Moles Birthmark Congenital Nevi
Congenital nevi are benign skin tumors composed of melanocyte-derived nevus cells, present at birth, or appearing by age 2. They are considered to be a type of birthmark, of which there are many variants. Roughly 1% of newborns have at least one melanocytic nevus. They may increase in size and become more heavily pigmented during puberty. Congenital melanocytic nevi are usually dark brown and raised, with an irregular verrucous surface. Most have increased course terminal hairs.
Congenital melanocytic nevi vary greatly in size. Depending on their location, large lesions may be disfiguring. The largest lesions are referred to as giant hairy nevi. Giant congenital nevi on the trunk are referred to as bathing trunk nevi. Congenital nevi 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.
The vast majority of congenital melanocytic nevi are benign and follow a life-long course of maturation. Nevi which deviate from this pattern are suspicious and biopsy is warranted. The risk of malignant degeneration occurring in congenital melanocytic nevi is controversial. In general, the risk of malignant change is increased in giant congenital melanocytic nevi with diameters greater than 20 cm with a lifetime risk of 5-8%. The lifetime risk of melanoma developing in smaller congenital nevi is unclear, but may be increased in those larger than 2 cm. Nevus cells in congenital nevi often extend into subcutaneous fat, therefore such malignant change may not be easily detected. For this reason, some dermatologists favor elective excision of congenital nevi when feasible, usually around the time of puberty.