Myxoid Solitary Fibrous Tumor of the Vulva: A Diagnostic Pitfall.

Solitary fibrous tumor (SFT) is a rare fibroblastic neoplasm that may occur at various anatomic sites, whereas vulvar involvement is exceptional. The myxoid variant of SFT, defined by extensive myxoid stromal change, is exceedingly uncommon and may present diagnostic challenges due to atypical radiologic and histologic features. We report a case of a 35-yr-old woman with a slowly enlarging vulvar mass radiologically interpreted as a benign cystic lesion. Histologic examination revealed a predominantly myxoid spindle cell tumor with staghorn vascular features in its periphery. Immunohistochemistry showed diffuse nuclear STAT6 and CD34 positivity, and molecular analysis confirmed a NAB2:::STAT6 fusion. This case highlights the diagnostic pitfalls associated with myxoid change in vulvar mesenchymal tumors and underscores the importance of immunohistochemical and molecular confirmation.