Clinically atypical moles may have no evident atypia on biopsy because the asymmetrical pigment of the mole can be created by diffuse pigment in the superficial dermal naevus cells.
A 32-year-old woman with olive skin presented with an isolated, asymmetrically pigmented mole (measuring 0.6 by 0.4 cm) on her mid back (Figure 1). Dermoscopy revealed a symmetrically shaped mole that had a fine peripheral pigment network and a dark brown, partly homogeneous central zone with a jagged perimeter and patchy milky veil (Figure 2). Excision biopsy revealed an epidermis with an elongated pigmented rete ridge system containing isolated melanocyte nests (Figure 3). The dermis had a diffuse infiltrate of naevus cells. The superficial dermal naevus cells were pigmented.