THE PATHOLOGICAL MEASUREMENT OF POLYP SIZE IS PREFERABLE TO THE ENDOSCOPIC ESTIMATE

Background: There is no standardized technique to measure polyp size. Estimation of polyp size at endoscopy is difficult. Polyp size measure ment by pathologists would seem to be an accurate alternative, but tis sue fixation may alter polyp size. To evaluate methods of determining polyp size, we compared endoscopists' estimates and pathologists' meas urements with measurements made by an independent examiner. Methods: P olyps were measured by an independent investigator before and after fo rmalin fixation. The investigator's measurement before fixation (the ' 'gold standard'') was compared with the endoscopists' estimates and th e pathologists' measurements. Results: Ten endoscopists removed 61 pol yps with a snare in 33 patients: 82% were adenomatous and 72% were ped unculated. Mean size was 0.85 +/- 0.6 cm (SD) (range: 0.3 to 3.6 cm, 2 6% greater than or equal to 1 cm). Polyps remained in formalin for a m ean of 239 minutes (46 to 1164 minutes). Polyps neither consistently s hrank nor enlarged in formalin (maximum change +/- 0.2 cm, r = 0.99 [p < 0.001]). Interobserver agreement between pathologists' and the inve stigator's post-formalin measurements showed that 55 of 57 polyps (97% ) were within +/- 0.3 cm. Endoscopists inaccurately estimated 11 of 56 polyps (20%) (> 0.3 cm difference from the independent examiner). Pol yp size was underestimated in three instances (range 0.5 to 0.9 cm) an d overestimated in eight (range 0.4 to 0.8 cm). In 5 of 11 instances ( 46%), this inaccuracy altered polyp size classification across the 1 c m threshold. Results were not dependent on endoscopist, histology, or polyp location. Conclusions: (1) Polyp size is not significantly affec ted by formalin fixation; 2) Endoscopists' estimates of polyp size are often unreliable; and, when possible, (3) Pathologists' measurements of polyp size should be used in clinical trials and in clinical practi ce.