Performing an ovariectomy in dogs and cats

The potential advantages and disadvantages of ovariectomy over ovariohysterectomy have recently been discussed.1 Proponents of ovariectomy assert that the procedure is a more efficient and less invasive method to sterilize female dogs and cats. However, in North America veterinarians have predominantly been trained to perform ovariohysterectomy. Since ovariectomy is unfamiliar, veterinarians may have concerns about the technique and whether uterine disease could occur as a consequence. With this article, I hope to describe the procedure in a way that allows you to perform it with confidence and to understand its effects.

ANATOMICAL CONSIDERATIONS

In carnivores, the ovary is located within the ovarian bursa, which is a peritoneal recess created by the mesosalpinx, mesovarium, and ovary itself. Some may refer to the mesosalpinx as the ovarian bursa. The ovary is attached dorsocranially to the suspensory ligament, which originates from the last rib.3 The short proper ligament of the ovary passes between the ovary and the tip of the uterine horn. The round ligament passes from the cranial end of the uterine horn within a fold of peritoneum laterally from the broad ligament toward the deep inguinal ring. Within the bursa, the ovary is attached along its length to a band of dense connective tissue joining the proper and suspensory ligaments. The opening to the bursa is a small slitlike orifice on the medial aspect.

Getty Images / Joana Carvalho

In bitches, the ovary is often almost completely enclosed.4 A mature bitch often has large fat deposits in the mesosalpinx and mesovarium, obscuring the location of the ovary and its blood supply. However, the ovary may be observed through a thin, round area of mesosalpinx on the lateral surface of the bursa.4 In queens, the mesosalpinx is much smaller, contains little fat, and partially covers the lateral surface of the ovary.

The uterine tube (also known as fallopian tube, oviduct, and salpinx) passes within the mesosalpinx from its origin adjacent to the ovary to join the tip of the uterine horn.4 The ovarian artery and vein have tortuous branchings within the mesovarium and supply the ovary, the uterine tube, the mesosalpinx, and a part of the suspensory ligament. The ovarian artery and vein each contribute a branch to the cranial portion of the uterine horn.5 The uterine artery parallels the uterine horn and terminates supplying the uterine tube. The ovarian and uterine veins roughly parallel the arteries but may anastomose.5

Terminology

INDICATIONS AND EFFECTS

Removing both ovaries eliminates the manufacture of hormones (estrogen, progesterone, inhibin, activin, and follistatin) and female gametes by the ovaries.6 This results in reproductive sterility and the elimination of estrous cycles, which prevents heritable diseases and reduces interference with the management of diabetes, epilepsy, and demodecosis.7 It prevents ovarian neoplasia, vaginal hyperplasia, vaginal prolapse, cystic endometrial hyperplasia, and pyometra and reduces the risk of mammary cancer in dogs if performed before 2 ½ years of age.7,8 Flank-based ovariectomy may be a practical treatment for feline mammary hyperplasia.9 And ovariectomy may improve the survival of dogs being treated for mammary cancer.10,11

Although bilateral ovariectomy eliminates naturally occurring cystic endometrial hyperplasia and pyometra, the possibility of uterine neoplasia remains. This risk appears to be low even in intact bitches, and the uterine tumors reported have mostly been benign.1

Unilateral ovariectomy is indicated for unilateral ovarian neoplasia or disease (cysts, infections) when maintenance of fertility is desired.

CONTRAINDICATIONS

Ovariectomy performed on a gestating animal will terminate the pregnancy. In dogs, pregnancies fewer than 30 days result in resorption, whereas longer-term pregnancies result in abortion with discharge of fetal material or even in live birth.12 Hence, ovariohysterectomy is preferred for gonadectomy of a gravid dog or cat if parturition is not desired.1

Similarly, ovariectomy is contraindicated when the uterus is diseased (e.g. pyometra, cysts, neoplasia, hyperplasia, hydrometra, mucometra, torsion, prolapse, and rupture). Again, ovariohysterectomy is necessary in these cases.1 Removing the ovaries in dogs less than 3 months old is associated with an increased risk of urinary incontinence.13 Ovariectomy performed during estrus in a bitch increases the risk of perioperative hemorrhage.9 Ovariectomy performed during diestrus (metestrus) in dogs with a previous history of clinical (overt) pseudopregnancy may cause a prolactin surge and induce clinical pseudopregnancy.14 Skin or urinary infections may increase the risk of postoperative complications.

APPROACHES FOR OVARIECTOMY

Midline

The midline approach is commonly used in dogs and cats and has been well-described in textbooks. For the purpose of ovariectomy, the incision is usually located beginning just caudal to the umbilicus and extended caudally. Although incision lengths of 2 cm or less have been advocated,15,16 especially in cats, other authors have specified 4 to 6 cm.17,18 Longer incisions (especially extended cranially) allow more adequate exposure to locate the ovaries and survey the abdomen for hemorrhage. Regardless of the incision length chosen, it should be adequate to allow you to safely and effectively remove the ovaries while minimizing discomfort and risk to the patient.

Flank

The flank incision is rarely described in American surgical textbooks. The flank approach is particularly useful for ovariectomy in cats with massive mammary hypertrophy.9 Bilateral flank ovariectomy has been advocated as providing better access to the ovarian pedicle.19 A comparison of left flank vs. midline ovariohysterectomy found less ligature-related hemorrhage with the flank approach.20

While bilateral flank approaches for ovariectomy have been described,19,21 other authors describe performing bilateral ovariectomy or ovariohysterectomy through a single incision in the left flank.9,22,23 The incision is usually located midway between the cranial aspect of the tuber coxae and the caudalmost aspect of the last rib. The incision is usually made in a transverse plane and ranges from 2 to 8 cm in length. After dissection through subcutaneous fat, a grid incision—which involves blunt separation along the direction of the muscle fibers— through the three muscular layers (abdominal external oblique, abdominal internal oblique, transversus abdominis) is made. Branches of the deep circumflex artery may be encountered with the transverse abdominal muscle layer and may require ligation.18 Alternatively, the layers may all be incised in a transverse plane instead of a grid.22

With practice, the unilateral flank approach is comparable in surgery duration to the midline approach for ovariohysterectomy.20,22 Performing a bilateral flank ovariectomy takes longer than performing a midline ovariectomy.21 In the event of a surgical complication, the grid approach through the flank is less readily expanded than the midline approach is. Obesity may hamper the usefulness of the flank approach, and you must carefully avoid injuring the spleen.

HOW TO PERFORM AN OVARIECTOMY

Click here for a step-by-step guide to performing an ovariectomy.

POTENTIAL COMPLICATIONS

• The forward placement of the midline incision, especially if short, may make it difficult to examine the uterus. A small incision may impede your locating the ovaries and inspecting them for hemorrhage before closure.

• Bleeding may occur at the torn edge of mesovarium spanning between the two ligature sites. This delicate structure is difficult to ligate but may be amenable to hemostatic clips.

• Ovarian remnant syndrome is generally regarded as caused by surgical error. Carefully locating the ovary visually or by palpation is essential, both before and after ligation. Locating it is difficult in obese or deep-chested animals in which exposure is awkward. Ligation and transection through the rather short proper ligament may make transection through the ovary more likely. Ligation and transection through the uterine horn should lessen the risk of an ovarian remnant; however, in a fat, older patient, the uterine horn may be difficult to ligate because of thickness and associated fat. The suture may tear through a friable uterine horn in an older patient, and hemostasis may be elusive. The uterine vessels may require ligation separate from the uterine horn.

• Ureteral ligation is a recognized complication of ovariectomy. It may occur if the ovarian pedicle is ligated too close to its origin and accidentally incorporates the ureter close to the kidney.1 Additionally, ureteral damage can occur if a hemorrhage is found after the release of the pedicle and the surgeon applies ligatures, clamps, or crushing pressure to hastily grasped tissues from the bloody abdominal gutter.24 Care must be taken to identify tissue before it is ligated.

• As with ovariohysterectomy, ovariectomy can result in urinary incontinence presumably because of the lack of ovarian hormones.25

• Pyometra and cystic endometritis do not occur in ovariectomized patients unless exogenous progestins are administered or ovarian remnants are left by the surgeon.1

• Medical records may fail to accurately reflect whether an animal was spayed through ovariectomy or ovariohysterectomy, and many owners may be unaware of which procedure has been performed. Leaving the uterus in situ, as with an ovariectomy, may lead to deleterious results if exogenous progestins are given, though there appears to be no indication for progestin administration in animals whose ovaries have been removed.

ADVANTAGES OF OVARIECTOMY OVER OVARIOHYSTERECTOMY

The midline incision for an ovariectomy is typically short and focused on the ovaries, while an ovariohysterectomy incision is usually a compromise attempting to provide exposure to the entire length of the internal reproductive tract. A shorter incision may reduce the chance of dehiscence and other wound complications. And since ovariectomy is limited to the ovarian region, the chances of damaging ureters distally near the uterine body should be nonexistent.1 Ovariectomy should not pose the risk of vesicovaginal or ureterovaginal fistula, which has been associated with ovariohysterectomy.26,27

Although an ovariectomy should be faster to perform than an ovariohysterectomy in the hands of an experienced surgeon, that was not found in one study.28 However, this study used an ovariohysterectomy technique in which electrosurgery was used and the broad ligaments were not ligated, which may have increased the time efficiency of the ovariohysterectomy since there would only be three major ligations as opposed to four major ligations in the ovariectomy.

In the procedures detailed earlier, ligation and transection through the tip of the uterine horn caudal to the proper ligament were described. Some authors specify that ligation and transection should be located through the proper ligament and not through the uterine tip.16,25 By not entering the lumen of the uterus, the possibility of vaginal bleeding is eliminated.1 It has similarly been claimed that ovariectomy through the proper ligament precludes stump granulomas.1 However, the proper ligament is quite short, and, especially in bitches, the mesosalpinx, mesovarium, and broad ligament may contain substantial fat that renders it difficult to ligate and transect accurately through the proper ligament while avoiding the fat-obscured ovary. Nevertheless, stump granulomas at the uterine horn tip in ovariectomies have not been described.1

Stump pyometras cannot occur in an ovariectomized animal.1 However, an ovarian remnant in an ovariectomized animal could result in pyometra.

In dogs with mammary cancer, a midline or flank ovariectomy may be preferred over an ovariohysterectomy because of its smaller incision, which is less likely to complicate concurrent mammary lump excisions. Cats with mammary hyperplasia may be treated by ovariectomy through a flank incision to minimize the risk of hemorrhage that would be incurred by a midline approach.

Since an ovariectomy is less invasive1,19 and requires less excision and ligation of tissues than an ovariohysterectomy does, it may result in less incision complications and pain. However, that was not found experimentally in one prospective study.28

CONCLUSION

Ovariectomy and ovariohysterectomy are equally effective in preventing reproduction and reducing the risk of mammary cancer. Ovariectomy and ovariohysterectomy share many of the same indications, but ovariectomy may be simpler and quicker to perform. And the less invasive procedure may result in less discomfort and less likelihood of complications. As a result, in young animals with normal uteri, ovariectomy may be preferred over ovariohysterectomy. With experience, veterinarians should encounter little difficulty in adopting a form of this procedure.

Eric E. Ehrhardt, DVM, MS

Fruit Valley Veterinary Clinic

7100 State Route 104

Oswego, NY 13126

REFERENCES

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21. Ibacache MPF. Evaluación de dos técnicas de abordaje quirúrgico utilizadas en la esterilización de hembras caninas (Evaluation of two surgical techniques used in sterilization of female dogs). Dissertation. Universidad Austral de Chile, 1997.

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