Pickhardt PJ et al. (2004) Location of adenomas missed by optical colonoscopy. Ann Intern Med 141: 352–359

Optical colonoscopy (OC) is well-established as the method of choice for detecting colorectal neoplasms. Estimates of its sensitivity, however, have relied on subsequent polyp detection by the same technique. Pickhardt and colleagues have completed the first study of the OC adenoma miss rate using a separate reference standard.

The study was part of a multicenter trial evaluating the performance of three-dimensional virtual colonoscopy (VC). A total of 1,233 asymptomatic adults who had been referred for colorectal cancer screening were subjected to same-day VC and OC. The prospective OC was carried out without knowledge of the VC interpretation. After unblinding of the VC results, a second-look OC was carried out in all cases where polyps had been missed.

Of 511 polyps (≥5 mm) detected by second-look OC, 55 (10.8%) were missed by the prospective OC. Second-look OC revealed that 21 of these were adenomatous polyps (≥6 mm). Fifteen of the missed neoplasms were nonrectal and the majority of these were located on the backside of a fold. The remaining six missed adenomas were in the rectum, and were within 10 cm of the anal verge in five cases. The OC miss rate for large (≥10 mm) adenomas was 12%.

Pickhardt et al. conclude that using VC as a reference standard had revealed a higher OC miss rate than had previously been reported. Although OC is a sensitive method for detecting colorectal neoplasia, they note that there are distinct 'blind spots' where important lesions may be missed.