Fine-needle aspiration cytology of Rosai-Dorfman disease of bone.

Sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease) is a rare, benign self-limiting condition of unknown etiology. Less than a quarter of cases have only extranodal involvement and a few cases of skeletal involvement of Rosai-Dorfman disease without associated lymphadenopathy have been reported in the literature. We herein report cytohistologic findings in a case of sole skeletal Rosai-Dorfman disease in a 51-year-old woman who presented with an expansile, heterogeneous lesion at T11 with cord compression and edema. A CT-guided fine-needle aspiration of T-11 lesion was performed and the sample was processed by ThinPrep technique. The ThinPrep smear showed characteristic features of Rosai-Dorfman disease including hypercellularity with moderate number of histiocytes in a background of lymphocytes, plasma cells, and neutrophils. The histiocytes possessed abundant, pale and vacuolated cytoplasm, rounded nuclei with smooth nuclear membranes, fine chromatin, and distinct nucleoli. The histiocytes showed emperipolesis of lymphocytes and neutrophils. The diagnosis was confirmed by concurrent biopsy with immunhistochemical study. Our case highlighted the role of fine-needle aspiration with ThinPrep technique in the diagnosis of Rosai-Dorfman disease.