Is in vivo measurement of size of polyps during colonoscopy accurate?

Purpose: Estimation of size of endoscopic lesions even by experienced endoscopists is inaccurate as shown by recent studies. We undertook this prospective study to determine the accuracy of measuring polyps during colonoscopy. Methods: After informed consent 83 consecutive polyps seen on colonoscopy done for clinical indications were measured by 1) visual estimation, 2) open biopsy forceps method, 3) aligning an Olympus linear probe (which had 2 mm markings up to 2 cm at the flexible distal end of the probe) parallel to the polyp, 4) Measuring the retrieved polyp against a ruler and 5) Pathologist's measurement of the formalin fixed polyp. Actual size of the polyp measured outside the body was taken as the standard against which other measurements were compared. Mean size, mean difference versus actual size (with 95% confidence limit), percentile difference versus the actual and Pearson correlation with the actual size were assessed. The paired t-test was used to compare actual to the other four methods. Inferences were made at the 0.05 level of significance. Results: 43 polyps were 5 mm or less, 30 were 6 to 10 mm and 10 were more than 10 mm in size. For all polyps the linear probe measurement agreed closely (0.91 on Pearson correlation with 95% CI of 0.34 to 0.40) with the actual followed closely by visual estimation. Conclusions: Polyp size estimation correlates best with the actual size if a linear probe is used and visual estimation is the next best. Open forceps method which is used in many studies is the least accurate way of measuring polyp size.