A prospective study of the accuracy and concordance between in-situ and postfixation measurements of colorectal polyp size and their potential impact upon surveillance

OBJECTIVES: To determine the differences between in-situ, prefixation and postfixation colorectal polyp measurements, their clinical impact upon determining adenoma surveillance intervals, and to compare postfixation measurements using three different devices. PATIENTS AND METHODS: A prospective study of 107 colorectal polyps resected from 65 consecutive patients (45 men, 20 women) undergoing colonoscopy as part of the Bowel Cancer Screening Programme was undertaken. The polyps were measured in situ, prefixation (study gold standard) and using three measurement devices (ruler, callipers and magnifying lens) postfixation in formalin. RESULTS: Prefixation ruler measurements were significantly higher than in-situ (P=0.02) and postfixation ruler measurements (P=0.04). No significant difference was observed between in-situ and postfixation ruler measurements (P=0.36), although in-situ measurements were more variable. In-situ measurements also generated more variation in surveillance intervals than postfixation measurements (9.3 vs. 5.6%). No significant difference was seen between measurements obtained by the three different devices postfixation (P=0.89). CONCLUSION: This study provides evidence supporting the use of postfixation polyp size measurements as advised by recent European pathology colorectal cancer screening recommendations. In the absence of a clinically significant difference between measurement devices, we advise the ruler to be used as a standard for postfixation measurements because of its widespread availability.