Polyps in the Bowel
Polyps in the Bowel explained
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 a little like a mushroom growing up from the lining of the bowel) or they can be much flatter and even have quite a broad base. Polyps are benign but they are important because some of them eventually become malignant. Most doctors think that all bowel cancers develop from polyps.
Polyps occur in the lowest part of the intestine, called the large bowel (which consists of all of the colon and the rectum). Polyps seem to be most common towards the lower part of the colon and also in the rectum.
Polyps seem to be very common indeed – especially for those of us who live in the West. About one in four people will have a polyp at some time in their life. Polyps tend to be 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.
Most polyps are small. They are usually less than one centimetre in size but can grow up to several centimetres. Usually the bowel only contains a single polyp but sometimes there can be more, although it is unusual to have more than five. Apart from coming in different shapes and sizes, polyps also vary in their appearances when looked at under a microscope. We realise that some types of polyp have no potential whatsoever to become cancers. The polyp which it is most important to detect and treat is called an adenoma.
The lining of the bowel constantly renews itself throughout our lives. There are many millions of tiny cells in the lining which grow, serve their purpose and then new cells take their place. Each of these millions of cells contains genes which give instructions to the cell on how to behave. When genes behave in a faulty manner, this can cause the cells to grow more quickly, eventually producing a small bump on the bowel surface which 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 instructions to make the cells grow more quickly, but to do so in an orderly manner. Some polyps remain very small throughout their lives while others continue to enlarge. Most polyps remain benign throughout life but about 1 in 10 will turn into cancer. We believe that all malignancies of the bowel begin as benign polyps; so removing benign polyps can prevent the development of cancer.
Usually polyps do not cause symptoms, and most people will never know if they have them. Occasionally they can cause bleeding from the back passage. Sometimes polyps produce an excess of mucus or slime which can be noticed on the 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.
Different types of polyps
Polyps can be detected either by colonoscopy or by a barium enema x-ray. Both methods require the bowel to be as clear as possible before the procedure so you will be asked to follow a special diet as well as take laxatives. Both techniques also involve a small tube being passed through the back passage. In the case of a barium enema this is to allow a liquid to be passed into the bowel that will show up on x-rays. In colonoscopy a soft flexible tube is passed along the back passage and then through the whole colon. Sometimes a shorter instrument called a sigmoidoscope is used but this can only pass up through the lower colon. If the barium enema does reveal a polyp, a colonoscopy will then be needed to remove it.
The most common reason to carry out an examination of the bowel is that a patient has noticed symptoms – particularly rectal bleeding. However, increasingly, patients are being asked to give a sample of their stool for a chemical test which can detect small quantities of blood that are not visible. This test is called ‘faecal occult blood’ and is likely to be much more widely used over the next few years. The idea is that unsuspected polyps might bleed a little – not enough for the blood to be visible – but enough for it to be picked up on a chemical test of the motion. Preventing bowel cancer by asking people to test their bowel motions in this way is called screening. Doctors recognise that many bowel cancers can be treated very early or can be prevented by screening.
There are a variety of different techniques to remove polyps but most consist of passing a wire through the colonoscope and looping the wire around the polyp like a lasso to remove it. This procedure is quite painless and only one examination is needed to clear the bowel of polyps. Occasionally, there may be too many polyps for all of them to be removed safely and the procedure may need to be repeated.
Once they have been removed all polyps are sent to the laboratory for microscopic analysis. This will show whether or not the polyp has been completely removed, whether it has the potential to develop malignancy and, of course, to be sure that cancer has not already developed.
You will probably need to have a follow-up examination if the microscopic 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 that time, your doctor may either suggest that nothing further need be done or that you should return for a further test in three to five years time.
We now know that up to 10% of people who tend to form 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 family have had polyps or bowel cancer – and especially if they have developed these at a young age – then your doctor may recommend that you have a colonoscopy every two years or so. 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 malignant potential.
You can eat normally and do not need to follow a special diet. A healthy diet which includes a wide variety of foods and plenty of fruit and vegetables is good for your general health. Aim to have 5 portions of fruit or vegetables each day and to drink at least 2 litres (8-10 cups) of fluid every day.
It is essential that we find out why such a relatively large number of people tend to form polyps. If we can do this, it should be possible to prevent polyps from forming. As we know that most, if not all, bowel cancers start as polyps, then it might be possible to prevent colon cancer from developing if we knew how to prevent polyps forming. We need to learn the detail of what factors in our genes make us likely to form polyps. Much research is also needed on which dietary factors are important.