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Letters to the Editor |
Department of Radiology, The Ottawa Hospital, General Campus, 501 Smyth Road, Ottawa, Ontario, Canada K1H 8L6, e-mail: rseppala@ottawahospital.on.ca
Editor:
Recent articles (1–3) in your journal have reviewed the important role of double-contrast barium enema examinations in screening for colorectal cancer. However, an editorial and an article based on results from the National Polyp Study published last year in the New England Journal of Medicine concluded that colonoscopy was far superior to the double-contrast barium enema examination for the detection of polyps and that only colonoscopy should be used for polyp surveillance (4,5). Radiologists can expect to be confronted with the results of that study, and they need to know why the conclusions are misleading.
The major deficiency of that study, in which polyp detection was compared with paired colonoscopic and double-contrast barium enema examinations, was the big disparity in the level of confidence between the two methods. For double-contrast barium enema studies, a high level of confidence that the radiologist was unlikely to miss lesions that were larger than 1 cm varied in different segments of the bowel, from 35% in the sigmoid colon to 69% in the rectum (average, 55%). In contrast, the colonoscopist’s high level of confidence that the cecum was reached and the entire colon was depicted varied from 91% in the cecum to 95% in the rectum (average, 93%).
Why was the level of confidence of the radiologists in the National Polyp Study so low? Certainly, they were qualified radiologists from reputable medical centers, and the technique was presumably good. One reason was the difference in the degree of colonic cleansing between the two procedures. The frequency of fecal matter being present during colonoscopy varied from 3% to 11% in different bowel segments, compared with 11%–31% during the double-contrast barium enema examination.
I believe that the main reason, besides poor colonic preparation, for the low level of confidence of the radiologists was perceptive error that undermined confidence. This has been documented (6) as the most common cause for radiologic misses. Some authors have even recommended double reading of the barium enema radiographs (7). Colonoscopists have an advantage over radiologists in that they are forced to look at the colonic lumen because that tells them where to advance the colonoscope. Radiologists are not forced in the same way to look at their radiographs. Every radiograph of the barium enema study should be examined carefully. In my experience, to study them all takes from 3 minutes for the easiest cases to almost 10 minutes for a colon that is redundant or involved with extensive diverticulosis. Only occasionally will colonoscopy have to be recommended as a supplementary procedure.
The double-contrast barium enema study lives and is an excellent method to study the colon, including polyp surveillance (6). My message to radiologists is that if this study is performed and interpreted properly, it is indeed accurate. This accuracy has been confirmed by the surgeons and gastroenterologists who continue to refer patients to me.
REFERENCES
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