I Once Caught a Fish This Big: Endoscopists' Estimate of Polyp Size

Abstract

Background: Polyp size ≥1cm has important implications for surveillance recommendations as well as risk for development of colon cancer. No study has looked at how accurately endoscopists estimate polyp size over an extended period of time while eliminating observation bias (the Hawthorne effect). Aim: To examine the accuracy with which endoscopists estimate polyp size, and determine how frequently an inaccurate estimate may lead to an inappropriate surveillance regimen. Methods: We performed a retrospective analysis linking our endoscopy database to pathology results over a 3-year period. The Hawthorne effect (bias created when the act of observation changes the outcome) was minimized due to the retrospective nature of this study. Only pedunculated polyps that were completely removed by snare and retrieved intact were included in this study. The estimate of the polyp size was recorded and compared to the pathologists' measurement (the gold standard). Patient age, the adequacy of preparation, the location of the polyp, the histopathology of the polyp, and whether a training fellow was involved were recorded. Linear regression was employed to examine predictors of accurate polyp size estimation. Results: 206 consecutive polyps were included in this study. The average age (±SD) of the subjects was 59.4 years (±12.2). 86% of the polyps were removed from the recto-sigmoid colon. The mean estimate of the largest dimension was 1.2cm (±0.6cm). The mean largest dimension measured by pathologists was 1.1cm (±0.7cm). In 61/206 polyps (29.6%), the estimate of polyp size was ≥1cm while the actual size was <1cm. The mean difference between estimated and actual size in this group was 0.4cm (±0.3cm). In 8/206 patients (3.8%), the estimate of polyp size was <1cm while actual size was ≥1cm. The mean difference in this group was 0.3cm (±0.1cm). As the polyp size increased, the difference between estimated and actual polyp size decreased (p<0.0001). No other variable predicted accuracy. Conclusions: Gastroenterologists often overestimate polyp size during routine colonoscopy. In over 30% of cases, this inaccuracy may have led to inappropriate surveillance recommendations. While larger polyps are more likely to be accurately sized, the age of the patient, the quality of the preparation, the location of the polyp, and whether a training fellow was assisting do not predict inaccuracy.