What is flexible sigmoidoscopy and how is it different to an examination of the whole large bowel (colon)?

When a person visits their doctor with symptoms that could be caused by bowel cancer they might be offered a test that can examine the whole large bowel (the colon) in order to detect abnormalities. This ‘whole colon’ examination is most likely to be a colonoscopy, a ‘virtual colonoscopy’ or a barium enema.

Colonoscopy is a procedure during which, usually under sedation, a tube (endoscope) with a small camera attached is inserted into the rectum and guided through the large bowel to examine its surface for abnormalities. Virtual colonoscopy is a newer test and uses x-rays to give 3-D images of the bowel. The barium enema examination involves passing a white liquid containing barium into the bowel through the rectum and then taking x-rays of the bowel.

Flexible sigmoidoscopy can also be used to examine the large bowel. Like colonoscopy, flexible sigmoidoscopy involves inserting a flexible tube into the rectum. However, unlike colonoscopy and virtual colonoscopy, flexible sigmoidoscopy is used to examine the lower part of the large bowel and the rectum only, and is not used to examine the whole colon.

Flexible sigmoidoscopy has several advantages over whole colon examinations. In particular, people do not need to complete a full bowel preparation before the procedure. Bowel preparation involves temporary dietary restrictions and taking laxatives to clear the bowel – some people find this difficult or inconvenient and it is also not suitable for everyone. People also do not need to be sedated for flexible sigmoidoscopy, which is generally required for colonoscopy. Some people find sedation an inconvenience because they are unable to return to work immediately, and it is also linked to a higher risk of complications.