Autoimmune pancreatitis

Abstract

This chapter outlines aspects of pancreatic imaging for type 1 autoimmune pancreatitis (AIP). AIP is subclassified as either type 1 (IgG4-related) or type 2 (granulocytic epithelial lesions) according to the International Consensus of Diagnostic Criteria for Autoimmune Pancreatitis. The imaging modalities reviewed are ultrasound (US), computed tomography (CT), and magnetic resonance (MR). Indications for endoscopic retrograde pancreatography (ERP) are also discussed in the context of the imaging findings. When diffuse, sausage-like swelling of the pancreas is demonstrated on US, CT, or MRI, ERP is generally unnecessary. Conversely, when only localized swelling is detected on imaging, ERP is essential to exclude pancreatic cancer. The US findings in the pancreatic parenchyma characteristic of AIP are a hypoechoic area with scattered hyperechoic spots within the region of swelling. Contrast-enhanced CT and MRI demonstrate delayed enhancement and a capsule-like rim around the pancreas in AIP. ERP and magnetic resonance pancreatography (MRP) can reveal irregular narrowings within the main pancreatic duct. These irregular narrowings can be either localized or distributed diffusely within the duct. Side branches arising from narrowed portions of the main pancreatic duct and (noncontinuous) multiple main pancreatic duct (skip lesions) are useful findings in the differentiation from pancreatic cancer. MRP cannot yet characterize irregular narrowing in the main pancreatic duct with sufficient accuracy to exclude pancreatic cancer, but skip lesions are useful to support the diagnosis. ERP is still required to distinguish these lesions in many clinical settings.