Inaccuracy and Bias in Endoscopic Size Estimation of Large Colorectal Polyps; Insights From a Prospective Cohort of 1828 En‐Bloc Resections

Endoscopic size estimation of large colorectal polyps influences treatment decisions and clinical outcomes; however, its precision remains unclear. This study aimed to assess the accuracy of endoscopic size estimation for colorectal lesions ≥ 20 mm utilizing data from an endoscopic submucosal dissection (ESD) cohort. This post hoc analysis included only en bloc resected lesions treated by ESD. Patients with neuroendocrine tumors, recurrent lesions, colitis-associated dysplasia, or insufficient data were excluded. Size accuracy was defined as a margin of error < 5 mm. Outcomes included the frequency of size errors ≥ 10 mm and ≥ 20 mm, terminal digit preferences in estimated size, and predictors for lesions estimated endoscopically at 20 mm but pathologically ≥ 25 mm. The reference standard was pathological size. Among 1889 lesions (1809 patients), 61 lesions (60 patients) were excluded. Finally, 1828 lesions (1749 patients) were evaluated. The accuracy of endoscopic size estimation was 53.4%. Errors ≥ 10 and ≥ 20 mm occurred in 19.1% and 4.5% of lesions, respectively. Endoscopic size estimation showed a strong terminal digit preference for 0 (65.2%) and 5 (30.0%). Among 366 lesions estimated at 20 mm, 97 (26.5%) were pathologically ≥ 25 mm. Polypoid lesions [odds ratio (OR) 2.8, 95% confidence interval (CI) 1.1-6.8] and laterally spreading tumors granular type (OR 2.0, 95% CI: 1.1-3.5) were predictors of underestimation. Endoscopic size estimation of large colorectal lesions can be inaccurate and influenced by digit bias, underscoring the need for improved measurement techniques (UMIN000010136).