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

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.