Ovarian Remnant Syndrome in Dogs
By Catherine Barnette, DVM

ovarian_remnant_syndrome_dogWhat is ovarian remnant syndrome?

Ovarian remnant syndrome is a condition that occurs when ovarian tissue remains inside the body after a female dog is spayed. This tissue can produce estrogen, triggering signs of heat in the dog.

In an unspayed dog, the ovaries produce a number of hormones, including estrogen. It is this estrogen that triggers your dog to go into heat. When your pet is spayed, the entire reproductive tract (including both ovaries and the uterus) is surgically removed. Therefore, your spayed dog no longer has ovaries, produces estrogen, or goes into heat.

“If a previously spayed animal shows signs of going into heat, this may indicate that functioning ovarian tissue, or ovarian remnant, is still present and producing estrogen.”

If a previously spayed animal shows signs of going into heat, this may indicate that functioning ovarian tissue (known as an ovarian remnant) is still present and producing estrogen. Ovarian remnants may be left behind during surgery, or may be caused by the presence of accessory ovarian tissue (a small piece of tissue that fragmented off the ovary and established enough of a blood supply to begin producing hormones).

What are the clinical signs of ovarian remnant syndrome?

The most obvious clinical sign of ovarian remnant surgery is when a previously spayed dog goes into heat. This can happen at any time after spay surgery, with a delay of months to years.

The most obvious signs of heat in the dog include swelling of the vulva and blood-tinged vaginal discharge. Additionally, a dog that is in heat may demonstrate behavioral changes, such as being more receptive to males, and will often be more attractive to male dogs. Dogs with functioning ovarian tissue typically go into heat every six to eight months.

How is ovarian remnant syndrome diagnosed?

Your veterinarian will diagnose the presence of ovarian remnant syndrome using one or more of the following diagnostic tests.

  1. Vaginal Cytology – This test involves taking a swab from your pet’s vagina while she is showing signs of heat. Your veterinarian will assess the sample under the microscope for the presence of a specific type of cell called cornified cells. If these cornified cells are found, this indicates that your pet is under the influence of estrogen. Possible sources of estrogen include an ovarian remnant, estrogen from external sources (for example, some topical hormonal creams used in human medicine), or other hormonal imbalances. This test is often used as a preliminary screening test for the presence of an ovarian remnant, though it is not specific for an ovarian remnant.

  2. Baseline Hormone Levels – A variety of studies have examined the use of baseline hormone testing in diagnosing ovarian remnant syndrome. However, these tests are not frequently recommended, due to low reliability. While abnormal hormone levels can indicate the presence of an ovarian remnant, normal hormone levels unfortunately do not rule out the presence of an ovarian remnant.

  3. Ultrasound – Ultrasound may be used to visualize ovarian tissue, if it is performed while the pet is in heat. The accuracy of this test, however, is influenced by the size of the ovarian remnant, the stage of the heat cycle during which the test is performed, and the skill of the ultrasonographer. Again, this test is not frequently used.

  4. Hormone Stimulation Test – This test is widely regarded as the most accurate test for diagnosing ovarian remnant syndrome. A synthetic hormone (hCG or GnRH) is administered while your pet is showing signs of heat. A blood sample is then drawn five to seven days later. If the blood test shows an increase in progesterone, this indicates the presence of functioning ovarian tissue.

How is ovarian remnant syndrome treated?

Ovarian remnant syndrome is treated by surgically removing the remaining ovarian tissue.”

Ovarian remnant syndrome is treated by surgically removing the remaining ovarian tissue. This surgery should be performed while your pet is in heat, in order to maximize the chances of being able to visualize the remaining ovarian tissue.

Rarely, a pet may develop signs of false pregnancy after being spayed, due to the sudden removal of hormones. Signs of false pregnancy involve behavioral changes and the development of mammary tissue. If you feel that your pet may be showing signs of false pregnancy, please contact your veterinarian. Signs of false pregnancy will typically resolve without treatment in one to two months.

What happens if ovarian remnant syndrome is not treated?

Pets with an untreated ovarian remnant are subject to the same risks as pets that are not spayed. The continued presence of estrogen predisposes dogs and cats to mammary gland tumors (breast cancer), ovarian tumors, and pyometra (infection of the uterus). How can a dog have pyometra when the uterus is removed as part of the spay surgery? When a dog is spayed, a small part of the uterus is left above the cervix, which is called the uterine stump. The uterine stump can be susceptible to infection from the hormonal effects of the ovarian remnant.

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