A unique cytoplasmic structure in papular histiocytoma.

Intracytoplasmic granules with a unique and highly complex ultrastructure, have been observed within the cellular infiltrate of the lesions of two patients with papular histiocytosis. Examination of serial sections has enabled construction of a three-dimensional model of these granules, which appear to be composed of an elaborate arrangement of membranes and vesicles. Two hypotheses (endocytosis and exocytosis) are proposed for the mode of formation of these unique cytoplasmic structures.