CT diagnosis of gallbladder adenomyomatosis: importance of enhancing mucosal epithelium, the 'cotton ball sign'

To determine the diagnostic value of the cotton ball sign and other CT features in patients with gallbladder (GB) wall thickenings (WTs). Three blinded readers reviewed the preoperative CT and MR images of 101 patients with pathologically confirmed GB adenomyomatosis (GA) (n = 34) and other benign (n = 29), malignant (n = 41), and premalignant (n = 2) GBWTs. Three readers analysed the morphological features of GBWT and presence of the “cotton ball sign”, defined as fuzzy grey dots in GBWT or a dotted outer border of the inner enhancing layer on contrast-enhanced (CE) CT. In addition, the “pearl necklace sign” on MR was analysed. In the GA group (n = 34), prevalence of the cotton ball sign and pearl necklace sign was 74% (25/34) and 44% (15/34), respectively. Presence of the cotton ball sign, smooth contour of the mucosa, double-layering enhancement, and enhancement degree weaker than the renal cortex on CT images were significant predictors of benign GBWT (p < 0.01). When differentiating GA from GB malignancy or premalignancy, accuracy of the cotton ball sign and pearl necklace sign was 81% (62/77) and 74% (57/77), respectively. The cotton ball sign on CE-CT showed higher sensitivity and comparable specificity to those of the pearl necklace sign in differentiating GA from malignancy. • Prevalence of the cotton ball sign on CT was 74% in gallbladder adenomyomatosis. • The cotton ball sign was useful in differentiating gallbladder adenomyomatosis from gallbladder cancer. • The cotton ball sign was more sensitive than the pearl necklace sign for adenomyomatosis diagnosis.