Duct-penetrating sign at MRCP: Usefulness for differentiating inflammatory pancreatic mass from pancreatic carcinomas

PURPOSE: To define the duct-penetrating sign at magnetic resonance (MR) cholangiopancreatography (MRCP) and to assess the usefulness of this sign for distinguishing an inflammatory pancreatic mass (IPM) from a conventional pancreatic carcinoma (CPC) compared with arterial phase computed tomography (hereafter, CT) and arterial phase MR imaging (hereafter, MR imaging). MATERIALS AND METHODS: MRCP, CT, and MR images were compared by means of receiver operating characteristic (ROC) analysis for 11 IPMs and 43 CPCs. With the MRCP images, a morphologic classification of the main pancreatic duct (MPD) was attempted for all lesions. On the basis of this classification and the enhancement patterns of a lesion, all readers graded the presence of IPM or CPC on a five-point scale for all images. RESULTS: On the MRCP images, the morphologic characteristics of the MPD were nonobstruction for IPM (28 of 33, 85%) and obstruction or irregular stenosis for CPC (124 of 129, 96%). At ROC analysis among all the techniques, MRCP images had the highest value (0.98) for significant areas under the ROC curve (CT, 0.84; MR, 0.76) (P <.001). For the duct-penetrating sign in the broad sense (nonobstructed MPD) and the sign in the narrow sense (only normal MPD), the sensitivity, specificity, and accuracy for diagnosis of IPM were 85%, 96%, and 94%, respectively, and 36%, 100%, and 87%, respectively. CONCLUSION: The duct-penetrating sign on MRCP images was more helpful to distinguish IPM from CPC than were the enhancement patterns on CT and MR images.