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Screening


52 year old man evaluated for screening shows a pedunculated polyp in the sigmoid colon on the 2-D axial image on the left and the 3-D endoluminal image on the right (white arrows).

There have been few published series comparing virtual colonoscopy and conventional colonoscopy for cancer screening (46, 55, 57). In a series of 42 patients with no symptoms having screening virtual colonoscopy and conventional colonoscopy, 67 percent of polyps 6 mm or wider were detected during the virtual colonoscopy (46). Sensitivity for polyps 5 mm or less in diameter was 20 percent. A report by Rex et al. on 46 patients being screened by virtual colonoscopy and traditional colonoscopy showed not only a low sensitivity of virtual colonoscopy in detecting small polyps (11 percent for polyps 5 mm or less in diameter) but also larger flat lesions as well (55). In this study, only 1 of 4 flat adenomas measuring more than 2 cm in diameter that were revealed with conventional colonoscopy were detected with virtual colonoscopy. The results of this study seem to suggest that virtual colonoscopy may not be an accurate screening test for colorectal polyps. However, as pointed out in an associated editorial on this series of patients, it is too early to pass judgment on virtual colonoscopy based on this single report (58). As with all new techniques, there is a learning curve and as experience with virtual colonoscopy increases, so will performance characteristics (25). Importantly, in these screening studies, virtual colonoscopy was done using single or dual-slice helical CT scanners with 5 mm collimation. Current technology allows for collimation of 1 mm or less.