Virtual Colonoscopy Not Ready for Use Yet
Conventional Colonoscopy Still Superior to Virtual in Detecting Polyps
WebMD News Archive
April 13, 2004 -- Virtual colonoscopy may sound like a good
idea, but a new study shows the experimental colon cancer screening technique
is not yet ready for widespread use.
Although previous studies have shown that virtual colonoscopy
was reasonably accurate at detecting large polyps when performed by an expert,
researchers found the computerized screening technique was far less reliable
when performed by a large number of doctors at various centers.
Virtual colonoscopy uses computer-generated images of the large
colon to detect polyps which can lead to cancerous growths. The technique is
less invasive than standard colonoscopy and it involves imaging the colon
without having to insert a long scope to view the inside of the colon.
The study showed that virtual colonoscopy detected only about
55% of growths that were at least 10 millimeters in diameter and 39% of smaller
growths of at least 6 millimeters. In contrast, conventional colonoscopy had
accuracy rates of 99% to 100% in detecting these growths.
Virtual Colonoscopy Needs More Work
Researchers say conventional colonoscopy is widely accepted as
the best available method for colorectal cancer screening. But many people are
reluctant to undergo the procedure, which requires the use of laxatives to
clean the colon and sedation during the procedure.
Computerized tomographic colongraphy (CTC) or virtual
colonoscopy has been proposed as a screening test to allow conventional
colonoscopy to be used more selectively and efficiently.
In this study, researchers looked at the how accurate the new
colon cancer screening method was in detecting lesions in the colon when
performed at nine major hospital centers on 615 adults aged 50 or older, who
were referred for routine colonoscopy. Virtual colonoscopy was performed first,
followed by conventional colonoscopy.
A total of 827 growths were detected, but researchers found
virtual colonoscopy missed two of eight cancers. In addition, the accuracy of
the technique varied considerably from center to center and did not improve as
the study progressed and researchers gained experience with the procedure.
"Our results indicate that CTC using these techniques is
not ready for routine use at this time, as many others have concluded,"
write researcher Peter Cotton, MD, of the Medical University of South Carolina,
and colleagues in the latest Journal of the American Medical
Association. "There is an obvious need for continuing collaboration
between radiologists and gastroenterologists in further evaluation of this
exciting new technology."
In an editorial that accompanies the study, David F. Ransohoff,
MD, of the University of North Carolina, Chapel Hill, says the results show
that the most pressing problem for virtual colonoscopy is that it might be
implemented too widely before the technical problems that affect its accuracy
are fully understood.
"The differences between what virtual colonoscopy can do
and what it will do if applied in ordinary practice circumstances are so great
that physicians must be cautious. There are many important steps yet to be
taken in learning how to implement this new technology appropriately" says