Autoimmune (IgG4) Pancreatitis



Autoimmune (IgG4) Pancreatitis


Brooke R. Jeffrey, MD

Michael P. Federle, MD, FACR





Key Facts


Terminology



  • Autoimmune form of chronic pancreatitis responding dramatically to steroid therapy


Imaging



  • Diffusely or focally enlarged pancreas with “halo” of low density (intensity)


  • Sausage-like; loss of fatty lobulation


  • ERCP with long strictures or discontiguous strictures


Top Differential Diagnoses



  • Pancreatic ductal carcinoma



    • Significant dilatation of main pancreatic duct proximal to narrowed segment


    • Atrophy of distal parenchyma


  • Chronic pancreatitis



    • Pain is chief complaint of patient


    • Calcifications and pseudocyst are common findings


    • Chronic alcohol abuse in most


Pathology



  • 2 distinct histologic subtypes (core biopsy not FNA is best for diagnosis)


  • Type 1: Dense lymphoplasmacytic infiltration and positive staining for IgG4



    • Often associated with other autoimmune diseases (cholangitis, thyroiditis, etc.)


  • Type 2: Periductal neutrophilic infiltrate with granulocyte-epithelial lesions and negative IgG4 staining


Clinical Issues



  • Lab findings: ↑ ↑ IgG4 (sensitive and specific), normal or ↑ serum amylase/lipase, ↑ ALP/GGT, ↑ bilirubin, ↑ ANA, ↑ autoantibodies, ↑ CA 19-9


  • Type 1 patients may have thyroiditis, dry eyes and mouth from Sjögren syndrome







(Left) Axial CECT in a 57-year-old man shows diffuse infiltration and enlargement of the pancreas with loss of normal fatty lobulation. There is a hypodense “halo” or capsule image around the pancreas, with relatively little spread into adjacent tissues. All symptoms and signs resolved with steroid therapy. (Right) Transhepatic cholangiography in a patient with autoimmune pancreatitis shows multifocal strictures image indistinguishable from those of primary sclerosing cholangitis.






(Left) Hematoxylin & eosin section of lymphoplasmacytic sclerosing pancreatitis illustrates that the inflammatory component consists of lymphocytes, numerous plasma cells, and eosinophils. (Courtesy M. Mino-Kenudson, MD.) (Right) IgG4 stain in lymphoplasmacytic sclerosing pancreatitis shows a large number of IgG4(+) plasma cells (> 10/HPF) in the periductal stroma. (Courtesy M. Mino-Kenudson, MD.)



TERMINOLOGY


Abbreviations



  • Autoimmune pancreatitis (AIP)


Synonyms



  • Lymphoplasmacytic sclerosing pancreatitis; primary sclerosing pancreatitis; nonalcoholic, duct-destructive, chronic pancreatitis


Definitions



  • Pancreatic involvement with fibroinflammatory disease responding dramatically to steroid therapy


IMAGING


General Features



  • Best diagnostic clue



    • Diffusely or focally enlarged pancreas with “halo” of low density (or signal intensity)


    • No vascular involvement, calcification, or pseudocyst


    • Lack of significant dilatation of main pancreatic duct


  • Location



    • May be focal and mass-forming, multifocal or diffuse


  • Morphology



    • “Sausage-shaped” appearance of body and tail of pancreas


Imaging Recommendations



  • Best imaging tool



    • MRCP and gadolinium-enhanced MR


CT Findings



  • Enlargement of pancreas



    • Usually diffuse, can be focal swelling


    • Sausage-shaped, loss of fatty lobulation


  • Enhancement is variable



    • Often less enhancement than expected in arterial phase


  • Diffuse or segmental narrowing of pancreatic duct


  • Low-attenuation “halo” surrounds pancreas


  • Minimal peripancreatic stranding


  • Stricture of common bile duct ± intrahepatic ducts



    • Indistinguishable from primary sclerosing cholangitis


MR Findings



  • Diffuse enlargement with low signal on T1WI


  • “Halo” of low signal on T2WI


  • Capsule-like rim of peripheral enhancement


  • Delayed enhancement of focal or diffuse parenchymal lesions


  • Multiple discontiguous strictures of main pancreatic duct and bile ducts on MRCP



    • Biliary strictures may simulate findings of primary sclerosing cholangitis


Ultrasonographic Findings



  • May have normal appearance on US


  • Diffusely enlarged hypoechoic gland with sausage-like appearance


Other Modality Findings



  • ERCP



    • Diffuse or segmental narrowing of main pancreatic duct


    • Long narrow strictures typically greater than 1/3 length of pancreatic duct


    • Lack of upstream dilatation of pancreatic duct distal to stricture


    • Multiple discontiguous strictures of pancreatic duct


    • Side branch ducts arising from stricture


DIFFERENTIAL DIAGNOSIS


Pancreatic Ductal Carcinoma



  • Significant upstream dilatation of main pancreatic duct distal to narrowed segment


  • Atrophy of parenchyma distal to mass


  • Encasement of major peripancreatic vessels


Chronic Pancreatitis



  • Pain is chief complaint of patient


  • Chronic alcohol abuse in most


  • Calcifications and pseudocysts are common findings


PATHOLOGY


General Features



  • Etiology



    • Unknown; autoimmune


    • Unclear whether IgG4 plays a pathogenic role in type 1 or is only an epiphenomenon


  • Genetics



    • Genetic studies suggest association with a specific human leukocyte antigen (HLA) type


  • Associated abnormalities



    • Often associated with other fibroinflammatory autoimmune diseases



      • Sjögren syndrome, sclerosing cholangitis, primary biliary cirrhosis, ulcerative colitis, SLE, thyroiditis


Staging, Grading, & Classification



  • 2 distinct histologic subtypes (core biopsy not FNA is best for diagnosis)



    • Type 1: Lymphoplasmacytic sclerosing pancreatitis (IgG4-related pancreatitis)



      • Serum IgG4 elevated twice normal in 80%


      • Mean age at presentation: 7th decade


      • Presentation: Obstructive jaundice 75%, acute pancreatitis 25%


      • Positive IgG4 tissue staining


      • Multiple organs involved in 60%


      • IBD in only 2-6%


      • Relapses after steroid therapy frequent


      • Imaging: Diffuse involvement of pancreas in 40% with focal lesions in 60%


    • Type 2: Idiopathic duct centric pancreatitis with granulocyte-epithelial lesions



      • Serum IgG4 not elevated


      • Mean age at presentation: 5th decade


      • Presentation: Obstructive jaundice 50%, acute pancreatitis 33%


      • No IgG4 tissue staining on histology


      • No other organs involved


      • Associated IBD in 16%


      • Few relapses after steroid therapy


      • Imaging: Focal pancreatic lesions in 85%



Microscopic Features

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Sep 20, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Autoimmune (IgG4) Pancreatitis

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