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Colorectal Cancer Health Center

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Virtual Colonoscopy, Real Accuracy

Study 'Validates' CT Scans for Colon Cancer Screening, but Worries Linger

Virtual Colonoscopy, Real Bowel Prep continued...

Johnson says that centers performing CT colonography should be equipped to offer same-day colonoscopy for patients who need it. Fletcher says it's important for patients to ask about this before choosing virtual colonoscopy as a screening option.

Virtual colonoscopy has a 14% false-positive rate. That's not bad, considering it's a screening test designed to catch as many polyps as possible. But patients who get a false alarm will have to undergo an unnecessary colonoscopy.

Of greater concern to Fletcher is the fact that CT scans see more of the body than just the bowel. For 16% of patients in the Johnson study, the scans detected non-bowel problems serious enough for further tests or urgent care.

"It's not trivial for your doctor to tell you, 'I found something in your kidney or on your adrenal gland,'" Fletcher says. "The odds of helping people are pretty low for those things outside the colon. And then there is the worry, the bother, of additional tests and of finding additional bad things you never knew about but cannot be changed now that you know."

Johnson has a completely different view of the issue.

"Colonoscopy cannot look outside the colon. CT colonography does," he says. "So there is an opportunity among patients age 50 and older to be able to look for other abnormalities that may be asymptomatic but may cause harm in the future. We can look for abdominal aortic aneurysms and tumors in other body parts."

Is Virtual Colonoscopy for You?

This year, the American Cancer Society, the American College of Radiology, and the U.S. Multi-Society Task Force on Colorectal Cancer added CT colonography to the list of colon cancer screening options.

The American Gastroenterological Association notes that only half of people get recommended colon cancer screening, and that virtual colonoscopy could improve this sorry statistic.

But GI doctors aren't yet ready to embrace CT colonography, says David A. Margolin, MD, director of colorectal surgery research at the Ochsner Clinic Foundation in New Orleans.

"CT colonography will, in the future, play a role in colon cancer screening," Margolin tells WebMD. "At centers of excellence, at a very few centers where the quality of software and the CT engineer and excellent radiologist training all converge, it is useful. But if you expect these kinds of results at every community hospital, you won't get it."

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