Bowel (colonic) polyps are small non-cancerous (benign) growths on the inside lining of the colon or back passage (rectum). They are common in older people. They usually cause no symptoms or problems. However, if a polyp is found, it is usually removed. This is because there is a small risk of a bowel polyp developing into a bowel cancer after several years.
What is a bowel (colonic) polyp?
A bowel polyp is a small non-cancerous (benign) growth that sometimes forms on the inside lining of the colon or back passage (rectum). Some people develop just one bowel polyp but it is not uncommon to develop two or more. However, it is uncommon to have more than five. A bowel polyp may have a stalk and a head which looks like a small mushroom growing from the lining of the bowel. Some are flatter and just look like a lump on the lining of the bowel.
Most bowel polyps develop in the part of the colon called the descending colon. The diagram shows a common site for a polyp to develop but they can occur anywhere in the colon or rectum.
Understanding the gut
The colon and back passage (rectum) are parts of the gut (gastrointestinal tract). The gut starts at the mouth and ends at the anus. When we eat or drink, the food and liquid travel down the gullet (oesophagus) into the stomach. The stomach churns up the food and then passes it into the small intestine.
The small intestine (sometimes called the small bowel) is several metres long and is where food is digested and absorbed. Undigested food, water and waste products are then passed into the large intestine (sometimes called the large bowel). The main part of the large intestine is called the colon, which is about 150 cm long. This is split into four sections, the ascending, transverse, descending and sigmoid colon. Some water and salts are absorbed into the body from the colon. The colon leads into the rectum which is about 15 cm long. The rectum stores stools (faeces) before they are passed out from the anus.
Types of bowel (colonic) polyp
Bowel polyps are generally 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, perhaps very rarely developing into a cancer.
These too are common. Most are small, usually less than a centimetre in diameter; however, sometimes they are 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, risk seems to vary depending on factors such as the size of the adenoma, and its exact subtype. Some subtypes are more prone to develop into bowel cancer than others.
Polyposis syndromes are a group of hereditary 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 and hyperplastic polyposis. These are rare syndromes, occur in young people and often cause multiple colonic polyps that have a high chance of developing into bowel cancer. Polyposis syndromes are not discussed further in this leaflet.
The rest of this leaflet is just about the common hyperplastic and adenoma polyps that commonly develop in older people.
Who develops bowel (colonic) polyps and what causes them?
Most bowel polyps develop in older people. About 1 in 4 people over the age of 50 years develop at least one colonic polyp. So, they are very common. The cause is not clear. The polyp is like a local fleshy overgrowth of tissue that lines the bowel. What causes this overgrowth to happen is not clear.
What are the symptoms of bowel (colonic) polyps in older people?
Most people with one or more bowel polyps do not have any symptoms. So, most affected people will never know that they have a bowel polyp. Occasionally, symptoms may occur. These include bleeding from the anus, mucus mixed in with stools (faeces), and, rarely, diarrhoea or constipation.
How are bowel (colonic) polyps diagnosed?
Most bowel polyps are diagnosed by this procedure. Colonoscopy is a test where an operator (a doctor or 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. See separate leaflet called Colonoscopy for more details.
Sometimes a bowel polyp is diagnosed by other tests such as a barium enema (a special X-ray test of the bowel) or sigmoidoscopy (like colonoscopy but using a shorter telescope).
Why would colonoscopy or other tests be done?
As mentioned, most bowel polyps do not cause symptoms. So, most people with bowel polyps will not be diagnosed. The tests mentioned above may be done if you have symptoms that indicate a bowel problem, or for various other reasons. For example, if you are found to have blood in your stools (faeces) following a routine screening test which is now offered to older people. See separate leaflet called Faecal Occult Blood Test for more details.
How are bowel (colonic) polyps treated?
If you are diagnosed with a bowel polyp, you will usually be advised to have it removed, even if it is causing no symptoms. This is to prevent the (small) risk of it developing into a cancer at some point in the future.
Most bowel polyps can be removed during a colonoscopy (described earlier). The colonoscope has a side channel down which grabbing devices can pass. These can be manipulated by the operator. The operator can therefore see and also remove a polyp during a colonoscopy. It is usually painless to have a polyp removed. 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 change.
Most 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 subtype and laboratory report, and your age. Once these factors are considered, some people are advised to have a routine colonoscopy at some point in the future.
Dr Tim Kenny
Dr Roger Henderson
Dr Adrian Bonsall