Congenital Mole (Nevus) Overview, Cause

Overview of Congenital Moles

Congenital nevi appear on approximately 1% of newborns. A congenital nevus (plural is nevi) is a mole that is present at or develops shortly after birth. A distinction is made between small and giant nevi.

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Traditionally, a giant congenital nevus is greater than 20 centimeters (cm) in diameter, while a small nevus 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 of Congenital Moles

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.

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