Benign atypical junctional melanocytic hyperplasia associated with intradermal nevi:: A common finding that may be confused with melanoma in situ

Over the past few years, consultation cases thought to represent melanoma in situ have been received that consisted of otherwise normal intradermal nevi with an abnormal but benign functional proliferation of melanocytes that we have termed benign atypical junctional melanocytic hyperplasia. In order to evaluate the incidence of this feature, 400 cases of intradermal nevi were reviewed. Of these, 25 (6.2%) qualified for Inclusion, making this a rather common phenomenon. Clinically, patient ages ranged from 18 to 64 years (mean, 35 years), with a male to female ratio of 1:1. Face (40%) and back (32%) were the most common locations. Histologically, the lesions were predominantly dome-shaped with an Intradermal component consisting of conventional nevus cells. Most importantly, each lesion exhibited prominent individual nevomelanocytic cells dispersed at uneven intervals along the dermoepidermal junction in Insufficient numbers to be considered compound nevi. The cells exhibited abundant pale to clear cytoplasm, an Increased nuclear:cytoplasmic ratio, and often exhibited prominent nucleoli. However, these lesions could be distinguished from melanoma in situ by the lack of several features Including lateral spread, upward epidermal migration, marked cytologic atypia, finely granular "smoky" melanin pigment, mitotic figures, and a subjacent host inflammatory response. All cases behaved in a benign fashion. Although benign atypical junctional melanocytic hyperplasia is a relatively common histological curiosity, it is a potential pitfall in the diagnosis of pigmented lesions.