Answer:
The incidence of malignant transformation is not accurately known and the literature reports ranges from 10% to 20%. These figures however are probably overestimation from special centers with known interest in the problem. The true incidence is probably closer to 5% from Scandanavian data where there is a national registry. Congenital nevi are classified as small (less than 1.5 cm in diameter), large (between 1.5 and 19.5 cm), and giant (greater than 20 cm).
Excision is recommended in the 6-9 month age range. Methods used include direct excision, direct excision with tissue expansion, and skin grafting, both meshed and unmeshed. When possible skin grafting is avoided in favor of skin expansion, and the skin of the child seems to be particularly accepting of repeated expansion procedures.