Colonoscopy - examining the colon

Reviewed by Mr Robert Diggory, consultant general surgeon and Dr John Pillinger, GP

What is colonoscopy?

The colon is another name for the large bowel. While the back passage and the lower parts of the colon can be viewed directly using small metal or plastic tubes, other methods are needed to inspect the rest of the bowel. This is usually done by a barium enema X-ray or by colonoscopy.

What is a colonoscope?

The colonoscope is a narrow, flexible fibre-optic 'telescope' about one metre long.

It is equipped with a powerful light to give the doctor a clear view.

The colonoscope can also blow air into the colon or suck it out if needed.

What is colonoscopy used for?

Colonoscopy enables the doctor to examine the lining of the bowel all the way through the colon and is, therefore, used to investigate bleeding, changes in bowel movements, abdominal pain and abnormalities revealed by other examinations such as barium enema, which require confirmation or biopsy.

It can detect inflammation, ulceration, polyps, diverticula and tumours. If necessary, tissue samples (biopsies) of the lining of the bowel can be taken for diagnosis.

What happens during the examination?

On the day before the examination, the patient will be given a laxative to ensure the bowel is empty. Nothing to eat or drink is allowed for six hours before the procedure.

Colonoscopy is done on an outpatient basis and takes about 20 to 40 minutes. A sedative is injected into a vein to induce a sleepy and relaxed feeling while the examination is carried out.

The person will be asked to lie on their side during the examination.

The colonoscope will be lubricated with some jelly and gently inserted into the bowel through the back passage. Some air may be blown gently into the bowel to improve the view of the bowel lining. This can make the person being examined want to pass wind but it is important not do so, until the doctor has all the pictures and samples needed.

Many doctors now prefer to watch the images from the colonoscopy on a TV screen next to the patient rather than look directly down the colonoscope, and patients are often allowed to view this if they want to.

Sometimes the doctor will need to take small samples of tissue. This is completely painless. This tissue is sent to the laboratory for specialised inspection and the results should be ready after a few days.

Afterwards, the patient will be allowed to doze until the effects of the sedation wear off before going home.

If a larger piece of tissue, such as a polyp, has been removed, it may be necessary to stay in the hospital for a few hours for observation for possible bleeding. Patients will not be able to drive home because of the sedation.

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