What are Congenital Melanocytic Nevi

Incidence: About 1% of newborns have at least one melanocytic nevus.

Onset: Present at birth, or appearing by age 2.

Course: The vast majority of congenital melanocytic nevi are benign and follow a life-long course of maturation. They increase in size and become more heavily pigmented during puberty.

Size: Congenital melanocytic nevi vary greatly in size.

Appearance: Congenital melanocytic nevi are considered to be a type of birthmark, of which there are many variants. They are usually dark brown and raised, with an irregular verrucous surface. Most have increased coarse terminal hairs.

Symptoms: Depending on their location, large lesions may be disfiguring.

Diagnosis: Depending on their onset, course and appearance, most congenital nevi are diagnosed. Nevi which deviate from the urdinary pattern of maturation are suspicious and biopsy is warranted.

Histopathology: Congenital nevi are benign skin tumors composed of melanocyte-derived nevus cells, they are usually compound nevi with nested nevus cells at the junction and also in the dermis. Nevus cells may extend into fat and invest adnexal structures and blood vessels.

Progression: The risk of malignant transformation is increased in giant congenital melanocytic nevi with diameters greater than 20 cm with a lifetime risk of 5-8%. Melanoma developing in smaller congenital nevi may have an increased lifetime risk in those larger than 2 cm.

Treatment: Nevus cells in congenital nevi often extend into subcutaneous fat, therefore a malignant change may not be easily detected. For this reason, elective excision when feasible (usually around the time of puberty) is favored.
















Melanoma developing in a congenital nevus