Mass-forming autoimmune pancreatitis

Case contributed by Dr Jan Frank Gerstenmaier

Presentation

This patient presented with marked pruritus, abnormal liver enzyme levels, weight loss, and a recent diagnosis of diabetes. No significant past medical history. Initial abdominal ultrasound showed biliary obstruction.

Patient Data

Age: 60
Gender: Male
CT

CT of pancreas

There is a 3.1 cm pancreatic head mass with separation of the normal appearing pancreas at the neck from the dilated pancreatic ducts suggesting infiltration of pancreatic neck.  The portal vein origin appears narrowed by tumour. The SMA is clear of disease. There is no adenopathy. Apart from intrahepatic duct dilatation, the liver is normal in appearance. 

The mass was considered 'borderline resectable'

The patient underwent ERCP. This revealed a stricture in the mid-third CBD. Brushings were performed, and a 7Fr plastic stent placed across the stricture. The impression was that of a malignant CBD stricture.

Brushings: Cellular specimen containing numerous groups of ductal cells which display varying degrees of architectural and cytologic atypia suspicious for adenocarcinoma. 

C4, suspicious for malignancy.

Nuclear medicine

18F-FDG PET-CT

Internal biliary drain in-situ. No remaining intra-or extrahepatic duct dilatation. There is low-grade FDG uptake only within the inferior head of pancreas (maximum SUV 2.3). No FDG-avid liver lesion.

Overall impression is that there is no significantly metabolically active pancreatic mead mass identified. Low grade metabolic activity may relate to inflammation caused by recent stent placement or a tumour with low-grade FDG uptake

Despite negative PET-CT, based on appearances on CT, and C4 cytology from ERCP brushings, the patient underwent a Whipple procedure.

Pathology

Whipple resection

including the head of pancreas, 5 x 4.5 x 4.5cm.

The resected specimen contained a 3 cm ill-defined firm pale mass in the pancreatic head with no significant dilatation of the pancreatic duct and grossly normal pancreatic neck tissue

Pathology

Histopathology and Immunohistochemistry

Microscopic sections revealed a fibro-inflammatory process with a prominent plasma cell component that extended into peri-pancreatic soft tissue. The inflammatory infiltrate had a prominent peri-ductal pattern and also involved small veins (venulitis). The involvement of the pancreatic head was patchy with intervening normal lobules of exocrine acini noted between fibrotic atrophic foci. IgG4 immunohistochemical staining revealed a high percentage of positivity within the plasma cells present (>30 per HPF).

The above features are consistent with the lobulocentric or lymphoplasmacytic sclerosing pancreatitis subtype of AIP, the significance of which includes an association with Sjogren's syndrome and a predilection for developing recurrent bile duct stenosis.

The final pathological diagnosis was autoimmune pancreatitis, grade 4/4.

Case Discussion

Autoimmune pancreatitis (AIP) resembles pancreatic carcinoma clinically and radiographically,and as such the diagnosis of autoimmune pancreatitis is challenging to make.
This particular form of pancreatitis that was first described in 1995 and has more recently been recognised as a manifestation of IgG4-RSD. It most commonly occurs in older men. As it is commonly associated with a biliary stricture, AIP often mimics pancreatic cancer presenting with painless jaundice, weight loss, diabetes mellitus. Patients with AIP may have a focal mass or diffuse pancreatic abnormality. In the USA, AIP has been reported to account for 2.5% of all cases undergoing Whipple’s resection, and for up to 20-23% of those with benign conditions1. AIP is commonly associated with sclerosing lesions in many other organs. Only 44% of cases of AIP have elevated IgG4-levels2.

The most important differentiation from AIP is pancreatic carcinoma. Features that are highly suggestive of AIP over carcinoma are1: diffuse enlargement of the pancreas with a capsule-like rim, and diffuse narrowing of the pancreatic duct. In AIP, areas of restricted diffusion on MRI scan can be diffuse, solitary or multiple, whereas pancreatic cancer typically shows only solitary abnormality. A serum IgG4 level of more than 2.8 g/l is highly suggestive of AIP3

PEt-CT has been suggested as an aid in differentiating AIP from pancreatic carcinoma4, 5 and in this case it was negative, i.e. did not show any significant metabolic activity in the pancreatic mass.

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Case information

rID: 21642
Case created: 6th Feb 2013
Last edited: 10th Aug 2016
Inclusion in quiz mode: Included

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