Diagnosis of Congenital Nevus
The distinction between congenital nevi and other forms of acquired nevi usually can be made on clinical examination. Any nevus larger than 1.5 cm is likely to be congenital. Some distinguishing pathological features, from skin biopsy, can help diagnose congenital nevi.
Melanoma often can be diagnosed from clinical presentation, but microscopic confirmation always must be obtained. The relationship between congenital nevi and melanoma is well documented, although the incidence of association has generated some disagreement. While the malignant potential for small congenital nevi, particularly of the limbs, is quite small and may not be above normal risk, melanoma can arise within very large congenital nevi, even within the first few years of life.