PLE-4583

A 28-year-old nulligravid woman comes for a routine health maintenance examination. She has had progressively severe dysmenorrhea over the past 6 months, adequately controlled by nonsteroidal anti-inflammatory agents. Pelvic examination shows a normal vagina and cervix. The uterus is retroverted and fixed, and there is nodularity of the cul-de-sac. A 6-cm left adnexal mass is palpated. Transvaginal ultrasonography shows a 7-cm septated adnexal mass. Four weeks later, there is no change in the size of the adnexal mass. Which of the following is the most appropriate diagnostic test?