IgG4-related retroperitoneal fibrosis mimicking renal pelvis tumor: a case report and literature review

Retroperitoneal fibrosis (RPF) is a rare disease characterized by the development of a fibroinflammatory mass in the retroperitoneum. Immunoglobulin-G4 related RPF was suggested as a secondary form of RPF and thought to be part of the spectrum of Immunoglobulin-G4 related diseases (IgG4-RD). Patients often present to the clinic because of flank pain. Ranging from mild to end-stage renal failure can be observed. The main purpose of treatment is to preserve renal function. As it is a rare condition, there is no definite treatment strategy. We report a case of 39-year-old man with left flank pain and diagnosis of IgG4-related RPF mimicking a renal pelvis tumor. A 39-year-old male patient presented with left flank pain. MRI suggested solid retroperitoneal mass associated with hydronephrosis in the left kidney collecting system. Upon identifying the retroperitoneal origin of the mass during nephroureterectomy, the procedure was concluded following the acquisition of frozen section and routine pathological samples from the lesion. In the histopathological examination, inflammatory cells were observed and specific immunohistochemistry for IgG-4 was detected focally positive. Following the placement of a DJ stent, immunosuppressive therapy was initiated with Prednol and Azathioprine. After a one-year follow-up period, during which the patient received immunosuppressive treatment and underwent tri-monthly DJ stent replacements, the DJ stent was subsequently removed, revealing complete regression of hydronephrosis. With the correct diagnosis and treatment of IgG4-related RPF, it is possible to prevent irreversible complications of the disease. Because it is a rare disease, case reports in the literature will be useful for treatment.