Autoimmune pancreatitis with atypical imaging findings that mimicked an endocrine tumor

Figure 1 Initial multi-detector computed tomography scan imaging. A: CT scan before contrast injection, coronal reconstruction: enlargement of the main pancreatic duct and the biliary ducts, with enlarged gallbladder; B: CT scan after contrast injection, arterial phase, axial slice: lesion of the head of the pancreas, moderately enhanced after contrast injection.

Figure 2 Initial magnetic resonance imaging (MRI) imaging. A: T2-weighted MRI, coronal slice: bicanalar dilation and enlarged gallbladder; B: T1-weighted MRI, axial slice: main biliary duct and gallbladder enlargement with a thick wall evocative of cholangitis; the main pancreatic duct is also irregularly enlarged.

Figure 3 Histological examination of periampular biopsies (notice that both duodenal mucosa and pancreatic parenchyma are visible). A, B: Hematoxylin-eosin staining (A: × 125, B: × 500): atrophic acini surrounded by a fibrous stroma, associated with periductal lymphoplasmocytic infiltration; C, D: Anti-IgG4 immunostaining (C: × 125, D: × 500): the plasma cell infiltration expresses IgG4.

Figure 4 MRI at the end of steroid therapy. T1-weighted MRI with gadolinium injection: normal main pancreatic duct and gallbladder; the mass in the head of the pancreas has totally disappeared.