Ovarian Remnant Syndrome in Small Animals

Chapter 218


Ovarian Remnant Syndrome in Small Animals




Ovarian remnant syndrome (ORS) is a reported complication after ovariohysterectomy (OHE), a common surgical procedure to prevent estrus, pregnancy, and pyometra and to decrease the incidence of tumors. Failure to remove all ovarian tissue may result in the continued secretion of reproductive hormones with overt signs of proestrus or estrus, uterine stump pyometra, or neoplasia of the ovary, mammary gland, and/or the vagina. Dogs with ORS have a higher rate (23.8%) of neoplasms (e.g., sex-cord stromal tumors in the residual ovarian tissue) than the reported incidence of 6.25% in sexually intact female dogs.


Recognizing bitches with ORS can be challenging, depending on the phase of the reproductive cycle. Most dogs with ORS are presented with periodic or continuous symptoms of vulvar swelling, serosanguineous vaginal discharge, and attractiveness to male dogs. The actual interval from OHE to the time of examination and diagnosis of ORS is highly variable and is attributed partially to failure of owners to recognize clinical signs of proestrus or estrus. The interval between OHE and diagnosis of ORS in animals with neoplasm is significantly longer than in animals without neoplasms.



Potential Causes for Ovarian Remnant Syndrome


Because remnant ovarian tissue is found in typical anatomic locations and is not considered ectopic tissue in dogs, surgical error is suspected as the cause of ORS. In dogs, location of remnant ovarian tissue is found more frequently in the region of the right ovarian pedicle, probably because the more cranial position of the right ovary and difficulty in exposure and removal of the right ovary during OHE. However, Miller (1995) found remnant ovarian tissue to be distributed equally between the right and left side.


Differences between dogs and cats provide further support for surgical error as the cause of ORS and may account for more dogs than cats being affected. Dogs have more adipose tissue surrounding the ovaries that can obscure exposure. The suspensory ligament of the ovary in dogs is more difficult to rupture to achieve adequate exposure, compared with cats. In addition, dogs typically have a deeper abdominal cavity, which makes it more challenging to exteriorize each ovary (Figure 218-1).



Other possible causes of ORS that have been proposed include the revascularization and autotransplantation of free-floating ovarian tissue that becomes separated from the ovary at the time of OHE or surgical inexperience (e.g., veterinarian with <5 years of experience that can lead to surgical errors). However, experience of the surgeon was not identified as a factor in some studies. Proper exposure of the ovary and appropriate placement of hemostats before placement of ligatures should ensure complete removal of ovarian tissue and prevent ORS.


Ectopic ovarian tissue (i.e., supernumerary ovaries or accessory ovarian tissue) has not been reported in dogs. However, accessory ovarian tissue located within the proper ligament of the ovary has been reported in cats, cows, and women. This tissue may be separated partially or completely from the ovary by connective tissue; therefore it may be difficult to distinguish from residual tissue because of improper placement of hemostats at the time of OHE.


Preexisting intraabdominal abnormalities (e.g., endometriosis, pelvic inflammatory disease, and previous abdominal surgery) that obscure identification of the ovaries at the time of surgical removal have not been reported in domestic animals.




Clinical Signs


Differential clinical signs should include vaginitis, stump pyometra, neoplasia, trauma, exogenous therapy, or coagulopathies. If at the time of OHE a functional corpus luteum is present, overt false pregnancy may occur after surgery but subsides in less than 4 weeks without treatment.


Clinical signs of ORS are consistent with the influence of estrogen. Clinical signs related to the functional remnant ovarian tissue include signs of proestrus and estrus with vulvar swelling and serosanguineous vaginal discharge and, in some cases, pyometra. Some dogs may show only behavioral signs of estrus. Dogs that do not show signs of proestrus or estrus but may have mammary gland enlargement may have a progesterone concentration consistent with luteal activity. Clinical signs may not be recognized in some animals for several years after OHE. Once cyclic estrus returns, dogs with ORS may have an extended interestrus interval (e.g., 8 to 9 months). Animals with neoplasms have a significantly longer interval (8 years) between OHE and diagnosis of ORS, compared with the interval between OHE and diagnosis of ORS for animals without neoplasms (1 year).


Affected queens may show normal estrus and may allow copulation but do not become pregnant if bred. The time interval from OHE to return to estrus could be days to years. Then estrus recurs at normal interval.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Ovarian Remnant Syndrome in Small Animals

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