[Ultrastructural aspects of juvenile xanthogranuloma]

An ultrastructural study of a juvenile xanthogranuloma is presented. Foamy histiocytes reveal several vacuoles of irregular profile containing a type of lipid which is not fixed by osmium tetraoxide. There are also myelin figures. Plasmatic membrane shows numerous digit-like foldings related to collagen fibers. Cytoplasm containing few organelles are restricted to a narrow band around the nucleus and delicate trasverse bandings among the vacuoles. Several intranuclear spheroidal corpuscles have been identified in the histiocytes. Genesis of these foamy histiocytes is discussed probably related to a metabolic derangement of an organelle but in no way related to phagocytosis of fragmented polymorphonuclear leukocytes or Lymphocytes.