Similar to a colonoscopy, sigmoidoscopy is an exam that uses an endoscope (a long, thin, flexible tube like device). It may be performed to diagnose the cause of gastrointestinal symptoms such as diarrhea, bleeding, abdominal pain, or abnormal x-ray results.
In a sigmoidoscopy the endoscope is placed into the rectum and advanced to the lower third of the colon. As such, the exam is limited because not all of the colon will be seen. The scope has a light and a camera on the end of it which allows the physician to examine the lining of the colon. A sigmoidoscopy may also be performed on patients 45 years old (or older) to screen for colon cancer and polyps.