Granulosa theca cell tumour in a pregnant mare: concentrations of inhibin and testosterone in serum before and after surgery

Abstract

CASE HISTORY: A 14-year-old Thoroughbred mare was presented for evaluation of a rapidly enlarging ovary at 73 days gestation. The mare's owner reported behavioural changes in the mare since she returned from stud, notably aggression towards other horses. CLINICAL FINDINGS: Transrectal palpation and ultrasonography of the reproductive tract revealed a viable pregnancy, an enlarged, multiloculated right ovary, and a normal-sized left ovary with a corpus luteum present. Concentrations of inhibin and testosterone in serum were 13.8 ng/mL and 1,150 pg/mL, respectively, being markedly higher than reference ranges. Concentration of progesterone was 4.5 ng/mL, consistent with the presence of functional luteal tissue. A presumptive diagnosis of a granulosa theca cell tumour (GTCT) was made, and the ovary was surgically removed. Histopathological examination of the removed ovary confirmed a benign GTCT. At 31 days after surgery concentrations of inhibin in serum had decreased 18-fold, and testosterone had decreased 10-fold. Pregnancy was reconfirmed at 115 days gestation by rectal palpation and transrectal ultrasonography. DIAGNOSIS: Granulosa theca cell tumour associated with elevated concentrations of inhibin and testosterone in serum. CLINICAL RELEVANCE: While ovarian enlargement and aggressive behaviour may be considered normal in some pregnant mares, a GTCT should be included as a differential diagnosis. Measurement of concentrations of inhibin and testosterone in serum are useful to support a presumptive diagnosis of GTCT in mares.