Congenital Nevi/Tissue Expansion

CONGENITAL NEVI

Define “congenital.”

Existing at birth.

Does “congenital” imply “hereditary”?

No.

What is a nevus?

A chronic benign lesion of the skin or mucosa, commonly known as “mole” or “birthmark”. Nevi may be either present at birth (congenital) or appear after birth (acquired).

What is a giant nevus?

Predicted to be greater than 20 cm in largest diameter in adulthood, correlating in an infant to 6 cm on the head and 9 cm on the body; greater than 1% body surface area on the head and neck, or 2% on the rest of the body; or, of a size that cannot be excised in a single procedure.

What is the incidence of congenital nevi?

1% to 2%.

What is the incidence of giant nevi?

For lesions greater than or equal to 9.9 cm, approximately 1 in 20,000.

Nevi results from a proliferation of what cells?

Melanocytes, of neuroectodermal origin.

In what layer(s) of the skin do nevi occur?

Dermis and epidermis.

For what cancer are nevi generally considered a risk factor?

Malignant melanoma.

What is the risk of melanoma in one who has a giant congenital nevus?

5% to 7% by the age of 60 is the most often reported range; however, reported incidence in the literature ranges from 0% to 42%.

What is an acquired nevus?

The more common “mole,” the occurrence of which begins in childhood and increases rapidly in adolescence and young adulthood.

How are nevi classified by location and histologic pattern?

Compound, intradermal, and junctional.

What is a compound nevus?

A nevus with fully formed nests of cells in the epidermis and newly forming cells in the dermis.

What is an intradermal nevus?

A nevus with nests of cells located exclusively within the dermis; clinically indistinguishable from a compound nevus.

What is a junctional nevus?

A nevus with nests of cells confined to the dermoepidermal junction; usually presenting as a small, discrete, flat, or slightly raised macule.

How are small congenital nevi managed medically?

Baseline photography and regular follow-up.

What features of small nevi warrant biopsy?

Those features suggestive of melanoma: asymmetry, border irregularity, color variegation, and diameter larger than 6 mm; in addition, any nevus that has changed appearance.

At what location(s) are congenital nevi associated with leptomeningeal melanoma?