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Extranodal Rosai–Dorfman disease as a pelvic mass

Rosai–Dorfman disease (RDD) is a rare histiocytic disorder of unknown cause. RDD most commonly involves the cervical lymph nodes, but extranodal involvement has been described. We report the case of a patient with extranodal RDD that presented as a retroperitoneal mass obstructing the left ureter. The patient underwent surgical resection of the mass, followed by a 5-month course of vinblastine. There was no evidence of progressive disease 22 months after surgery.