Large retroperitoneal leiomyoma developed from the pelvic floor to the buttocks.

Retroperitoneal leiomyoma is a very rare disease, with little reported information on its origin. Herein, we report a case of a large retroperitoneal leiomyoma that developed from the pelvic floor. A 44-year-old woman had a large mass protruding outside the body from the right hip. Imaging revealed a large tumor developing from the pelvic floor to the buttocks. It was difficult to identify the place of origin. Upon preoperative biopsy, the patient was diagnosed with retroperitoneal leiomyoma. Tumor removal with abdominoperineal and partial vaginal resection was performed. Based on the histological findings of the surgical specimens, she was diagnosed with a retroperitoneal leiomyoma (gynecologic type) via immunohistochemistry, the tumor cells were positive for αSMA, desmin, estrogen receptor(ER), and progesterone receptor(PgR), but negative for myoglobin, S-100, CD34, and MIB-1.This is a case of a large retroperitoneal leiomyoma that was successfully removed via abdominoperineal and partial vaginal resection.