Bowel polyps

We don’t know exactly what causes bowel polyps. They grow in the lower part of your bowel – the large intestine (colon) and the rectum (the lower part before your bottom.) The lining of your bowel is always renewing itself. Polyps happen when one area grows more than it should. This is sometimes because of a problem with the genes (inherited from your family) which control growth of the cells lining your bowel.

Below is a picture of your gastrointestinal system with the colon shown as the darker pink part at the left and top of the small intestine. The inserted image at the top shows a bowel polyp.

Image credit: Blausen.com Wikimedia Commons

Bowel polyps look like pink blobs, sometimes on a stalk, They range in size from a tiny dot to  a few centimetres across. There are different types of bowel polyp:

Hyperplastic bowel polyps

• These are a common type.
• They're small (usually less than half a centimetre).
• They are usually harmless and rarely turn into cancer.

Adenomas

• These are usually less than 1 cm across, but can grow to a few centimetres. 
• They have a small risk of becoming cancerous – if this does happen it takes between 5 and 15 years. 
• You can't always tell a noncancerous polyp by how it looks, so if one is found during a colonoscopy it's usually removed for further testing.
• Most polyps aren't cancerous but most cancers do begin in adenomas that have been in your bowel for years.
• Because cancer begins in polyps, looking for them and removing them is an important way of preventing bowel cancer. 

Polyposis syndromes

• Some families have rare genetic conditions which cause large numbers of polyps at young ages.
• They are at high risk of bowel cancer and have special monitoring plans.

You have a greater chance of developing polyps if you:  

• are over 50 years of age – 1 in 4 people aged over 50 have bowel polyps
• are male – bowel polyps are slightly more common in men
• have a family/whānau member with bowel polyps or bowel cancer
• eat a lot of fatty food
• smoke
• have 3 or more alcoholic drinks a day
• don't take regular exercise
• are overweight
• have a condition that affects your gut, eg, colitis, Crohn's disease or inflammatory bowel disease (IBD).

Most people with polyps don't know they have them, because polyps don't usually cause symptoms. Some larger polyps can cause:

• a small amount of rectal bleeding (blood in your poos)
• mucus (slime) in your poo
• diarrhoea (runny poos) or constipation.

Bowel polyps are usually found during investigation of bowel symptoms (eg, bleeding) or screening for bowel cancer. Screening might be done because of known risk factors like inflammatory bowel disease or a family history of bowel cancer. If you have a family history of bowel cancer there are screening guidelines which take into account how close the relationship is, the age of your relative and how many relatives have been affected. These will be used to estimate your risk of developing bowel cancer and whether you should be screened. If you have a family member who's had bowel cancer make an appointment to see your healthcare provider to discuss it.

Checks can be done done via a sigmoidoscopy to check the last part of your bowel, or a colonoscopy to check the whole length of your large bowel. 

The National Bowel Screening Programme checks for any blood in your poo. If blood is found, then a colonoscopy will be arranged for you.

Bowel polyps can be removed during your colonoscopy. 

• The doctor or nurse passes a long wire loop through a colonoscope (a long, soft flexible tube containing a tiny video camera and a light) and around the base of the polyp. The loop is pulled tight, cutting off the polyp. You won't feel anything as you will be given a medicine to numb the area first.
• An operation (surgery) is rarely needed to remove polyps but may be necessary if the polyps are very large or can't be reached safely during the colonoscopy.
• After removal, the polyp is sent to a laboratory to check for any signs of cancer. 

If polyps are found, there's a higher chance that you will grow more polyps in the future. You will be offered another colonoscopy in a few years time to find any more polyps that could turn into bowel cancer.  How often you need to be checked for polyps depends on your risk of developing bowel cancer, your age and the type and number of polyps found during your colonoscopy. Your doctor or nurse will give you more information on this.