This 33 year old woman presented with a pigmented papule on her 3rd toe. It was biopsied to rule out melanoma. Acral nevi are a subset of melanocytic nevocellular nevi, which can have atypical clinical and histologic findings, but are benign. Clinically, the lesions often have irregular but sharp borders, likely due to the presence of dermatoglyphs. Histologically, they may also have atypical features. The most notorious and often striking feature is upward migration of melanocytes. This can mimic the pagetoid growth of melanoma in situ. Other features include overall symmetry, maturation with syringotropism, and lack of mitotic activity or significant cytologic atypia [J Cutan Pathol 2008;35:889-898].
The melanocytes proliferate along the junction, with foci of lentiginous growth. There are large nests, positioned along the retia. In one focus, single cells and few aggregates ascend into the epidermis. These are not cytologically atypical.