Understanding the gut
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 colon and back passage (rectum) are parts of the gut (gastrointestinal tract).
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.
Understanding 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.
Kinds 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, but 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.
Proneness to bowel (colonic) polyps and its causes
Most bowel polyps develop in older people. About 1 in 4 people over the age of 50 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.
Indications 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 one’s 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 round 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.
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 one has symptoms that indicate a bowel problem, or for various other reasons. For example, if one is found to have blood in the stools (faeces) following a routine screening test which is now offered to older people.
Therapeutics of bowel (colonic) polyps
If one is diagnosed with a bowel polyp, one 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 which 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, to check the type of the polyp, and whether it is non-cancerous (benign) or showing signs of cancerous change. Most will show full removal and be totally benign.
Follow up depend on factors such as the size of the polyp, the exact subtype and laboratory report, and one’s age. Once these factors are considered, some people are advised to have a routine colonoscopy at some point in the future.
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.