New techniques for performing equine laparoscopic ovariectomy

Ovariectomy in the horse has been most commonly used for removal of abnormal ovaries such as granulosa thecal cell tumors. Behavioral modification through ablation of estrous has become more popular and consequently more common. Recently laparoscopy has been used to perform ovariectomies taking advantage of the minimally invasive nature of the technique. Laparoscopy alone, is especially advantageous in cases of behavioral modification with normally sized ovaries, or ovaries up to 15 cm in diameter. Laparoscopy can also be used as an adjunct to an open approach with laparoscopic-assisted techniques. The ovaries can be removed with the horse standing, in lateral recumbency, or in dorsal recumbency. One of the main benefits of using laparoscopy for the removal of abdominal structures is the direct visualization and tension-free ligation and transection that is often possible.

Photo 1: A. Standing but sedated horse in stocks with head support, B. Epidural site.

Preparation for surgery

A rectal examination should be performed prior to laparoscopic ovariectomy to identify any ovarian or uterine abnormalities and to assess potential limitations of the procedure, specifically the size of the ovary. Transrectal ultrasonography of the ovaries is useful to determine the presence of cystic structures within the ovary. Aspiration of cystic fluid from an enlarged ovary may reduce the overall size of the ovary and improve the ability to ligate the ovarian pedicle and extract the amputated ovary through a flank incision. In one mare, 1700 ml of fluid was removed from the ovary prior to ligation and transection using a laparoscopic-assisted technique. The largest non-cystic ovary that has been removed by the author in a standing mare was about 15 cm in diameter. The suitability of the patient's temperament for restraint in standing stocks and standing procedures can also be determined at this time.

The mare is generally fasted for 24 hours to reduce the volume of intestinal contents and improve the working area within the abdomen. Some surgeons prefer to feed the horses a pelleted ration for up to a week prior to surgery to reduce the bulk of the colon. Non-steroidal anti-inflammatory drugs, such as flunixin meglumine or phenylbutazone should be administered pre-operatively, while antibiotics can be used at the surgeon's discretion.

Surgical techniques

Standing Laparoscopy

For standing laparoscopy, the mare is restrained in standing stocks. The tail head and one or both flanks are clipped and aseptically prepared depending on the need to remove one or both ovaries. The author prefers to use 40 mcg/kg of detomidine brought to a total of 10 to 12 ml with 0.9 percent NaCl as a caudal epidural to provide systemic sedation and analgesia of the ovarian pedicles. One or both flanks are anesthetized using either lidocaine or mepivicaine in an inverted "L" or paravertebral pattern. Care should be taken to use only as much local anesthetic as needed. The author prefers to use no more than 50 ml per flank. The tail is tied to keep it from entering the surgical site and the head is supported (see Photo 1). A blindfold is recommended to limit stimulation of the sedated horse, and the ears can be plugged with gauze. The surgical field is draped to allow access to one or both flanks as needed. The equipment cart with the video monitor is placed behind the animal. The surgeon and the surgical assistant stand on the same side of the horse.

Photo 2: The left flank with laparoscopy portals.

A 1 cm incision is made through the skin and external abdominal oblique fascia in the desired flank at the level of the ventral margin of the tuber coxae, midway between the caudal border of the ribs and the tuber coxae. If a bilateral ovariectomy is to be performed the author begins the surgery on the left side to take advantage of the spleen to reduce the likelihood of visceral puncture. A mare urinary catheter is then inserted through the incision by using a steady, firm motion in a slightly downward angle, directing towards the opposite stifle. The presence of the catheter within the abdomen is confirmed by the sound of air entering the abdomen and the loss of negative intra-abdominal pressure. The catheter is then connected to the insufflator and the abdomen is insufflated to a pressure of 15 mmHg with carbon dioxide.

Photo 3: Intra-abdominal photograph showing the left ovary.

Once insufflation pressure has been achieved, the laparoscopic and instrument ports are placed. The primary trochar is located 5 to 10 cm dorsal and 2 cm rostral to the insufflation catheter. A 12 mm skin incision is performed and a 10-12-mm trochar is inserted with a slow but steady twisting motion. The trochar is removed from the sleeve, the insufflation tubing is attached, and the laparoscope is inserted. The author prefers 15 to 20 cm long cannulas with blunt trochars for flank surgery. Pyramidal shaped sharp trochars may lacerate blood vessels or increase the likelihood of puncturing deeper structures. The laparoscope is attached to the light source, video camera and video monitor. An initial exploration of the abdomen is performed and the secondary ports are then placed by replacing the insufflation catheter with one port and inserting another port 5 to 10 cm ventral to the original insufflation incision (see Photo 2, 17).

Photo 4: Intra-abdominal photograph showing the left ovary with ovary sharply dissected from the uterus using sharp dissection.

Once the ports and instruments have been placed, the ovary is identified and grasped with the claw-toothed grasping forceps (see Photo 3). Ten millimeter serrated scissors are used to transect the proper ligament of the ovary, located at the caudal pole of the ovarian pedicle between the uterus and the ovary (see Photo 4). This area is minimally vascularized and also results in transection of the mesosalpinx and uterine tube, which isolates the ovarian blood supply and provides better ligature security.

Many techniques have been used to ligate the ovarian pedicle including; suture, laser, staples, bipolar cautery, ultrasonic devices such as the Autosonix (Kendall Animal Health/USSC), and a specialized cautery device such as the Ligasure (Valley Lab) (See Photo 5). Using sutures to ligate the pedicle is generally the most cost effective, but requires more practice than using the other devices. Surgical devices like the Autosonix and Ligasure incorporate cutting devices in the instruments that reduce the need to exchange instruments frequently.

Photo 5: Methods of ligation. A. Ligation using size 1 Maxon and 4-S Modified Roeder knot, B. Autosonix ultrasonic coagulating and cutting device, C. End of Ligasure instrument.

Using sutures

When using sutures, the author prefers to use a 4-S modified Roeder knot loop ligature using #1 Maxon. This particular combination is shown to have almost the same knot security as a square knot in previous studies. The suture loop is inserted into the abdomen through a cannula. The grasping forceps are released from the ovary and passed through the suture loop before regrasping the ovary. The suture loop is then manipulated over the ovary and positioned around the ovarian pedicle. It can be very helpful to twist the ovary into the loop. Advancing the knot pusher tightens the loop, and the long end of the suture is cut with the 5 mm scissors inserted down the same port the suture exits. A second ligature is placed in a similar manner.

Photo 6: Intra-abdominal photograph showing transected ovarian pedicle.

Removing the ovarian pedicle

Before amputation of the ovarian pedicle, it is important to ensure that the claw-toothed grasping forceps have a secure hold on the ovary to minimize risk of dropping the amputated ovary. Once a secure hold on the ovary has been obtained, the 10 mm scissors are used to transect the pedicle distal to the ligatures. The pedicle is closely inspected for hemorrhage (see Photo 6, p. 20). If any hemorrhage is observed, laparoscopic vascular clamps are useful to check the bleeding. If both ovaries are to be removed, the forceps continue to grasp the ovary while the right ovary is removed using a similar technique. After both ovaries have been amputated, the ovaries can be removed from the abdomen separately on each side or one ovary may be passed under the small colon, so both ovaries can be removed through the same incision. The portal holding the grasping forceps and ovary is enlarged and Oschner forceps are used to assist in extracting the ovary through the abdominal wall. Alternatively, a larger diameter trochar can be placed to extract the ovaries without losing insufflation. It is important to make the incisions large enough to remove the ovaries without difficulty. Otherwise the ovaries can be dropped from the grasping forceps making loss of the ovaries possible and retrieval more difficult.

Photo 7: A mare's left flank after an incisional closure.

To close the incisions, a size 0 monofilament absorbable suture (Maxon) is used to close the external abdominal oblique fascia in the extended incision(s) and a size 2-0 nylon suture material is used to close the skin incisions (see Photo 7, p. 20).

Laterally recumbent laparoscopic ovariectomy

Laterally recumbent laparoscopic ovariectomy has been used to remove single granulosa thecal cell tumors that are between 15 and 20 cm, or in mares that are not amenable to standing surgery. The animals are fasted for 24 hours, anesthetized and placed in lateral recumbency with the affected ovary up. An epidural using detomidine, morphine, or a combination of the two can be used for post-operative pain relief. A local line block using local anesthetic is not necessary but can provide a reduction in inhaled anesthetic necessary for surgical anesthesia. A similar surgical approach as for the standing flank laparoscopy is used. Only the uppermost ovary can be removed via this technique(see Photo 8, p. 20). A portal through the 17th intercostal space for the telescope can provide more room for surgical manipulation. Incisions are closed as described for the standing laparoscopy.

Dorsally recumbent laparoscopic ovariectomy

Dorsally recumbent laparoscopic ovariectomy has been used to remove normally sized ovaries for behavioral modification and moderate sized granulosa thecal cell tumors. A surgery table that can tilt at least 30 degrees is necessary to move the abdominal content rostral in order to access the ovaries.

Photo 8: Laterally recumbent mare. A. External view, B. Intra-abdominal view.

The animals are prepared for surgery as previously described. It is very important to reduce the bulk of the colon for this procedure, and some surgeons place the mares on a pelleted ration to achieve this. The mares are anesthetized and placed into dorsal recumbency. The entire ventral abdomen is clipped and aseptically prepared for surgery. A 1 cm incision is made through the skin and subcutaneous tissue at the umbilicus. A stab incision is made through the linea alba but not through the peritoneum. A teat cannula or mare urinary catheter is placed through the incision and into the peritoneal space. There is no negative pressure in the abdomen in dorsal recumbency therefore the surgeon will not hear the sound of air entering the abdomen. Presence of the insufflation catheter in the peritoneal space is determined by the ability to freely move the end of the catheter and slow intra-abdominal pressure increase when the insufflator is connected and turned on. Once an intra-abdominal pressure of 15 mmHg is achieved, the insufflation cannula is removed and replaced with a 10/12-mm diameter cannula with a blunt trochar. Ten to 15 cm long cannulas are adequate when performing dorsal recumbent laparoscopy. The mare is placed into Trendelenberg position with the head down and the hindquarters up. Tilting of approximately 30 degrees is necessary to provide access to the ovaries. Two other portals are established in the inguinal areas. These cannulas can be placed under direct observation from the umbilical portal. The ovaries are identified, ligated and transected as previously described. One of the inguinal incisions is enlarged and the ovary(ies) removed from the abdominal cavity. The body wall incisions are closed using size 0 or 1 Maxon in a cruciate pattern for the 1-cm incision, and in a simple continuous pattern for the extended incision. The skin is apposed using size 2-0 nylon in a simple continuous pattern, or size 2-0 Maxon in an intradermal pattern.

Benefits of laparoscopic ovariectomy include the minimally invasive technique that is used, often requiring smaller incisions that would be necessary with a traditional open approach. If a tissue macerator was used, even smaller incisions would be necessary, but the cost of the macerator and the specimen bags would increase the expense to the client making the slightly larger incisions less of an issue. By using a telescope, direct visualization of the ovary and ovarian pedicle before, during, and after transection reduce the likelihood of complications. The use of laparoscopy also can provide a tension free ligation and transection, which provides less pain in the post-operative period. One of the main benefits of the standing flank laparoscopic ovariectomy is obviating the need for general anesthesia, and subsequent recovery. The mares can be back in training in two weeks.

Suggested Reading

• Veterinary Endosurgery, Freeman LJ Editor, Mosby, St. Louis, 1999.

• Endoscopic Surgery. Hendrickson DA Editor, The Veterinary Clinics of North America: Equine Practice. W.B. Saunders, Philadelphia, Volume 16:2, 2000.

• Equine Diagnostic and Surgical Laparoscopy. Fischer AT Editor, W.B. Saunders, Philadelphia, 2002.