The oral blue nevus: histogenetic implications of its ultrastructural features.

Three cases of oral blue nevus are presented. A comparison of the ultrastructural features of blue nevus cells with those of schwannoma cells indicates that, among other similarities, both exhibit a surrounding external lamina (basement membrane). The significant difference is that blue nevus cells are capable of synthesizing melanin as evidenced by the presence of the entire melanosome maturation sequence within their cytoplasm, a feature not seen in the cells of schwannomas. This fundamental difference suggests that blue nevus cells are more closely related to melanocytes, although they possess some of the characteristics of Schwann cells.