Congenital nevi are by definition present at birth; multiple studies confirm the presence of a pigmented mole in 1% of the newborn population. The vast majority of congenital nevi are the small type. In clinical practice, isolated medium-sized lesions are rarely encountered. Large congenital moles are very rare, and are estimated to occur in 1 of every 20,000 live births. Current nomenclature is based on their size during infancy.
• Large congenital melanotic nevus (LCMN): >20 cm diameter
• Medium congenital melanotic nevus (MCMN): 1.5 to 20 cm diameter
• Small congenital melanotic nevus (SCMN): <1.5 cm diameter
As moles are basically benign hamartomas composed predominantly of nevus cells, it is not surprising that congenital nevi have an acquired counterpart. Some of the other benign hamartomas of skin first appear after birth. In a population of newborns who were examined and found to be free of pigmented nevi at birth, a reevaluation at 2 to 3 years revealed moles in 25%, and half of these "acquired" lesions showed a "congenital pattern" on microscopy. These acquired congenital-pattern melonotic nevi (AcpN) were also clinically different from common acquired moles, tending to be larger in size and with speckles and variegated color. This report has established AcpN as a distinct entity. At the present time their true incidence is unknown because it is uncertain how late in life they may continue to appear. Other benign hamartomas, such as Becker's nevus, for example, may not become clinically apparent until well into early adulthood.
LCMN are striking lesions, which often cover major anatomic areas. This explains the many descriptive eponyms listed above. These nevi usually change during infancy and childhood. After birth, the lesions may extend, but for the most part their growth is concordant with that of the child. It is common for them to become thickened and rugose; these features are especially common when they occur over the scalp. Several small or medium-sized satellite CMN are common in the same infant, and these may be spread over wide anatomic areas. As the child matures, the color of the LCMN often lightens;
however, at puberty the hairs on their surface become coarser, darker, and more noticeable. About 20% of patients experience varying degrees of chronic pruritus. Nodular and lobular areas may develop due to growth of the nevus or the occurrence of other hamar-tomas within the mole. In a small percentage of cases, total regression has been reported; one of the authors has personally seen two cases of regressed MCMN and is following a patient with a LCMN where several medium-sized satellites have regressed along with substantial regression of the main lesion.
LCMN are without question potential precursor lesions for malignant melanoma. The incidence of malignant change is quoted from 5 to 20% over a lifetime. At present the true incidence appears to be 5 to 15%. Half of these melanomas occur before age 3 years. Malignancies often arise deep in the mole, masking the early clinical signs for melanoma. The benign evolutionary changes described, and the presence of other benign tumors arising inside the nevus, make these lesions extremely difficult to follow.
Small and medium-sized CMN generally grow concordantly with the individual. These are often striking lesions and the majority of teen-aged and adult victims consider them "ugly" or embarrassing. Like the large version, they tend to become hairier, coarser, and more noticeable with age. These nevi may lighten in color, but also may become more raised and mammillated. Confirmed reports of melanoma arising in these smaller CMN are published, and although the lifetime risk appears to be much smaller than with the large type, the risk is not nonexistent. One study calculated a 21-fold lifetime risk based on historical information regarding a preexisting birth lesion. The same report calculates a 3- to 10-fold increased lifetime risk based on histologic findings. All previous attempts at quantifying the incidence fail to take into account the more common AcpN. Some investigators suggest that malignant change in a SCMN is very rare in the first two decades of life. Again, however, reports of such change exist and it should be recalled that it was only a few decades ago that the common wisdom considered all childhood melanoma to be nonexistent.
Evolution of Skin Lesions
See Evolution of Disease Process section above.
Provoking Factors None.
Self-treatment is not a problem.
Supplemental Review From General History None indicated.
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