type of polyp that has been removed, the laboratory report about the polyp, and your age. Once these factors are considered, some people are advised to have regular colonoscopies in the future to make sure no more bowel polyps develop.
Do I need surgery?
If you have many polyps (especially if you have a polyposis syndrome) then you may need to have an operation to remove part of your bowel. This is because it isn't possible to completely remove all the polyps by using colonoscopy.
Further reading and references
Colonoscopic polypectomy and endoscopic mucosal resection: A practical guide; British Society of Gastroenterology (2008)
Guidelines for colorectal cancer screening and surveillance in moderate and high risk groups; British Society of Gastroenterology (May 2010)
Colonoscopic surveillance for prevention of colorectal cancer in people with ulcerative colitis, Crohn's disease or adenomas; NICE Clinical Guideline (March 2011)
Combined endoscopic and laparoscopic removal of colonic polyps; NICE Interventional Procedure Guidance, September 2014