a rare case of a giant cystic leiomyoma presenting as a retroperitoneal mass

background: giant retroperitoneal uterine leiomyomas are uncommon. degenerative changes of a leiomyoma may lead to unusual presentation resulting in misdiagnosis preoperatively. the final diagnosis can be made either intraoperatively or histologically. case: we report a 45-year-old multiparous women presented with abdominal distension and fatigue for six months. abdominopelvic sonography and computed tomography showed a large cystic mass that filled the pelvis and abdomen. with the preoperative diagnosis of a malignant tumor, a laparotomy was planned. intraoperatively, a cystic mass originated from the uterus near the left side of the broad ligament extending to the retroperitoneal space was observed. total hysterectomy and bilateral salphingo-oopherectomy was administered. the histology revealed a leiomyoma with cystic degeneration. conclusion: retroperitoneal leiomyomas should be kept in mind in the diferrential diagnosis of a giant cystic mass in abdomen