Stephen J. Birchard DVM, MS, Diplomate ACVS

Monday, April 21, 2014

Ovarian Remnant Syndrome in Dogs and Cats: Why does it happen and how to prevent it.

Ovarian remnant syndrome in dogs and cats: 
21 cases (2000–2007)

Journal of the American Veterinary Medical Association Mar 2010, Vol. 236, No. 5, Pages 548-553


The authors of this paper looked at clinical cases of dogs and cats with ovarian remnant syndrome (ORS) after ovariohysterectomy. The cases were from the veterinary teaching hospitals at The Ohio State University and University of California - Davis. Here are some key points of the study:

  • The most common clinical signs were those of proestrus and estrus;
  • Clinical signs in some cases took years to develop, even up to 9-10 years in 3 animals (Fig 1);
  • Results of abdominal ultrasonography were suspicious for an ovarian remnant in 11 of 12 animals; 
  • All residual ovarian tissues were in normal locations, not ectopic;
  • Retained right ovaries were more common than left;
  • Long term follow up on 18 cases showed resolution of clinical signs after surgical removal of the retained ovary.

The authors concluded from the study that the results indicated surgical error was the most likely cause of ovarian remnant syndrome. 


Ovarian remnant may be more common than we think, especially considering the length of time that clinical signs can develop after ovariohysterectomy. In our experience the entire ovary is usually found, not a small fragment of it. Possible causes could be: separation of the ovary from the uterine horn during tugging of the uterus to exteriorize the ovary, or incorrect placement of hemostatic clamps when preparing it for removal. 

Ovarian remnant syndrome should be suspected in any dog or cat with signs of estrus or estrus-related disorders like vaginal hyperplasia or prolapse. Diagnosis can be substantiated via vaginal cytology, ultrasonography, and hormonal assays.

Key PointPerform abdominal exploratory on dogs and cats with ovarian remnant syndrome while they are in heat. The ovary and associated vasculature will be easier to identify during this phase of the reproductive cycle.


The ovaries, especially in obese animals, can be difficult to identify. Careful palpation of the firm, bean like structure is necessary in many animals to be sure that clamp placement is proximal to the ovary and on the vessels in the ovarian pedicle. Adequate surgical exposure is a key element in removal of the entire ovary. After removal of the ovaries and uterus, opening the ovarian bursa will confirm that the entire ovary has been removed.

Have you seen any cases of ovarian remnant syndrome in dogs or cats? Post comments or questions here or on Facebook. 

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