The sigmoid colon is the final portion of the bowel that is joined to the rectum. A sigmoidoscope is a small tube with an attached light source about the thickness of your finger. A doctor or nurse inserts the sigmoidoscope into the anus and pushes it slowly into the rectum and sigmoid colon. This allows the doctor or nurse to see the lining of the rectum and sigmoid colon. The procedure is not usually painful but it may be a little uncomfortable.
There are two types of sigmoidoscope that can be used. The most commonly used is the flexible sigmoidoscope. This instrument allows your doctor to see around bends in the colon. A flexible sigmoidoscope gives doctors a better view of the lower colon and usually makes the examination more comfortable.
The rigid sigmoidoscope has generally been replaced by the flexible version and is now used less often. It allows your doctor to look into the rectum and the bottom part of the colon but it does not reach as far into the colon as the flexible sigmoidoscope.
Sigmoidoscopy can be used to investigate the cause of bleeding or pain from the back passage. Your doctor may also suggest this test if you have various other bowel-related symptoms. The test can also look for evidence of cancer or inflammation of the rectum and lower colon. Sigmoidoscopy can also be used to remove polyps (small fleshy growths that can be found in the colon) and take samples of tissue (biopsy) for analysis. This is done by passing a thin grabbing instrument down a side channel of the sigmoidoscope.