Computed Tomography Colonography: A Current Appraisal

Abstract

Computed tomography (CT) colonography (CTC) is a specialized CT examination of the abdomen and pelvis in which imaging data, combined with advanced imaging software, provides a comprehensive, full structural evaluation of the colorectum using multiple types of image displays. CTC has been in development and in clinical trials since 1996. The radiology scientific literature is rich in reports of its advancement and effectiveness. The purpose of this article is to briefly update the reader on the current estimates of CTC performance, safety, patient acceptance, and other relevant clinical issues. The publication of the National CTC Trial (ACRIN 6664) completed the clinical validation of CTC as a screening application. 1 This trial, the largest to date evaluating the effectiveness of CTC, evaluated 2,600 asymptomatic adults who were prescheduled for colonoscopy screening at 15 centers across the United States (including both academic and private practices). All patients were 50 years of age and had a full bowel preparation before undergoing both state-of-the-art CTC and colonoscopy (which served as the reference standard). The mean standard error sensitivity, specificity, positive and negative predictive values, and area under the receiver operating characteristic curve for patients with adenomas 1 cm were 0.90 0.03, 0.86 0.02, 0.23 0.02, 0.99 0.01, and 0.89 0.02, respectively. 1 The sensitivity for adenomas 0.6 cm was 0.78 and 0.8 cm was 0.87, with specificities of 0.88 and 0.87, respectively. These performance estimates are similar to those reported by Pickhardt et al 2 and indicate that CTC can be performed at a high level at many institutions, including community hospitals. These estimates of performance are also similar to those reported for colonoscopy.2 Of CTC screening patients, 12% would have been referred for colonoscopy if a polyp threshold of 6 mm was selected, including CT false positives. Estimates of performance for polyps 5 mm were not possible because readers were instructed not to report lesions smaller than this threshold. Segmental unblinding was not performed, so the performance of colonoscopy was not determined in this trial. The safety profile for CTC is excellent. In the experience of the Working Group on Virtual Colonoscopy, no cases of colon perforation have been reported in 11,000 screening examinations. 3 Of 21,000 total CTC examinations, only 1 perforation occurred, in a patient with an occlusive sigmoid carcinoma, for a perforation rate of 0.005%.3 A higher perforation rate (0.03%) has been reported from the United Kingdom, but is comparable with the perforation risk for barium enema examination. 4 Today, most centers performing CTC use a me