A 42-year-old woman has had menometrorrhagia for the past 2 months. She has no history of prior irregular menstrual bleeding, and she has not yet reached menopause. On physical examination, there are no vaginal or cervical lesions, and the uterus appears normal in size, but there is a right adnexal mass. An abdominal ultrasound scan shows the presence of a 7-cm solid right adnexal mass. Endometrial biopsy shows hyperplastic endometrium, but no cellular atypia. What is the most likely lesion that underlies her menstrual abnormalities?

The mass is probably producing estrogen, which has led to endometrial hyperplasia. Estrogen-producing tumors of the ovary are typically sex cord tumors, such as a granulosa-theca cell tumor or a thecoma-fibroma, the former more often being functional. Teratomas can contain various histologic elements, but not estrogen-producing tissues. Endometriosis can give rise to an adnexal mass called an endometrioma, which enlarges over time. Endometrial glands are hormonally sensitive, but they do not produce hormones. Corpus luteum cysts are common, but they are unlikely to produce estrogens. Metastases to the ovary do not cause increased estrogen production. Polycystic ovarian syndrome would involve both ovaries.