Virtual Colonoscopies Show Value For Some Patients, But Polyps Will Be Missed

Main Category: Colorectal Cancer
Article Date: 13 Mar 2009 - 0:00 PDT

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The value of CT colonography, also called virtual colonoscopy, is under debate as Medicare considers halting coverage of these procedures as a diagnostic method for detecting colorectal cancer and precancerous growths. Research findings from meta-analyses performed by ECRI Institute suggest that CT colonography appears most promising for screening asymptomatic, average-risk patients; however, it will miss some important polyps and cancer that would have been detected by colonoscopy. For asymptomatic high-risk patients and symptomatic patients, the percentage of patients correctly identified as having colorectal polyps or cancer may be too low to be useful.

"While some patients may prefer CT colonography, it may not be the best choice for everyone," Meredith Noble, an ECRI Institute researcher, notes. "Although CT colonography may be a useful alternative for patients with contraindications to colonoscopy or for whom colonoscopy cannot be completed, it may be less useful for patients who will inevitably require a subsequent therapeutic colonoscopy."

ECRI Institute (http://www.ecri.org), an independent, nonprofit organization that researches the best approaches to improving patient care, analyzed recent studies on the comparative effectiveness of CT colonography to traditional colonoscopy. Researchers focused on five key issues: 1) diagnostic performance for detecting clinically important polyps or cancer, 2) impact on long-term clinical outcomes, 3) patient preferences, 4) adverse events, and 5) impact of offering CT colonography on patient compliance with CRC screening recommendations. Researchers reviewed 17 publications of studies that reported on 7,460 patients.

According to ECRI Institute's research, CT colonography correctly identified between 86% and 95% of asymptomatic, average-risk patients with large polyps and cancers that were identified by colonoscopy and between 76% and 95% of symptomatic patients with large polyps and cancers. No firm conclusions could be drawn regarding the proportion of asymptomatic high-risk patients with important polyps that would be identified by CT colonography, but the studies ECRI Institute analyzed reported that CT colonography identified no more than 85% of these patients.

Long-term follow-up data is not available to compare the clinical outcomes (including side effects) of patients diagnosed or screened with CT colonography to the outcomes of patients who underwent colonoscopy. Information is also insufficient to gauge the possible long-term effects of repeat radiation exposure from CT colonography at the regular recommended intervals for colorectal cancer screening.

Nine studies ECRI Institute analyzed suggest that the majority of patients who underwent both CT colonography and colonoscopy for screening and diagnosis preferred CT colonography. However, a lack of evidence prevented ECRI Institute from determining whether offering CT colonography increases overall patient participation in colorectal cancer screening.

Both procedures involve the same patient bowel preparations. However, no sedative is administered for CT colonography. CT colonography involves taking a series of scans in a 15-20 minute procedure. Computer software translates the scans into a readable format. Because CT can only take pictures, suspicious polyps cannot be removed during this procedure. If suspicious polyps are identified, a subsequent colonoscopy should be scheduled, and if a facility cannot do it the same day as the colonography was performed, the patient must repeat the bowel preparation procedure for the follow-up colonoscopy.

About ECRI Institute

ECRI Institute, a nonprofit organization, dedicates itself to bringing the discipline of applied scientific research to healthcare to uncover the best approaches to improving patient care. As pioneers in this science for 40 years, ECRI Institute marries experience and independence with the objectivity of evidence-based research. ECRI Institute is designated a Collaborating Center of the World Health Organization and an Evidence-based Practice Center by the U.S. Agency for Healthcare Research and Quality.

ECRI Institute
http://www.ecri.org

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