Difficulties of morphologic diagnosis of congenital melanocytic nevi

Morphologic diagnostics of melanocytic neoplasms can cause considerable difficulties. There are no absolute criteria to determine the malignancy potential in controversial cases. A clinical and morphologic observation of an intradermal nevus with histologic features of congenital nevus is presented. The features of congenital nevus – involvement of epithelium of skin appendages, growth around appendages and vessels, invagination of nevoid cells in the lumen of lymphatic vessels – are revealed. In differential diagnosis of melanocytic neoplasms of the skin, a morphologist should evaluate not only the presence/absence of signs of atypism and polymorphism of nevomelanocytes, but also signs characteristic of congenital nevi – growth around skin appendages with possible involvement of epithelium, as well as accumulations of nevomelanocytes around vessels with possible presence of nevomelanocytes in the lumen of lymphatic vessels. Expression of HMB-45 and CyclinD1 in few superficial melanocytes, low proliferative activity (as measured by Ki67) along with histologic features allow diagnosing melanocytic nevus with congenital features.