Clinical, morphological and differential diagnosis chartecteristics of atypical melanocytic nevi

Abstract

Dysplastic nevi are a group that is histologically characterized by architectural and cytological atypia and are considered as an intermediate group of pigmented lesions between normal and malignant melanoma. Like all other pigmented neoplasms, they are the result of exposure to genetic and phenotypic factors, solar hypersensitivity and chronic ultraviolet exposure. Clinically, dysplastic nevi are larger than the common ones, larger than 6 mm, asymmetrical, with a slightly uneven surface and uneven borders, poorly demarcated from the surrounding skin and usually with bicolored areas. These are difficult to diagnose melanocyte lesions, and the histological criteria determining their belonging to this group include the presence of architectural disorders, cytological atypia and manifestations of an immune response by the macroorganism. Architecturally, they manifest with a lentiginous type of melanocyte proliferation in which melanocytes are distributed at the border with the basal layer of the elongated, rounded apical and hyperpigmented epidermal ridges. Cell proliferation at the tips of the epidermal ridges displaces basal keratinocytes and coalesces with the formation of bridge structures around the dermal papillae. Their cytological characteristics include different variations. In nevi with a dominant lentiginous architectural appearance, basal melanocytes with cytoplasmic retraction are often observed. Small, rounded nevus cells, elongated cells with varying pigmentation, and epithelioid cell types were observed in nest-dominated forms of the atypical nevus. Beyond these cell types, the appearance of cytological atypism in intraepidermal melanocytes is a major criterion for diagnosing nevi as atypical. The cells have a varying degree of nuclear atypism, involving no more than 5% of all cells. Based on the criteria, atypism is divided into three degrees - mild, moderate, and severe. The International Melanoma Pathology Group recommends dysplasia to be classified into two groups only – low- and high-grade.