A histologic comparison of congenital and acquired nevomelanocytic nevi.

A reliable microscopic differentiation of nevomelanocytic nevi (NMNs) as congenital or acquired would be useful in defining a histogenic relationship between cutaneous melanoma and congenital NMN. In order to delineate histologic differences between congenital NMN and acquired NMN, a standardized assessment was conducted blindly, using a sample of consecutive surgical specimens of NMN submitted to a children's hospital pathology file. Despite significant histologic differences between congenital NMN and acquired NMN, the lack of a reliable prevalence rate for the proportion of congenital NMNs among all NMN specimens submitted for pathologic examination precludes a precise estimate of predictive value for diagnosing a given NMN as congenital or acquired based on histologic features alone. The results of this study can be used neither to support nor to refute a histologic association between cutaneous melanoma and congenital NMN.