Ovarian remnant syndrome is a condition in female dogs and cats where they continue to go into heat after they have been spayed. Most cases are due to ovarian tissue being left behind in the body. Typically, the spay procedure involves removing the uterus and both ovaries. Some surgeons, especially in Europe, will remove the ovaries and leave the uterus. However, leaving the ovaries is almost never done as it leaves the animal still at risk for the health conditions spaying is intended to prevent (such as pyometra). If an ovary is forgotten, or a small fragment of the ovary is accidentally left inside the animal, it will continue to produce hormones and make her go into heat.
There is another possible cause of ovarian remnant syndrome, which is when there is ovarian tissue that has developed in an abnormal location. In this rare case, a completely correct spay can be done and yet the animal will still go into heat because she has extra ovarian tissue somewhere it shouldn’t be.
The solution to ovarian remnant syndrome is surgical. Usually a hormonal blood test is run to confirm the problem, and then an exploratory surgery is recommended. Unfortunately, this surgery is more invasive and more difficult than a normal spay. Since the uterus is absent, there is no easy organ to follow down to the ovaries. The abdomen has to be opened up wide to allow the surgeon to get to the right location. Additionally, the piece of ovary can be very small. Because of this, most vets who do this procedure want it to be done while the animal is actively in heat. The heat cycle increases blood flow to the ovarian tissue and makes it a bit easier to find. If the animal is one of the rare few that has extra ovary tissue somewhere it shouldn’t be, the surgery is even more challenging.
Removing the remaining piece of ovary solves the problem. To confirm successful removal, often the piece of tissue is sent for testing to confirm it is ovarian. The heat cycles should not recur again, and the pet’s risk of health issues like ovarian tumors and pyometra is eliminated.
Its important to keep in mind that an animal’s history may not be accurate, and that impacts the diagnosis of ovarian remnant. A previous owner or a rescue organization may report that a dog or cat has been spayed, when that is actually not the case. It can be quite difficult to differentiate ovarian remnant syndrome from an animal who just hasn’t been spayed yet! It is best to confirm the history as much as possible prior to deciding when to proceed with surgery, as a normal spay is best done when the animal is not in heat – completely opposite of an ovarian remnant exploratory surgery.