Congenital melanocytic nevi and risk of melanoma

The presence of congenital melanocytic nevi (CMN) is determined in utero. The location, size, and number of CMN may be of cosmetic concern with significant psychosocial implications. They may also be associated with symptoms such as pruritus, eczema and/or xerosis, and skin fragility; however, the most medically concerning issue is the association of CMN with the risk of developing cutaneous melanoma, extracutaneous melanoma, and neurocutaneous melanocytosis. Patients with CMN are currently risk-stratified based on the projected adult maximum diameter of the largest CMN and the number of CMN (satellites) present. In small and medium CMN, the absolute risk of developing cutaneous melanoma is estimated to be approximately 0.3% with a relative risk of 9.5. Although patients with large CMN are at increased risk for developing primary cutaneous melanoma within the CMN, they are also at increased risk for developing primary melanoma within the central nervous system in association with central nervous system melanocytic deposits, an entity known as neurocutaneous melanocytosis. The absolute risk for developing melanoma in patients with large CMN is estimated to be between 1.25% and 10% with a relative risk between 52 and 1,046. Regarding the risk for the presence of neurocutaneous melanocytosis, the risk correlates with the number of CMN, with the lowest risk in those with a single CMN and with risk escalation as the number of CMN increases. We provide an overview of the existing evidence about the risk of melanoma and neurocutaneous melanocytosis in patients with CMN. The role of clinical examination, dermatoscopy, magnetic resonance imaging scanning of the central nervous system, and the role of surgery in the management of CMN of varying sizes is discussed.