A 26-year-old woman experiences the sudden onset of left-sided lower abdominal pain with radiation to the back, pelvis and thigh. Following a negative test for pregnancy, abdominal radiography shows an enlarged left ovary with multiple calcifications. Laparoscopy reveals adnexal torsion and an ovarian tumor. Ovariectomy is performed. The tumor is most likely ?

The radiographic calcifications are highly suggestive of a mature teratoma (dermoid cyst). This tumor is composed of all three germ layers and often contains skin (including adnexal structures, such as sebaceous glands and hair follicles), bone, teeth, cailage and gastrointestinal, neurologic, respiratory and thyroid tissues. As the tumor enlarges, it is at risk of torsion. Granulosa cell tumor presents with signs and symptoms of excess estrogen production. Brenner tumor is rare and histologically resembles transitional epithelium of the bladder. Serous cystadenoma is commonly bilateral. Struma ovarii is a monodermal teratoma composed of functional ectopic thyroid tissue.