Erdheim-Chester Disease Presenting as a Solid Renal Mass.

Erdheim-Chester disease is a rare, systemic histiocytic disorder, usually presenting due to bone manifestations. The most commonly seen urologic manifestation is retroperitoneal fibrosis, leading to ureteral obstruction. We describe a patient with a solid right renal mass, initially concerning for renal cell carcinoma, in addition to diffuse retroperitoneal fibrosis and a chronically obstructed left kidney. The renal mass and retroperitoneal fibrosis are thought to be caused by Erdheim-Chester disease based on imaging findings and biopsy results.