Accuracy of virtual colonoscopies validated

But gastroenterologists caution that traditional colonoscopies remain the only test that can both detect early cancer and remove precancerous polyps.

By Susan J. Landers — Posted Oct. 20, 2008

Print  |   Email  |   Respond  |   Reprints  |   Like Facebook  |   Share Twitter  |   Tweet Linkedin

Virtual colonoscopies are poised to take off as a major screening tool for colorectal cancer -- the nation's second-leading cause of cancer death.

Findings from the American College of Radiology Imaging Network National CT Colonography Trial demonstrated that the noninvasive technique is as accurate as traditional colonoscopies at finding colorectal cancer and large precancerous polyps. Results from this large, multicenter study were published in the Sept. 18 New England Journal of Medicine.

The hope is that the wide adoption of virtual colonoscopies will encourage more people to be screened. Although screenings have increased in recent years to nearly 61% of those 50 and older, people still fall through the cracks, according to Centers for Disease Control and Prevention data.

In addition, a study published Sept. 8 in Cancer indicates that many colorectal cancer survivors do not receive recommended follow-up screenings.

The promise of CT colonography for screening has been building in recent years. In March, the American Cancer Society, the American College of Radiology and the U.S. Multi-Society Task Force added virtual colonoscopies to their list of recommended tests to detect cancer and polyps. The task force includes representatives of the American College of Gastroenterology, the American Gastroenterological Assn. and the American Society for Gastrointestinal Endoscopy.

"I think the clinical validation of the technique is complete," said C. Daniel Johnson, MD, lead investigator of the ACRIN trial and chair of the radiology department at Mayo Clinic's Scottsdale, Ariz., facility. In disclosures for the article, Dr. Johnson and other ACRIN investigators reported links to firms working on screening aids and techniques.

"Indeed, this study provides another push for noninvasive/minimally invasive screening by CT colonography," said David Kim, MD, assistant professor of abdominal imaging at the University of Wisconsin School of Medicine and Public Health. Dr. Kim, who was not involved in the ACRIN trial, was lead author of another study published last year in NEJM showing that colonoscopy and colonography had similar detection rates for large polyps. He reported serving on the advisory board for a laxative manufacturer and receiving lecture fees from a diagnostic software firm.

The ACRIN trial is the largest so far to compare the two technologies. It enrolled more than 2,600 men and women 50 and older at 15 sites across the country. The participants were scheduled for a standard screening colonoscopy and then agreed to have a virtual colonoscopy, or CT colonography, on the same day. The day before the exams, participants underwent colon-cleansing procedures prescribed by gastroenterologists.

The virtual and traditional screening results were compared, and researchers found that the virtual screenings identified 90% of the large polyps found by colonoscopies.

A cautionary note

In marking the study's findings, gastrointestinal specialists raised some cautions. "Colonoscopy is the only test that can both detect cancer at an early curable stage and prevent cancer by removing precancerous polyps," said a statement from the American Gastroenterological Assn.

The findings "underscore the reality that many patients who have polyps detected by CT colonography will still have to undergo complete colonoscopy," said American College of Gastroenterology President Amy Foxx-Orenstein, DO.

Plus, the virtual procedure also might cause some discomfort, she said, because it requires that the abdomen be insufflated with air or gas. Patients are not sedated for this procedure as they are for a colonoscopy.

"It is important for patients to understand that CT colonography does not at present represent a painless or risk-free procedure, nor does it eliminate the need for bowel cleaning, which patients report as a barrier to screening," she added.

The AGA statement also said CT colonography was less likely to detect small polyps measuring 5 mm to 9 mm. But it's not clear whether those smaller polyps pose a risk.

Additional obstacles must be overcome before virtual colonoscopy hits the mainstream. "The professional organizations need to review and adopt the evidence and insurance companies need to agree to cover it," Dr. Johnson said. To that end, "the Centers for Medicare and Medicaid Services are currently reviewing the technique for reimbursement."

"Once reimbursement has been established, it is anticipated that the use of [CT colonography] in screening will dramatically increase," Dr. Kim predicted.

Currently, only a few large-scale screening programs use colonography, he noted. Among them is a program at the University of Wisconsin where local HMO coverage for virtual screenings has been established. The Wisconsin program began in 2004 and has screened more than 5,000 people, he said. A few military hospitals also have established programs.

Back to top


10-year screening intervals measuring up

Guidelines recommending 10-year intervals between traditional colonoscopies for those at average risk for colorectal cancer appear to be on target, according to a study in the Sept. 18 New England Journal of Medicine.

The 10-year re-screening recommendation that has been adopted by several organizations was based on studies of flexible sigmoidoscopy, plus a surveillance study indicating that polyps develop slowly, said Durado Brooks, MD, MPH, the American Cancer Society's director of prostate and colorectal cancer.

"What our study does is perhaps add a bit of support for that 10-year interval," said the study's lead author, Thomas Imperiale, MD, professor of medicine at Indiana University Medical Center and a research scientist at Regenstrief Institute for Health Care, both in Indianapolis.

The study of more than 1,200 people who had received an initial screening colonoscopy after age 50 found no cancers after five years.

"This study documents that colonoscopic re-screening intervals of five years or more are safe in patients who have a normal baseline examination," Dr. Brooks said.

Coverage of colonoscopies by Medicare for people at high risk for colorectal cancer began in 1997, and other insurers followed. Dr. Imperiale expects that another study soon will examine their 10-year record. "My guess is that we aren't that far away from someone putting together a group of patients screened 10 years ago and re-screening them after 10 years and seeing what is found on colonoscopy."

Back to top

External links

"Accuracy of CT Colonography for Detection of Large Adenomas and Cancers," abstract, New England Journal of Medicine, Sept. 18 (link)

"Five-Year Risk of Colorectal Neoplasia after Negative Screening Colonoscopy," abstract, New England Journal of Medicine, Sept. 18 (link)

Back to top



Read story

Confronting bias against obese patients

Medical educators are starting to raise awareness about how weight-related stigma can impair patient-physician communication and the treatment of obesity. Read story

Read story


American Medical News is ceasing publication after 55 years of serving physicians by keeping them informed of their rapidly changing profession. Read story

Read story

Policing medical practice employees after work

Doctors can try to regulate staff actions outside the office, but they must watch what they try to stamp out and how they do it. Read story

Read story

Diabetes prevention: Set on a course for lifestyle change

The YMCA's evidence-based program is helping prediabetic patients eat right, get active and lose weight. Read story

Read story

Medicaid's muddled preventive care picture

The health system reform law promises no-cost coverage of a lengthy list of screenings and other prevention services, but some beneficiaries still might miss out. Read story

Read story

How to get tax breaks for your medical practice

Federal, state and local governments offer doctors incentives because practices are recognized as economic engines. But physicians must know how and where to find them. Read story

Read story

Advance pay ACOs: A down payment on Medicare's future

Accountable care organizations that pay doctors up-front bring practice improvements, but it's unclear yet if program actuaries will see a return on investment. Read story

Read story

Physician liability: Your team, your legal risk

When health care team members drop the ball, it's often doctors who end up in court. How can physicians improve such care and avoid risks? Read story

  • Stay informed
  • Twitter
  • Facebook
  • RSS
  • LinkedIn