AJR:193, November 2009
James E. Duncan, Michael P. McNally, W. Brian Sweeney, Andrew B. Gentry, Duncan S. Barlow, Donald W. Jensen, Brooks D. Cash
OBJECTIVE. The purpose of this study was to determine the discrepancy between CT colonography (CTC) and optical colonoscopy (OC) measurements for both anus-to-cecum length and anus-to-polyps distance and then determine whether a conversion factor could be generated to equate these CTC and OC distances.
MATERIALS AND METHODS. We retrospectively reviewed CTC and OC reports from patients who had undergone both procedures as part of an established protocol. The anus-to-cecum measurement recorded on a single proprietary CTC workstation was com_pared with the OC cecal length for each patient. Likewise, anus-to-polyp distances were com_pared as measured by the radiologist and endoscopist.
RESULTS. Three hundred thirty-eight patients and 437 polyps were identified with com_plete data from both CTC and same-day OC. The average anus-to-cecum distance measured at CTC was 189 cm (range, 75-257 cm) and at OC, 108 cm (range, 65-150 cm). For polyps proximal to the splenic flexure (n = 145), the CTC anus-to-polyp measurement was on aver_age 1.7 times that measured at OC. For left-sided polyps (n = 292), the CTC measurement was, on average, within 12 cm or 1.3 times that of the OC anus-to-polyp measurement. All the differences between CTC and OC measurements of cecal length and polyp distances were found to be statistically significant using a paired Student's t test of means (p < 0.001).
CONCLUSION. Anus-to-cecum and anus-to-polyp distances are disparate but com_parable using a conversion factor of 0.57 for the CTC anus-to-cecum measurement and 0.59 for right-sided CTC anus-to-polyp or 0.78 for left-sided CTC anus-to-polyp measurements. These anus-to-polyp conversion factors could potentially augment current CTC guidelines for accurate and precise polyp localization and removal at endoscopy.