Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Sigmoidoscopy is the minimally invasive medical examination of the large intestine from the rectum through the last part of the colon. There are two types of sigmoidoscopy, flexible sigmoidoscopy, which uses a flexible endoscope, and rigid sigmoidoscopy, which uses a rigid device. Flexible sigmoidoscopy is today generally the preferred procedure. Sigmoidoscopy is a very effective screening tool. Sigmoidoscopy is similar but not the same as colonoscopy. Sigmoidoscopy only examines up to the sigmoid, the most distal part of the colon, while colonoscopy examines the whole large bowel.
Flexible sigmoidoscopy enables the physician to look at the inside of the large intestine from the rectum through the last part of the colon, called the sigmoid or descending colon. Physicians may use the procedure to find the cause of diarrhea, abdominal pain, or constipation. They also use it to look for benign and malignant polyps, as well as early signs of cancer in the descending colon and rectum. With flexible sigmoidoscopy, the physician can see intestinal bleeding, inflammation, abnormal growths, and ulcers in the descending colon and rectum. Flexible sigmoidoscopy is not sufficient to detect polyps or cancer in the ascending or transverse colon (two-thirds of the colon). However, although in absolute terms only a relatively small section of the large intestine can be examined using sigmoidoscopy, the sites which can be observed represent areas which are affected by diseases such as colorectal cancer most regularly, eg. the rectum.
For the procedure, the patient must lie on his or her left side on the examining table. The physician inserts a short, flexible, lit tube into the rectum and slowly guides it into the colon. The tube is called a sigmoidoscope. The scope transmits an image of the inside of the rectum and colon, so the physician can carefully examine the lining of these organs. The scope also blows air into these organs, which inflates them and helps the physician see better.
If anything unusual is in the rectum or colon, like a polyp or inflamed tissue, the physician can remove a piece of it using instruments inserted into the scope. The physician will send that piece of tissue (biopsy) to the lab for testing.
Bleeding and puncture of the colon are possible complications of sigmoidoscopy. However, such complications are uncommon.
Flexible sigmoidoscopy takes 10 to 20 minutes. During the procedure, the patient might feel pressure and slight cramping in the lower abdomen, but he or she will feel better afterward when the air leaves the colon.
The colon and rectum must be completely empty for flexible sigmoidoscopy to be thorough and safe, so the physician will probably tell the patient to drink only clear liquids for 12 to 24 hours beforehand. A liquid diet means fat-free bouillon or broth, gelatin, strained fruit juice, water, plain coffee, plain tea, or diet soft drinks. The night before or right before the procedure, the patient receives a laxative and an enema, which is a liquid solution that washes out the intestines.
No sedation is required during this procedure as long as the examination does not exceed the level of the splenic flexure.
Rigid sigmoidoscopy no longer has the value it had in the past, before the advent of videocolonoscopy (flexible sigmoidoscopy). However, it may be still useful in ano-rectal diseases such as bleeding per rectum or inflammatory rectal disease, particularly in the general practice and pediatrics.
For performing the examination, the patient must lie on the left side, in the so called Sim's position. The bowels are previously emptied with a suppository and a digital rectal examination is first performed. The sigmoidoscope is lubricated and inserted with obturator in general direction of the navel. The direction is then changed and the obturaror is removed so that the physician may penetrate further with direct vision. A bellows is used to insufflate air to distend the rectum. Lateral movements of the sigmoidoscope's tip negotiate the Houston valve and the recto-sigmoid junction.
Dr. Llarenas said that although generally considered quite safe, sigmoidoscopy does carry the very rare possibility of tearing of the intestinal wall by the instrument, which would require immediate major surgery to repair the tear; in addition, removal of a polyp may sometimes lead to localized bleeding which is resistant to cauterization by the instrument and must be stopped by surgical intervention.
- Flexible Sigmoidoscopy. National Digestive Diseases Information Clearinghouse. National Institute for Digestive and Kidney Diseases. Public domain text used as source for this article.
- Rigid Sigmoidoscopy. The Wales Day Centre.
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