Dec. 2, 2003 (Chicago) — Three-dimensional virtual colonoscopy is as sensitive as conventional colonoscopy for the detection of polyps and may be slightly more sensitive for the detection of larger polyps that require resection, according a presentation here at the 89th annual meeting of the Radiological Society of North America.

Lieutenant Colonel J. Richard Choi, ScD, MD, and Perry J. Pickhardt, MD, presented the findings of a multicenter study showing that the virtual procedure had a 93.8% sensitivity rate for adenomatous polyps, or those exceeding 10 mm compared with 87.5% for the conventional procedure. The study, as well as an accompanying editorial, will be published this week in the New England Journal of Medicine.

These findings broaden physicians' options for colorectal cancer screening because the less invasive procedure may be more palatable, Dr. Pickhardt said. He is an associate professor of radiology at the University of Wisconsin Medical School in Madison, but he participated in the research while a staff radiologist at the National Naval Medical Centers in Bethesda, Maryland. Dr. Choi is chief of the computed tomography division at Walter Reed Army Medical Center in Washington, D.C.

"If virtual [colonoscopy] is targeted to people of average risk, it may mean that more people get colorectal cancer screening," Dr. Pickard told Medscape. "Only half of such patients get colorectal cancer screening of any kind, and less than 15% get conventional colonoscopy." Barriers typically consist of restricted access to screening, long waiting lists, and patient acceptance of colonoscopy, he said.

"Virtual colonoscopy is meant to add to the diagnostic armamentarium, not to replace conventional colonoscopy," Dr. Choi told Medscape. He added that physicians should counsel patients that the virtual procedure still requires the same preparation and pretreatment diet of clear liquids.

The study, which was funded by the Department of Defense, involved 1,233 participants. Of these, 1,208 were of average risk; 25 participants had familial risk factors. Average age of participants was 57.8 years; 505 were women and 728 were men. Immediately after the virtual procedure, participants underwent conventional colonoscopy, and the investigators compared the results of the two procedures.

The virtual procedure involved "fly-through" computed tomography (CT), which uses three-dimensional images and animation. The virtual procedure involves a two-inch deep probe approximately one finger-width in diameter. Two-dimensional images were used to validate polyps found or for confirmation and problem-solving.

On a by-patient basis, the virtual procedure had a sensitivity of 93.8% for adenomatous polyps, 93.9% for polyps 8 to 10 mm in diameter, and 88.7% for those 6 to 8 mm in diameter. For the conventional procedure, those rates were 87.5%, 91.5%, and 92.3%, respectively. The specificity for virtual colonoscopy was 96.0% for adenomatous polyps, 92.2% for those 8 to 10 mm, and 79.6% for those 6 to 8 mm.

Both of the malignancies diagnosed in the study were visible on virtual colonoscopy compared with one visible on the conventional procedure. Patients were in the CT suite an average of 14.1 minutes compared with an average of 33.0 minutes in the colonoscopy suite, which did not include recovery room time. Including the time required to recover from sedation, the conventional procedure required an average of 95.9 minutes. Time required to interpret the virtual colonoscopy findings averaged 15.9 minutes, 17.1 minutes, and 24.0 minutes in the three participating centers.

"This study suggests that virtual colonoscopy can detect polyps of 6 mm or larger as accurately as conventional colonoscopy in a population with low prevalence of colorectal neoplasia," write Martina M. Morrin, MB, and Thomas LaMont, MD, in the accompanying editorial in the New England Journal of Medicine. The editorialists point out that physicians still do not agree about the size of polyps that need to be monitored or excised.

"This is a very promising study," Dr. Morrin, a radiologist at Beth Israel Deaconess Medical Center and an assistant professor of radiology at Harvard Medical School in Boston, Massachusetts, told Medscape. She added that physicians will need to counsel patients that the preparation is still a fact of life in colorectal cancer screening. "An adequate prep is incredibly important," she said. "It may be one of the most important issues to address to ensure the accuracy of the virtual colonoscopy."

RSNA 89th Scientific Assembly and Annual Meeting: Abstract C08-283. Presented Dec. 1, 2003.
N Engl J Med. 2003;349:2261-2265, 2191-2200

Reviewed by Gary D. Vogin, MD