Diagnosis, treatment, and outcome of luteoma in a mare

A 5-year, grade mare in a commercial recipient herd was presented for transrectal palpation and ultrasonography; mare had a follicle on the left ovary that continued to grow for ~ 2 months with typical cyclic activity on the right ovary. Blood was submitted for granulosa cell tumor (GCT) endocrine panel (inhibin B, testosterone, and antimüllerian hormone [AMH]). Serum testosterone concentrations (49.5 pg/ml; normal range: 20-45 pg/ml) and AMH concentrations (> 14 ng/ml; normal range: 0.1-6.9 ng/ml) were higher, and inhibin B concentrations were normal (61.9 pg/ml; normal range: 60.1-100 pg/ml). Based on abnormal left ovarian structure and GCT panel results, left ovariectomy was performed; left ovarian luteoma was diagnosed histologically. Mare resumed cyclicity on the right ovary and returned to the recipient mare herd. Increased inhibin B and AMH concentrations were previously reported in 2 mares with luteoma (diagnosed after ovariectomy); however, this is the first report documenting increased testosterone concentrations. Although luteoma is an uncommon diagnosis, it should be considered as a differential for abnormal ovarian structures, abnormal behavior, and altered ovarian hormone profile.