CT colonoscopy has 90 percent agreement rate with optical colonoscopy

Nearly 90% of colon polyps greater than or equal to 6 mm in size detected at CT colonoscopy were demonstrated to represent true polyps at subsequent optical colonoscopy (the traditional method of viewing the colon and removing precancerous growths), according to a new study by researchers from the University of Wisconsin Hospital and Clinics in Madison, WI.

"We analyzed the findings of 363 CTC-detected lesions in 244 patients who subsequently underwent optical colonoscopy," said Tyler Prout, MD, lead author of the study. The researchers found that optical colonoscopy verified the presence of polyps in 321 of the 363 CTC-detected instances, making for an overall positive predictive value of 88.4%, he said. In addition, the combined group of polyps with either sessile or pedunculated morphology yielded a matching lesion at optical colonoscopy 91.8% of the time, Dr. Prout added.

"From a practical standpoint, this is very important, because if CTC is to be an effective screening tool it, must not only have a high sensitivity, but have sufficiently high concordance rate at subsequent optical colonoscopy to avoid unnecessary colonoscopies," said Dr. Prout.

Exact polyp size had little effect on the concordance rate, said Dr. Prout. "In our more recent experience, we do nearly as well detecting the smaller 6-7 mm polyps as those that are 1 cm or greater. Moreover, when comparing these results to our earlier experience, we find our positive predictive value at the 6-7mm polyp size threshold to be much improved; now 85%, whereas it was previously just over 50%," said Dr. Prout. "We believe that this finding can be attributed to a combination of factors, some of the most important of which include colonic preparation and method of image analysis. Our colonic preparation includes both fluid and stool tagging. For image analysis, we employ a primary 3D evaluation complemented by focused review of 2D multiplanar reformats for confirmation. This is in contradistinction from many studies that utilize primary 2D interpretation," said Dr. Prout.

The full results of this study were presented during the American Roentgen Ray Society's annual meeting in Orlando, FL.