Diffuse irregular narrowing of the main pancreatic duct, and stenosis of the intrapancreatic bile duct on endoscopic retrograde cholangiopancreatography (ERCP). Rare pancreatic calcification or cyst formation. Marked responsiveness to treatment with corticosteroids. Histopathology
Histopathologic examination of the pancreas reveals a characteristic lymphoplasmacytic infiltrate of CD4- or CD8-positive lymphocytes and IgG4-positive plasma cells, and exhibits interstitial fibrosis and acinar cell atrophy in later stages. At the initial stages, typically, there is a cuff of lymphoplasma cells surrounding the ducts but also more diffuse infiltration in the lobular parenchyma. However, localization and the degree of duct wall infiltration are variable. Whereas histopathologic examination remains the primary method for differentiation of AIP from acute and chronic pancreatitis, lymphoma, and cancer. By Fine Needle Aspiration (FNA) the diagnosis can be made if adequate tissue is obtained. In such cases, lymphoplasmacytic infiltration of the lobules are the key finding. Rarely, granulomatous reaction could be observed. It has been proposed that a cytologic smear primarily composed of acini rich in  chronic inflammatory cells (lymphocytes, plasma cells), with rare ductal epithelial cells lacking atypia, favors the diagnosis of AIP. The sensitivity and the specificity of these criteria for differentiating AIP from neoplasia are unknown.
Two-thirds of patients present with either painless jaundice due to bile duct obstruction or a "mass" in the head of the pancreas, mimicking carcinoma. As such, a thorough evaluation to rule out cancer is important in cases of suspected AIP.Type 1 AIP typically presents in a 60–70-year-old male with painless jaundice. In some cases, imaging reveals a mass in the pancreas or diffuse pancreatic enlargement. Narrowing in the pancreatic duct called strictures may occur. Rarely, Type 1 AIP presents with acute pancreatitis. Type 1 AIP presents with manifestations of autoimmune disease (IgG4 related) in at least half of cases. The most common form of systemic involvement is cholangitis, which occurs in up to 80 percent of cases of Type 1 AIP. Additional manifestations include inflammation in the salivary glands (chronic sclerosing sialadenitis), in the lungs resulting in scarring (pulmonary fibrosis) and nodules, scarring within the chest cavity (mediastinal fibrosis) or in the anatomic space behind the abdomen (retroperitoneal fibrosis) and inflammation in the kidneys (tubulointerstitial nephritis).AIP is characterized by the following features:

Scleral Icterus (yellow eyes), jaundice (yellow skin) which is usually painless, usually without acute attacks of pancreatitis. Relatively mild symptoms, such as minimal weight loss or nausea. Increased serum levels of gamma globulins, immunoglobulin G (IgG) or IgG4. The presence of serum autoantibodies such as anti-nuclear antibody (ANA), anti-lactoferrin antibody, anti-carbonic anhydrase II antibody, and rheumatoid factor (RF). Contrast-enhanced CT demonstrates a diffusely enlarged (sausage-shaped) pancreas.