Post-operatively, “E” received a constant rate infusion of intravenous lidocaine and crystalloid fluids for 24 hours to help her with post-operative pain and prevent dehydration. She received intravenous antibiotics for two days and Banamine for three days. She was discharged from the hospital with instructions for 30 days of strict stall rest followed by a gradual reconditioning program. She did well post-operatively and had no complications. Her stallion-like behavior resolved by 30 days post-operatively and she reportedly had normal estrus cycles.
EDUCATION:
Granulosa Thecal Cell Tumors (“GCTs”) are the most common tumor of the equine female reproductive tract. The tumors are benign and can occur in mares of any age. The most common clinical sign, or perhaps the one that is most easily observed, is stallion-like behavior. However, there are other common clinical signs that may be less noticeable such as if the mare is always in heat (persistent estrus) or if the mare never comes into heat (persistent anestrus). These clinical signs occur because granulosa cell tumors alter normal sex hormones. The stallion-like behavior is associated with elevated blood testosterone levels. Some mares do not exhibit stallion-like behavior but these mares may show other signs that are seemingly unrelated to the reproductive system such as abdominal discomfort, lameness, and anemia.
Mares with abnormal / aggressive behavior or abnormal cycles should be palpated and ultrasound per rectum. A normal ovary measures ~5x3x3 cm but can vary considerably due to follicular activity and stage in the reproductive cycle. A normal ovary also has a prominent depression called the ovulation fossa, where the egg is released into the fallopian tube. In mares with a GCT, the affected ovary is often enlarged and the ovulation fossa is most often not palpable. On transrectal ultrasound examination the affected ovary has a classic multiloculated appearance. The tumor may also appear solid or having large cyst-like areas. These tumors may be similar in appearance to ovarian hematomas so imaging an abnormal ovary is not a definitive diagnosis for GCT.
Most GCTs are unilateral (only affect one ovary). The non-affected ovary is often smaller than normal and reproductively inactive. Rarely mares will continue to cycle on the normal, unaffected ovary despite the presence of a tumor on the opposite ovary. We have very rarely seen GCTs on both ovaries (ie bilateral). Granulosa Cell Tumors are almost always confined to one or both ovaries, and very, very rarely spread to other organs within the abdominal cavity.
If a GCT is suspected based upon behavior or ultrasound examination of the ovaries, testing the mare’s hormones is recommended. We generally recommend measuring the levels of three hormones: Inhibin, Anti-Mullerian Hormone (AMH) and Testosterone. Inhibin is a hormone that is normally produced in low levels in cycling mares, is nearly indetectable in pregnant mares; it is often elevated in mares with GCTs. Anti-Mullerian Hormone is normally produced in small quantities by the ovary; mares with GCTs will often secrete an abnormally high amount of AMH. Serum testosterone is not as sensitive as Inhibin or AMH for the diagnosis of a granulosa cell tumor, but elevated testosterone levels are supportive of a GCT diagnosis.
Treatment for a granulosa cell tumor involves surgical removal of the affected ovary or (in rare cases) ovaries. The good news is that prognosis for reproductive function in a mare with a unilateral (one-sided) granulosa cell tumor is very good. In mares with a unilateral GCT, once the affected ovary is removed, the opposite ovary often starts cycling normally and the mare can get pregnant or produce embryos for embryo transfer. Time to resumption of normal activity by the remaining ovary varies but usually occurs less than one year after surgery (and frequently within 6 months).
Take Home Message: If your mare is not cycling normally or is displaying aggressive “stallion-like” behavior, we recommend having an ultrasound examination of her ovaries and possible bloodwork to evaluate her reproductive hormones.
