New study reveals virtual colonoscopy as less sensitive than conventional colonoscopy

Arlington 13 April 2004Findings of a new multicentre study by Cotton et al. published in the Journal of the American Medical Association comparing standard colonoscopy with CT colonography for the detection of colorectal cancer reveal that this technology, in the form used most often in the United States, while of significant interest, is not presently a viable option for routine colorectal cancer screening. The study utilized abdominal-pelvic CT scanning and the radiologists relied primarily on two-dimensional images but three-dimensional "fly-throughs" of the colon that simulate conventional colonoscopy were also evaluated.

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The study found that the sensitivity of CT colonography for detecting patients with one or more lesions sized at least 6 mm was 39 percent, and for lesions sized at least 10 mm it was 55 percent, this compared with 99 percent and 100 percent respectively when examined using conventional colonoscopy also referred to as complete colonoscopy. Only marginal improvements occurred when the three-dimensional results were evaluated. These findings contrast sharply with findings by Pickhardt et al. recently published in the New England Journal of Medicine in December 2003.

One of the new study's co-authors, Douglas K. Rex, M.D., FACG, is currently president of the American College of Gastro-enterology and director of endoscopy at Indiana University Hospital in Indianapolis, Indiana. Dr. Rex offers his perspective on how the methodology used by Cotton et al. resulted in findings differing from those by Pickhardt et al., as well as the state of the art of conventional colonoscopy and potential future applicability of CT colonography.

Dr. Rex commented: "This is the third largest study in the literature. Other studies using 2D imaging had equally poor results. Given these disparate results, we need to see verification of the results obtained in the Pickhardt study using new methods before CT colonography can be considered as appropriate for colorectal cancer screening."

New colorectal cancer screening strategies, including virtual colonoscopy and faecal DNA testing, generally will not match the reliability of complete colonoscopy although they may offer the potential to enhance the acceptability of colorectal cancer screening to some persons who are not candidates for complete colonoscopy. Virtual colonoscopy has not yet been endorsed by any multi-disciplinary guideline group as an effective colorectal cancer screening strategy. The principle obstacle to endorsement thus far has been the wide range and frequent lack of effectiveness in clinical trials.

Conventional colonoscopy is itself a dynamic technology. Improvements in bowel preparation, sedation and sensitivity for adenomas are being actively investigated and developed. Dr. Rex stated: "Virtual colonoscopy is a diagnosis-only test, whereas conventional colonoscopy is the only strategy that allows us to both visualize the entire colon and remove polyps in a single session. Considering all available literature, complete colonoscopy as currently performed remains the clear gold standard for the diagnosis of colorectal cancer and adenomas."

The American College of Gastro-enterology issued information for people considering a colorectal cancer screening test. Recommended by medical and cancer groups for colorectal cancer screening, complete colonoscopy detects smaller polyps, even below 1 cm. This test allows removal of suspicious polyps without surgery at the time of the exam.

CT colonography or virtual colonoscopy is an X-ray test designed to look for colon polyps and cancers. First, a radiology technician inserts a tube into the rectum and air is pumped into the colon until it is fully distended. Then, the patient is asked to hold his breath while lying on his back and a CT scan is performed. The patient then turns over onto the stomach and again he holds his breath while a second CT scan of the abdomen and pelvis is performed.

The bowel-cleansing regimen is the same for both a regular colonoscopy and CT colonography. On the day before the procedure, the patient stays on clear liquids all day and on the evening before and the morning of the procedure, laxatives are taken to flush waste from the colon.

With CT colonography, because no sedation is used, the distention of the colon with gas can be painful. In several studies, patients experience more pain and discomfort with CT colonography than with a regular colonoscopy, because the latter involves the administration of sedatives.

One recent study using special methodology found that CT colonography was able to detect colon polyps as well as regular colonoscopy. This result has not yet been verified in other studies. Previous studies of CT colonography had shown a very wide range of results. On average, previous results showed that CT colonography was clearly inferior to regular colonoscopy for detection of colon polyps, with many false negatives and false positives.

At least 30 percent, and in some studies 50 percent, of patients having a CT colonography will need a regular colonoscopy to remove detected polyps. In the case of complete colonoscopy, for most people the test will be once every ten years. The patient has the assurance that the physician has examined the entire colon.

Information on the previous study by Pickhardt et al. published in the New England Journal of Medicine is available in the VMW January 2004 article National Naval Medical Center provides landmark research for Virtual Colonoscopy study.


Leslie Versweyveld

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