Autoimmune pancreatitis (AIP) is a special type of chronic pancreatitis mediated by autoimmunity. The classic manifestation of AIP is diffuse pancreatic enlargement, some of which are characterized by focal enlargement. Clinically, it is divided into diffuse AIP (DAIP) and focal AIP (FAIP) according to morphology. FAIP can be clinically manifested as obstructive jaundice, peripancreatic lymphadenopathy and vascular involvement, which may mimic pancreatic cancer (PC). CT/MRI is the important imaging tool for diagnosing pancreatic diseases. However, due to the overlap of the imaging features of FAIP and PC, it is challenging to differentiate the two by CT/MRI. Endoscopic ultrasound (EUS) can clearly display the pancreatic parenchyma and pancreatic duct system and has become a routine modality for the evaluation of pancreatic diseases. The aim of this study is to construct a diagnosis model for distinguishing between FAIP and PC by comparing the EUS characteristics of the two, and further validate its diagnostic efficacy.

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.

Inclusion Criteria:

• Patients with difficulty in distinguishing between FAIP and PC

Exclusion Criteria:

• Referred patients with a history of having being conclusively diagnosed as AIP or PC; Patients with DAIP; Patients with alcoholic pancreatitis, hypertriglyceridemia pancreatitis or pancreatitis due to gallstones; Patients with pancreatic cystic tumors, pancreatic neuroendocrine tumors or solid pseudopapillary tumors of pancreas; Patients who cannot undergo EUS due to unsuitable conditions.

In derivation sample, the patients conclusively diagnosed as FAIP or PC are retrospectively collected.

In validation sample, the patients with difficulty in distinguishing between FAIP and PC are prospectively enrolled. In the end, the patient with a diagnosis that is neither FAIP nor PC and the patient without conclusive diagnosis are withdrawn from the study.

The protocol of the study is private.