The difference in colon polyp size before and after removal

Background: Accurate knowledge of polyp size is important in assessing cancer risk in both clinical studies and individual patients. We sought to determine if a difference exists between the endoscopic estimation of colon polyp size and the actual measurement after removal. Methods: We measured polyps in a systematic fashion. Using open biopsy forceps as a guide, the largest diameter of 31 pedunculated polyps was estimated endoscopically. The polyp was then removed by snare polypectomy and directly measured by a technician who was blinded to the endoscopic estimate. Each polyp was also measured after formalin fixation by a pathologist who was blinded to previous measurements. Results: There was a significant difference between the endoscopic estimates and the postoplypectomy measurements. Endoscopic estimates on average were 1.6 mm greater than the postpolypectomy measurements (p<0.005), representing an 18% difference. Twenty-three of the 31 (74%) endoscopic estimates were larger than the postopolypectomy measurements. There was not a significant difference between the postpolypectomy and postfixation measurements. Conclusions: The size of polyps measured endoscopically is significantly larger on average than postpolypectomy measurements. This is most likely due to factors involved in the removal of the in vivo polyp.