Variation of Agreement in Polyp Size Measurement Between Computed Tomographic Colonography and Pathology Assessment: Clinical Implications

Abstract

Clinical management of polyps discovered by computed tomographic (CT) colonography depends on polyp size. However, size measured by CT colonography is an estimate, and its agreement with other measures is not well characterized. We hypothesized that size measurement by CT colonography varies substantially compared with measurement by other methods. We performed a secondary data analysis of a multicenter study of CT colonography in comparison with colonoscopy. Polyp size was determined by CT colonography, at colonoscopy, and measurement prefixation with a ruler. Agreement was assessed using descriptive statistics and Bland-Altman methodology. Six hundred trial participants completed both tests. Ninety-five percent limits of agreement indicated that estimates of size by CT colonography were between 52% lower to 64% higher than prefixation polyp size estimates. Ninety-five percent limits of agreement stratified by categories of clinical importance indicated that estimates of size by CT colonography were between 44% lower to 84% higher for polyps 0.6 cm or smaller, 44% lower to 44% higher for polyps 0.6 to 0.9 cm, and 48% lower to 22% higher for polyps smaller than 0.6 cm, 44% lower to 44% higher for polyps 0.6 cm to 0.9 cm, and 48% lower to 22% higher for polyps larger than 0.9 cm compared with prefixation estimates. Analysis of participants with 1 identified polyp in the same colon segment showed that categorization based on CT colonography measurement (ie, <0.6 cm, 0.6-0.9 cm, or >0.9 cm) differed from prefixation measurement for 43% of participants. Polyp size estimation by CT colonography varies from prefixation and colonoscopic measures of size. Future studies should clarify whether size estimation by CT colonography is sufficiently reliable as a primary factor to guide clinical management.