Isolated IgG4-related cholecystitis mimicking locally advanced gallbladder cancer: a case report.

Immunoglobulin G4 (IgG4)-related disease is a fibroinflammatory condition that can involve multiple organs. Isolated involvement of the gallbladder is exceptionally uncommon and often radiologically indistinguishable from gallbladder carcinoma, resulting in diagnostic uncertainty before surgery. A 77-year-old man presented with right upper abdominal discomfort lasting 1 month. Cross-sectional imaging revealed irregular gallbladder wall thickening with contrast enhancement, raising suspicion for resectable gallbladder cancer. The patient underwent a radical cholecystectomy with partial hepatectomy. Histopathological analysis demonstrated dense lymphoplasmacytic infiltration, storiform fibrosis, and marked infiltration of IgG4-positive plasma cells exceeding established diagnostic thresholds, consistent with IgG4-related cholecystitis. The postoperative course was uneventful, and no additional treatment was required. IgG4-related cholecystitis should be considered in the differential diagnosis of gallbladder malignancy, particularly in atypical or indeterminate cases. However, when imaging findings strongly suggest carcinoma, radical surgical resection remains an appropriate oncologic approach.