Extranodal Rosai-Dorfman disease in childhood.

We describe two children with Rosai-Dorfman disease who presented with exophthalmos, leukocytosis, an elevated sedimentation rate and hypergammaglobulinemia. Both became blind as a result of this condition. One child had associated bilateral cervical lymphadenopathy. Investigation revealed involvement of the nasal fossae and retro-orbital spaces by tumoural masses histologically consistent with the diagnosis of sinus histiocytosis with massive lymphadenopathy (SHML). Immunohistochemical studies suggest that these histiocytes are activated macrophages derived from a phenotype hybrid between "professional" phagocytic cells and immune accessory cells, expressing lysosomal antigens, S-100 protein but rarely, CDla. An underlying immune dysfunction may be central to the pathogenesis of this disease.