Congenital nevi appear on approximately 1 percent of newborns. A congenital nevus (plural: nevi) is a mole that is present at or develops shortly after birth. A distinction is made between small and giant nevi.
While congenital nevi are typically larger than common acquired nevi, they cannot always be distinguished by size alone. They often are round or oval, clearly demarcated, and sometimes slightly elevated. Pigmentation usually is even, although some congenital nevi have a speckled appearance. Coarse, dark, hairs may be present, and the surface sometimes has a pebbled texture.
Familial tendencies exist. Approximately 1 in 20,000 newborns is found to have a large congenital nevus. Melanocytes (pigment-producing skin cells) are found in utero at about 40 days gestation, and it is thought that congenital nevi develop between the 2nd and 6th months of gestation.
Congenital nevi, large and small, cannot be prevented. However, malignant changes can be avoided by careful monitoring and, perhaps, prophylactic removal.
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.
For those who develop melanoma in a large congenital nevus, the prognosis usually is poor. Signs of malignant change include sudden development of a nodule, an ulcer, or itching within the lesion, as well as pain, bleeding, and pigment changes.
Treatment of congenital nevi depends on size of the lesion, location, perceived risk for melanoma, and cosmetic outcome. The lifetime risk of malignant degeneration in a large congenital nevus is approximately 6 percent. In these cases, melanoma can arise in the first few years of life, and excision should be considered as soon as possible. Management is based on the individual and should be determined after consultation with parents and the medical team. When lesions are so extensive as to involve most areas of the skin, excision is not feasible and clinical follow-up is important to detect any early changes.