• IRSD: Spectrum of disorders characterized by tumor-like lymphoplasmacytic infiltration and varying degrees of fibrosis in different organs
Pancreas is most commonly affected organ (autoimmune pancreatitis) followed by salivary glands and biliary tree
• ISC: Biliary manifestations of IRSD frequently associated with autoimmune pancreatitis (AIP)
Manifested as wall thickening and biliary strictures
IMAGING
General Features
• Best diagnostic clue
Bile duct wall thickening and strictures in setting of autoimmune pancreatitis
• Location
ISC classified based upon stricture location
– Type 1: Distal (intrapancreatic) common bile duct (CBD)
Most common type: May mimic pancreatic adenocarcinoma or cholangiocarcinoma
– Type 2: Strictures distributed throughout intra- and extrahepatic ducts
May mimic primary sclerosing cholangitis
– Type 3: Strictures of duct bifurcation and distal duct
May mimic cholangiocarcinoma
– Type 4: Isolated hilar stricture
May mimic cholangiocarcinoma
• Size
Variable: Focal or diffuse involvement of biliary tree
• Morphology
Concentric bile duct wall thickening and hyperenhancement
Typically long smooth stricture with upstream biliary ductal dilatation
Radiographic Findings
• ERCP
Distal CBD stricture and irregularity of main pancreatic duct (due to concomitant AIP) most frequent findings
Strictures of intra- and extrahepatic ducts rarely occur without pancreatic duct involvement
Long, smooth strictures (particularly of distal CBD) without irregularity
CT Findings
• Circumferential focal or diffuse bile duct wall thickening
Most commonly affects distal CBD, but can affect any portion of biliary tree
Hyperenhancement of affected bile duct: Enhancement may persist during delayed phase
No vascular invasion, metastatic disease, or other secondary findings of malignancy
• No clear association between ISC and malignancy, but involved sites in biliary tree may rarely appear mass-like and mimic malignancy (inflammatory pseudotumor)
• Diffuse gallbladder wall thickening (due to either lymphoplasmacytic infiltration and transmural fibrosis or superimposed cholecystitis)
• Findings of concomitant autoimmune pancreatitis
Focal, multifocal, or diffuse (sausage-shaped) pancreatic enlargement with hypodense pancreatic capsule
Enlargement of pancreas with a paucity of peripancreatic inflammation, fluid, or stranding
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