What happens during a flexible sigmoidoscopy?

Anthony L. Komaroff, MD
Internal Medicine
A flexible sigmoidoscopy can be performed in your physician's office or in the hospital. You'll receive instructions in advance on how to clean out your bowels -- usually by fasting and taking a laxative the night before the test and using an enema an hour or two before your appointment. While you lie on your side, the doctor inserts a lubricated flexible scope (about half an inch wide and 2 feet long) through your rectum into your colon. The scope has a light and video camera, along with mechanisms for adding air or washing the area to get a better view. The exam takes about 20 minutes.
A sigmoidoscopy usually takes 10-20 minutes. Most people do not need to be sedated for this test, but this is an option you may discuss with your doctor. Sedation may make the test less uncomfortable, but it requires some time to recover from, as well as having someone with you to take you home after the test.
You will likely be asked to lie on a table on your left side with your knees positioned by your chest. Your doctor should do a digital rectal exam, or DRE (inserting a gloved, lubricated finger into the rectum), before inserting the sigmoidoscope. The scope is lubricated to make it easier to insert into the rectum, but may feel cold. The sigmoidoscope may stretch the wall of the colon, which may cause bowel spasms or lower abdominal pain. Air will be placed into the sigmoid colon through the scope so the doctor better see the walls of the colon better. During the procedure, you might feel pressure and slight cramping in your lower abdomen. To ease discomfort and the urge to have a bowel movement, it helps to breathe deeply and slowly through your mouth. You will feel better after the test once the air leaves your colon.
If a small polyp is found during the test your doctor may remove it with a small instrument passed through the scope. The polyp will be sent to a lab to be examined by a pathologist. If a pre-cancerous polyp (an adenoma) or colorectal cancer is found during the test, you will need to have a colonoscopy at a later date to look for polyps or cancer in the rest of the colon.

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