Virtual Colonoscopy, Real Accuracy
Study 'Validates' CT Scans for Colon Cancer Screening, but Worries Linger
WebMD News Archive
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
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
"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
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."