CD1A and sinus histiocytosis with massive lymphadenopathy: Rosai-Dorfman disease (RDD) is a histiocytic disorder of unknown etiology characterized by massive lymphadenopathy and the histological hallmark finding of the presence of an intact cell within the cytoplasm of another cell, also known as emperipolesis, with positive immunohistochemical staining for S100 and CD68 but negative for CD1a [1].