Location of adenomas missed by optical colonoscopy.

BACKGROUND Previous estimates of the adenoma miss rate with optical colonoscopy (OC) are hindered by the use of OC as its own reference standard. OBJECTIVE To evaluate the frequency and characteristics of colorectal neoplasms that are missed prospectively on OC by using virtual colonoscopy (VC) as a separate reference standard. DESIGN Prospective, multicenter screening trial. SETTING 3 medical centers. PARTICIPANTS 1233 asymptomatic adults who underwent same-day VC and OC. MEASUREMENTS Colorectal neoplasms (adenomatous polyps) missed at OC before VC results were unblinded. RESULTS Fourteen (93.3%) of 15 nonrectal neoplasms were located on a fold; 10 (71.4%) of these were located on the backside of a fold. Five (83.3%) of 6 rectal lesions were located within 10 cm of the anal verge. LIMITATIONS Estimation of the OC miss rate depended on polyp detection on both VC and second-look OC and therefore underestimates the true OC miss rate, particularly for smaller polyps. CONCLUSIONS Most clinically significant adenomas missed prospectively on OC are located behind a fold or near the anal verge. The 12% OC miss rate for large adenomas (>or=10 mm) when state-of-the-art 3-dimensional VC is used as a separate reference standard is increased from the previous 0% to 6% estimates derived by using OC as its own reference standard.