Two cases of Granulosa Cell Tumour (GCT) in the Mare  

Case Report

J. R. Crabtree, Equine Reproductive Services, Malton, North Yorkshire

Introduction

The Granulosa Cell Tumour (GCT) is the most common ovarian tumour in the mare. It is predominantly slow growing, unilateral and benign. Transrectal palpation and ultrasound examination usually reveals an enlarged multicystic structure with obliteration of the ovulation fossa and a small inactive contralateral ovary. Behavioural abnormalities such as prolonged anoestrus, aggressive or stallion-like behaviour and persistent oestrus may be demonstrated. This report details two cases with different presenting signs and ultrasonographic findings.

Case details - Case One

History: An 11 year old maiden 16.2hh TBx bay mare was presented to a commercial stud farm for covering. When teased it was evident that the mare was not in standing heat. The mare was presented for gyneacological examination after the mare failed to tease positive on a further two attempts.

Clinical findings: The mare had an enlarged right ovary which was palpably firm and round, no ovulation fossa was evident. The left ovary was small and the uterus and cervix lacked tone. Trans-rectal ultrasonography was performed using a SonoSite Titan¹ 5-10 MHz linear probe (Figure 1a,b). This demonstrated a right ovary measuring 7 cm in diameter and a multi-cystic appearance with one large follicle like structure measuring approximately 35 mm. The contralateral ovary was small and inactive (follicles <5 mm). The uterus and cervix were consistent with a mare in anoestrus. A provisional diagnosis of GCT was made on the basis of clinical and ultrasonographic findings. 250 micrograms cloprostenol (Estrumate²) were administered by intramuscular injection once daily for two days. The mare showed no response to this treatment.

Clinical pathology: Bloods were taken and submitted for laboratory analysis of progestagens, oestrone sulphate, testosterone and inhibin (Table 1). Results showed low progestagens at 0.04 ng/ml (laboratory reference range (rr)^†: 0-1ng/ml oestrus or anoestrus, >2 ng/ml dioestrus or pregnancy), normal oestrone sulphate at <1.0 ng/ml (rr: 0-10 ng/ml for a non-pregnant mare), normal testosterone at <0.1 nmol/ml (rr: <0.5 nmol/ml) and elevated inhibin at 1.21ng/ml (rr: 0.1-0.7 ng/ml for a non-pregnant mare), consistent with the diagnosis of GCT.

Fig. 1a).

Fig. 1b).

Figure 1. Ultrasound images of the ovaries of case one. 1a). The  right ovary measures 7.08 cm with the caliper, note the multicystic/honeycomb nature of the ovary. 1b). The small and inactive left ovary, depth of image set to 9.6cm for both images in order to compare.

Treatment: The right ovary was removed via a right flank laparotomy under general anaesthesia; the ovarian pedicle was ligated with double row of staples using a TA 90 stapler (Figure 2). The mare had an uneventful recovery.

 

Figure 2.  Right ovary from case one measuring approximately 8 cm in diameter, note single follicle like structure and correlation to ultrasound image.

Case Two

History: A 13 year old multiparous 16.2hh TBx bay mare presented to the author for routine gyneacological examination as part of a frozen semen AI programme. The mare reportedly had cycled normally earlier in the season but then after a prolonged period of dioestrus had begun mounting other mares in the paddock and demonstrating flehmen.

Clinical findings: The mare had an enlarged right ovary which was palpably firm and round with a small contralateral ovary. The uterus and cervix lacked tone. Trans-rectal ultrasonography was performed using a SonoSite Titan¹ 5-10 MHz linear probe (Figure 3a,b). The enlarged right ovary measured 11.7 cm in diameter with a thick wall and multiple large compartments and some hyperechogenic bodies, the contralateral ovary was small and inactive. The uterus and cervix were consistent with a mare in anoestrus. 250 micrograms cloprostenol (Estrumate²) were administered by intramuscular injection once. The mare showed no response to this treatment. After 10 days the ovary had increased in diameter by 1.8 cm. A provisional diagnosis of granulosa-theca cell tumour (GtCT) was made on the basis of history (stallion like behaviour) and clinical findings and surgery scheduled.

Clinical pathology: Bloods were submitted for a hormone profile (Table 1). Results showed low progestagens at 0.02 ng/ml, elevated testosterone at 1.8 nmol/ml and inhibin at 1.64ng/ml, consistent with the diagnosis of GtCT.

Treatment: The right ovary was removed via midline laparotomy under general anaesthesia; the pedicle was ligated with several transfixed ligations before transection (Figure 4a,b). Histological examination confirmed the diagnosis of GtCT.

Table 1. Hormone profile results

	1	2	Ref. range†
Progestagens (ng/ml)	0.04	<0.02	0-1*
Oestrone Sulphate (ng/ml)	<1.0	-	0-10**
Testosterone (nmol/l)	<0.1	1.8	<0.5
Inhibin (ng/ml)	1.21	1.64	0.1-0.7**

^†  Beaufort Cottage Laboratories, Newmarket, U.K.

* 0-1ng/ml - oestrus or anoestrus, >2 ng/ml - dioestrus

** For non-pregnant mares

Fig. 3a).

Fig. 3b).

Figure 3. Ultrasound images of the ovaries of case two. 3a). The right ovary measures 11.7 cm with the caliper, note multiple large compartments and hyperechogenic bodies. 3b). The left ovary measures 2.7 x 4.24 cm and shows no follicular activity. Note depth change from 12 to 6.1cm from a) to b).

Fig. 4a).

Fig. 4b).

Figure 4. Right ovary from case two. 4a). entire ovary measuring approximately 15x17.5cm. 4b). Ovary in section partially deflated due to loss of fluid, two ‘clots' of fluid which were free floating in the ovary. Note correlation to ultrasound image.

Discussion

This case report illustrates the variable presenting signs of GCT in the mare. These cases differ due to the different hormone activities of the tumours.

McCue (2007) summarises the key features of granulosa cell tumours in the mare. Progestagens are almost always low as ovulation and formation of a hormonally active corpus luteum does not occur. Serum testosterone is elevated in approximately 40-60% of affected mares and this indicates that a significant theca cell component is present in the tumour, i.e. a granulosa-theca cell tumour. Testosterone is responsible for the stallion-like behaviour as seen in case two. Inhibin is elevated in approximately 90% of mares with a GCT and it is hypothesized that this hormone is responsible for the inhibition of the contralateral ovary.

Surgical removal of the affected ovary usually results in a return to cyclic activity in the remaining ovary within approximately 6-8 months. It was reported that the mare in case two returned to cyclic activity 5 months after ovariectomy. At the time of writing the report the mare in case one was only two months post surgery.

Manufacturers' addresses

¹ BCF Technology Ltd., Livingston, Scotland, U.K.

² Schering-Plough Ltd., Middlesex, U.K.

References

McCue, P.M. (2007) Ovarian Abnormalities. In. Current Therapy in Equine Reproduction, Ed: J. C. Samper, J. F. Pycock, A. O. McKinnon, Saunders Elsevier, St. Louis. pp. 87-92.

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James R. Crabtree BVM&S MRCVS.