HYPERMELANOTIC NEVUS - CLINICAL, HISTOPATHOLOGIC, AND ULTRASTRUCTURALFEATURES IN 316 CASES

We report on a series of benign melanocytic nevi that have unique clin ical, histopathologic, and ultrastructural features. Between March 199 3 and February 1994, 316 examples of hypermelanotic nevi were received by the dermatopathology laboratory at Denver General Hospital. Our st udy identified the clinical characteristics, histopathologic criteria, and ultrastructure of this lesion. Clinically, the lesions were dark brown to black macules or papules. The most common location was the ba ck. There was a slight female predominance, and the mean age of our pa tients was 40 years. Histopathologically, the nevus showed the followi ng characteristics: (a) melanin within a compact stratum corneum, (b) small nests of nevus cells at the dermal-epidermal junction and (in 52 % of the cases), nests within the papillary dermis, (c) heavy melanin within keratinocytes in the lower epidermis, (d) a sparse to moderate lymphocytic infiltrate and melanophages in the superficial dermis, and (e) an absence of cytologic atypia. Electron microscopy revealed that abundant melanin was packaged in melanosome complexes within keratino cytes. Less pigmented melanocytes and nevus cells contained well-devel oped dendritic processes and golgi, indicative of efficient melanin tr ansfer. According to our retrospective case control analysis, patients with hypermelanotic nevi were older and more likely to be male than t hose with ordinary nevi. Hypermelanotic nevi were more likely than con trols to be junctional nevi; they were smaller, dark brown or black in color, and clinically suspicious for melanoma. We propose the name '' hypermelanotic nevus'' to describe this benign lesion, which is often biopsied to exclude melanoma.