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An ultrastructural study of a juvenile melanoma.

An unusual variant of juvenile melanoma, namely a sclerosing juvenile melanoma occurring on the buttock, has been studied by light and electron microscopy. The diagnosis of a pigment tumour was confirmed by the presence of structures common to these lesions, i.e. melanosomes, intracytoplasmic fibrils and microvilli on the cell surface. The tumour consisted of two cell configurations, namely a multinucleated giant cell and a second cell made up of two separate cells lying in close apposition, the cytoplasm of one cell being dark and the other light. This tumour can be differentiated from a benign naevus by the bizarre histological appearance on light microscopy. On electron microscopy the distinction is made by the presence of the very large multinucleated giant cells, the apposition of the light and dark cells, the scanty melanosomes and the presence of intracytoplasmic lumina. The value of electron microscopy in the determination of the nature of unusual skin tumours is discussed.