Virtual colonoscopy compared with conventional colonoscopy: a developing technology

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Abstract
Aim To determine the accuracy of computed tomography colography (virtual colonoscopy) in detecting colorectal polyps and colorectal cancer. Design Blinded comparison of virtual colonoscopy (initially supine‐only scans and later supine plus prone scans) with the criterion standard of conventional colonoscopy. Subjects and setting 100 patients aged 55 years or over referred to a public teaching hospital for colonoscopy, July 1997 to January 2000, because of colonic symptoms or a family history of bowel cancer. Main outcome measures Presence and size of polyps and other lesions; certainty of polyp identification on virtual colonoscopy (on 100‐point visual analogue scale); sensitivity and predictive values of virtual colonoscopy. Results Conventional colonoscopy identifed 121 polyps in 47 patients; 28 of these polyps, in 19 patients, were identified by virtual colonoscopy. Sensitivity of virtual colonoscopy for detecting polyps (using supine plus prone scans) was 73% for polyps with diameter ≥ 10mm (95% CI, 39%–94%) and 19% for smaller polyps (95% CI, 10%–31 %) (P < 0.001); corresponding figures for supine‐only scans were 57% (95% CI, 18%–90%) and 11% (95% CI, 4%–24%), respectively. Ten polyps identified at virtual colonoscopy were considered false‐positive findings (8%). The value of finding a polyp on virtual colonoscopy (with thresholds of 5 mm for diameter and 30 points for certainty score) was assessed as a predictor of finding a polyp (diameter > 5 mm) on conventional colonoscopy. Positive and negative predictive values were 88% and 89%, respectively, for supine plus prone scans. Conclusion Although virtual colonoscopy shows potential as a diagnostic tool for colorectal neoplasia, it is currently not sufficiently sensitive for widespread use.