Immunoglobulin G4‐related disease mimicking gallbladder cancer with associated choledochal cyst: A case report of a malignant masquerade

Immunoglobulin G4 (IgG4)‐related disease is a recently described autoimmune disease that can involve diverse organ systems, causing pancreatitis, cholangitis, retroperitoneal fibrosis, and thyroiditis to name a few. Key histological features include storiform fibrosis, obliterative venulitis, and intense inflammatory infiltrate composed of lymphoplasmacytic cells. The disease has a tendency to present with mass‐forming lesions, often difficult to differentiate from malignant processes. We report the case of a 48‐year‐old male from an area endemic for gallbladder cancer (north India). He presented with a short history of abdominal pain and was found to have asymmetric thickening of the gallbladder wall with a soft‐tissue mass invading the adjacent liver. In addition, the bile duct was dilated throughout its extent. A clinical and radiological diagnosis of gallbladder cancer with choledochal cyst was made, and the patient underwent radical cholecystectomy with bile duct excision. Histopathology surprisingly demonstrated IgG4‐related disease with no evidence of malignancy. Notably, serum levels of immunoglobulins were found to be normal. Preoperative diagnosis was challenging due to the absence of other manifestations. IgG4‐related disease is a possible diagnostic pitfall and should be included as a possible differential diagnosis for gallbladder masses.