Teaching Case

A Japanese woman with no significant previous history was referred for the management of a recently diagnosed mass of the pancreatic head (investigated outside by CT and MRI, not available). She reported epigastric pain, obstructive jaundice, weight loss. She had hyperbilirubinaemia, alterated liver function, normal neoplastic markers, elevated IgG4 (5.34g/l).

Endoscopic ultrasound detected a diffuse pancreatic enlargement with hypoechoic parenchyma. A fine needle agobiopsy was performed and revealed the presence of lymphoplasmacytic infiltrates and fibrosis. Endoscopic retrograde cholangiopancreatography showed a 2 cm-long stricture of the intrapancreatic portion of the main biliary duct with dilatation of the upper biliary tree and, after mechanic dilatation, a plastic prosthesis was released.
A dynamic quadriphasic contrast-enhanced CT showed a diffuse and homogeneous pancreatic enlargement with smooth borders. The most affected areas were hypodense in the pancreatic phase with higher attenuation in the venous and delayed phases. A hypodense capsule-like rim with delayed enhancement was detected around the whole pancreas. There was mild dilatation of the main pancreatic duct with wall contrast enhancement due to periductal inflammation (“enhanced duct” sign) and the pancreatic duct was focally undetectable in the most affected areas.

A. Background:
AIP is a rare form of chronic pancreatitis classified into two subtypes: type 1 (lymphoplasmacytic sclerosing pancreatitis), the manifestation of IgG4-related disease, and type 2 (idiopathic duct-centric pancreatitis). Type 1 AIP is associated with IgG4-positive lymphoplasmacytic infiltrate and “storiform” fibrosis, while type 2 is characterized by granulocytic epithelial lesions and ductal damage. Type 1 AIP is more prevalent than type 2 and is the only subtype diagnosed in Japan. [1, 2]
B. Clinical Perspective:
AIP presents with mild abdominal symptoms, weight loss and obstructive jaundice, mimicking the presentation of pancreatic adenocarcinoma. The differential diagnosis could be challenging, but the association with increased serum gamma globulin, IgG4 and auto-antibodies is helpful. AIP should also be distinguished from acute non-necrotizing pancreatitis and pancreatic lymphoma. According to the International Consensus Diagnostic Criteria for AIP there are five essential features: parenchymal or ductal imaging, serological and histological findings, associated organ involvement, response to steroid therapy. [1, 3, 4]
C. Imaging Perspective:
Two imaging patterns have been described: a diffuse form, with enlargement of the whole pancreas, and a focal form, with a mass-like appearance. Diffuse AIP can be differentiated from non-necrotizing acute pancreatitis thanks to its dynamic features (it is hypodense in the pancreatic phase with delayed enhancement), the peripheral rim enhancement and the absence of peripancreatic fluid or stranding. It should be also distinguished from pancreatic lymphoma, which is constantly hypodense and usually associated to adenopathies or splenic lesions.
On the other hand, focal AIP should be differentiated from adenocarcinoma and the capsule-like rim, the dynamic features, the smooth borders and the absence of pancreatic duct’s dilatation usually assist the diagnosis, which should be confirmed by fine needle agobiopsy.
In this case it was not necessary to repeat a MRI, but otherwise it can assist the diagnosis showing parenchymal fibrosis and peripheral halo as T2 hypointense areas with delayed enhancement, while MRCP as well as ERCP can assess the ductal abnormalities (strictures of the main pancreatic duct with wall enhancement). [1]
D. Outcome:
The patient started steroid therapy with prompt clinical benefit and is now under follow-up. Type 1 AIP usually has a dramatic response to steroid therapy, but also a high relapse rate (60 % at 3 years). CT and MRI are useful to assess treatment response and the recurrence of disease. [1]
E. Take Home Message, Teaching Points:
Even if AIP can mimic other pancreatic diseases, the presence of delayed enhancement and a capsule-like rim supports the diagnosis of AIP.