Pelvic retroperitoneal leiomyoma.

Primary retroperitoneal leiomyomas are a rare and unusual differential diagnosis in the acute abdomen. A 26-year-old woman presented with chronic constipation and acute abdominal pain. The diagnostic workup included contrast computer tomography, transabdominal ultrasonography, and colonoscopy that revealed an 8-cm homogeneous pelvic tumor with rectal compression. Retroperitoneal leiomyoma was suspected on imaging studies and finally confirmed after tumor excision and immunohistochemical staining.