An electron microscopic study of balloon cell nevus

One case of balloon cell nevus was studied with the electron microscope. Intra-epidermal balloon cells contained numerous nonmelanized melanosomes which tended to coalesce. Large cavities were produced in typical mature balloon cells as the result of degeneration of these coalesced melanosomes. Some melanosomes remained intact after coalescence and produced conglomerates of melanosomes. Kerátinocytes phagocytosed these abnormal balloon cell melanosomes. Intradermal balloon cells were surrounded with basal lamina, were often multinucleated, and contained a relatively small number of poorly developed melanosomes which were not melanized. It was concluded that the balloon cells and nevus cells belong to the same cell type and that the ballooning phenomenon represents a self-destructive process.