Teaching Case

A patient with mild upper abdomen pain underwent US examination that depicted a focal lesion of the head and the uncinate process of the pancreas, associated to dilation of the common bile duct. CT examination confirmed these findings.

The patient came at our attention with mild upper abdominal pain. No history of alcohol abuse and liver or pancreatic diseases was relevated, but solely previous treatment with radioiodine for thyroid hyperthyroidism (Grave’s disease). Laboratory examination revealed increased serum levels of alkaline phosphatase (896 U/l), γ-glutamyl transferase (761 U/l), alanine transaminase (96 U/l) and aspartate transaminase (265 U/l). Ca19.9, IgG and pancreatic enzymes were normal. US detected a hypoechoic mass-like enlargement of the head and uncinate process of the pancreas. The common bile duct was dilated (9mm), and the main pancreatic duct was normal (figure 1). After US contrast-medium administration, the lesion showed a quite homogeneous enhancement in the early phase (15-20”) with a greater gradual wash-out than the surrounding pancreatic parenchyma (figure 2). Multidetector CT confirmed the presence of the lesion, associated to compression of the distal tract of the common bile duct (figure 3-11). On unenhanced images the lesion appeared hypoattenuating compared with the surrounding pancreatic parenchyma while (figure 4) and after contrast medium administration, it showed a poor enhancement in the pancreatic phase (40”) (figure 5-6), an isodense aspect in the venous phase (70”) (figure 7-8) and a slightly hyperdense pattern in the delayed acquisition (180”) (figure 10). Few dilated small pancreatic ducts with periductal enhancement were depicted within the mass. Peripancreatic lymph-nodes were visualized. Dilation of the main pancreatic duct, calcifications and atrophy of the gland body-tail were not observed. The patient underwent pancreaticoduodenectomy and pathological examination revealed focal autoimmune pancreatitis (AIP) and hyperplastic lymph-nodes.

AIP is a disease characterized by peculiar pathologic findings (fibrosis and lymphocyte infiltration), laboratory data (increased serum IgG levels and autoantibody), and effectiveness of corticosteroid therapy. AIP shows a male preponderance and affects usually patients in fifth-seventh decades. Association with other autoimmune diseases (for example Grave’s disease) has been reported. Pathologically, AIP is classified in diffuse and focal type, which usually involves the pancreatic head. Lymphocytic inflammatory infiltrate, fibrotic changes and variable degree of parenchymal atrophy are the main histologic features. Patients may present with obstructive jaundice, mild upper abdominal pain, weight loss and easy fatigability. Laboratory examinations may show an increased levels of IgG and/or IgG4 and the presence of autoantibodies (antinuclear, anti-carbonic anhydrase antibodies, etc.) pointing out the autoimmune origin of this disease. US examination depicts homogeneous, low echogenic, diffuse or focal enlargement of the pancreas, sometimes associated with dilation of the intrahepatic and common bile ducts. After US contrast-media administration, the involved pancreatic parenchyma shows from mild to moderate hyperechoic enhancement, related to the grade of inflammatory involvement and its fibrotic evolution. On CT, the diffuse type of AIP appears as a uniform swelling of the pancreas with well-defined outline. Sometimes it can be observed an hypodense rim-like capsule surrounding the pancreas showing a delayed post-contrast enhancement (related to fibro-inflammatory changes involving peripancreatic adipose tissue). In the focal type, CT examination depicts a mass-like lesion located in the head and/or in the uncinate process. Before contrast-medium administration, this focal enlargement typically has smooth margins and it appears homogeneous and iso-hypoattenuating respect the surrounding pancreas. On contrast-enhanced images the lesion usually shows a hypodense appearance in pancreatic phases and become isodense or slightly hypodense in the venous phase. Dilation of the main pancreatic duct and biliary tree may be depicted. Parenchymal calcifications, pseudocysts, vascular invasion, inflammatory involvement of the mesentery, the anterior pararenal fascia and the lateroconal fascia are typically absent. MR examination demonstrates a homogeneous, focal/diffuse pancreatic enlargement, generally hyper-isointense in T2-weighted images and hypointense in T1-weighted sequences compared to the liver. In gadolinium-enhanced T1-weighted images, the involved pancreatic parenchyma shows a homogeneous enhancement. A capsule-like rim surrounding the pancreas appears as a hypointense peripheral band on both T1 and T2-weighted images and may show delayed enhancement. MRCP and ERCP often show diffuse/focal narrowing of the pancreatic duct. In the absence of supporting clinical findings and serologic marker levels, a focal form of autoimmune pancreatitis may be extremely difficult to differentiate from pancreatic cancer on the basis of imaging features alone. Imaging features that can help in differentianting autoimmune pancreatitis from pancreatic cancer include homogeneous enhancement of the involved pancreas, absence of substantial pancreatic duct dilatation and parenchymal atrophy, and the absence of vascular encasement or metastatic disease. Concomitant diffuse pancreatic ductal narrowing and common bile duct/intrahepatic biliary strictures that resemble primary sclerosing cholangitis should also raise the probability of a diagnosis of autoimmune pancreatitis. Corticosteroid therapy can determine resolution of clinical manifestation, normalization of laboratory alterations, and complete or partial regression of pancreatic abnormalities.