Thickening of the Uterus Lining and Fluid-filled Sac in Dogs

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Pyometra and Cystic Endometrial Hyperplasia in Dogs

The abnormal thickening (pyometra) of the uters' lining can occur in dogs at any age, although it is more common in dogs that are six years of age or older. Cystic endometrial hyperplasia, meanwhile, is a medical condition characterized by the presence of pus-filled cyst inside the dog's uterus, causing the endometrium to enlarge (also known as hyperplasia).

Prognosis is often positive for both conditions; however, if the dog's cervix is closed, it can be a life threatening condition requiring immediate medical attention.

These two conditions can affect both dogs and cats. If you would like to learn more about how pyometra and cystic endometrial hyperplasia affects cats, please visit this page in the PetMD health library.

Symptoms and Types

Signs may include:

  • Abdominal distention (from an enlarged uterus)
  • Vulvar (vaginal) discharge
  • Closed cervix
  • Lethargy
  • Depression
  • Lack of appetite
  • Vomiting
  • Frequent urination


One of the known causes of this condition in dogs is repeat exposure to estrogen and progesterone. The formation of cystic endometrial hyperplasis is often progressive, often following the development of a thickened uterine lining.

Intact older female dogs that have never given birth are at a higher risk of developing pyometra or cystic endometrial hyperplasia.


Your veterinarian will perform an examination to review the type and severity of your dog’s discharge, as well as to view whether the cervix is open or closed. X-rays and ultrasounds will be used detect the size of the uterus, and to determine if the dog is pregnant.

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