In the U.S., colon cancer leads to almost 60,000 deaths a year. Most physicians believe many of these deaths could be prevented by early detection and removal of precancerous polyps larger than 6 mm in size.
Late last year, virtual colonoscopy was trumpeted as the best new thing for colon cancer screening. But don't call for a virtual colonoscopy appointment just yet; it seems the procedure may not be ready for widespread use. A conventional colonoscopy may still be your best bet at detecting the early stages of colon cancer for at least a few more years.
Virtual colonoscopy is a minimally invasive procedure that may be more appealing to some than traditional colonoscopy. Where traditional colonoscopy relies on an endoscope snaking through the rectum into the colon to search for precancerous polyps, virtual colonoscopy uses a CT (computed tomography) scan to construct a three-dimensional image of the lining of the colon. A radiologist then "reads" the image to search for polyps. With a virtual colonoscopy scan, the only thing inserted into the rectum is a small catheter used to pump air into the colon. This eliminates the risk of perforation of the bowel and the need for sedation.
Both procedures, however, require the patient to undergo rigorous preparation of the bowel. Most patients report that this preparation, which involves 24 hours of a clear liquid diet and the use of laxatives, is the worst part of either test.
Another downside to virtual colonoscopy is that polyps found during the procedure cannot be removed, making an additional conventional colonoscopy (and bowel preparation) necessary for polyp removal. But the majority of 50 year olds undergoing a virtual colonoscopy as their first screening test would not need both procedures; only roughly 15% are likely to have polyps discovered.
In many studies virtual colonoscopy has proved its worth. A U.S. military study published in the New England Journal of Medicine last December showed virtual colonoscopy was as effective as regular colonoscopy at finding polyps larger than 5 millimeters in size.
Results from another study published in the Journal of the American Medical Association this spring are not as promising. In this multi-center study, the sensitivity (ability to detect) of virtual colonoscopy was only 39% for polyps at least 6 mm in size and just 55% for polyps at least 10 mm in size. Conventional colonoscopy, on the other hand, showed a sensitivity of 99% and 100%, respectively. Questions have been raised as to how well trained the participating radiologists were in this procedure: Some did much better than others, and the disappointing results may reflect more on a lack of training than on limitations of the technique.
Technology for virtual colonoscopy will improve within the coming years. And more radiologists will become familiar with the procedure. So, in the future, the reliability of virtual colonoscopy should improve for everyday use.
Virtual colonoscopies may not be dependable enough yet, but this doesn't mean you should avoid getting tested. A conventional colonoscopy may not be a picnic, but it could save your life. The American Cancer Society recommends that anyone over 50 years old follow one of these testing schedules: yearly fecal occult blood test; flexible sigmoidoscopy every 5 years; yearly fecal occult blood test plus flexible sigmoidoscopy every 5 years; double-contrast barium enema every 5 years; or colonoscopy every 10 years. So don't wait. Call now for an appointment.
July 2004 Update
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