Congenital melanocytic nevus syndrome: An association between congenital melanocytic nevi and neurological abnormalities.

Congenital melanocytic nevus syndrome describes congenital melanocytic nevi (CMN) associated with extracutaneous abnormalities, most often involving the nervous system. CMN syndrome is usually caused by postzygotic mutations in the neuroblastoma RAS viral oncogene homolog (NRAS) gene. CMN, collections of melanocytes within the skin, are typically multiple in number and serve as a visible, cutaneous marker of this syndrome. CMN can be classified by predicted maximum diameter in adulthood as well as other clinical features such as anatomic location, color heterogeneity, hypertrichosis, number of satellite nevi, nodules, and surface rugosity. Common neurological abnormalities in CMN syndrome include melanin with the central nervous system (CNS), seizures, and neurodevelopmental delays. Early screening magnetic resonance imaging (MRI) of the CNS during the initial months of life is crucial for predicting the risk of neurodevelopmental abnormalities, seizures, and the need for neurosurgical intervention. Children with a normal screening CNS MRI or intraparenchymal melanosis alone tend to have favorable outcomes. Prognosis otherwise varies widely given the breadth of neurological abnormalities that can occur in CMN syndrome, however if primary melanoma develops in the skin or CNS then outcomes are typically poor.