Large/giant congenital melanocytic nevus

Large or giant congenital melanocytic nevus (CMN) is a pigmented skin lesion composed of melanocytes that is present at birth. A congenital melanocytic nevus is classified as 'large' when its projected adult size is 20 cm or greater in diameter, and 'giant' when it exceeds 40 cm. These nevi most commonly appear on the trunk but can occur anywhere on the body. They typically present as dark brown to black, often hairy, raised or textured plaques that may be accompanied by multiple smaller satellite nevi scattered across the skin. The condition arises from somatic (postzygotic) mutations, most frequently in the NRAS gene, occurring during embryonic development. The primary body systems affected include the skin and, in some cases, the central nervous system. Neurocutaneous melanocytosis (also called neurocutaneous melanosis) is a serious complication in which melanocytes proliferate within the leptomeninges of the brain and spinal cord, potentially causing seizures, hydrocephalus, and neurological deterioration. Patients with large or giant CMN, particularly those with numerous satellite lesions, carry an increased lifetime risk of developing malignant melanoma, estimated at approximately 2–5% over a lifetime, which can arise within the nevus itself or at extracutaneous sites. Psychosocial impact due to the cosmetic appearance of the lesion is also a significant concern, especially in children. There is currently no curative treatment for large or giant CMN. Management is multidisciplinary and may include serial surgical excision with tissue expansion, dermabrasion, laser therapy, and curettage in the neonatal period, though none of these approaches completely eliminate melanoma risk. Regular dermatologic surveillance and neurological monitoring (including MRI of the brain and spine in high-risk patients) are recommended. Psychological support and counseling are important components of care. Research into targeted therapies, such as MEK inhibitors directed against the RAS-MAPK pathway, is ongoing but remains investigational.

Common questions about Large/giant congenital melanocytic nevus