Virtual Colonoscopy: Facing Reality

The Facts About Virtual Colonoscopy

What is virtual colonoscopy?

Virtual colonoscopy, also called CT colonography, is an X-ray test that looks for cancer and precancerous growths, known as polyps, in the colon (large bowel). Virtual colonoscopy is based on a CT scan of the abdomen and pelvis.

How is virtual colonoscopy performed?

On the day prior to the examination, the patient stays on clear liquids and takes laxatives to thoroughly cleanse the colon. On the day of the examination, a tube is placed in the rectum and the colon is filled with air, followed by an abdominal-pelvic CT scan, which is then repeated with the patient lying in a different position.

Is virtual colonoscopy painful?

Because air is pumped into the colon, cramping may result. By contrast, in a conventional colonoscopy most patients receive sedative drugs that alleviate discomfort. In the largest study of virtual colonoscopy, 300 patients underwent both virtual colonoscopy and conventional colonoscopy. Of these patients, 64 percent preferred conventional colonoscopy, and patients found that virtual colonoscopy caused more pain and more lack of respect than conventional colonoscopy.

Is virtual colonoscopy accurate?

Results of published studies have been quite mixed. For detecting large polyps (greater than 1cm), some studies have shown virtual colonoscopy to be almost as accurate as conventional colonoscopies, and others have found conventional colonoscopy to be much FACING REALITY: The Facts About “VIRTUAL” COLONOSCOPY better. However, most polyps (90 percent) are smaller than 1 cm. While there is always some possibility that a very small polyp may avoid detection by either technique, studies demonstrate that conventional colonoscopy is much more accurate than virtual colonoscopy.

If I have virtual colonoscopy, will I need conventional colonoscopy also?

If polyps are detected, or if virtual colonoscopy is technically inadequate, conventional colonoscopy is still needed. In the largest study of virtual colonoscopy, two-thirds of patients had an abnormality that required conventional colonoscopy. Conventional colonoscopy permits direct visualization of the colon, any polyps or other suspicious lesions. Virtual colonoscopy is an examination based on X-ray technology, which uses indirect images. If the virtual colonoscopy’s indirect image is inconclusive in any way, the patient will almost certainly be referred for a conventional colonoscopy with its more reliable direct visualization. Many patients who choose to have a virtual colonoscopy will end up having a second, more definitive test, the conventional colonoscopy.

Is virtual colonoscopy recommended by experts?

No expert panel or national organization, including the American Cancer Society, has endorsed the use of virtual colonoscopy for colorectal cancer screening. While there have been some attempts by experts to evaluate the effectiveness, costs and benefits of virtual colonoscopy, at this time, there has been no definitive demonstration to support either its overall effectiveness or cost-effectiveness.