Supernumerary ovary found by ultrasonogram and FSH measurement after an extensive operation for a yolk sac tumor of the ovary.

A rare case of supernumerary ovary found by a transvaginal ultrasonogram and follicle-stimulating hormone (FSH) measurement is presented. The patient was a 32-year-old female who underwent an extensive operation for a yolk sac tumor of the ovary. An asymptomatic cystic tumor was found during follow-up. There was no evidence of recurrence or metastasis of the yolk sac tumor. Although histological confirmation was not possible because the patient refused removal of the mass, a diagnosis of supernumerary ovary was made because changes in the shape of the cystic mass completely correlated with changes in the serum FSH level.