Polyoma virus nephropathy-related mass lesion in an apparently immunocompetent patient.

Polyoma virus is a recognized cause of hemorrhagic cystitis, viral nephropathy, and ureteral stricture in renal and stem cell transplant recipients. Rarely, polyoma virus causes native kidney and bladder pathology in heavily immunosuppressed patients. We report a unique case of native kidney polyoma virus nephropathy, urothelial ulceration, and renal pelvic fibrosis presenting as a mass lesion in a non-debilitated, apparently immunocompetent man. Based on radiologic, ureterorenoscopic, and urine cytologic findings, a laparoscopic nephrectomy was performed. However, nephrectomy revealed a hemorrhagic scar-like lesion, with urothelial ulceration, but no neoplasm or malignancy. Histopathologic evaluation and immunostaining revealed polyoma viral infection in the nearby renal medulla. This case adds polyoma virus nephropathy to the differential diagnosis of non-neoplastic and reactive masses, which may mimic renal malignancy.