Histopathologic diagnosis of pigmented lesions of the skin.

The present review deals with the histopathologic diagnosis of the commonest pigmented lesions of the skin with emphasis on melanocytic tumors. The discussed entities are systematized in pigmented lesions with and without an increase in the number of melanocytes, i.e. melanocytic hyperplasia, and in those that actually are melanocytic neoplasias. Histopathological, ultrastructural, and immunohistochemical features of relevance for the differential diagnosis are discussed in depth. One section is dedicated to the immunohistochemical markers of melanocytic lesions, the other one to the electron microscopy of malignant melanoma. Neoplasms simulating malignant melanoma and the less frequent variants of this tumor are also discussed. The diagnosis of pigmented lesions of the skin represents one of the most frequent and difficult challenges in dermatopathology, and useful clues for the differential diagnosis, especially of melanocytic dysplasias and neoplasias, are presented in the present article.