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Follicular Cysts in Small Animals


Clare M. Scully

, MA, DVM, MS, DACT, Louisiana State University, Department of Veterinary Clinical Sciences

Reviewed/Revised Jul 2023
Topic Resources

One of the most common causes of documented persistent estrus in bitches are follicular ovarian cysts. Follicular ovarian cysts originate due to failure to ovulate and should be differentiated from other cysts developing from or within the ovaries or the ductal remnants adjacent to them such as cystic rete ovarii, paraovarian cysts, and subsurface epithelial structures and from ovarian neoplasia (granulosa cell tumor). The follicles are thin walled, fluid filled, and > 8 mm in their widest dimension.

Persistent estrus has been defined as physical and behavioral signs of proestrus and estrus, and presence of cornified vaginal epithelium confirmed on vaginal cytologic evaluation, for at least 6 weeks. This can be difficult to diagnose in queens due to the nature of their estrous cycle Manipulation of the Estrous Cycle in Dogs and Cats The estrous cycles of dogs and cats are not as easily manipulated as in other species. Most protocols are not based on controlled studies, so manipulation of the estrous cycle in valuable breeding... read more .

Clinical Signs of Follicular Cysts in Small Animals

Clinical signs of follicular cysts in small animals include:

  • vulvar swelling

  • serosanguineous discharge

  • alopecia along the neck, trunk, and perineum with chronic exposure to high estrogen

Skin may appear hyperpigmented with hyperkeratosis. Many are found incidentally and have no clinical signs associated with them.

Diagnosis of Follicular Cysts in Small Animals

Diagnostic tests that are useful in follicular cysts in small animals include vaginal cytologic evaluation, hormone assays, and ultrasonography. ­

Vaginal cytologic findings include predominately cornified epithelial cells in response to estrogen, but RBCs, polymorphonuclear cells, and bacteria may also be present.

Estrogen concentration is elevated.

Follicular cysts are usually visible on ultrasonography as anechoic structures with thin walls.

Treatment of Follicular Cysts in Small Animals

Ovulation may be induced with gonadotropin-releasing hormone (50 mcg/dog, IM, once) or human chorionic gonadotropin (1000 U, half IV, half IM; or 22 U/kg, IM, every 24 hours for 3 days).

Ovariohysterectomy is the preferred treatment because dogs induced to ovulate after persistent estrogen exposure may be predisposed to cystic endometrial hyperplasia or pyometra.

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