Superficial congenital compound melanocytic nevus. Another pitfall in the diagnosis of malignant melanoma

We reviewed the histology of 42 superficial congenital compound melanocytic nevi and found features that simulate malignant melanoma. In some, there were asymmetry and poor circumscription, an increased number of single melanocytes, which predominated over nests of melanocytes in some high power fields, single melanocytes were not equidistant from one another, scatter of single melanocytes was above the dermoepidermal junction, and there was confluence of nests of melanocytes, which are features in common with a malignant melanoma.

Fifty-six percent of the cases had three to four criteria present, and 92% of the cases had three to six criteria present. The mean age of the patients at the time of biopsy was 20 years, and the mean size of the nevus at time of biopsy was 1.7 cm.

Appreciation that simulation of a melanoma in situ by the epidermal component of a superficial congenital compound melanocytic nevus in older children and adults is an expected finding and may be similar to congenital nevi biopsied shortly after birth has not been emphasized. Awareness of these simulants may prevent misinterpretation of a benign superficial congenital compound melanocytic nevus as a malignant melanoma.