Congenital nevomelanocytic nevi (CNN) are pigmented lesions of the skin usually present at birth; rare varieties of CNN can develop and become clinically apparent during infancy. CNN may be any size from very small to very large. CNN are benign neoplasms composed of cells called nevomelanocytes. which are derived from melanoblasts. All CNN, regardless of size, may be precursors of malignant melanoma.
Causes of Congenital Nevomelanocytic Nevus
Congenital and acquired nevomelanocytic nevi are presumed to occur as the result of a developmental defect in neural crest-derived melanoblasts. This defect probably occurs after 10 weeks in utero but before the sixth uterine month; the occurrence of the “split” nevus of the eyelid is an indication that nevomelanocytes migrating from the neural crest were in place in this site before the eyelids split (24 weeks).
Treatment
Small Nevi Nevi <1.5 cm that are not known to be present at birth should be assumed to be acquired and be managed according to the appearance and growth pattern. Atypical-appearing CNN should be removed. Small CNN should be removed before age 12 years.
Large Nevi Nevi >1.5 cm that are not obviously dysplastic melanocytic nevi should be managed as CNN when the history is not available.
Alternatives Prophylactic excision, periodic follow-up for life, or patient’s parents or patient advised to see physician only if a change (color, pattern, size) in the lesion.
Surgical Excision Surgical excision is the only acceptable method.
Small and large CNN: Excision, with fullthickness skin graft, if required; swing flaps, tissue expanders for large lesions.
Giant CNN: Risk of development of melanoma is significant even in the first 3 to 5 years of age, and thus giant CNN should be removed as soon as possible. Individual considerations are necessary (size, location, degree of loss of function, or amount of mutilation). New surgical techniques utilizing the patient’s own normal skin grown in tissue culture can now be used to facilitate removal of very large CNN. Also, tissue expanders can be used.
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