Melanocytic nevi in neonates.

The histologic features of seven congenital nevi within 3 months of birth were studied, together with the ultrastructural features of one of the lesions examined microscopically within 48 hours of birth. All seven lesions showed melanocytic hyperplasia within the epidermis and within pilosebaceous and eccrine sweat units. Nevus cells within the dermis were located in proximity to the adnexae. Melanocytic hyperplasia within the epidermis showed a variety of patterns, at least one of which simulated the atypical melanocytic hyperplasia seen in the superficial spreading type of melanoma. The fine structure of the melanosomes in one case studied by electron microscopy resembled hair-bulb melanosomes. They were distinctly different from melanosomes characteristic of epidermal melanocytes, nevus cells, or melanoma cells.