Juvenile xanthogranuloma. Ultrastructural and immunocytochemical studies.

Morphologic features of three cases of juvenile xanthogranuloma (JXG) were consistent with the current concept of a benign process, although the lesion in one case grew steadily to an extensively infiltrating large mass, which clinically suggested a malignant growth. Ultrastructurally, the lesion consisted of morphologically different developmental stages of histiocytes, probably reflecting different functional levels. An interesting finding was the presence of occasional subplasmalemmal linear densities between these cells. These densities were at times symmetrically opposed, forming desmosomelike junctional complexes. Immunohistochemical study for the presence of lysozyme, alpha 1-antitrypsin, and S100 protein by the avidin-biotin-peroxidase complex was performed in all three cases. All immunostains were negative except the positive lysozyme stain in two cases. The ultrastructural and cytochemical characteristics of histiocytes in JXG were similar to epithelioid cells in the lymph node, suggesting that JXG is a reactive lesion.