A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps

Background Virtual colonoscopy is a new method of imaging the colon in whic h thin-section, helical computed tomography (CT) is used to generate high-r esolution, two-dimensional axial images. Three-dimensional images of the co lon simulating those obtained with conventional colonoscopy are then recons tructed off-line. We compared the performance of virtual and conventional c olonoscopy for the detection of colorectal polyps. Methods We prospectively studied 100 patients at high risk for colorectal n eoplasia (60 men and 40 women; mean age, 62 years). We performed virtual co lonoscopy immediately before conventional colonoscopy. We inserted a rectal tube and insufflated the colon with air to the maximal level that the pati ent could tolerate. We administered 1 mg of glucagon intravenously immediat ely before CT scanning to minimize the degree of smooth-muscle spasm and pe ristalsis and to reduce the patient's discomfort. Results The entire colon was clearly seen by virtual colonoscopy in 87 pati ents and by conventional colonoscopy in 89. Fifty-one patients had normal f indings on conventional colonoscopy. In the other 49, we identified a total of 115 polyps and 3 carcinomas. Virtual colonoscopy identified all 3 cance rs, 20 of 22 polyps that were 10 mm or more in diameter (91 percent), 33 of 40 that were 6 to 9 mm (82 percent), and 29 of 53 that were 5 mm or smalle r (55 percent). There were 19 false positive findings of polyps and no fals e positive findings of cancer. Of the 69 adenomatous polyps, 46 of the 51 t hat were 6 mm or more in diameter (90 percent) and 12 of the 18 that were 5 mm or smaller (67 percent) were correctly identified by virtual colonoscop y. Although discomfort was not specifically recorded, none of the patients requested that virtual colonoscopy be stopped because of discomfort or pain . Conclusions In patients at high risk for colorectal neoplasia, virtual and conventional colonoscopy have similar efficacy for the detection of polyps 6 mm or more in diameter. (N Engl J Med 1999;341:1496-503.) (C) 1999, Massa chusetts Medical Society.