CHICAGO—An advanced three-dimensional (3D) fly-through-reality form of virtual colonoscopy is an effective frontline screening tool for an average-risk, asymptomatic population, according to a prospective, multicenter trial. "It is accurate for finding clinically important polyps, and it is comparable in sensitivity to the accepted gold standard of conventional colonoscopy," Perry Pickhardt, MD, associate professor of radiology, University of Wisconsin, Madison, said at a press conference at the 89th Annual Meeting of the Radiological Society of North America (RSNA).
Virtual colonoscopy is generated from regular CT scans, obtained after insertion of a small flexible rectal catheter, with postprocessing done by specialized software. The 3D method of performing virtual colonoscopy in this study differs from techniques employed in previous investigations that involve two-dimensional (2D) or axial slice scanning for polyp detection, explained Dr. Pickhardt, who participated in the study when he was a researcher at the National Naval Medical Center, Bethesda, Maryland.
Virtual colonoscopy is especially useful in an average-risk screening population "because these are the people who are least likely to have a large polyp that would need to be removed," he said.
This study was performed at three hospitals, the National Naval Medical Center, the Naval Medical Center, San Diego, and Walter Reed Army Medical Center, Washington, DC. It was recently published in the New England Journal of Medicine (349:2191-2200, 2003).
In the study, a total of 1,233 asymptomatic patients underwent standard colon preparation and virtual and conventional colonoscopy on the same day. For the virtual colonoscopy, "no intravenous contrast was used and no intravenous sedation or pain control was needed," Dr. Pickhardt said.
The mean age of the patients was 58 years, which is slightly older than the recommended age for an initial screening colonoscopy. The vast majority of the patients in the study were at average risk for colon cancer; only 32 patients had a significant family history of colon cancer. The rate of completion of conventional colonoscopy was high—99.4%—"which means that the endoscopists involved were quite skilled," he said.
A total of 1,310 polyps were found in 622 patients. Most of the polyps (966) were diminutive in size—5 mm or less—and had no clinical significance; 344 polyps were 6 mm or larger, 210 of these were adenomas, and 2 were malignant. Of note, virtual colonoscopy identified both cancers, while conventional colonoscopy missed one.
