Gastroenterology - Bowel Polyps

Most polyps (90%) are called adenomas by medical professionals. They are very common (occurring in 15-20% of the population) and most of them are not cancerous.

What is a polyp?

A polyp is an overgrowth of the cells that line the inside of the bowel wall. Some people develop a single polyp while others may have two or more. About one in four people over the age of fifty will develop at least one colonic polyp. Polyps are important as, if they are not removed, some may eventually become a cancer in the colon (large bowel) or rectum (back passage) although this takes many years to develop.

Why do polyps develop?

It is not really known why polyps develop. The lining of the bowel constantly renews itself – millions of tiny cells grow, serve their purpose and die, as new cells replace them. Each cell contains genes that determine the behaviour and function of the cell. If a gene becomes faulty it can cause the cells to grow more quickly and bunch up on the side of the bowel wall, forming a polyp.

You may have a greater chance of developing polyps if:

• You are over 50 years of age
• You have had polyps before
• You have Inflammatory Bowel Disease
• Someone in your family has had polyps or cancer of the large bowel
• You eat a lot of fatty foods
• You smoke
• You drink alcohol
• You don't take regular exercise
• You are overweight

What are the different types of polyps?

There are two main types of polyps:

Hyperplastic polyps

These are very common and are usually small – less than half a centimetre in diameter. They are generally regarded as harmless and rarely develop into cancer and as a rule, tend not to be followed up.

Adenomas

These are also common. Most are less than one centimetre in diameter but some may grow to be quite large (3 - 4cm).
Most adenomas are benign (not cancerous) but if left, about 1 in 10 will change and become malignant (cancerous). This process generally takes place over several years.
 
There are different types of adenomas. Some types are more prone to changing into cancers than others. Most bowel cancers develop from a polyp that has been present for 5-15 years.

Polyps may be raised on a stalk (pedunculated) or flat (sessile).

Symptoms of polyps

Most people are unaware of having polyps as they often produce no symptoms.
Some polyps can however produce a small amount of bleeding or an excess production of mucus (slime) with bowel motions. A change in bowel habit may occur and very large polyps may lead to a blockage in the bowel, but this is extremely rare.

Treatment for polyps

Polyps are generally removed at the time of your colonoscopy. There are several methods for doing this but the most common are as follows:

Snaring

A wire is passed around the polyp and tightened which cuts the polyp off. Sometimes an electric current is passed through the snare which will cauterize any blood vessels to prevent bleeding. Snaring is like cutting the polyp off with cheese wire and is painless.

Endoscopic mucosal resection (EMR)

This an alternative way of removing larger polyps which sometimes can take longer than removing smaller polyps.
The endoscopist injects a saline solution into the lining of the bowel wall to lift the polyp up. This makes it easier to snare and remove the polyp. Sometimes dye with adrenaline is added to the solution to make the area easier to find should you need a further colonoscopy.

If a polyp is bigger than 2cms it may not be completely removed but some samples taken from it which will be sent to the laboratory. This is because larger polyps have a greater chance of cancerous changes within them. The site of the polyp will be tattooed. The laboratory results will be discussed with your consultant and then a decision made to recommend a further colonoscopy or an operation to remove the polyp.

Removing polyps causes a risk of bleeding, which can occur immediately or up to 14 days after the procedure. This generally stops on its own but very occasionally requires a further colonoscopy or a blood transfusion.

There is also a small risk of causing a hole in the bowel wall (perforation). This happens in approximately 1 in every 500 patients who have a polyp snared or 1 in every 100 patients having EMR. This may require treatment through the endoscope, by antibiotics or rarely, by an operation.

Surgery

An operation is occasionally needed to remove part of the bowel if the polyp is too large to be removed at colonoscopy by snaring or EMR, or there is concern that the polyp may be cancerous.

What happens after the polyp has been removed?

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 become cancerous and of course, to be sure that cancer has not already developed.

Once a polyp has been removed will I need any further checks?

Follow-up after polyp removal varies. but some people will require further colonoscopies because polyps can recur. Some bowel polyps run in families. This is uncommon, but if this condition is diagnosed, colonoscopy checks will be at regular intervals as advised in the national guidelines written by the British Society of Gastroenterology, the details of which are included in the references on the following page.

References

www.nhs.uk/conditions/bowel-10/9/2019.

BSG (2009) Guidelines for colorectal cancer screening and surveillance in moderate and high risk groups (update from 2002) BSG: London

American Society for Gastrointestinal Endoscopy (2008) Endoscopic mucosal resection and endoscopic submucosal dissection. Gastrointestinal Endoscopy Vol 68, No1: 11-18

Polyps in the bowel. Patient information leaflet. Available from http://www.bsg.org.uk/patients/general/polyps-in-the-bowel.html