Background: Generally, retroperitoneal fibrosis is an idiopathic process that envelopes and displaces ureters, causing hydronefrosis and renal failure. CT scan is the best choice for diagnosis. Other aetiologies described are malignancies, drugs, aorta aneurisms and immunological or rheumatological diseases.
Case presentation: A 53-year-old male with hypertension and diabetes was operated on radical nephrectomy for renal mass. Pathological examination showed sarcomatoid renal cell carcinoma, Fürhman 3 grade, pT2 N0. Within 6 months of surgery, control CT scan demonstrated a left retroperitoneal mass, without separation with pancreas queue and spleen hilium, suggesting local relapse. Resection of the mass with splenectomy and partial pancreatectomy en bloc was performed. Microscopic evaluation revealed a dense collagenic tissue with a prominent inflammatory infiltrate, and the immunohistochemical study was negative for cytokeratin AE1-AE3. There was no evidence of malignancy in the histological examination. All these findings aided to diagnose a retroperitoneal fibrosis.
Conclusions: Sometimes retroperitoneal fibrosis can simulate or is associated to malignancies. Presentation of a retroperitoneal fibrosis simulating local relapse of sarcomatoid renal cell carcinoma has not been previously reported in the English literature.