What is a sigmoidoscopy?

Donald Petroski, MD
A sigmoidoscopy is one of the options used to screen for colorectal cancer. In this test, the rectum and sigmoid colon are examined using a flexible lighted instrument called a sigmoidoscope. During the procedure, abnormal growths in the rectum and sigmoid colon can be removed for analysis.

The lower colon must be cleared of stool before sigmoidoscopy, but the preparation is less involved than that required for colonoscopy. Most people are not sedated for the procedure. It is recommended every five years along with a fecal occult blood test (FOBT) every three years for people at average risk who have had negative test results. Because only the left side of the colon is checked, most doctors suggest other tests that check a larger area of the colon.
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Sigmoidoscopy is a diagnostic procedure that allows the physician to examine the lower part of the large intestine -- the rectum and bottom two feet of the colon. It is helpful in identifying the causes of diarrhea, abdominal pain, constipation, abnormal growths and bleeding. A thin, flexible tube is inserted into the large intestine through the rectum. The tube has a tiny light and camera at its end that is connected to a TV monitor, allowing the doctor a good view of this part of the large intestine. If necessary, the doctor may take a small tissue sample (biopsy) from the lining of the intestine to look at later under a microscope. A sigmoidoscopy typically takes 5-10 minutes, requires only an enema for preparation, and can be done without sedation. Patients may experience some cramping and discomfort during this procedure. Physicians may also couple a sigmoidoscopy with another procedure known as a double-contrast barium enema. With this, barium is infused into the rectum via an enema tube and an x-ray is taken of the area. The barium helps produce a clearer, more detailed x-ray of the area.
Flexible sigmoidoscopy or sigmoidoscopy uses a sigmoidoscope, a slender, lighted tube about the thickness of a finger. It is placed into the lower part of the colon through the rectum. This allows the physician to look at the inside of the rectum and lower part of the colon for cancer or polyps. This exam only evaluates about one third of the colon. The test is often done without any sedation, so it can be uncomfortable. Before the test, you will need to take an enema or other prep to clean out the lower colon. If polyps are found, the patient must return for a full colonoscopy.

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