Pyometra is a potential life-threatening infection of the uterus that occurs most often in intact females over 6 years of age. It is characterized by thickning of uterus linings.
Cystic endometrial hyperplasia, on the other hand, is the medical condition which is characterized by pus-filled cyst inside the dog's uterus, causing endometrium to enlarge (hyperplasia).
Prognosis is positive for both conditions unless dog's cervix is closed. In such circumstances, the condition becomes life-threatening.
Common symptoms associated with this condition are
Abdominal distention (from an enlarged uterus)
Vulvar (vaginal) discharge
Lack of appetite