Patterns of congenital nevocellular nevi. A histologic study of thirty-eight cases.

A series of thirty-eight cases of congenital nevocellular nevi were excised and studied histologically. Depending on the extent of nevoid cell dermal infiltration, four histologic patterns were observed: diffuse or patchy infiltration of the upper dermis alone, or diffuse or patchy infiltration of the upper and deep dermis with nevoid cells in or below the lower one third of the reticular dermis. Nevoid cells extended into the deepest reticular dermis in only 37% of these patients. There was no significant correlation between the four histologic patterns and age, sex, location, or lesion size. Two cases recurred after surgery but none underwent malignant change. The patients who developed recurrent nevi in the surgical site postexcision manifested the diffuse upper and deep dermal pattern of nevoid cell infiltration. We interpret this observation as due to incomplete excision of the primary lesion, reflecting the difficulty of removing congenital nevi with this histologic pattern. We conclude from this study that: (1) congenital nevocellular nevi show at least four typical histologic patterns; (2) the nevoid cells of congenital nevi do not necessarily extend into the deep dermis; and (3) of the four histologic patterns seen in congenital nevi, that one showing diffuse and deep placement of nevoid cells on biopsy requires more aggressive excision to prevent recurrence.