A derivation sample is established by retrospectively collecting the EUS images of about 100 FAIP patients and about 200 PC patients who were diagnosed for the first time in Peking Union Medical College Hospital in the past 6 years and underwent EUS at the same time. The parenchymal and ductal changes of pancreas were defined according to the Rosemont criteria. The parenchymal characteristics included hyperechoic foci/strands and lobularity, and the ductal changes included main pancreatic duct (MPD) dilation. Other EUS characteristics not included in the conventional criteria were described based on the literatures, including pancreatic diffuse hypoechogenicity, focal hypoechogenicity, pancreatic diffuse enlargement, focal enlargement, peripancreatic hypoechoic margin, common bile duct (CBD) dilation, bile duct wall thickening, lymphadenopathy and vessel involvement. The EUS characteristics of the two groups of patients are included in the multivariate stepwise logistic regression and receiver operating characteristics (ROC) analyses to construct a differential diagnosis model in derivation sample. Further, the differential diagnosis model will be prospectively validated by calculating the sensitivity and specificity in about 90 patients who are going to undergo EUS due to the difficulty in distinguishing between FAIP and PC. Diagnosis of AIP meets the revised Mayo clinic criteria (revised HISORt criteria) including features of histology, imaging, serology, other organs involvement and response to steroid therapy. Diagnosis of pancreatic duct adenocarcinoma is confirmed by surgical pathology or by cytology/histology after EUS-guided fine needle aspiration or biopsy.
