What is the difference between Colonoscopy, Sigmoidoscopy and Virtual Colonoscopy?

All are early screening procedures for colorectal cancer. It is recommended that everyone undergo one of these procedures starting at age 50, and at regular intervals thereafter. For individuals with increased risk factors, such as family history of colorectal cancer, rectal bleeding, abdominal pain, or a change in bowel habits, testing should be done before age 50.

All three studies require preparatory bowel cleansing consisting of a clear liquid diet and laxatives the evening before the procedure. Colonoscopy is the most thorough study. A fiber optic scope is used to inspect the entire colon where polyps or other suspicious tissue are removed for testing. Sedation is necessary when undergoing a colonoscopy because of discomfort caused by the test.

Flexible sigmoidoscopy is similar to colonoscopy, but is done with a shorter scope, which extends only into the lower colon. It does not examine the upper colon, and is therefore less complete than a colonoscopy. However, it involves much less discomfort, does not require sedation and is a reasonable alternative for individuals having no special risk factors.

Virtual colonoscopy is the newest procedure. The bowel is inflated with air, and a computed tomographic (CT) scan, a special type of x-ray, is taken of the entire colon. It is still considered somewhat experimental and may be less sensitive than direct observation methods, but is easier on the patient.

If any suspicious lesions are found during either a sigmoidoscopy or virtual colonoscopy, a full colonoscopy is then required for direct examination and biopsy of lesions. Flexible sigmoidoscopy can usually be done by your primary care physician. Colonoscopy requires a visit to a specialist in Gastroenterology. Virtual colonoscopy is a radiological procedure done at special imaging centers.

Brian D. Borsook, M.D., Ph.D.
Diplomate, American Board of Family Practice; Licensed Psychologist
Member, South Bay Independent Physicians Medical Group, Inc.
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