Pathologic and clinical features of RDD. (A-E) Representative images of nodal RDD from tissue biopsies (A-B) and fine-needle aspiration (C-E). (A) Mixed RDD/LCH case with sinus expansion. The large RDD histiocytes display conspicuous emperipolesis with pale cytoplasm, as compared with the intermixed LCH cells with dense eosinophilic cytoplasm and convoluted nuclei (original magnification [OM] ×400; hematoxylin and eosin [H&E] stain). (B) The RDD histiocytes show pale watery-clear cytoplasm, a central round nucleus with a conspicuous nucleolus, and emperipolesis (OM ×1000; H&E stain). Cell block preparation shows clusters of RDD histiocytes (OM ×400; H&E stain) (C), with nuclear and cytoplasmic staining for S100 (OM ×1000) (D) and fascin (OM ×1000) (E); the trafficking intact leukocytes are negative. (F) A child with immunodeficiency and RDD with massive cervical lymphadenopathy. (G) RDD of the skin showing red nodular lesions. (H) Tongue enlargement resulting from oral RDD.