The pathologic 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 measurement by pathologists would seem to be an accurate alternative, but tissue fixation may alter polyp size. To evaluate methods of determining polyp size, we compared endoscopists' estimates and pathologists' measurements with measurements made by an independent examiner.

METHODS: Polyps were measured by an independent investigator before and after formalin fixation. The investigator's measurement before fixation (the "gold standard") was compared with the endoscopists' estimates and the pathologists' measurements.

RESULTS: Ten endoscopists removed 61 polyps with a snare in 33 patients: 82% were adenomatous and 72% were pedunculated. Mean size was 0.85 +/- 0.6 cm (SD) (range: 0.3 to 3.6 cm, 26% > or = 1 cm). Polyps remained in formalin for a mean of 239 minutes (46 to 1164 minutes). Polyps neither consistently shrank nor enlarged in formalin (maximum change +/- 0.2 cm, r = 0.99 [p < 0.001]). Interobserver agreement between pathologists' and the investigator'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). Polyp size was underestimated in three instances (range 0.5 to 0.9 cm) and 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 cm threshold. Results were not dependent on endoscopist, histology, or polyp location.

CONCLUSIONS: (1) Polyp size is not significantly affected 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 practice.