Bowel Polyps
A polyp is a protuberance from the lining of the bowel wall. It may be shaped like a mushroom or a mountain.
They start off benign, but can convert to cancer.
They can occur in any part of the alimentary canal but are most common in the colon and rectum.
A polyp is a protuberance. It is usually composed of the lining cells of a body part e.g. bowel, nasal, sinuses, vocal cord, gastric or small bowel.
In the large bowel, colon or rectum, the lining cells, (mucosa) together with the underlying connective tissue and even muscle, proliferate to form an outgrowth termed an “adenoma” – after the type of cell.
The polyp may be flat because of convolutions have a large surface area (villous), or a stalk like a mushroom (pedunculated tubular). There are two physical types of adenoma, the pedunculated adenoma or the villous adenoma and a mixture termed a tubular villous adenoma.
Most of the polyps have the potential to become malignant (cancerous). There is a type of polyp called hyperplastic, which do not become cancerous. A hyperplastic polyp is thought to be due to chronic irritation.
The polyps may be multiple or single and they run in families like bowel cancer. They can occur all over the bowel but is most common on the left side of the bowel.
Cancer may occur in quite a small polyp but as the polyps become larger they are more likely to become cancerous.
The cells on the surface of the polyp undergo certain changes before becoming cancerous (dysplasia). If there is severe dysplasia this indicates that a cancer is more likely to occur.
Cancer in Situ
This indicates that the cancer is developing but the cells have not spread at all – polypectomy cures these patients.
Presentation
polyps may:
a) bleed, the commonest symptom
b) be painful – occasionally
c) associated with a change in bowel habit
d) large flat villous adenomas secrete large amounts of fluid and mucous – giving diarrhoea and may even cause a change in the body electrolytes
Bleeding
Bleeding from the lower part of the bowel (sigmoid and rectum) is usually obvious as fresh blood on the toilet paper, the bowl or mixed in the motion itself.
When the bleeding comes from higher up – the right side and the transverse colon, the blood takes time to pass around to the rectum and the blood is altered so that it is not macroscopically obvious. This is termed “occult” or hidden bleeding.
If this bleeding – occult or obvious then the patient becomes anaemic (tiredness and lethargy).
The occult bleeding can be detected before anaemia becomes obvious by testing the faeces – faecal occult blood test.
Detection of Polyps
Polyps low in the rectum can be detected by examination with a glove or sigmoidoscopy – the lower 20 – 25 cms.
Polyps on the left side – by flexible sigmoidoscopy.
Colonoscopy – detects the polyps throughout the entire rectum and colon.
Treatment
Removal of a polyp is termed “polypectomy”. This is done via a colonoscope. The bowel has to be prepared the day before the procedure and an Anaesthetic is usually required.
A snare – like a lasso, is placed via the colonoscope. It is then passed around the neck of the polyp and the polyp is removed by cutting and coagulation diathermy. Occasionally polyps are too large to remove this way and then open surgery to remove part of the bowel is required.
Risks
Bleeding
The raw edge or the stump that is left may bleed. This usually settles by itself but transfusion is occasionally required. Surgery may even be required.
Perforation
This may occur as the bowel wall is very thin where the polyp is removed. The diathermy used may burn the bowel wall and this can then leak 24 hours later. If there is significant risk of this occurring, then surgery is the preferred treatment.
If perforation does occur there is usually severe abdominal pain and urgent surgery is required.
There are the general risks of any Anaesthetic involved. Generally speaking colonoscopy is a very safe procedure.