Estimating the size of colorectal polyps endoscopically: random guess or systematic error?

Background: Size of colorectal polyps reflects potential for malignancy and helps define advanced lesions. Studies measuring ability of endoscopists to estimate polyp size show significant variation. The aim of this study was to determine if there is a linear relationship between endoscopic and pathologic polyp size.

Methods: Data for adenomas removed completely by snare, in one piece, were retrieved from a prospectively recorded polyp database. Endoscopic estimate of maximum diameter was compared to that on the pathology report by linear regression analysis.

Results: There were 126 polyps in 126 patients, 85 men and 41 women. Mean age was 63.2 ± 12.9 years. Mean endoscopic polyp size was 12.2 ± 9.3 mm and mean pathology size was 9.3 ± 6.9 mm. Endoscopically, 16 polyps were ≤ 5 mm, 62 were from 6 to 10 mm, 21 were from 11 to 15 mm, and 27 were from 16 to 55 mm. Twenty-nine polyps were right sided, 86 were left and 11 were rectal. Regression of endoscopic size against pathology size yielded a significant r of 0.761. Using the regression formula of endoscopic size = 0.7 + 1.175× pathology size an endoscopic estimate of 10 mm (= advanced adenoma) means a pathologic size of 8 mm. For a pathologic size of 10 mm, an endoscopic estimate of 12 mm is needed. A large polyp is ≥20 mm; for this endoscopist a 20 mm polyp is really 16.4 mm.

Conclusions: The relationship between endoscopic and directly measured size is linear over all polyp diameters, and likely represents a systematic error.