CHICAGOAn 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 high99.4%"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 size5 mm or lessand 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.