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Congenital Moles

Traditionally, a giant congenital nevus is greater than 20 centimeters (cm) in diameter, while a small nevi is less than 1.5 cm. A more practical classification has been suggested, depending on the ease of surgical removal and the anatomic location of the mole. For example, a nevus that cannot be easily stitched and may require a graft after removal is considered large. Similarly, a nevus that occupies a significant proportion of one anatomic area, such as the neck or an extremity, would be considered large. On the other hand, a nevus that can be removed relatively simply or that occupies a minor portion of an anatomic area is considered small.

Cause

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.

Signs and Symptoms

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.

Large congenital nevi, particularly those overlying the head, neck, or spine, has been associated with melanocyte proliferation in the soft tissues surrounding the brain and spinal cord. This may be of clinical importance, as it can give rise to excessive fluid accumulation around the brain, seizures, or melanoma. The incidence of this melanocyte proliferation is not known, as it is not always symptomatic.

Congenital nevi typically grow in proportion to the developing child, although rapid periods of enlargement can be seen.

Diagnosis

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.

Treatment

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.

Laser treatment may lighten areas of the nevus and improve its appearance, but it is not recommended because it doesn't remove the deeper pigment cells where malignant changes occur.

Management of small congenital nevi remains controversial because there is little agreement on their associated potential for malignancy. Nevertheless, most dermatologists believe that small congenital nevi can become malignant, though the percentage is quite low.

Photographs are useful in tracking these nevi, which typically evolve and change as a child grows. In general, small congenital nevi have minimal risk for melanoma before the age of 12. At that time, the risk increases and it becomes more difficult for parents to monitor the lesions. Some doctors advocate following the lesions, and others suggest removing all small congenital nevi. An atypical-looking nevus should be evaluated for excision as soon as possible.

Prognosis

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.

Prevention

Congenital nevi, large and small, cannot be prevented. However, malignant changes can be avoided by careful monitoring and, perhaps, prophylactic removal.

Moles (Nevi), Congenital Nevus reprinted with permission from dermatologychannel.net
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