Vulvovaginal melanocytic lesions: a review

Pigmented lesions of the vulva and vagina occur commonly and can be challenging both clinically and microscopically. Vulvovaginal melanotic macules are the most common pigmented vulvar lesion. Mucosal vitiligo can be confined to the anogenital region. Acquired melanocytic nevi of the vulva comprise approximately 10%–12% of pigmented vulvar lesions. Blue and Spitz (spindled and epithelioid cell) nevi can occur rarely in the vulvovaginal area. Although pigmented and lentiginous in histologic appearance, melanocytic lesions associated with lichen sclerosus have a “trizonal” pattern of growth, similar to recurrent nevi, which can be helpful in distinguishing them from melanoma. Atypical genital nevi are symmetrical and circumscribed and are typically comprised of confluent growth of nests of melanocytes with variable size and shape and melanocytes demonstrate uniform cytologic atypia. In contrast to dysplastic nevi, atypical genital nevi often do not have a prominent host response and display a broad pattern of fibrosis instead of fibrolamellar fibrosis. Nuclear immunostains such as Sox10 and MiTF can be very helpful in assessing the margins of vulvar melanoma which frequently are multifocal. Recognition of these features can be helpful in classifying the pigmented lesions of the vulva.