Contrast coating for the surface of flat polyps at CT colonography: a marker for detection

To assess the frequency of oral contrast coating of flat polyps, which may promote detection, and influencing factors within a screening CT colonography (CTC) population.

This was a retrospective, observational study performed at one institution. From 7,426 individuals, 123 patients with 160 flat polyps were extracted. Flat polyps were defined as plaque-like, raised at most 3 mm in height and reviewed for contrast coating. Factors including demographic variables such as age and sex, and polyp variables such as polyp size, location and histology were analysed for effect on coating.

Of 160 flat polyps (mean size 9.4 mm ± 3.6), 78.8 % demonstrated coating. Mean coat thickness was 1.5 mm ± 0.6; 23.8 % (n = 30) demonstrated a thin film of contrast. Large size (≥10 mm) and proximal colonic location (relative to splenic flexure) were predictive variables by univariate logistic regression [OR (odds ratio) 3.4 (CI 1.3-8.9; p = 0.011), 2.0 (CI 1.2-3.5; p = 0.011), respectively]. Adenomas (OR 0.37, CI 0.14-1.02; p = 0.054) and mucosal polyps or venous blebs (OR 0.07, CI 0.02-0.25; p < 0.001) were less likely to coat than serrated/hyperplastic lesions. Age and sex were not predictive for coating (p = 0.417, p = 0.499, respectively).

Surface contrast coating is common for flat polyps at CTC, promoted by large size, proximal location and serrated/hyperplastic histology. Given the difficulty in detection, recognition may aid in flat polyp identification.

• Oral contrast coats the surface of most flat colorectal polyps at CT colonography. • Large size, proximal colonic location and serrated/hyperplastic histology increase polyp coating. • Contrast coating increases diagnostic confidence for flat polyps. • Contrast coating may help in flat polyp detection at CTC.