Abstract
Classification of squamous vulvar precancerous lesions is based on the concept of vulvar intraepithelial neoplasia (VIN) and incorporates a three grade evaluation of the intensity of dysplastic changes (VIN I, II and III). On the basis of histological features, VIN has been subdivided into the usual VIN (u-VIN) and differentiated VIN (d-VIN), which represent the two basic pathways of the pathogenesis of vulvar squamous cell carcinoma.
Although u-VIN is etiologically associated with the human papillomavirus (HPV) infection and histologically corresponds to cervical intraepithelial neoplasia, d-VIN represents the HPV-negative sequence of vulvar carcinogenesis, which is linked to lichen sclerosus (LS) and lichen simplex chronicus (LSC). u-VIN preferentially occurs in relatively young women with a history of cervical, vaginal or vulvar premalignant lesions. On the other hand, d-VIN usually affects postmenopausal women without anamnestic data of other dysplastic lesions of the lower female genital tract. d-VIN is characterized by a higher tendency of stromal invasion than u-VIN and its malignant potential is analogous to carcinoma in situ (VIN III).
The histological appearance of d-VIN is subtle with basal atypia and a well-preserved differentiation of the superficial parts of the squamous epithelium, therefore it is frequently misdiagnosed for u-VIN I, LS or LSC in vulvar biopsies. Primarily because of the low diagnostic reproducibility of the u-VIN I category and the doubts about its precancerous potential as well as due to the questionable differentiation between u-VIN II and III, a revised VIN classification was proposed in 2004.
The grading of vulvar precancerous lesions was abandoned, the u-VIN I category was discontinued and u-VIN II and III were merged. In the revised terminology, the term u-VIN represents HPV-associated high grade precancerous vulvar lesions (formerly u-VIN II and III) and d-VIN encompasses HPV-negative high grade dysplasias.