On this page:
- What is flexible sigmoidoscopy?
- What are the sigmoid colon and rectum?
- How is flexible sigmoidoscopy different from colonoscopy?
- How to Prepare for a Flexible Sigmoidoscopy
- How is a flexible sigmoidoscopy performed?
- Points to Remember
- Hope through Research
- For More Information
What is flexible sigmoidoscopy?
Flexible sigmoidoscopy is a procedure used to see inside the sigmoid colon and rectum. Flexible sigmoidoscopy can detect inflamed tissue, abnormal growths, and ulcers. The procedure is used to look for early signs of cancer and can help doctors diagnose unexplained changes in bowel habits, abdominal pain, bleeding from the anus, and weight loss.
What are the sigmoid colon and rectum?
The sigmoid colon is the last one-third of the colon. The colon comprises three main parts: the ascending colon, the transverse colon, and the sigmoid colon—sometimes called the descending colon. The colon absorbs nutrients and water and forms stool.
The rectum is about 6 inches long and connects the sigmoid colon to the anus. Stool leaves the body through the anus. Muscles and nerves in the rectum and anus control bowel movements.
How is flexible sigmoidoscopy different from colonoscopy?
Flexible sigmoidoscopy enables the doctor to see only the sigmoid colon, whereas colonoscopy allows the doctor to see the entire colon. Colonoscopy is the preferred screening method for cancers of the colon and rectum; however, to prepare for and perform a flexible sigmoidoscopy usually requires less time.
How to Prepare for a Flexible Sigmoidoscopy
To prepare for a flexible sigmoidoscopy, one or more enemas are performed about 2 hours before the procedure to remove all solids from the sigmoid colon. An enema is performed by flushing water, laxative, or sometimes a mild soap solution into the anus using a special wash bottle.
In some cases, the entire gastrointestinal tract must be emptied by following a clear liquid diet for 1 to 3 days before the procedure—similar to the preparation for colonoscopy. Patients should not drink beverages containing red or purple dye. Acceptable liquids include
- fat-free bouillon or broth
- strained fruit juice
- plain coffee
- plain tea
- sports drinks, such as Gatorade
A laxative or an enema may also be required the night before a flexible sigmoidoscopy. A laxative is medicine that loosens stool and increases bowel movements. Laxatives are usually swallowed in pill form or as a powder dissolved in water.
Patients should inform their doctor of all medical conditions and any medications, vitamins, or supplements taken regularly, including
- arthritis medications
- blood thinners
- diabetes medications
- vitamins that contain iron
How is a flexible sigmoidoscopy performed?
Examination of the Sigmoid Colon
During a flexible sigmoidoscopy, patients lie on their left side on an examination table. The doctor inserts a long, flexible, lighted tube called a sigmoidoscope, or scope, into the anus and slowly guides it through the rectum and into the sigmoid colon. The scope inflates the colon with air to give the doctor a better view. A small camera mounted on the scope transmits a video image from inside the colon to a computer screen, allowing the doctor to carefully examine the tissues lining the sigmoid colon and rectum. The doctor may ask the patient to move periodically so the scope can be adjusted for better viewing.
When the scope reaches the transverse colon, the scope is slowly withdrawn while the lining of the colon is carefully examined again.
Biopsy and Removal of Colon Polyps
The doctor can remove growths, called polyps, during flexible sigmoidoscopy using special tools passed through the scope. Polyps are common in adults and are usually harmless. However, most colon cancer begins as a polyp, so removing polyps early is an effective way to prevent cancer. If bleeding occurs, the doctor can usually stop it with an electrical probe or special medications passed through the scope.
During a flexible sigmoidoscopy, the doctor can also take samples from abnormal-looking tissues. Called a biopsy, this procedure allows the doctor to later look at the tissue with a microscope for signs of disease.
Tissue removal and the treatments to stop bleeding are usually painless. If polyps or other abnormal tissues are found, the doctor may suggest examining the rest of the colon with a colonoscopy.
A flexible sigmoidoscopy takes about 20 minutes. Cramping or bloating may occur during the first hour after the procedure. Bleeding and puncture of the large intestine are possible but uncommon complications. Discharge instructions should be carefully read and followed.
Patients who develop any of these rare side effects should contact their doctor immediately:
- severe abdominal pain
- bloody bowel movements
Points to Remember
- Flexible sigmoidoscopy is a procedure used to see inside the sigmoid colon and rectum.
- One or more enemas are performed about 2 hours before the procedure to remove all solids from the sigmoid colon.
- In some cases, the entire gastrointestinal tract must be emptied—similar to the preparation for colonoscopy.
- A sigmoidoscope transmits a video image from inside the colon to a computer screen.
- A doctor can biopsy abnormal-looking tissues during a flexible sigmoidoscopy.
- Polyps can be removed using special tools passed through the sigmoidoscope.
- If polyps or other abnormal tissues are found, the doctor may suggest examining the rest of the colon with a colonoscopy.
- A flexible sigmoidoscopy takes about 20 minutes.
Hope through Research
The National Institute of Diabetes and Digestive and Kidney Diseases conducts and supports basic and clinical research into many digestive disorders.
Participants in clinical trials can play a more active role in their own health care, gain access to new research treatments before they are widely available, and help others by contributing to medical research. For information about current studies, visit www.ClinicalTrials.gov.
For More Information
Fact sheets about other diagnostic tests are available from the National Digestive Diseases Information Clearinghouse at www.digestive.niddk.nih.gov, including
- ERCP (Endoscopic Retrograde Cholangiopancreatography)
- Lower GI Series
- Liver Biopsy
- Upper GI Series
- Upper GI Endoscopy
- Virtual Colonoscopy
International Foundation for Functional Gastrointestinal Disorders
P.O. Box 170864
Milwaukee, WI 53217–8076
Phone: 1–888–964–2001 or 414–964–1799
National Digestive Diseases Information Clearinghouse
The National Digestive Diseases Information Clearinghouse (NDDIC) is a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The NIDDK is part of the National Institutes of Health of the U.S. Department of Health and Human Services. Established in 1980, the Clearinghouse provides information about digestive diseases to people with digestive disorders and to their families, health care professionals, and the public. The NDDIC answers inquiries, develops and distributes publications, and works closely with professional and patient organizations and Government agencies to coordinate resources about digestive diseases.
Publications produced by the Clearinghouse are carefully reviewed by both NIDDK scientists and outside experts. This publication was reviewed by Michael Wallace, M.D., Mayo Clinic.
This publication is not copyrighted. The Clearinghouse encourages users of this publication to duplicate and distribute as many copies as desired.
NIH Publication No. 09–4332
Page last updated November 27, 2013