Introduction Large adenomatous colonic polyps (>10 mm) are associated with an increased risk of development of adenocarcinoma. Recent national guidelines require the ability to distinguish polyps above and below 10 mm in size to determine the optimal surveillance interval.1 There is no standardised technique to measure polyp size either in the literature that underpins current guidelines or in practice. Visual estimation at endoscopy is widely used. Small prospective studies have shown this method to be inaccurate when compared to direct measurement in the pathology department.2 This retrospective study aims to establish the accuracy of visual estimation of polyp size in usual clinical practice comparing to direct measurement.
Methods A search for the word “polyp” was performed on the pathology reports for all colonoscopies and flexible sigmoidoscopies performed during a 1-year period. The pathology and endoscopy reports of the resultant cases were reviewed. Only adenomas completely removed by snare polypectomy without lifting and retrieved intact, where both endoscopic and measured sizes were recorded, and where the measured size was 5 to 15 mm were included. The direct measurement was subtracted from the visual estimate to give a size difference. The paired-sample t-test was used to test the null hypothesis that there was no difference between the mean sizes determined using the two methods for the group as a whole or for individual endoscopists.
Results In a total of 4285 procedures, 79 polyps met the criteria for inclusion. In 39 cases (49%), the difference between visual estimate and direct measurement was >2 mm. In ascertaining whether a polyp was above or below the 10 mm cut-off, visual estimate and direct measurement were discordant in 21 cases (27%). Despite these disparities, there was no overall tendency to over or underestimate polyp size for the group as a whole (mean difference 0.05 mm p=0.88). Of the 15 individual endoscopists, the two with the highest procedure counts both showed significant tendencies to underestimate polyp size, while a third showed significant overestimation.
Conclusion In clinical practice, visual estimation of polyp size is often inaccurate. Individual endoscopists may systematically over or underestimate polyp sizes. Direct measurement should be preferred in determining surveillance intervals.
Competing interests None declared.
References 1. National Institute for Health and Clinical Excellence. Colonoscopic Surveillance for Prevention of Colorectal Cancer. 2011. http://www.nice.org.uk/guidance/CG118
2. Schoen, et al. The pathologic measurement of polyp size is preferable to the endoscopic estimate. Gastrointest Endosc 1997;46:492–6.