Primary retroperitoneal fibrosis presenting as a renal mass

A 67-year-old male was incidentally found to have a large left perinephric mass with a poorly functioning left kidney. A differential diagnosis of renal cell carcinoma, lymphoma, retroperitoneal fibrosis (RPF), and IgG4 renal disease was suggested on imaging studies and biopsy of the mass. A left radical nephrectomy was performed as malignancy could not be ruled out. The final diagnosis was RPF without periaortitis and the patient is doing well at 9 months of follow-up. RPF, although characterized as a manifestation of periaortitis and large vessel vasculitis, might also present as an isolated perinephric mass without aortic involvement. Surgical management is an alternative, especially when malignancy is suspected.