Autoimmune pancreatitis mimicking a pancreatic adenocarcinoma

An 84-year-old man was admitted to the emergency department, referring to painful right upper quadrant abdominal pain and jaundice. Blood tests revealed mild leukocytosis and a cholestatic pattern of liver test abnormalities. Urgent abdominal ultrasound showed intra-and extrahepatic bile duct dilation. The patient was admitted for cholangitis, and an MRI was programmed.

MRI showed a dilation of the extra and intrahepatic bile duct secondary to the globular pancreatic head, with amputation and slight retrograde dilation of the main pancreatic duct (Figures 1a, 1b, 1c, 2a and 2b). A primary pancreatic neoformation was suggested and a whole-body multiphasic CT was recommended for staging.

CT showed similar results to the MRI with no involvement of other organs. The arterial (3a and 3b) and venous (3c) phases show a pancreatic parenchyma attenuation of 85 HU and 86 HU, respectively.

CA 19-9 levels were measured and resulted negative. Endoscopic retrograde cholangiopancreatography with fine needle aspiration was also performed.

Treatment with corticosteroids was started, and three weeks later, a follow-up MRI (Figures 4a, 4b, 4c, 5a, 5b and 5c) showed global decrease in the size of the pancreatic gland, as well as decrease globulosity of the pancreatic head, a resolution of the bile ducts, and pancreatic ducts dilatations.

Background

Autoimmune pancreatitis (AIP) is a rare form of pancreatitis that reportedly occurs in 7% of chronic pancreatitis cases and is divided into two subtypes [1,2]. Type 1 AIP—lymphoplasmacytic sclerosing pancreatitis (LPSP)—is the pancreatic manifestation of a systemic IgG4-mediated inflammatory process in which other organs can be involved and is characterised by an increased number of IgG4+ cells in tissue and serum. Type 2 AIP—idiopathic duct-centric pancreatitis (IDCP)—is a pancreas-specific disorder and has no extrapancreatic involvement and lack of IgG4 elevation [1,3,4].

Clinical Perspective

AIP predominantly affects men (60%), with a peak incidence between 40 and 60 years. In the acute phase, AIP commonly presents as obstructive jaundice, mild abdominal pain or recurrent acute pancreatitis. In later phases, it can manifest as a pancreatic mass, atrophy, calcifications, and exocrine and endocrine insufficiency symptoms. Patients with type 1 AIP (LPSP) may also present symptoms associated with other diseases of the IgG4-associated spectrum [3–5]. 85% of cases present with a pancreatic mass and, as such, pancreatic adenocarcinoma must be ruled out as the main diagnostic suspicion [6].

Imaging Perspective

In imaging, AIP lesions often show as a low-dense area on CT, a hypointense area on T1W, a hyperintense area on T2W and DWI, and a delayed enhancement when contrast is used.

Three distinct morphologic patterns have been described for AIP:

• Diffuse enlargement (50–70%): Also known as sausage-shaped pancreas, is the most characteristic finding in AIP. A low-attenuating rim of soft tissue (capsule rim sign) is also seen in around 30–40% of patients but is very specific for AIP.
• Focal/segmental (most common in type 2): It often involves the head or uncinate process of the pancreas and can easily be confused with any pancreatic tumour.
• Multifocal forms (5%).

The presence of extrapancreatic lesions associated with IgG4-disease could provide a clue for the diagnosis of type 1 AIP [3,5].

CT attenuation values of pancreatic parenchyma in AIP differ from those with normal parenchyma and pancreatic carcinoma, bringing an important diagnostic clue [1,7].

Outcome

High-dose of corticosteroids is the most common treatment regimen in both type 1 and type 2 AIPs [3], with relapse being far more common in type 1 AIP (60%) compared to type 2 AIP (5%) [2,8,9].

In the case presented, fine needle aspiration was performed and revealed moderate lymphoplasmacytic infiltrate and fibrosis with the storiform pattern as well as elevated levels of IgG4 and IgG4/Total IgG ratio. New blood tests showed elevated IgG4 levels in serum. Characteristics in imaging, blood tests, fine needle aspiration and response to corticosteroids were consistent with focal autoimmune pancreatitis. Nonetheless, close clinical and imaging control was recommended.

Take Home Message

AIP is a rare entity composed of two clinically and histopathologically distinct forms of steroid-responsive pancreatitis: type 1 (IgG4 related), and type 2. AIP diagnosis requires a high index of suspicion, and imaging plays an essential role in its diagnosis and differentiation from pancreatic ductal adenocarcinoma.

All patient data have been completely anonymised throughout the entire manuscript and related files.