Focal autoimmune pancreatitis mimicking pancreatic head carcinoma

Case contributed by Dr Donald Luke Mathew


Obstructive jaundice. Ultrasonography revealed a bulky pancreatic head.

Patient Data

Age: 45 years
Gender: Male

Axial arterial, coronal and sagittal portal venous CT pancreas reveal focal enlargement of the head of pancreas with loss of the normal peripheral lobulation. No significant differential enhancement compared with the rest of the pancreatic parenchyma. The uncinate process is rounded. Body and tail of the pancreas are of normal appearance.

Borderline dilatation of the main pancreatic duct in the body and tail. Dilated CBD with mildly enhancing wall, with abrupt cut-off at the superior margin of the head of pancreas; mild intrahepatic duct dilatation also present. Peripancreatic fat plane is preserved. Borderline-enlarged/prominent peripancreatic and mesenteric lymph nodes. Mild edema of the mesenteric fat.

Follow-up CT 6 months later


Subtotal resolution of the focal pancreatic swelling and peripancreatic reactive nodes. Biliary and pancreatic duct dilatation is no longer seen. Mild mesenteric fat edema persists.

Case Discussion

The following CT findings were discussed in favor of focal autoimmune pancreatitis (versus pancreatic carcinoma) with the hepatobiliary surgeons:

  • no significant differential enhancement of the head cf. body and tail
  • mild CBD dilatation with lack of upstream main pancreatic duct dilatation
  • no distal pancreatic atrophy
  • no infiltration, or encasement, of peripancreatic fat, vessels, etc.
  • no convincing metastases 

Abrupt narrowing of the CBD with wall thickening and enlarged peripancreatic lymph nodes raised suspicion of malignancy, although here, lymph node enhancement was much more intense than that seen in carcinoma.

Ampullary biopsy performed.
Immunohistochemistry highlighted a mixture of CD3- and CD20-positive T and B lymphocytes and numerous CD138- and IgG-positive plasma cells (150/hpf).

IgG4 was positive in scattered plasma cells (8/hpf).

IgG4/IgG ratio was 0.05.

The patient was started on steroids and the bilirubin level returned to normal.

The follow-up CT 6 months later showed near-total resolution of the apparent mass and resolution of the biliary dilatation.

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