Ovarian Remnant Syndrome in Cats

What is ovarian remnant syndrome?

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

In an intact female cat, the ovaries produce hormones, including estrogen and progesterone. Estrogen is the hormone that triggers your cat to go into heat. When your cat is spayed, the entire reproductive tract (including both ovaries and the uterus) is surgically removed. Because your spayed cat no longer has ovaries that produce estrogen, it does not go into heat.

If a previously spayed cat shows signs of heat, it may indicate that functioning ovarian tissue 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 syndrome is when a previously spayed cat goes into heat. This can happen at any time after spay surgery, with a delay of months to years.

"The most obvious clinical sign of ovarian remnant syndrome is when a previously spayed cat goes into heat."

In cats, the signs of heat are primarily behavioral. Signs of heat in cats include increased vocalization (to attract males), restlessness, increased efforts to get outside or escape the home, and increased affection with owners. These cats will often stand with their hind end in the air, treading their rear feet when petted on their lower back. Cats with functioning ovarian tissue typically go into heat seasonally, going through multiple cycles in the spring and summer.

Occasionally, an ovarian remnant in a cat may start producing progesterone, causing signs of false pregnancy, including behavioral changes and development of mammary tissue. If you think your cat may be showing signs of false pregnancy, contact your veterinarian.

How is ovarian remnant syndrome diagnosed?

Several tests (often in conjunction) can support a diagnosis of an ovarian remnant, but a definitive diagnosis requires finding the remnant and identifying it with a microscope (histopathology) as ovarian tissue. Your veterinarian may also want to confirm that your cat has not been exposed to anything containing estrogen, such as certain creams.

1. Vaginal cytology: This preliminary screening test involves taking a swab from your cat’s vagina while she is showing signs of heat. Your veterinarian will assess the sample under a microscope for the presence of a specific type of vaginal cell called cornified cells. If cornified cells are found, it indicates that your cat is under the influence of estrogen and may have an ovarian remnant. Other conditions can cause estrogen exposure, so your veterinarian may recommend additional testing. If cornified cells are not found, this could indicate your cat is no longer in heat (estrus) and your veterinarian may recommend repeating the cytology. Vaginal cytology can be challenging in cats, as they can come in and out of heat frequently.
2. Baseline hormone levels: There are several baseline hormone levels your veterinarian can use to support a diagnosis of ovarian remnant syndrome. These may include anti-Mullerian hormone, luteinizing hormone (LH), or progesterone. These tests have limitations, so your veterinarian may recommend running more than one test to increase accuracy. Your veterinarian may recommend giving a specific medication two weeks before testing progesterone levels. If a remnant is present, the progesterone level will be high in response to this medication.
3. Ultrasound: Ultrasound may be used to visualize ovarian tissue in your cat when performed while she is in heat, or after she has been stimulated to ovulate (see below). The accuracy of this test, however, is influenced by the size of the ovarian remnant, the stage of your cat’s estrous cycle, and the skill of the ultrasound specialist. Ultrasound may be recommended prior to surgery to identify the approximate location of the remnant, which can reduce the time your pet needs to be under anesthesia.

How is ovarian remnant syndrome treated?

Ovarian remnant syndrome is treated by surgically removing the remaining ovarian tissue. This surgery should be performed while your cat is in heat or, more commonly, after your cat is in heat and has undergone treatment to stimulate ovulation. Ovulation is often stimulated because the length of a cat’s heat cycle is variable, and your cat may not still be in heat if surgery is scheduled for several days later.

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

To stimulate ovulation, your veterinarian will first confirm that your cat is in heat by performing vaginal cytology. They will then inject a medication to stimulate ovulation, which is confirmed by testing progesterone levels in a blood sample two weeks later. If progesterone levels are elevated, ovulation was successfully stimulated, and surgery can be scheduled in the upcoming weeks. This is done to maximize the visibility of the remaining ovarian tissue. It can be challenging to locate ovarian tissue, so referral to a specialist may be recommended. 

What happens if ovarian remnant syndrome is not treated?

Cats with an untreated ovarian remnant are subject to the same risks as cats that are not spayed. The continued presence of estrogen predisposes cats to mammary gland tumors (breast cancer), ovarian tumors, and pyometra (infection of the uterus). Pyometra is a serious and life-threatening condition that requires urgent veterinary care. (See handout “Pyometra in Cats” for more information.)

How is pyometra possible if the uterus was removed as part of the spay surgery?

When a cat is spayed, a small part of the uterus, called the uterine stump, is left above the cervix. The uterine stump can be susceptible to infection from the hormonal effects of the ovarian remnant.