Special site nevi in pregnancy

Nevi of special sites occur on genital, breast, flexural, and acral skin. Lesions at these locations have distinctive histologic features and display both architectural and cytologic atypia. They can simulate dysplastic nevi or melanoma and therefore cause diagnostic concern. Rarely, pregnancy can induce changes in the color and size of pigmented lesions. Pregnancy can also lead to increased histopathological atypia that can occur in the absence of any clinical change in appearance. A 28-year-old woman was found to have a previously undiagnosed nevus on her perineal region at her first antenatal visit at 8 weeks. The lesion did not appear to change during pregnancy and was removed at the time of delivery. Histologic examination revealed nests of nevus cells at the dermoepidermal junction and focally in the upper papillary dermis which varied in size and shape. There was focal pagetoid spread of melanocytes. No mitotic figures were present. A consultation diagnosis was made of a compound nevus on a "special site." We will discuss the features of special site nevi, changes in nevi during pregnancy, and review the current literature. It is important to differentiate these atypical but benign nevi from more concerning lesions.