Inverted follicular keratosis of the vulvar skin: a lesion that can be confused with squamous cell carcinoma.

Although seborrheic keratoses of the vulva are described in textbooks, to our knowledge, inverted follicular keratosis has not been reported. A 27-year-old woman underwent an excisional biopsy for a small lesion of the left labium majus. Squamous cell carcinoma was considered in the clinical differential diagnosis. The initial pathologic diagnosis suggested squamous cell carcinoma in situ, and the consultation diagnosis was superficially invasive squamous cell carcinoma. On pathologic examination, a symmetrical, endophytic, epithelial tumor was observed consisting of a proliferation of basaloid cells with many areas of reactive squamous cells showing numerous squamous eddies, focal reactive nuclear atypia, and occasional mitotic figures. After the pathologic diagnosis of inverted follicular keratosis was made, a history of close perineal shaving and total body tanning was obtained. Because inverted follicular keratosis is postulated to be related to follicular injury, it is likely that the trauma of close shaving is a significant etiologic factor. There is less evidence that ultraviolet ray exposure is of etiologic importance.