[Melanocytic nevi]

Abstract

Acquired melanocytic naevi are believed to have been developed from epidermal melanocytes that completed their migration from the neural crest to the dermo-epidermal junction in fetal life or to arise from dermal melanocytes that have become arrested in the dermis during fetal migration and have never reached their normal site. Uncommon in infancy, naevi increase in frequency during childhood and adolescence and then more slowly to a plateau in middle age. During old age their prevalence falls. Studies on epidemiology suggest that melanocytic naevi are commoner when sun exposure is constant and intense and with some individual characteristics. Giant congenital melanocytic naevi, a positive family history of melanoma are risk factors responsible for the development of melanomas and require surveillance. In the great majority of naevi, removal is not required except if clinical suspicion.