Oviductal Adenoma in a Mare

A 10-year-old Rocky Mountain Saddle Horse mare was initially presented for erratic estrous cycles, infertility, and an enlarged ovary. The initial differential diagnosis list comprised neoplastic and nonneoplastic ovarian conditions. The primary differential diagnosis of granulosa cell tumor was deemed less likely because of clinical findings and laboratory results. Because of the chronic nature and apparent infertility resulting from the abnormal ovary, surgery was elected to remove the affected ovary. Exploratory laparotomy confirmed the presence of the enlarged ovary; however, a larger oviductal tumor was discovered. Both the ovary and tumor were removed and the mare recovered uneventfully. The mare cycled normally, conceived, delivered a healthy foal, and is currently in late gestation with her second pregnancy.