Autoimmune pancreatitis:Multimodality non-invasive imaging diagnosis

Autoimmune pancreatitis(AIP)is characterized by obstructive jaundice,a dramatic clinical response to steroids and pathologically by a lymphoplasmacytic infiltrate,with or without a pancreatic mass.Type 1AIP is the pancreatic manifestation of an Ig G4-related systemic disease and is characterized by elevated Ig G4serum levels,infiltration of Ig G4-positive plasma cells and extrapancreatic lesions.Type 2 AIP usually has none or very few Ig G4-positive plasma cells,no serum Ig G4 elevation and appears to be a pancreas-specific disorder without extrapancreatic involvement.AIP is diagnosed in approximately 2%-6%of patients that undergo pancreatic resection for suspected pancreatic cancer.There are three patterns of autoimmune pancreatitis:diffuse disease is the most common type,with a diffuse,"sausage-like"pancreatic enlargement with sharp margins and loss of the lobular contours;focal disease is less common and manifests as a focal mass,often within the pancreatic head,mimicking a pancreatic malignancy.Multifocal involvement can also occur.In this paper we describe the features of AIP at ultrasonography,computed tomography,magnetic resonanceand positron emission tomography/computed tomography imaging,focusing on diagnosis and differential diagnosis with pancreatic ductal adenocarcinoma.It is of utmost importance to make an early correct differential diagnosis between these two diseases in order to identify the optimal therapeutic strategy and to avoid unnecessary laparotomy or pancreatic resection in AIP patients.Non-invasive imaging plays also an important role in therapy monitoring,in follow-up and in early identification of disease recurrence.