Back-to-back colonoscopy studies have shown that a substantial proportion of colorectal lesions are missed during a single examination, with adenoma miss rates reported between 17% and 28% in the literature. Small, flat, serrated, and right-sided lesions are particularly prone to being overlooked and contribute to interval post-colonoscopy colorectal cancer. We aimed to evaluate the incremental diagnostic yield of a complete second-look colonoscopy performed immediately after a standard high-definition examination.

This prospective study included 67 consecutive adults undergoing screening or surveillance colonoscopy with adequate bowel preparation (Boston score ≥6). After a first complete inspection, an immediate second pass from rectum to cecum was performed under identical conditions. All detected lesions were characterized by size, morphology, and location, and resected. The primary outcome was the proportion of lesions identified exclusively during the second inspection.

The first pass detected 93 polyps; the second pass revealed 30 additional lesions, corresponding to a miss rate of 24.4%, consistent with previously published back-to-back studies. Missed lesions were significantly smaller (mean 4 mm), predominantly flat (Paris IIa), and mostly located in the proximal colon. Histology included tubular adenomas, sessile serrated lesions, and hyperplastic polyps. Subtle borders and pale coloration were common features of missed lesions. The incremental yield was consistent across endoscopists and independent of bowel cleanliness within the inclusion threshold.

Immediate back-to-back colonoscopy substantially improves detection of clinically relevant lesions, particularly serrated and right-sided polyps associated with interval cancer. Selective application of second-look inspection may benefit high-risk patients and provide a valuable quality assessment tool for endoscopy units. Emphasizing slow, meticulous mucosal inspection remains essential to reduce post-colonoscopy colorectal cancer risk.