There are a few cases where a GCT has been detected following these tumours bleeding and rendering the horse weak and lethargic due to the blood loss. These mares would have had clinical signs directly related to the blood loss including pale mucus membranes, low red cell counts, and blood in the abdomen.
Veterinary practitioners skilled in rectal palpation can make a preliminary diagnosis of a GCT based on the large size of the ovary, the consistency it palpates, the lack of an ovulation fossa, and the reduced size of the contralateral ovary, but confirmation is usually done with ultrasonography and blood tests. Many GCTs have a characteristic honeycombed or small cyst-like appearance with areas of fibrous tissue and a lack of normal ovarian stromal tissue. The ovary on the other side is small and has no or very few follicles visible and there is seldom evidence of ovulation tissue. This will change depending on how long the tumour has been active as in the early stages of the tumour, some follicular activity may be apparent – but the longer the tumour is allowed to grow and secrete hormones, the more atrophied and nonfunctional the contralateral ovary will become. The exception to this would be in the rare case of bilateral ovarian GCTs occurring, and in these cases hormonal assays are the only way to confirm the diagnosis.
GCT release high levels of hormones (anti-Mullerian hormone, testosterone, and inhibin) that circulate and are detected via receptors in the brain and on the contralateral ovary, causing suppression of follicular development in this ovary. Using this knowledge, tests have been developed to detect elevations in theses hormones to confirm a diagnosis of a GCT. Currently, AMH levels are the most accurate hormone assays to confirm the presence of a GCT, with their sensitivity being close to 98%.
Several decades ago, inhibin was the hormone of choice for detecting these tumours, but it was less accurate at confirming the tumour and more difficult to get a laboratory to perform, so is infrequently performed now. Testosterone has also been used as an indicator of GCT but can be elevated for other reasons and is much less reliable in detection of a positive case.
TREATMENT OF CHOICE
Treatment of choice is surgical removal of the affected ovary, and this can be performed several ways. The preferred method is to remove the affected ovary whilst the mare is heavily sedated rather than using a general anaesthesia, although this is not always possible.