Rosai-Dorfman disease: unusual cause of diffuse and massive retroperitoneal lymphadenopathy.

Rosai-Dorfman disease (RDD), originally described as sinus histiocytosis with massive lymphadenopathy, is a rare histiocytic proliferative disorder with a distinctive microscopic appearance. Patients usually present with massive cervical lymphadenopathy. However other nodal sites (mediastinal and inguinal) are also frequently involved. The retro-peritoneum is an infrequent site of involvement. This uncommon entity should also be included in the list of differential diagnoses of diffuse and massive lymphadenopathy, which includes includes infectious/granulomatous conditions, lymphomatous and metastatic disease.