This factsheet is about polyps in the bowel

A polyp is a fleshy growth on the inside of the bowel. Some people may develop just a single polyp, while others can have two or more at a time. Polyps can either be on a stalk (in which case the polyp looks like a mushroom growing from the lining of the bowel) or they can be much flatter and even have quite a broad base. Polyps are usually benign (non cancerous) but they are important because some of them may eventually become malignant (cancerous). Most experts now believe that many bowel cancers develop from polyps and doctors are most concerned about detecting and treating a type of polyp called an adenoma polyp as they are most likely to become cancerous in the future. It is thought that around 1 in 10 adenomatous polyps will become cancerous. Polyps seem to be very common, especially in the West, and are slightly more common in men than women. They are rather unusual below the age of 40 and seem to occur most often in people over the age of 60.

Polyps in the colon (bowel).


Causes of polyps in the bowel

The lining of the bowel, like other organ linings, constantly renews itself throughout our lives. There are many millions of tiny cells in the lining, which grow, serve their purpose and die before new cells then take their place. Each of these millions of cells contains genes, which give instructions to the cell on how to behave and grow. When genes behave in a faulty manner, this can cause the cells to grow quicker, eventually producing a small bump on the bowel surface that we call a polyp.

A polyp, or more strictly the particular type of polyp called an adenoma, starts out as a tiny bump on the surface of the bowel. The genes give faulty instructions that can make the cells grow more quickly but they do so in an orderly manner. Some polyps remain very small (less than one centimetre) while others continue to enlarge up to several centimetres. Most polyps remain benign but it is thought that most malignancies of the bowel begin as benign polyps; so by removing benign polyps we can help to prevent the development of the rare ones that may become cancer.

We now know that up to 10% of people who tend to have polyps may do so because the likelihood of that happening is inherited. In most cases neither polyps nor indeed bowel cancer tend to run in families but when a number of members of the same family have had polyps or bowel cancer – especially if they have developed these at a young age – then there is an increased risk.


What are the usual symptoms of polyps in the bowel? 

Usually polyps do not cause symptoms and most people will never know if they have them. Polyps are often discovered at colonoscopy (see below) as part of an investigation into bowel changes or symptoms and usually the polyps are not the cause of those symptoms.

Occasionally they can cause bleeding from the back passage or may produce an excess of mucus or slime, which can be noticed on motions when opening the bowel. Very occasionally a polyp can grow so large as to cause a blockage of the bowel but, unless this occurs, polyps do not cause pain.

How are polyps in the bowel diagnosed?

Rectal bleeding is a symptom of polyps, both benign and malignant as well as other potentially serious conditions. Investigations will be carried out to determine whether any of the above are the cause of the bleeding.

  • Faecal occult blood test:

This can pick up blood that is usually not visible to the naked eye. The results of this test can aid any potential diagnosis or decision about referral to a specialist.

  • Colonoscopy:

This is where a tube, linked to a highly magnified video system, is passed, via the anus, into the colon and, where possible, the nearest part of the small intestine. A colonoscopy gives a very accurate picture of the lining of the intestine and allows the doctor to check for polyps. Sometimes a shorter instrument called a sigmoidoscopy is used but this can only allow inspection of the lower colon and, if it reveals a polyp, a colonoscopy will still then be needed to remove and to check that there are no more polyps elsewhere in the colon. In most cases, sedation is given to minimise any feelings of discomfort.

  • CT Pneumocolon Scans:

This involves air being introduced into the colon by a small tube, to improve the views of the bowel whilst the scanning is underway.

  • Barium Enema X-Ray:

A barium enema is a test that helps to highlight the large bowel so it can be clearly seen on an X-ray. During the test, a white liquid called barium is passed into your bowel through your bottom.

Except for the faecal occult blood test, all of the above will require the bowel to be as clear as possible before the procedure. A special diet is followed and laxatives are taken beforehand.


What treatment is available for polyps in the bowel?

There are a variety of different techniques to remove polyps but most consist of passing a wire through the colonoscope and looping wire around the polyp – like a lasso – to remove it. This procedure is quite painless and only one examination is usually needed to clear the bowel of polyps. Occasionally, there may be too many polyps for all of them to be removed safely at once and so the procedure may need to be repeated.

Once they have been removed all the polyps are retrieved if possible and sent to the laboratory for microscopic analysis. This will show whether the polyp has been completely removed, where or if it has the potential to develop malignancy and, of course, to be sure that cancer has not already developed.

Removal of a polyp using a coloscope and a looping wire.


How can polyps in the bowel affect me over time?

Polyps rarely cause day to day problems. However the main concern is that they may be malignant and cause cancer in the future. You will probably need to have a follow-up examination if the microscope findings indicate the polyp has any malignant potential. If so, your doctor will recommend a repeat colonoscopy in the future to check whether new polyps have grown.

Depending on what is found at the time, your doctor may suggest that nothing further is required or that you should return for a further test in one to five years time. If you have a family history of either polyps or bowel cancer then your doctor may recommend that you have a regular colonoscopy. If you are an individual who tends to form polyps, your bowel should be regularly inspected and any polyps that have formed should be removed. Your doctor may mention the term ‘adenoma’ which is the most common type of polyp that has cancerous potential.

You do not need a special diet and can eat normally. However, a healthy diet, which includes a wide variety of foods and plenty of fruit and vegetables, is good for your general health and bowel motions. Aim to have regular fruit and vegetables (with meals as well as snacks) and to drink at least two litres (8-10 cups) of fluid every day.

What to ask your doctor?

  • What type of polyp do I have, is it benign or malignant?
  • How often should I have a follow up colonoscopy?
  • Has my family history been noted and taken into account?
  • What other follow up do I need?