Rigid sigmoidoscopy is actually an examination of the rectum (lower bowel just above the anus/ back passage) and not sigmoid (part of bowel above the rectum).
During the test the doctor will use an instrument called rigid sigmoidoscope (or proctoscope) that is a short plastic tube that is about 10 inches (25 cm) long and about 1 inch (2.5 cm) wide. It allows examination of the rectum and the bottom part of the colon, but it does not reach as far into the colon as the flexible sigmoidoscope.
It is simple and easily performed in clinic, but at times might not offer good views if your bowels are not empty and full of stool. Sometimes you might be advised to take a suppository (medication to empty your back passage).
The test can be used to examine any growths (cancer or polyps) and inflammation in the rectum. You can also take a biopsy (sample) during the test.