Superficial Myofibroblastoma in the Vulva Mimicking Aggressive Angiomyxoma: A Case Report and Review of the Literature

Background: Superficial myofibroblastoma (SMF) is a very rare benign mesenchymal tumor in the female lower genital tract. Only 46 cases have been reported in the English language literature, among which only 7 cases arose in the vulva. Sometimes SMF histologically mimics aggressive angiomyxoma (AA) in which massive myxoid change in stroma is characteristic. We herein report a case of vulvar SMF with prominent myxoid stroma and review the literature with the emphasis on the differential diagnosis of SMF and AA. Case presentation: a 37-year-old woman presented with a painless mass in the vulva. Magnetic resonance imaging (MRI) showed a well-circumscribed 7 cm mass in the subcutis of the vulva. The tumor was resected. Histopathologically, the tumor was characterized by sparsely populated spindle-shaped cells in the fibromyxoid stroma. Thin-walled blood vessels were detected. Mitoses or pleomorphism was not found. Tumor cells were positive for vimentin, ER, PgR, and desmin. Some cells were positive for alpha-SMA and CD34. All cells were negative for S100 protein. Conclusions: because SMF and AA show different clinical prognoses, distinguishing SMF from AA is important. However, SMF may share many common histological features with AA: superficial localization (above fascia), sharp borderline from adjacent tissue, expansive growth pattern; a specific vascular pattern will lead to an accurate diagnosis of SMF. Familiarization with the histological characteristics of the two entities will help to make a prognostic prediction.