Histologic and imaging features of mural nodules in mucinous pancreatic cysts

Mural nodules predict malignancy within pancreatic cysts, but it is not clear whether endoscopic ultrasound (EUS) and computed tomography (CT) accurately identify nodules. We assessed images and the histology of mural nodules in branch duct intraductal papillary mucinous neoplasms (BD-IPMNs) and mucinous cystic neoplasms (MCNs) and identified criteria to distinguish mural nodules from mucus.

We reviewed pathology specimens and EUS and CT images from consecutive patients with resected BD-IPMNs or MCNs. A blinded interobserver study of the EUS images was then conducted to identify features that distinguished nodules from mucus. After education about these features, the raters interpreted the EUS images again.

On the basis of histologic analysis, 22 of 57 cases had epithelial nodules. Cancer or high-grade dysplasia was found in 23% of cysts with nodules versus 3% without nodules (P = .02). On the basis of reports, EUS detected epithelial nodules with 75% sensitivity and 83% specificity, whereas these values were 24% and 100%, respectively, for CT. Mucus accounted for 65% of intracystic lesions detected by EUS and was often diagnosed by using change in body position and fine-needle aspiration. Interobserver analysis identified 3 features that were detected by EUS (echogenicity, edge, and rim) that distinguished mucus from epithelial nodules. The diagnostic accuracy of the raters improved from a mean of 57% to 79% after education about these features (P = .004); accuracy was 90% when all 3 features of mucus were present.

Malignancy is associated with epithelial nodules in BD-IPMNs and MCNs, but most echogenic lesions detected in cysts by EUS are mucus. Knowledge of features that discriminate mucus from mural nodules improves the diagnostic accuracy of EUS.