You may have heard of “virtual” (or CT) colonoscopy. Many people are attracted to the idea because they dread the invasiveness of being “scoped.” With virtual colonoscopy, no colonoscope is inserted. Instead, the colon is visualized by a CT scan. It may sound like a great alternative, but it really isn’t.
Studies on virtual colonoscopy have had some promising results. One in the New England Journal of Medicine in 2008, for instance, found that the test is good at identifying larger polyps and cancer in people at average risk.
The advantages of virtual colonoscopy are obvious. No sedation is needed, the test is almost noninvasive (just a short tube is inserted in the rectum to inflate the colon) and there’s little or no risk of complications. So more people may be willing to undergo it.
But there are plenty of disadvantages as well. You still have to clean out your colon as you would before a regular colonoscopy. Moreover, the doctor can’t take a biopsy or remove polyps during the procedure. If polyps are found, a regular colonoscopy should be done to remove them (usually on another day, requiring another bowel prep). Virtual colonoscopy should be done every five years, rather than ten, because it may be less accurate. In particular, the test often misses smaller polyps. Medicare and most insurance plans won’t pay for it unless a conventional colonoscopy can’t be done for some reason.
Unlike regular colonoscopy, the virtual test can also detect suspicious growths outside the colon. That’s often promoted as a plus, but it probably isn’t. The overwhelming majority of such findings, sometimes called “incidentalomas,” are not cancer or are small cancers that will never cause harm. But their discovery leads to invasive procedures and, often, unnecessary treatments. And the key fact is, there’s no evidence that routine CT screening of other organs saves lives.
Another big drawback: Like any CT scan, virtual colonoscopy exposes you to radiation. That worries me because the test has to be repeated periodically, radiation exposure is cumulative, and Americans are already being exposed to increasing amounts of radiation from medical scans.
For these reasons, the U.S. Preventive Services Task Force, American College of Gastroenterology and American Cancer Society do not recommend virtual colonoscopy. We agree.