Virtual colonoscopy: Virtually promising

04/12/05

INDIANAPOLIS — In an editorial published in the April 19 issue of the Annals of Internal Medicine, Indiana University School of Medicine gastroenterologist Thomas Imperiale, M.D., says virtual colonoscopy may become one of the most valuable assessment tools available for colorectal cancer screening.

"I expect a lot from a screening test — zero risk, high sensitivity, high specificity, reasonable ease and convenience, and cost effectiveness," said Dr. Imperiale, who is professor of medicine and Regenstrief Institute research scientist. "That may be a lot to ask, but I think CT colonography (also known as virtual colonoscopy) has the potential to meet all of these criteria, especially if the need to take a laxative preparation can be eliminated."

"Colonoscopy is currently used as a screening test for colorectal cancer, but it didn't start out as one," he explained. "The cumulative potential for side effects from the laxative preparation, the need for conscious sedation, lost sleep, time lost from work, the need to arrange for someone to drive the patient home, and risk for perforation exceed my threshold for what a good screening test should be."

Colonoscopy became a common tool for screening primarily by default, he said. "Colonoscopy has evolved into an acceptable screening test in part because many people believe that there are no other good options."

Although it is not yet ready to be used as a screening test, virtual colonoscopy may prove to be highly sensitive, highly specific, reasonably convenient, cost effective, and low risk, according to Dr. Imperiale.

Physicians have come to accept colonoscopy as "the best test" for colorectal cancer because it's the most accurate test in a single application. Before the popularity of colonoscopy for screening, it was a diagnostic and therapeutic procedure. Unlike colonoscopy, most screening tests only screen for disease. Colonoscopy is a screening test, a diagnostic test and a therapeutic procedure all in one, which may be considered an advantage by some people; however the downsides must be considered.

There are a few examples of truly good screening tests for any cancer, according to Dr. Imperiale, who thinks that PAP smears are probably the best currently available screening tools because they are reasonably sensitive, specific, and inexpensive, and the test itself has no risk.

"To some extent, the absence of a truly good screening test for colorectal cancer has caused us to lower our standards for what a good screening test should be," he said. "If there were a truly good screening test for colorectal cancer, screening rates would be higher than current rates, which are under 50 percent. We need better screening tests, and virtual colonoscopy has the potential to fill that need."

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