'Virtual' colon test is called unreliable
By Lindsey Tanner
CHICAGO -- Virtual colonoscopy -- a cancer-detecting procedure that gives doctors a computer-generated 3-D view of the colon -- is less reliable than previously thought and not ready for widespread use, researchers say.
Its accuracy varies considerably, depending on the training and methods of the doctors performing it, according to a study of 600 patients at nine major clinics.
In conventional colonoscopy, a long, flexible viewing tube about the thickness of a garden hose is inserted in the rectum and threaded several feet into the colon. A device on the end of the tube is used to remove suspicious growths, which are later tested for cancer.
Virtual colonoscopy is designed to take some of the discomfort out of the examination. A narrower rectal catheter is inserted, and a CT scanner produces images of the colon.
In the latest study, the patients underwent virtual colonoscopy first, then traditional colonoscopy on the same day.
The virtual method detected 55 percent of patients with at least one suspicious polyp at least 10 millimeters in diameter, compared with a 100 percent success rate for traditional colonoscopy. For smaller tumors, at least 6 millimeters in diameter, the results were worse: 39 percent for virtual colonoscopy versus 99 percent for the traditional method.
Eight patients ultimately were diagnosed with cancer; virtual colonoscopy missed two of them.
As recently as December, a widely reported study found that virtual colonoscopy was at least as accurate as the conventional variety.
But the authors of the new research said many of the previous studies were largely based on data from a single hospital and did not take real-world conditions into account.
The leader of the research team called the latest findings "a bucket of cold water" thrown on the growing enthusiasm for virtual colonoscopy.
While the technique might be effective "in the hands of experts, it has yet to be proven that this expertise can be taught and disseminated reliably into daily practice," said the research team, led by Dr. Peter Cotton, a gastroenterologist at Medical University of South Carolina.
Nevertheless, Cotton said doctors should not give up on virtual colonoscopy. "I suspect that in five years' time, with better software and training and maybe some more intelligent computing this will become a useful technique," he said.
The study appears in the Journal of the American Medical Association.