Paravaginal female adnexal tumor of probable Wolffian origin mimicking vaginal spindle cell epithelioma on biopsy

Female adnexal tumor of probable wolffian origin (FATWO) is a tumor of low malignant potential that arises predominantly in the broad ligament, mesosalpinx, and ovarian hilus. The rarity of FATWO increases its susceptibility to misdiagnosis as other tumors, especially when it occurs at an unusual site. We report a 29-year-old woman with a 7.2 cm left paravaginal FATWO that invaded into the vaginal lumen. The initial biopsy demonstrated features suggestive of vaginal spindle cell epithelioma, but with increased Ki67 proliferation index. Pathologists should be aware that the common sieve-like architecture of FATWO may not be apparent on small biopsies, which by sampling error may demonstrate predominantly the less common spindle cell architecture. Awareness of FATWO in the differential diagnosis of paravaginal tumors may help to avoid misinterpretation as vaginal spindle cell epithelioma, a previously unappreciated pitfall in the diagnosis of FATWO.