This 10 year old female presented with a pigmented papule on her vulva. A subset of genital nevi look unremarkable clinically but have atypical histologic features. This is well-described in the literature. Genital nevi include those on the labia, mons, perineum, penis and scrotum. The histologic features may mimic nodular melanoma. Often times, these nevi have large expansile nests, located at all positions along the retia. There is typically loss of cellular cohesion. There may be cytologic atypia, both epidermally and dermally. Rare mitoses may even be observed. Because it is rare for premenapausal women to develop vulvar melanoma, these features should be heavily scrutinized and the lesion excised if in doubt [J Cutan Pathol 2008;35:889-898].
The melanocytic nests are large and expansile. They are located at all positions along the retia. There is the appearance of loss of cellular cohesion within the nests. Individual melanocytes are enlarged. Mitotic activity is not appreciated.