A computed tomography scan that provides a “virtual colonoscopy” of the large intestine appears just as adept at detecting colorectal neoplasia as standard optical colonoscopy. Virtual colonoscopy is a rapidly evolving technique in which data from computed tomography (CT) are used to generate both 2-dimensional and 3-dimensional displays of the colon and rectum. In a report in the December 4 issue of The New England Journal of Medicine, a team led by researchers from the National Naval Medical Center in Bethesda, Maryland, says “This minimally invasive method for the examination of the whole colon, also called CT colonography, could provide an attractive alternative for use in widespread screening, since it requires no intravenous administration of sedatives, analgesia, or recovery time.” While the report notes that the performance characteristics of virtual colonoscopy have been encouraging in trials involving cohorts of patients with an increased number of polyps, “the results in populations with a lower prevalence of polyps have been disappointing, and the large studies conducted to date have not evaluated an asymptomatic, average-risk screening population.” In the new study, 1233 asymptomatic adults (728 men and 505 women; mean age, 57.8 years) underwent same-day virtual and optical colonoscopy. Radiologists used the 3-dimensional endoluminal display for the initial detection of polyps on CT virtual colonoscopy. For the initial examination of each colonic segment, the colonoscopists were unaware of the findings on virtual colonoscopy, which were revealed to them before any subsequent reexamination. The sensitivity and specificity of virtual colonoscopy and the sensitivity of optical colonoscopy were calculated with the use of the findings of the final, unblinded optical colonoscopy as the reference standard. The sensitivity of virtual colonoscopy for adenomatous polyps was 93.8% for polyps at least 10 mm in diameter, 93.9% for polyps at least 8 mm in diameter, and 88.7% for polyps at least 6 mm in diameter. The sensitivity of optical colonoscopy for adenomatous polyps was 87.5%, 91.5%, and 92.3% for the 3 sizes of polyps, respectively. The specificity of virtual colonoscopy for adenomatous polyps was 96.0% for polyps at least 10 mm in diameter, 92.2% for polyps at least 8 mm in diameter, and 79.6% for polyps at least 6 mm in diameter. Two polyps were malignant; both were detected on virtual colonoscopy, and one of them was missed on optical colonoscopy before the results on virtual colonoscopy were revealed. “Our results show that virtual colonoscopy with a 3-dimensional emphasis is an effective tool for the detection of colorectal neoplasia in asymptomatic adults with an average risk of colorectal cancer. These findings support the concept of a colon-screening center that offers virtual colonoscopy to patients, with the opportunity for same-day or next-day therapeutic optical colonoscopy, if needed. Such an endeavor would require close collaboration among radiologists and gastroenterologists,” the authors conclude. An editorial in the Journal by Dr. Martina M. Morrin, Assistant Professor of Radiology and Dr. Thomas LaMont, Chief of Gatroenterology at Beth Israel-Deaconess Medical Center in Boston, highlight several factors that might account for the new findings: (1) the use of water-soluble and barium contrast material to tag residual fluid and retained stool, thereby enabling the imaging software to digitally remove all opacified fluid and stool from the image by a process known as electronic cleansing. “All virtual colonoscopic studies were performed with the use of multidetector CT scanners, which permit faster, higher-resolution imaging than the single-detector scanners that have been used previously,” they state; (2) the exclusion of hyperplastic polyps may have resulted in higher estimates of the sensitivity of virtual colonoscopy. “At the same time, the classification of hyperplastic polyps as false positive findings resulted in lower estimates of the specificity of virtual colonoscopy,” Morrin and Lamont write; and (3) the use of a primary 3-dimensional approach for the detection of polyps rather than the currently accepted 2-dimensional approach with 3-dimensional imaging used only to resolve uncertainties may have contributed to their high detection rates. Still, the editorial writers say the performance of virtual colonoscopy described in the report “is impressive, with detection rates for adenomas similar to those achieved with conventional colonoscopy. “If the results of this well-designed study are reproducible on a wider scale, and if the important questions regarding the appropriate size threshold and the surveillance of smaller polyps can be resolved, then screening virtual colonoscopy is ready for prime time.” For more details, see N Engl J Med, (December 4), 2003;349:2191–2200.