|
| 
Information About Congenital Nevus What is a congenital nevus?
As mentioned on the Home page, a congenital nevus is a mole that is present birth. In some cases the nevi are very pale at birth and become obvious shortly after birth. These moles usually do not run in families (usually are not inherited).
Congenital nevi vary tremendously in size. They are somewhat arbitrarily divided into small, medium and large categories. To be considered a large (or so-called Giant Nevus), the lesion must be more than 20 cm in greatest dimension as an adult. In other words, a nevus can be considered a Giant Nevus in a child even if it is less than 20 cm in diameter if it is estimated that it will be greater than 20 cm in diameter when the child becomes an adult. This means that in an infant a 6 cm nevus on the trunk or a 9 cm nevus on the scalp would be considered a Giant Nevus.
Giant nevi often involve more than one anatomic zone. They may not be confined to the back but, rather, may involve, for example, the back, buttocks and one thigh. With time these nevi tend to become more hairy and more textured—hence the term Giant Hairy Nevus. The presence of hair or the quality of the hair has no effect on the prognosis of a nevus. The patients with large nevi may also have multiple small congenital nevi, surrounding the main nevus, known as satellite nevi.
The main reason to remove these lesions surgically is that most parents consider them unsightly and would rather their children have the scars associated with surgery than have the hairy, pigmented lesion.
Malignant melanoma. The more difficult problem is the risk for malignant transformation of the congenital nevus to malignant melanoma. The lifetime risk for melanoma arising in small congenital nevi is between 0%-5%. The risk in large congenital nevi is definitely higher and is estimated to be between 5-10%. What has not been proven is that removing the nevi surgically actually reduces the risk of melanoma. What is clear is that the melanomas that arise in large nevi are more likely to develop in the first decade of life. Therefore, if surgery is recommended, it should be done as early in life as possible. Of note, no melanoma has ever been reported in a satellite of a large nevus.
Neurocutaneous melanosis. Some patients with large nevi also have the nevus cells in their central nervous system. This is called neurocutaneous melanosis. Neurocutaneous melanosis can usually be seen on an MRI scan. Patients with this entity may develop hydrocephalus (excessive fluid on the brain) or even malignant melanoma in the central nervous system.
Treatment. Although other forms of treatment have been attempted, the standard treatment is surgical excision. Excision can be performed in one stage for smaller lesions but larger lesions require multiple stages or placement of tissue expanders. Tissue expanders are like balloons that are placed below the normal skin, adjacent to the nevus, and are gradually inflated in the doctor’s office over the course of weeks or months, until extra skin is created. The nevus, or a portion of it, is then excised and the extra skin created by the expander is used to close the wound. Large nevi frequently require several stages of expansion and excision. In some places like the nose, ears or eyelids, better results are obtained by removing the mole and replacing the skin with skin grafts taken from another part of the body.
|
