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Cornell Richard P. Riney Canine Health Center

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Ovarian remnant syndrome (ORS)

Ovarian remnant syndrome (ORS) occurs when ovarian tissue is inadvertently left in the body following ovariohysterectomy (spay). This may occur if part of the ovary is left behind, if a fragment of the ovary becomes detached during handling and falls into the abdomen, or if there is naturally occurring ovarian tissue in an uncommon location. 

Clinical signs

Ovarian remnant syndrome does not cause symptoms until the dog enters her estrous (heat) cycle. Dogs typically cycle twice yearly. Signs of heat are related to elevated estrogen levels produced by ovarian tissue, and may include:

  • Vaginal discharge (may contain blood)
  • Vulvar swelling
  • Mammary development
  • Behavioral changes such as playful behavior with male dogs
  • Attraction of male dogs
  • Mating postures (standing still with the tail moved to one side)

Diagnosis

Diagnosis of ORS is made by measuring blood levels of several different hormones. Progesterone and anti-Mullerian hormone (AMH) are both produced by the ovary and indicate the presence of ovarian tissue if either or both are elevated. Luteinizing hormone (LH) is produced by the brain; in dogs with ovarian tissue, this hormone will be low. 

If these hormones do not indicate the presence of ORS, the adrenal glands may be the source of estrogen (which can lead to estrous-like symptoms) in a condition known as hyperadrenocorticism. 

Treatment

Treatment of choice for ORS is surgical removal of the remnant while the dog is showing signs of estrus, as this is when the tissue is easiest to locate. This requires a thorough exploratory surgery.

Outcome

  • Several years may pass between when an ovariohysterectomy (spay) was performed and when symptoms of ORS are noted.
  • If left in place, there is a risk of the fragment developing into a tumor.
  • Repeated exposure to estrogen and progesterone (as will happen with repeated estrous cycles) increases her risk for mammary cancer.

  • Successful removal of the ovarian tissue is curative.

     

This health topic was developed as part of a collaboration between the Cornell Richard P. Riney Canine Health Center and Embark Veterinary, Inc. You can learn more about the hereditary risks of other canine health conditions by exploring our genetics articles.

Updated Aug. 2024