Extranodal Rosai-Dorfman Disease : Retroperitoneum
This is a case of extranodal Rosai-Dorfman disease that presented as large retroperitoneal mass in a young male. A CT-guided biopsy yielded scanty material. Due to the rarity of this lesion, it was not considered initially in the differential diagnosis and the findings were thought to be suspicious for lymphoma. The correct diagnosis was established on the resected specimen which measured 11 cm in size. The image shows sheets of foamy histiocytes admixed with lymphoplasmacytic infiltrate in a fibrotic background. A solitary lymphoid follicle is present. See higher magnification in the next 3 images.