Periodic size changes in a supernumerary ovary with associated corpus luteal cyst.

Supernumerary ovaries are extremely rare. Herein is reported a case of supernumerary ovary detected in a 31-year-old woman who complained of lower abdominal pain on her left side. Ultrasonography indicated a cystic mass in the pelvis, the size of which fluctuated periodically. A laparotomy was performed and indicated two normal ovaries in addition to a cystic mass in the cul-de-sac. Histology of the mass confirmed the presence of both normal ovarian tissue and cystic corpus luteal tissue consistent with the presence of a supernumerary ovary. Examination of the patient's medical history suggested that the supernumerary ovary was likely to be of embryonic origin, and not caused by surgical treatment or inflammation. This is the first report of a supernumerary ovary that was associated with periodic episodes of pain and changes in size, and a giant corpus luteal cyst near the rectum.