Renal Pelvis Involvement of Immunoglobulin G4-Related Disease Mimicking Malignancy on 18F-FDG PET/CT.

A 70-year-old woman with bilateral submandibular gland enlargement was referred to our hospital. Submandibular gland biopsy indicated immunoglobulin G4 (IgG4)-related disease (IgG4-RD) involvement. Contrast-enhanced CT was undergone for evaluation of IgG4-RD and revealed a mass located at the left renal pelvis. F-FDG PET/CT showed bilateral FDG-avid submandibular gland and a hypermetabolic mass in the left renal pelvis. The lesions were decreased in both size and metabolism on follow-up PET/CT 2 months after treatment with prednisone. This case illustrated a rare site for IgG4-RD, and the renal pelvis involvement should be considered into differential diagnosis in patients with IgG4-RD history.