Immunoglobulin G4-Related Inflammatory Pseudotumor With Cystic Features Mimicking Renal Cancer

Immunoglobulin G4-related disease is a systemic fibroinflammatory disorder that affects the kidney, presenting as an immunoglobulin G4-related inflammatory pseudotumor. These renal inflammatory pseudotumors are usually solid, and cystic presentations have not been previously described.

We report a 77-year-old man who presented with a Bosniak category III renal cystic mass and periaortic fibrous thickening. Increased serum immunoglobulin G4 levels indicated immunoglobulin G4-related disease; however, a malignant process could not be definitively ruled out. The patient underwent robot-assisted radical nephrectomy, and histopathologic assessment confirmed a cystic immunoglobulin G4-related inflammatory pseudotumor.

This is the first report of a renal immunoglobulin G4-related inflammatory pseudotumor with cystic features. Increased knowledge of immunoglobulin G4-related disease as a potential cause of cystic renal lesions, particularly in patients with systemic findings, may improve preoperative diagnosis.