Recently the Annals of Internal Medicine reported the results of a study that indicated that a colonoscopy may miss more colon cancers than once believed, particularly small cancers in the fold of tissues or at the anal entrance.
Colonoscopy is a procedure in which a colonoscope (lighted tube) is passed through the rectum into the colon and into the lower end of the small intestine. The procedure is performed to examine the lower portion of the gastrointestinal tract for early signs of cancer, ulcers, inflamed tissue or bleeding. Pictures and biopsies and may be taken for further evaluation by the physician. Virtual colonoscopy, a newer type of colonoscopy still being evaluated extensively in clinical studies, utilizes x-rays and computers to produce 2 or 3-dimensional images of the rectum, colon and the lower end of the small intestine.
Previous studies evaluating virtual colonoscopy always compared results of the procedure to optical colonoscopy. In this study, 1,233 participants underwent both optical colonoscopy and virtual colonoscopy and results were compared for both types of procedures. Prior to the study, it was believed that the miss rate of lesions >1cm with optical colonoscopy was 0-6%. After both optical and virtual colonoscopy, results were evaluated and it was determined that approximately 10% of polyps were missed by optical colonoscopy. Fifty–five of the 511 polyps found by virtual colonoscopy were missed by optical colonoscopy. Of these 55, 21 of these polyps measured 6mm or greater. The majority of these polyps were located on a fold in the tissue or near the anal entrance. Virtual colonoscopy missed 14% of the polyps (6mm or greater) that were located by optical colonoscopy.
Researchers concluded that optical colonoscopy may miss more polyps and small colon cancers than previously thought, particularly those smaller in size and those in the folds of tissue in the colon or at the anal entrance. The researchers believe that neither test is perfect, as each misses 10-14% of polyps measuring 6mm or greater. Despite these findings, however, optical colonoscopy remains the gold standard for detecting and diagnosing colorectal diseases and significantly improves survival in colorectal cancer when used as a screening tool.
Reference: Pickhardt P, Nugent P, Mysliwiec P, and et al. Location of adenomas missed by optical colonoscopy. Annals of Internal Medicine. 2004; 141: 352-359.
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