Coexistence of IgG4-Related Disease and Renal Anastomosing Hemangioma: A Rare Diagnostic Challenge.

IgG4-related disease (IgG4RD) is a chronic inflammatory condition that can mimic malignancies. This report describes an 83-year-old male diagnosed with IgG4RD, in whom a left kidney mass was incidentally discovered. Despite glucocorticoid treatment for IgG4RD, the mass did not shrink, and imaging could not exclude malignancy, prompting surgical resection. Pathological examination revealed a rare benign tumor, renal anastomosing hemangioma (AH) with numerous IgG4-positive cells surrounding it. This case raises the possibility that chronic interstitial inflammation associated with IgG4RD may contribute to the development of renal AH, underscoring the need for further research with additional cases to better understand this relationship.