Diagnosis of a uterine leiomyoma using hysteroscopy and a partial ovariohysterectomy in a mare

Abstract

A 14-year-old quarter horse mare had a 2-year history of infertility and the presence of a mass in the right uterine horn. Prior to surgery, the mass was determined to be invasive by using ultrasonography and hysteroscopy. A partial ovariohysterectomy was performed. The mass was diagnosed histologically as a uterine leiomyoma.

A 14-year-old quarter horse mare was referred to the Western College of Veterinary Medicine with a 2-year history of infertility and a mass in the tip of the right uterine horn.

Transrectal palpation revealed a round, firm mass at the tip of the right uterine horn. On transrectal ultrasonography (5mh₃ linear probe, UST-588U-5, B-mode Aloka SSD-500; Aloka Company, Tokyo, Japan), the mass appeared to be dense and encapsulated, and measured 6.5 × 6.0 cm on cross-section.

The uterus was insufflated with air and examined using a 1 m videoendoscope (Olympus GIF 130; Melville, New York, USA). The mass was seen to be protruding into the lumen of the right uterine horn near the tip. The luminal surface of the mass appeared necrotic (Figures 1 and 2). A biopsy of the endometrium was obtained at this time. A presumptive diagnosis of a leiomyoma was given. Differential diagnoses were leiomyosaroma, rhabdomyosarcoma, and carcinoma (1).

Figure 1. Image obtained by hysteroscopy. Shows a large mass protruding into the lumen. Surface of the mass appears necrotic.

Figure 2. Image obtained by hysteroscopy showing the large necrotic surface on the luminal side of the mass.

The future reproductive potential of this mare was an important component when considering the treatment options. The endometrial biopsy was given a grade IIB rating, using the modified Kenney-Doig system (2). When this biopsy grade was combined with the other physical and reproductive examination findings, a partial ovariohysterectomy to remove the mass was recommended.

The mare was placed in dorsal recumbency and the mass was approached through a right sided diagonal paramedian incision. Hemostasis of the right ovarian pedicle was achieved with an automatic stapling device (TA-go, AutoSuture; US Surgical Corporation, Norwalk, Connecticut, USA). The ovarian pedicle was then transected and the right ovary removed. The right uterine horn was then exteriorized. The automatic stapling device was used to ligate the right uterine horn, 7 cm proximal to the tip. The uterine mass and 7 cm of the right uterine horn were then removed. Both the uterine mass and the right ovary were sent for histological evaluation.

The mare had an elevated heart rate and appeared to be uncomfortable following recovery from surgery. She was administered flunixin meglumine (Banamine; Schering-Plough, Kenilworth, New Jersey, USA), 1.1 mg/kg bodyweight (BW), IV, q12h for 2 d. Her demeanor improved by day 3, postoperatively, and she was discharged with no further medication, but with instructions for stall rest for 2 wk and no artificial insemination or natural service breeding for 2 m or at least 3 m, respectively.

The histological report identified the uterine mass as a leiomyoma (Figure 3), which confirmed the original presumptive diagnosis. There are many causes of infertility in the mare, including neoplasia of the reproductive organs. In general, uterine tumors are rare in horses, with leiomyomas being the most common type (2). A leiomyoma is a benign neoplasia of smooth muscle. Most uterine leiomyomas in mares range in size from 2.5 to 5.0 cm, can be solitary or multiple, and are often pedunculated so that sometimes they can be removed with a surgical snare (3). Larger leiomyomas are rare in horses (4).

Figure 3. Cross section of the mass taken after surgical removal. Histopathologic examination identified the mass as a uterine leiomyoma.

In an abattoir study, leiomyomas were found to have a low frequency of occurrence as they represented only 1% to 2% of all neoplasia in sheep, cattle, and pigs (3). In general, uterine tumors are a rare occurrence in horses (5). A retrospective study that reviewed all uterine tumors that were diagnosed in the last 20 y was conducted at 20 American veterinary colleges. Twenty-seven cases were found and 7 of these were confirmed leiomyomas, giving leiomyomas a frequency of 26% (4). Other sources have cited the frequency of uterine leiomyomas as ranging from 10% to 50% (3).

It is possible for a tumor and a pregnancy to occupy the same space. Grant (6) reported a 13-year-old pregnant mare with a solitary uterine leiomyoma. The mare carried the fetus to full term; however, the foal was born with distorted distal phalangeal joints on all 4 limbs. There have been reports of a familial pattern to uterine leiomyomas in the mare. Romagnoli et al (4) reported that 2 half-sibling Appaloosa fillies were presented for examination in a 2-week period with masses protruding from their vulvas (7). The masses were diagnosed histologically as a leiomyoma and a fibroleiomyoma, respectively. Both of these mares had been sired by the same stallion but were born and raised on different farms. A familial association for uterine fibromas in horses has also been reported (7).

This mare's infertility can be explained in various ways. A low grade endometritis is usually the most common reason for infertility in mares with uterine tumors. A second plausible explanation is that the implantation of the embryo was impaired by the mucosal damage caused by the tumor. A third theory is that the transuterine migration of the embryo was affected by the mass itself. It is also possible that all 3 of these factors together could contribute to infertility.

The future fertility of this mare was evaluated before the owners selected a treatment option. The endometrial biopsy was performed in advance of the surgery to determine the degree of generalized endometrial damage, in order to inform the owners of the potential fertility of the mare. A grade IIB biopsy carries a 10% to 50% chance of a mare conceiving and carrying to term without veterinary intervention (2). This information along with the other physical and reproductive examination findings allowed the owners to elect for a partial ovariohysterectomy to remove the tumor with hopes of restoring fertility to this mare.

Ovariohysterectomy is indicated in horses to resolve cases of pyometra that are unresponsive to medical therapy, for example, in cases of macerated or mummified fetuses and for the removal of uterine tumors (8). Since a partial ovariohysterectomy was performed on this mare, a functioning ovary and about 75% of the uterus remained. Santschi and Slone (7) reported successful pregnancy in 2 mares that had a partial ovariohysterectomy performed to remove a uterine leiomyoma and an abscess, respectively. The maximum amount of a uterine horn that can be removed and still result in pregnancy is unknown, but 1 successful pregnancy with full term gestation was achieved after 50% of 1 horn had been removed (9). Since only 7 cm of the right uterine horn was removed in this mare, the prognosis for fertility after removal of this tumor was good. At the time of this report, the following breeding season has not commenced; therefore, no information is available as to her present fertility. CVJ