A pigmented differentiating neuroblastoma: a light and ultrastructural study.

An unusual case of a 4-year-old girl with a differentiating neuroblastoma arising in a thoracic sympathetic ganglion in which the neoplastic cells contained large amounts of melanin is described. Ultrastructural study showed the melanin granules were not associated with premelanosomes but appeared to be of lysosomal origin similar to neuromelanin seen normally in neurons of the substantia nigra and elsewhere in the central and peripheral nervous systems. The melanin in this neoplasm ws ultrastructurally distinct from that demonstrated in other types of pigmented neural crest neoplasms which have been studied ultrastructurally. The melanin in these latter neoplasms has been associated with premelanosomes and appears identical to melanin formed in epidermal melanocytes, so-called cutaneous or neural-crest-type melanin. The ultrastructural findings in this case demonstrate that neuromelanin can occur in melanotic tumors of neural crest origin, although its occurrence is much less common than that of cutaneous (neural crest) melanin.