Ovarian tumors seen in mares include fibroma, dysgerminoma, ovarian teratoma, granulosa cell tumor, luteoma, serous cystadenoma, adenocarcinoma, thecoma, and fibrothecoma (6,8,14,19). Of these, granulosa cell tumors are the most common, followed by teratomas (20,21). Fibromas are benign mesenchymal tumors and macroscopically appear as well delimited, ovoid or round, formations similar to other ovarian tumors such as thecoma and fibrothecoma. Histologically they consist of intersecting bundles of spindle cells. Though benign, fibromas may undergo focal sarcomatous changes (14).

Ovarian tumors including ovarian fibroma can trigger hormonal imbalances that significantly impact mare health and performance, particularly during training. This causes the mare to exhibit stallion-like behavior and become difficult to handle. Other potential clinical signs of ovarian fibroma in mares include anestrus, abnormal estrous cycle, and abdominal pain (3,19,20). These clinical signs are not specific to fibromas and can be observed with other ovarian tumors as well (5). Therefore, ultrasound and rectal palpation are performed to identify enlarged ovaries, and hormonal assays measuring serum testosterone and inhibin concentrations provide further diagnostic information (6,14,20). Histological examination remains the most reliable method to confirm the diagnosis of ovarian fibroma (14,20).

Ovariectomy is a well-established surgical procedure for the treatment of ovarian diseases, including fibromas in mares. Laparoscopy offers several advantages over other surgical approaches, such as colpotomy and laparotomy (14,20,21). Laparoscopic ovariectomy, a minimally invasive technique performed under sedation or general anesthesia, has gained popularity as it allows improved visualization of the retroperitoneum and results in reduced postoperative pain and faster healing time facilitated by minimal incisions (5,13,21). Additionally, it is associated with fewer complications compared to colpotomy and laparotomy (12,20,21).

This case report describes the successful use of standing laparoscopic ovariectomy for the removal of an enlarged ovarian fibroma in a mare. The procedure involved removing the affected ovary and histopathological examination of the ovarian tissue to confirm the diagnosis. This report contributes to the current literature on a surgical approach using laparoscopic ovariectomy in a standing mare with fibroma, potentially benefiting future clinical practice in equine surgery.

A 4-year-old Thoroughbred mare weighing 543 kg showed stallion-like behavior and was unmanageable during training. In pre-examination, an enlarged left ovary was detected through palpation. The mare was presented at Jeju National University Equine Hospital for investigation of abnormal behavior, diagnosis, and treatment. A transrectal ultrasound detected an enlarged left ovary, leading to suspicion of an ovarian tumor (Fig. 1). A standing laparoscopic ovariectomy was selected for surgical removal of the left ovary, definitive diagnosis, and treatment because of the advantages of the laparoscopic approach, such as improved visualization, reduced postoperative pain, and faster healing time.

Figure 1. Ultrasonographic image of the enlarged left ovary (white dotted line). Three weeks before hospitalization. Scale bar = 1 cm.

The horse was restrained in a stock. Detomidine hydrochloride (0.02 mg/kg IV, Detomidine, Provet Veterinary Products, Turkey) was administered for the sedation and a 14 gauge over-the-needle catheter was placed in the right jugular vein. Additional detomidine hydrochloride (0.01 mg/kg IV) and butorphanol tartrate (0.02 mg/kg IV, Butophan, Myungmoon Pharm. Co., Ltd, Republic of Korea) were administered for a urinary catheter placement and preparation of the surgical sites. The left paralumbar fossa was clipped and prepared surgically through a povidone-iodine scrub. Throughout the surgery, sedation and analgesia was maintained through a continuous rate infusion (CRI) of a mixture of butorphanol (0.036 mg/kg/h), detomidine hydrochloride (0.013 mg/kg/h), and lidocaine (2 mg/kg/h) in 500 mL normal saline administered at a rate of 0.3 mL/kg/h. Flunixin meglumine (1.1 mg/kg IV, Fotis, Dongbang. Co., Ltd, Republic of Korea) and penicillin G (12,500 IU/kg IM, PPS, Daesung Microbiological Lab. Co., Ltd, Republic of Korea) were administered prior to surgery.

A standing laparoscopic ovariectomy was performed using the John P. Caron method (2,3). Three cm long skin incisions were made for three laparoscopic portals in the left paralumbar fossa. The first was the camera portal and the second and third were the instrument portals. The camera portal was positioned in the 17th intercostal space parallel to the ventral limit of tuber coxae. A 9 cm × 11 mm trocar (Karl Storz Co., Ltd, Germany) was placed as a camera port, and a 30 cm × 10 mm 30° telescope was inserted through the trocar. The second and third portals were placed caudal and caudoventral to the camera port and 11 cm × 5 mm trocars were located at each of the portals. The three ports were positioned to permit triangulation (Fig. 2A). Pneumoperitoneum was achieved by carbon dioxide (CO₂) insufflation which was maintained at a pressure of 10 mmHg for sufficient operating space to ensure adequate visualisation through the camera and manipulation of instruments in the abdominal cavity. Lidocaine (Lidocaine HCl inj. 2%, Daihan Pharm. Co., Ltd, Republic of Korea) was injected into the mesovarium through the endoscopic needle for local anesthesia. A traumatic forcep was inserted through the second port and was used to grasp the left ovary. An advanced bipolar cautery system (Daiwha Corp., Ltd, Republic of Korea) was used for the resection of the mesovarium, mesosalpinx, and proper ligament. The vascular pedicle was transected and the ovary was extracted successfully after expansion of the port. The length of the ovary was about 8 cm (Fig. 3). The dissected ovary was sent to a laboratory for a definitive diagnosis. Hemostasis of the ovarian pedicle was confirmed and the trocars were removed. At the incision site, the muscle layers were closed with absorbable suture (Vicryl-W9231, Ethicon Inc, USA) in a simple interrupted pattern, and a horizontal mattress suture was used to close the skin using nonabsorbable sutures (Blue nylon NB125, Ailee Co., Ltd, Republic of Korea).

Figure 2. The positions of the three portals are triangulated (red line). The first portal is positioned at the 17th intercostal space parallel to the ventral limit of tuber coxae and the second and third portals caudal and caudoventral to the first portal.

Figure 3. The left ovary removed by surgery showed enlargement and the length of the ovary was about 8 cm. Scale bar = 1 cm.

The mare received thiamine hydrochloride (0.5 mg/kg IV, Vitacom inj, Handong Co., Ltd, Republic of Korea), menadione sodium bisulfite (0.5 mg/kg IV, Vitamin K3, Samyang Anipharm Co., Ltd, Republic of Korea), and omeprazole (1 mg/kg PO, Abguard^®, Abler Inc, USA) after surgery. The mare was discharged on the second day of hospitalization. After the mare was discharged, regular dressing changes were done to keep the incision site clean and flunixin meglumine (1.1 mg/kg IV, Fotis, Dongbang. Co., Ltd) and penicillin G (12,500 IU/kg IM, PPS, Daesung Microbiological Lab. Co., Ltd) were injected for 7 days. The mare’s stallion-like behavior and training unmanageability resolved without postoperative complications.

The histopathologic examination of the ovarian tissue revealed spindle-shaped elongated cells with ovoid nuclei, scant eosinophilic cytoplasm, and very low mitotic figures without any evidence of malignancy. The ovary was confirmed as fibroma through hematoxylin and eosin stain (H&E stain) and Masson’s trichrome stain (Fig. 4).

Figure 4. (A) Hematoxylin & Eosin (H&E) staining. Bar = 50 μm. Neoplastic spindle cells have oval nuclei and an eosinophilic cytoplasm. (B) Masson’s trichrome stain. Bar = 50 μm. Collagen stroma is stained blue with Masson’s trichrome stain.

A standing laparoscopic ovariectomy was successfully performed on a mare presenting with stallion-like behavior and an enlarged ovary. Histopathological examination confirmed that the resected ovary was a fibroma, the rarest type of equine ovarian tumor. The standing laparoscopic ovariectomy used in this case has been shown to improve visualization, reduce the time for returning to the intended use, and involve minimal incisions that can heal faster. The mare recovered without complications and returned to racing within 3 months.

The diagnosis of ovarian tumors often relies on a combination of diagnostic tools, including clinical signs, ultrasound imaging, rectal palpation, hormonal assays, and histopathological examination (6,14,20). The initial diagnosis, in this case, was based on the mare’s clinical presentation of stallion-like behavior and the presence of an enlarged ovary detected through palpation. While this provided a preliminary diagnosis, hormonal assays that measure serum testosterone and inhibin concentrations could offer additional support for diagnosis. Though these were not performed in this case, they can be considered in future cases (6,14,20).

In the histological examination, the ovarian mass was well-circumscribed but non-encapsulated with fibrous tissues, and the mass was composed of spindle-elongated cells with ovoid nuclei and scant eosinophilic cytoplasm, and very low mitotic figures. These spindle cells produce collagen materials. Collagen fibers were arranged in interwoven fascicles and showed a whorling appearance (Fig. 4A). Numerous newly formed small blood vessels were seen in the mass. The collagen stroma was stained blue with Masson’s trichrome stain (Fig. 4B). No evidence of malignancy was found in this tumor, which was identified as a fibroma.

Ovariectomy is the choice of the treatment for ovarian tumors, such as granulosa cell tumor, fibrothecoma and fibroma (1,4). Ovariectomy can be performed through colpotomy, laparotomy, and laparoscopy (14,20,21). The choice of the method is based on the size of the affected ovary, bilaterality of the affected mare, available surgical equipment, the length of the ovarian pedicle, and the preference of the surgeon (14,17,20). Colpotomy is used if the ovary is smaller than 10 cm. The complications of colpotomy include wound infection, incision dehiscence, and hemorrhage (20,21). Laparotomy can be performed through the flank, midline, and paramedian approaches (20,21). The flank approach can be performed in a standing position and is used if the ovary is smaller than 15 cm (20). The median and paramedian approaches are not limited by the size of the ovary but can be performed only under general anesthesia (20).

The standing laparoscopic ovariectomy was selected due to its demonstrated improvements in visualization, reduced recovery time, and minimal incisions requiring less healing time (5,13,21). Laparoscopy can be performed under either general anesthesia or standing sedation (5,12,21). General anesthesia may lead to complications, including bone fracture, ataxia, pulmonary edema, and hypoxemia (10). Standing sedation is performed with fewer drugs than general anesthesia and provides the benefit of fewer complications compared to general anesthesia. Standing position also allows for better visualization of the retroperitoneum (5,21). However, standing sedation could lead to complications such as collapse and excitement. Therefore, an adequate dose of the drugs used for sedation and careful monitoring of the horse’s condition are essential during surgery.

For standing laparoscopy, sedation, and analgesia were achieved through a combination of an alpha-2 agonist and an opioid (12). In earlier studies, sedation and analgesia were stably maintained during the surgical period through CRI of an alpha-2 adrenergic agonist such as dexmedetomidine, opioids such as butorphanol, and combinations such as ketamine with lidocaine, detomidine with acepromazine and buprenorphine, or butorphanol with an alpha agonist such as xylazine, detomidine, or romifidine (4,7,15). In this case, detomidine and butorphanol were administered initially, and the combination of butorphanol (0.036 mg/kg/h), detomidine (0.013 mg/kg/h), and lidocaine (2 mg/kg/h) was administered through CRI. Constant sedation and analgesia during surgery were maintained without any complications.

The previously reported complications of laparoscopic ovariectomy include thermal damage of the viscera, splenic or bowel puncture, hemorrhage, cecal dysfunction, and mild colic (5,9,16,18). The tenting phenomenon is another complication of laparoscopic ovariectomy in horses resulting from the insertion of the 1st cannula through the middle of the paralumbar fossa where the parietal peritoneum is not firmly attached to the underlying musculature (2,22). Also, the cost of laparoscopic surgery is high because of the need for additional equipment compared to laparotomy and longer surgical time if the surgeon is not skilled in using the equipment (5,11). Nevertheless, laparoscopic ovariectomy has fewer complications compared to traditional ovariectomy methods such as laparotomy. In traditional ovariectomy, hemorrhage, pain, incisional infection, incisional dehiscence, edema, and even death have been reported (17,20).

In laparoscopy, complications can be reduced by the caution of the surgeon, careful postoperative monitoring, and the surgeon’s advanced skills (2,5,9,17). To prevent the tenting phenomenon, studies have suggested that the 1st cannula be inserted through the 17th intercostal space where the parietal peritoneum is firmly attached to the underlying musculature (2,22). In this case, the standing unilateral laparoscopy was performed cautiously by the surgeon, and the primary cannula was inserted through the 17th intercostal space to prevent tenting. Consequently, the undesirable behavior of the mare was minimized without any complications and the mare returned to her earlier activities. The mare even participated in competitive racing three months after surgery.

This case highlights the successful use of standing laparoscopic ovariectomy for a mare presenting with a fibroma, the rarest of equine ovarian tumors. The minimally invasive nature of the procedure facilitated a rapid recovery without complications, allowing the mare to return to athletic activity within a reasonable timeframe. Therefore, standing laparoscopic ovariectomy stands out as a valuable surgical technique for the management of equine ovarian tumors, particularly considering its superior visualization, faster recovery times, and minimal invasiveness compared to traditional methods.

The authors wish to thank the vets and auxiliary staffs involved with this case at Jeju National University Equine Hospital for their contribution and support.

The authors have no conflicting interests.