GI docs find value in virtual colonoscopy

May 31, 2006

While radiologists have long supported virtual colonoscopy, their gastrointestinal colleagues have been skeptical. Research presented in May at the Digestive Disease Week meeting in Los Angeles suggests these clinicians are embracing the radiology technique.

While radiologists have long supported virtual colonoscopy, their gastrointestinal colleagues have been skeptical. Research presented in May at the Digestive Disease Week meeting in Los Angeles suggests these clinicians are embracing the radiology technique.

The message from researchers in the fields of gastroenterology, endoscopy, and gastrointestinal surgery is that VC may be as effective as standard colonoscopy to screen average-risk individuals.

In an attempt to improve rates of screening while maintaining accuracy, investigators have been examining optimal use of VC. Studies have previously suggested that VC is comparable to optical colonoscopy, and interim results from a study from the National Naval Medical Center support those findings.

Dr. Brooks Cash, director of clinical research at the naval center, and colleagues prospectively examined 760 asymptomatic participants who were at average risk for colon cancer. Researchers used various treatment and follow-up protocols depending on polyp size.

If the VC identified a polyp larger than 10 mm, or more than three polyps larger than 6 mm, participants underwent same-day optical colonoscopy.

Patients with one or two polyps measuring 6 mm to 9 mm underwent optical colonoscopy after one year. Patients with no polyps greater than 6 mm had optical colonoscopy within five years.

The one-year delay in the removal of polyps is a novel feature of this trial, one that investigators hope will be allow them to glean information about the natural history of colonic polyps in this patient population, according to Cash.

Findings from the study suggest that VC is comparable in accuracy to optical colonoscopy to detect polyps larger than 10 mm, with an overall detection sensitivity of 96.4% compared to 96.3% with optical colonoscopy.

While VC sensitivity falls as polyp sizes get smaller, VC detection of smaller polyps (6 to 9 mm in size) was comparable to that of optical colonoscopy with a 83.6% accuracy (sensitivity 77.3%, specificity 85%). Optical colonoscopy's sensitivity for these polyps was 88.2%.

The investigators concluded that VC is an effective method to screen for precancerous colorectal lesions in people at average risk of cancer.

"It is also important to realize that we are at the vanguard of this technology and our results may not be indicative of the results that would be obtained in the general community," Cash said. "VC remains an innovative practice that needs more study before it can be widely recommended, though our current results are certainly very promising."

Another study, however, cautions against leaving alone polyps less than 1 cm. Dr. Douglas Rex, director of endoscopy at Indiana University Hospital, and colleagues closely evaluated more than 10,000 polyps under 1 cm and found that if all of these polyps are ignored, a substantial majority of colorectal neoplasms will be left in place to grow.

Researchers examined 8798 polyps that were smaller than 6 mm and an additional 1282 polyps that were between 6 mm and 9.9 mm. Analysis showed that almost half of the polyps smaller than 6 mm were either adenomas or advanced adenomas.

This rate was even higher for polyps between 6 mm and 9.9 mm. Adenomas made up 58.7% of these polyps and an additional 5.7% were advanced adenomas.

"If we move to a policy of leaving polyps less than one centimeter in place, as has been suggested by some experts for patients who undergo virtual colonoscopy, then we'll be leaving more than 90% of the neoplasms in the colon in place," Rex said.

He called this approach a major shift in colorectal cancer prevention strategy, which currently is based on colonoscopy with resection of all detected neoplasms. He said such a change requires very careful evaluation.

For more information from the Diagnostic Imaging archives:

Virtual colonoscopy gets an A for safety

Tools for CT colonography advance toward clinical use

3D CT colonography overcomes diverticulosis

'Filet view' software streamlines CT colonography