Surgery of the female equine reproductive tract (Proceedings)

Ovarian Surgery

Common indications for surgery of the equine ovary include:

• Ovarian mass, commonly unilateral

• Tumor

• Ovarian hematoma

• Ovarian abscess

• Ovarian cyst

• Bilateral ovariectomy to prevent estrus in riding mares of no breeding potential

• Bilateral ovariectomy to create a "jump mare"

Tumors of the equine ovary may arise from 3 tissues of origin:

• Epithelial cell: adenoma, adenocarcinoma, cystadenoma, carcinoma. These tumors are rare, but metastasize frequently.

• Germ cell: dysgerminoma (highly malignant), teratoma (incidental)

• Sex cord stromal tumor: granulosa cell tumor

Granulosa cell tumors (GCT)

GCT are the most frequently reported tumor of the equine ovary. Mares with GCT frequently present with the following complaints from owners: nymphomania or continuous estrus (failure to cycle normally), anestrus, aggression or stallion-like behavior, or perhaps no behavior change (rare), or simply failure to conceive. GCT are typically detected on rectal palpation as an enlarged ovary with the contralateral ovary being much smaller in size or dormant. Transrectal ultrasound is used to confirm ovarian enlargement by finding a characteristic loculated, cystic-like appearance of the ovary. It is important for the veterinarian to confirm these findings on repeated palpations over a 6-8 week time frame. Hormonal assays play a critical role in the diagnosis of GCT. Serum levels of testosterone, progesterone and inhibin are helpful in confirming a diagnosis of GCT. Most mares with GCT tumors will show elevated levels of testosterone and inhibin, but not all. Of the mares with GCT, 87% and 54% will show elevated levels of inhibin and testosterone, respectively. The Endocrinology Lab at UC Davis charges $50 for the GCT pane (http://www.vetmed.ucdavis.edu/PHR/endolab.htm).

GCT have been reported in juvenile fillies and also bilaterally in adults, but this is rare. Unlike other tumors, GCT rarely metastasize or appear on the contralateral lateral ovary following removal. Surgical removal of the ovary is the treatment of choice, with mares returning to normal estrous behavior within 6-8 months.

Ovarian hematoma, abscess and cyst

Mares with ovarian hematomas may present with signs of either acute or chronic colic. Ovarian hematomas often occur following ovulation due to the high level of anti-coagulant contained with follicular fluid. Once bleeding is initiated, the capsule of the ovary is stretched, causing pain. In the acute stage, mares may show evidence of abdominal pain, stamping or shifting of the hind feet and flag their tails. Transrectal ultrasound will show an enlarged ovary with either swirling hyperechoic fluid or clotted blood. The decision to remove the ovarian hematoma is based upon the size of the ovary, degree of pain and chronicity of the condition. Mares with smaller size hematomas may slowly resolve over time. Mares with larger hematomas that are persistently painful may require ovariectomy. Ovarian abscesses are unusual, and caused by either hematogenous spread of infection or secondary infection an ovarian hematoma. Mares may present with symptoms of chronic abdominal pain, peritonitis, fever of unknown origin or failure to cycle normally. Once diagnosed, ovarian abscesses should be removed in case of rupture with secondary peritonitis and adhesions formation. Ovarian cysts are generally diagnosed on transrectal ultrasound and are removed when they repeatedly interfere with normal reproductive cycles.

Ovariectomy

Traditionally, the difficulty and complications associated with ovariectomy involve exteriorization of the ovary from the abdominal cavity or visualization of the ovary within the abdomen and control of hemorrhage. Surgical approaches to the equine ovary can be divided into standing procedures and those performed under general anesthesia. Standing approaches include: culpotomy (vaginal), flank and laparoscopic flank. Approaches to the ovary under general anesthesia include: flank, ventral midline, paramedian, oblique paramedian, laparoscopic. The decision for surgical approach is determined by the following factors: temperament of the mare, size of the ovary, whether the procedure is unilateral or bilateral, surgeon preference/experience and availability of specialized equipment (laparoscope, stapling devices, etc). It is also important to plan carefully before surgery. Fasting the mare for 24-48 hours prior to surgery and the administration of mineral oil via a nasogastric tube to soften feces can facilitate the surgical procedure and limit post-operative complications. It is recommended that ovariectomy be performed when the mare is anestrus or not in the immediate post-foaling period to reduce the degree of edema in the reproductive tract. Finally, owners must be made aware of the risk of the procedures, cost, post-operative care involved, expected behavioral change and time at which the mare may return to work.

Colpotomy

Prior to surgery, the mare should be placed on broad spectrum antibiotics (continued for 5 days post-op) and receive proper analgesia (flunixin meglumine, caudal epidural anesthesia). The mare should be restrained in stocks, a tail wrap applied and the tail secured over head. Her bladder should be emptied via a urinary catheter, feces evacuated from the rectum and the perineum, vulva and vagina aseptically prepped. A 10 blade is used to incise the vagina at the 10am and 2pm positions. As the incisions are full-thickness, some surgeons prefer to tag the 10 blade with suture in order to prevent losing the blade in the abdomen inadvertently. The surgeon should be careful to avoid the bladder, urethra and urogenital artery. Once through the vagina, the peritoneum may be bluntly perforated the incisions manually enlarged. The surgeon should locate ovary, and place a lidocaine-soaked gauze 4x4 (tagged with suture) on the ovary and pedicle to provide analgesia. An ecraseur is carried into the abdomen via the vagina and a chain loop is placed over the ovary. Ecrasement (transaction of the ovary at the pedicle) is done over 3-4 minutes. The ovary is held in the surgeon's non-dominant hand and brought out of the abdomen following transection. The pedicle is checked for hemorrhage. Culpotomy is an inexpensive method of ovariectomy that requires little equipment. Other advantages include limited recovery time (2 weeks). However, complications following culpotomy can be fatal. These include: inadvertent removal of part of the gastrointestinal tract (usually small colon – fecal balls may feel like ovaries without prior fecal softening) or bladder, lack of control over hemorrhage, evisceration through the vaginal incisions, seromas/hematomas at the incision (this can lead to straining and evisceration), peritonitis and vaginal adhesions. It should be noted that culpotomy is a technique that should be used for normal ovaries, as the hemorrhage and large incisions associated with ovarian tumor removal increase the risks of culpotomy greatly.

Standing flank

If the mare has an enlarged ovary, part of the consideration as to a flank approach should include how well the ovary can be exteriorized from the flank. Transrectal palpation should be performed to assess if any other structure is adhered to the ovary or if the ovary feels mobile enough to be brought to the flank. Prior to surgery, the mare should be placed on broad spectrum antibiotics and receive proper analgesia (flunixin meglumine) for about 3-5 days post-operatively. The mare should be restrained in stocks, a tail wrap applied and the tail secured to a hind leg. The paralumbar fossa should be clipped and aseptically prepped. A line block or inverted L block using carbocaine or lidocaine should be placed prior to a final prep. A vertical skin incision is made just distal to the tuber coxae. The incision is carried through the external oblique, internal oblique and transverse abdominal muscles. The peritoneum may be bluntly incised or transected with Metzenbaum scissors. The ovary is identified, anesthetized with a gauze 4x4 soaked in lidocaine and the pedicle ligated. This may be done with suture (large, absorbable), a stapling device (TA 90 or ecraseur) or electrocautery/coagulation (Ligasure). At times, ligation and transaction of the pedicle must be done within the abdomen. The ovary is removed from the abdomen following transaction and the pedicle is checked for hemorrhage. The abdomen is closed in 4 layers (peritoneum and transverse abdominal, internal oblique, external oblique muscles and skin). Two months rest is required to heal the flank incisions before returning to riding exercise or free turn-out. Standing flank surgeries can be performed on enlarged ovaries, but control of hemorrhage can be more difficult. It is does not always require sophisticated equipment, however, complications with the healing of flank incisions is not unusual (dehiscence, seromas etc.)

Ovariectomy under general anesthesia

Ventral midline or paramedian approaches to the abdomen are useful in the removal of large unilateral tumors or when exploration of the abdomen is also required. A midline approach should start at the base of the mammary gland and extend cranial to allow manipulation and removal of the ovary. A paramedian approach can be made, with the oblique paramedian providing excellent access to the ovary. The incision is made at the cranial aspect of the udder and continues towards the fold of the flank. Skin, abdominal tunic and muscle fibers, internal rectus sheath and peritoneum are incised. The ovary is located, and oftentimes reduced in size by aspiration of the contents with a needle prior to exteriorization and transection. Transection may occur via use of sutures, stapling devices, an ecraseur or an electrocautery/coagulation unit (Ligasure). Closure of the previously described layers of body wall is performed. While a ventral midline incision has the greatest holding strength, oblique paramedian incisions are inherently not as strong. Also, a very large ovarian mass may be too large to fit through a paramedian approach. Regardless of the approach, mares will require 2-3 months of recovery time prior to riding exercise. Post-operative complications of ovariectomies performed under general anesthesia include: myopathy, neuropathy, unexplained death, incisional dehiscence, evisceration, peritonitis, pain and hemorrhage.

Laparoscopic ovariectomy

Removal of an ovary via a laparoscope can be performed as a standing procedure or under general anesthesia. Mares need to be fasted for 2 days prior to surgery. The use of the laparoscope should be limited to normal ovaries or tumors less than 10-15 cm diameter. Laparoscopic equipment is expensive and requires training on the part of the surgeon to gain proficiency. With the use of proper laparoscopic equipment and experience, complications such as hemorrhage, inadvertent removal of the wrong body part, inadvertent damage to surrounding viscera and post-operative pain are reduced An advantage to laparoscopic procedures is faster recovery time due to smaller incisional size.

Surgery of the equine uterus Cesarean Section

Indications for a cesarean section include emergency (dystocia-foal malpositioned, too large or contracted) and scheduled (abdominal wall compromise, prepubic tendon rupture or recent incisions, pelvic obstruction) procedures. Regardless of the reason for a cesarean section, a separate team is always needed to resuscitate the foal and should be assembled prior to surgery. Due to the often critical need to deliver the foal quickly, the abdomen is clipped and prepped before induction. Mares are positioned in dorsal recumbency following induction and general anesthesia. A final prep is done, and the mare draped for a ventral midline incision. The skin, subcutaneous tissues and linea alba are sharply incised for 30-45cm. The uterus is palpated, and if possible, the pregnant horn containing a rear leg of the foal is exteriorized. The uterus is packed off with lap sponges and an incision is made in the uterus from the hock to hoof. If the foal is malpositioned, this may not be possible, and any part of the uterus which can be exteriorized is chosen. The uterine wall and chorioallantois is incised and the amniotic membrane is bluntly ruptured. The foal's rear legs are exteriorized, usually with the aid of obstetrical chains and handles, and the remainder of the foal is delivered. The surgeon clamps the umbilical cord and transects it before passing the foal to an assistant. The chorioallantois is detached from the edge of the cut uterus by approximately 3 cm to ensure that it is not included in the suture line to repair the uterine wall (retained placenta can result). If the edge of the uterine wall bleeds profusely, a hemostatic suture may be place using #1 Vicryl in a continuous pattern. The uterine wall is repaired with 2 layers using inverting patterns (usually a Cushing followed by a Lembert) with absorbable material (usually #2 Vicryl). The uterus is lavaged thoroughly before replacing it in the abdomen. The abdomen is generally lavaged with sterile saline before closure. Abdominal closure as follows: linea alba – simple continuous or inverted cruciates, #3 Vicryl; subcutaneous – subcuticular pattern, 2-0 Vicryl; skin – staples or absorbable suture). Oxytocin may be given during surgery after uterine closure or immediately upon recovery to aid in expulsion of the placenta. Mares should be maintained on broad spectrum antimicrobial therapy and NSAIDs for 3-5 days, longer is complications occur. Common complications of cesarean section include: hemorrhage, dehiscence, endometritis, retained placenta and infertility. Owners should be aware that fertility will naturally decline the year the cesarean section occurred, and return to normal the following year.

Uterine cyst

Uterine or endometrial cysts can be a cause of infertility. Typically diagnosed on rectal ultrasonography, the presence of cysts can be confirmed with uterine endoscopy. Removal of cysts can be achieved with mechanical curettage, rupture with endometrial biopsy forceps or laser ablation. Before surgery, the mare should be placed in a set of stocks, sedated, the tail wrapped and reflected to the side, and an aseptic prep applied to the perineum. A 1M endoscope should be sterilized with glutaraldehyde and rinsed with sterile saline prior to use. If using mechanical disruption of the cyst, the uterus can be distended with air to facilitate visualization during the procedure. If laser ablation is chosen, the uterus should be distended with sterile saline. A diode or Nd:YAG laser can be used to ablate the cyst.

Uterine torsion

Uterine torsions typically occur in the 9-11th month of gestation, with most mares presenting for signs of acute colic. Diagnosis of a uterine torsion is typically made upon rectal palpation by identifying a taut broad ligament coursing dorsal to caudal in the direction of the torsion. Torsions may occur in either the clockwise or counter clockwise direction, usually cranial to the cervix. Portions of the gastrointestinal tract, generally the small colon, may be involved with the torsion which can make diagnosis more complicated. Ultrasonographic exam of the uterus and fetus prior to anesthesia or surgery to determine fetal viability determine the method of correction. If the fetus is non-viable, a hysterotomy should be performed.

Correction of a uterine torsion may be performed by rolling the mare under general anesthesia, through a standing flank or via a midline incision under general anesthesia. Reduction of a uterine torsion via rolling is accomplished by anesthetizing the mare and rolling her 360 degrees in the direction of the torsion. Placing a wood plank in the flank may facilitate reduction of the torsion by holding the gravid uterus in place. Surgical management allows for inspection of the uterus to determine the degree of compromise, evaluation of the gastrointestinal tract and the ability to perform a hysterectomy. Surgical treatment may be accomplished through a standing flank incision or by a ventral midline incision under general anesthesia. If a flank approach is elected, the flank towards which the uterus is twisted is chosen. Should any degree of uterine compromise such as rupture, partial-thickness tears or devitalization be suspected, a ventral midline celiotomy approach should be made.

Uterine prolapse

Uterine prolapse is a rare condition of the mare. It is usually a consequence following dystocia, foaling, abortion or aggressive treatment of retained fetal membranes using oxytocin and traction. Mares with uterine prolapse will show marked discomfort, and prompt treatment of the condition is important for survival of the mare. Initial efforts should be aimed at controlling the mare's pain with sedation so as to work safely around her. The mare's cardiovascular status should be assessed as the associated hypovolemia may require correction with resuscitative fluids prior to reduction of the torsion. The uterus should be rinsed with sterile saline and elevated to the level of the perineum to reduce pressure on the broad ligaments and vasculature. If the fetal membranes are still attached, they should be removed if possible. Reduction of the prolapse may be attempted in the standing sedate mare with caudal epidural analgesia or under general anesthesia with the hind limbs elevated. Application of sterile water-based lubricant is useful. Reduction can be accomplished using gentle pressure to evert the uterus, taking care to ensure that the uterine horns are properly positioned. The uterus may be distended with sterile saline post-reduction to facilitate uterine horn eversion. Fluid should be removed after eversion to help reduce straining. A Caslick's is placed to ensure reduction and limit contamination of the reproductive tract. Broad spectrum antimicrobials and anti-inflammatories are provided for several days. Oxytocin should be avoided for at least 2 days and uterine lavage may be initiated 24 hours after reduction. Complicating factors such as intestinal herniation, uterine vasculature compromise or rupture, uterine tear or bladder prolapse limit prognosis.

Surgery of the udder Mastectomy

Indications for mastectomy in the horse include: trauma, neoplasia, chronic mastitis, phythiosis and habronemiasis. Medical therapy should be attempted prior to removal, and ideally, surgery should not occur when the mare should is lactating. Either hemimastectomy or radical mastectomy may be performed. Broad spectrum antimicrobial therapy, non steroidal anti-inflammatory medication and tetanus prophylactus should be provided. Caudal epidural analgesia with morphine (0.1 mg/kg) may also be helpful in controlling post-operative pain. The mare is placed in dorsal recumbency and a standard aseptic prep applied. For radical mastectomy, an elliptical incision is made centered on the entire udder. For hemimastectomy, the incision is made on the affected side, centered at the teat. Following the skin incision, the subcutaneous tissues are dissected with scissors. Blunt dissection is used to separate the gland from the body wall. It is important to start the dissection at the caudal aspect of the mammary gland and work in a cranial direction to optimize control of hemorrhage. Careful identification of large vessels followed by ligation or cauterization using a Ligasure ensures adequate hemostasis. The obturator and internal pudendal veins lie at the caudal aspect of the udder. The external pudendal artery and vein appear at the level of the body wall prior to branching into the cranial and caudal mammary arteries. Theses vessels may be of substantial size in lactating mares or in those with chronic inflammation. Following removal of the affected gland or glands, the defect may be closed primarily or left open to heal by second intention. If closed by primarily, penrose drains should be placed to prevent seroma formation. A stent may be placed for recovery.