Equine granulosa cell tumours among other ovarian conditions: Diagnostic challenges.

Background: Granulosa cell tumours (GCT) are the most common ovarian tumours in mares. While the classical presentation may not represent diagnostic challenges, diagnosis is not easy in the early stages.

Objectives: Illustrate the variability in the presentation and serum biomarkers associated with ovarian abnormalities in the mare.

Study Design: Retrospective case series.

Methods: Nonclassical cases of GCTs and other ovarian conditions were identified and behaviour, GCT endocrine results, palpation and ultrasonographic findings are described and the diagnostic value of each is discussed.

Results: Mares in this case series with GCTs had been presenting clinical signs ranging from no behavioural changes to behaviours including aggression, stallion-like and inability to work under saddle. Hormonal profiles of endocrinologically functional GCTs can be erratic and unpredictable. The clinical form and ultrasonographic appearance may also vary with time from an initially enlarged/anovulatory follicular structure that later develops a multicystic 'honeycomb' appearance. Mares with GCTs can also present with persistent anovulatory follicles or apparent luteal tissue that are unresponsive to treatment. If both ovaries are of relatively normal size and symmetry, but hormonal biomarkers are markedly increased (AMH >10 ng/mL, inhibin B and/or testosterone >100 pg/mL; 0.37 nmol/L), it is likely that a functional GCT is present. Still, it can be a challenge to decide which ovary to remove. Post-surgical endocrine testing can be helpful, especially if histopathology is not performed or a GCT is not found.

Main Limitations: Cases limited to 14.

Conclusions: Granulosa cell tumours present with a wide variety of clinical signs that do not fit what is commonly described as 'classic'. Only if AMH, testosterone and inhibin B concentrations are markedly increased, and there is an abnormally enlarged ovary, the diagnosis of a GCT is more confident. In the presence of normal size ovaries, normal hormonal biomarkers and abnormal behaviour, it is more likely that the ovaries are not involved.