These fluid-filled structures develop within the ovary and result in prolonged secretion of estrogen, continued signs of proestrus or estrus, and attractiveness to males. Ovulation may not occur during this abnormal estrous cycle. Follicular cysts should be suspected in any bitch showing clinical manifestations of estrus for >21 days, or when proestrus plus estrus have lasted for >40 days. Estrous cycles due to follicular cysts in queens may be difficult to differentiate from normal, frequent cycles.
The primary differential diagnosis is functional ovarian granulosa cell tumor. Assessment of vaginal cytology with presence of cornified cells indicates increased serum estrogens.
The treatment of choice is ovariohysterectomy. If the animal is to be bred, induction of luteinization of the cystic follicles may be accomplished by using GnRH (25 mcg, IM) or human chorionic gonadotropin (500–1,000 IU/dog or 250–500 IU/cat, IM).