CT colonography proponents scope easier target

November 28, 2004

Proponents of CT colonography may lower the bar in measuring the imaging modality against conventional colonoscopy. After a wave of mediocre sensitivity results, many experts are asking whether it should be compared instead with optical colonoscopy or air contrast barium enema.

CT colonography shows a pedunculated adenoma in the sigmoid colon. The lesion was removed colonoscopically. (Provided by E. Paulson)

Proponents of CT colonography may lower the bar in measuring the imaging modality against conventional colonoscopy. After a wave of mediocre sensitivity results, many experts are asking whether it should be compared instead with optical colonoscopy or air contrast barium enema. The desultory results were presented at the opening CT colonography session on Sunday morning. Session moderator Dr. C. Daniel Johnson, a professor of radiology at the Mayo Clinic, Rochester, described CT colonography's position in the colorectal carcinoma screening arena in medieval terms."It's a jousting match," he said. "We don't know if CT colonography is going to be our Sir Galahad and win the battle for us."The first blow to CT colonography's armor was the presentation of the Duke multicenter prospective comparison of optical colonoscopy, CT colonography, and air contrast barium enema. In 614 patients, the study found that the sensitivity for 1-cm polyps was 48% for air contrast barium enema, 59% for CT colonography, and 98% for optical colonoscopy. For polyps greater than 6 mm, sensitivity was 41% for barium enema, 55% for CT colonography, and 99% for optical colonoscopy, according to Dr. Erik K. Paulson, director of abdominal imaging division at Duke. Despite the lower sensitivities achieved compared with conventional colonoscopy, the study was the first to show that CT colonography was significantly better than air contrast barium enema for polyps greater than 6 mm, Paulson said.In a second study, Dr. Hanno Hoppe from the University Hospital in Bern presented results from a single-center trial comparing CT colonography and conventional colonoscopy. The prospective study examined patients using four-slice CT with 2-mm collimation in both supine and prone positions. Sensitivity by polyp for CT colonography was 71% for polyps greater than 10 mm and 61% for polyps greater than 6 mm. Sensitivity dropped to 50% for polyps 6 to 9 mm in size and 25% for polyps smaller than 5 mm.Sensitivity improved when data were ordered by patient and when smaller polyps were excluded. "CT colonography had a high by-patient sensitivity (95%) and specificity (98%) for detection of clinically important polyps greater than or equal to 10 mm in size," Hoppe said.The 92% sensitivity and 96% specificity achieved by the landmark Pickhardt study last year set radiologists on fire, but this current batch of studies was more in line with the Cotton study and its 67% sensitivity, Johnson said.During a panel discussion at the end of the session, the consistent release of lower sensitivity results may have led experts to question whether CT colonography shouldn't be compared not with optical colonoscopy at this point, but rather with barium enema and other tests used for colon cancer detection."For now, I think radiologists should keep as many imaging tools as we can in our tool belt for imaging the colon," Johnson said. "This session shows that for CT colonography, we're just not there yet."For more information from the online Diagnostic Imaging archives:Duke study renews challenge of CT colonographyRadiologists enter round two of colonoscopy debate3D virtual colonoscopy gets thumbs upVirtual colonoscopy