What is a congenital nevus?

A congenital nevus, also known as a mole, is a type of pigmented birthmark that appears at birth or during a baby’s first year. These occur in 1% to 2% of the population. These moles are frequently found on the trunk or limbs, although they can appear anywhere on the body.

Most congenital nevi usually do not cause health problems, but a small percentage may develop into skin cancer (melanoma) later in life. The risk of melanoma increases with the size of the nevus.

A rare form of congenital mole is the large congenital melanocytic nevus (LCMN), which occurs in approximately 1 in 20,000 newborns worldwide. LCMN are more than 20 cm2 (which is about 8 inches in width) in adulthood. Some physicians may also refer to these as giant congenital nevi (GCN), which are technically congenital moles that are larger than 40 cm2 in adulthood.

At birth, LCMN and GCN are much smaller in width, but grow proportional to a child’s growth to reach over 20 cm2. These moles have the greatest risk of developing melanoma. When removing these very large moles, a plastic surgeon can help with the surgical excision and any reconstruction that may be needed to minimize scarring and improve appearance.

Signs and symptoms

Congenital nevi (the plural of nevus) can be many colors and may reflect the background color of the skin. Most congenital nevi are a shade of brown.

Long, dark or thick hair may be present in the nevus when it first appears, or can develop over time.

Causes

Congenital nevi are thought to be caused by a genetic mutation, called a sporadic mutation, which develops randomly as a baby grows in the womb. The condition is not inherited.

Treatment

Congenital moles will need to be monitored for skin cancer. Some may also be removed for cosmetic or functional reasons, especially when the placement of a mole causes emotional distress for a child.

Surgical excision remains the standard treatment for removing a congenital nevus. Your child’s physician may recommend the removal of moles with concerning changes, if it is a LCMN or GCN, and if the mole interferes (or may interfere) with your child’s functional development.

For moles that are not malignant and do not present functional concerns, removal is not required.  Your child’s physician will observe the mole and may decide to remove it if surgical excision is necessary.

Large lesions may require excision in stages, and your child’s healthcare team may need to use tissue expanders: This procedure allows the body to “grow” extra skin that can be used to replace tissue lost during the removal of the mole.

Specialists involved with the care and removal of congenital nevi include dermatologists and plastic surgeons. Larger excision and reconstructive efforts benefit from a dedicated care team.

Outlook

Most congenital nevi do not cause health problems and may just require monitoring for the development of skin cancer.

Large congenital nevi are associated with an increased risk of developing an aggressive form of skin cancer known as melanoma. The larger the congenital nevus (e.g. giant congenital nevi), the higher the risk of developing melanoma.