CT colonography detects 90% of large polyps under optimal conditions
Clinical Question
Clinical Question
Clinical Question
How accurate is computed tomographic colonography as a screening test for colorectal cancer?
Bottom Line
Bottom Line
Bottom Line
Computed tomographic (CT) colonography will detect approximately 90% of large polyps and adenocarcinomas. The benefits include no need for sedation and a lower risk of perforation; the harms include the need for subsequent colonoscopy in approximately 1 in 6 patients, the varying expertise of radiologists, and exposure to ionizing radiation. The lifetime risk of cancer from the radiation of a CT colonography program is estimated to be 0.14%, or approximately 1 in 600 (Gastroenterology 2005;129:328-37) and must be balanced against the reduction in the risk of colon cancer and the risks of optical colonoscopy. The decision to adopt this technology on a large scale should include a careful and objective assessment of these benefits and harms.
(LOE = 1b)Reference
Reference
Reference
Johnson CD, Chen MH, Toledano AY, et al. Accuracy of CT colonography for detection of large adenomas and cancers. N Engl J Med 2008;359(12):1207-1217.
[PMID:18799557]Study Design
Study Design
Study Design
Cohort (prospective)
Funding
Funding
Setting
Setting
Setting
Outpatient (specialty)
Synopsis
Synopsis
Synopsis
These researchers recruited 2600 adults, 50 years and older, who were free of significant bowel symptoms. Each had a standard bowel preparation, then underwent CT colonography using a 16-row scanner, and had an optical colonoscopy. Radiologists and endoscopists were masked to the results of the other study; radiologists were additionally randomized to reviewing either 2-dimensional images only or a combination of 2-dimensional and 3-dimensional images. If a lesion 10 mm or larger was detected on CT colonography but not on the initial optical colonoscopy, a second "unblinded" optical colonoscopy was scheduled 90 days later. The average age of the study participants was 58 years, 48% were men, and 9% had a family history of polyps or colon cancer. The sensitivity of CT colonography increased with lesion size; on a per patient basis, it was only 65% for detection of lesions of at least 5 mm, 84% for detection of lesions of at least 7 mm, and 90% for detection of lesions of at least 10 mm in diameter. The corresponding sensitivies on a per polyp basis were 59%, 75%, and 84%, respectively. Specificity was 86% for lesions of at least 10 mm, resulting in a positive predictive value of only 23% and negative predictive value of 99%. Using a cutoff of 5 mm for referral, 17% of patients would have been referred for follow-up colonoscopy, and approximately 1 in 4 would have actually had a large polyp or cancer. Sensitivity also varied considerably between radiologists, from less than 70% to 100%, and was not associated with the number of examinations.
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