Autoimmune pancreatitis: Multimodality non-invasive imaging diagnosis

Abstract

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 1 AIP is the pancreatic manifestation of an IgG4-related systemic disease and is characterized by elevated IgG4 serum levels, infiltration of IgG4-positive plasma cells and extrapancreatic lesions. Type 2 AIP usually has none or very few IgG4-positive plasma cells, no serum IgG4 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 resonance and 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.

IgG4-Unrelated Type 1 Auto Immune Pancreatitis Manifesting with Pancreatic Head Mass Mimicking Cancer

“…At MRI the involved portion is hypointense on T1-weighted images, slightly hyperintense on T2-weighted images, and has heterogeneously diminished enhancement in the early phase and delayed enhancement in the late phase of contrast enhancement. The capsule-like rim is usually hypointense on both T1 and T2-weighted images, and has delayed moderate enhancement on contrast-enhanced MR[2]. All these features were present in our patient.Magnetic resonance cholangiopancreatography (MRCP) has become popular as a noninvasive method for obtaining high quality images of the pancreaticobiliary tree but there has been a controversy in usefulness of MRCP in diagnosis of AIP.…”

“…Response to steroids is based on objective data such as radiologic evidence a dramatic decrease in the pancreatic mass or other organ involvement, resolution of the obstructive jaundice without biliary stenting, and normalization of liver function tests. If there is no such improvement or if the cancer antigen 19.9 level is rising, then the diagnosis of AIP should be reconsidered [2]. Our patient has responded dramatically to the steroid therapy both clinically and radiologically, confirming the diagnosis of type 1 AIP.…”

“…It was first characterized in 1961 from a patient showing signs of pancreatic damage with associated au-How to cite this paper: Arrami, A., Billah, N.M., Addioui, T. and Nassar, I. toimmunity. The term AIP was first used in 1995 by Yoshida et al to describe a type of chronic pancreatitis associated with a Sjogren-like syndrome [2]. In 2002, the Japan Pancreas Society (JPS) proposed the world's first clinical diagnostic criteria for AIP (JPS 2002) [3], which was revised in 2006 (JPS, 2006).…”

“…In 2002, the Japan Pancreas Society (JPS) proposed the world's first clinical diagnostic criteria for AIP (JPS 2002) [3], which was revised in 2006 (JPS, 2006). Subsequently, the International Consensus Diagnostic Criteria (ICDC) was proposed in 2011 and AIP was divided into type 1 and type 2 with distinct histopathology and clinical features [2] [3]. Type 1 is more frequent than type 2 and shares some clinical, biological and radiological features with PC making the differential diagnosis very difficult [1].…”

“…Bile duct abnormalities can be also recognized; these include smooth narrowing of the intrapancreatic portion of the common bile duct, or irregularity and stricturing of the intra-and extra-hepatic bile ducts with features similar to those seen in primary sclerosing cholangitis. Enhancing duct wall thickening is also a recognized feature and, less commonly, intra-hepatic bile duct dilation may also be observed[2] [6].At DWI, AIP and PC are both detected as high signal intensity areas at high b-values images; however, PC usually presents as a solitary area, while diffuse or multiple high-intensity areas are suggestive for AIP. It has been found that mean ADC values are significantly lower in AIP than in PC, which has ADC values lower than normal pancreatic parenchyma.…”