Ovarian Cysts

Introduction

Cysts associated with the ovary and surrounding structures are common. They may be congenital or acquired.

Congenital

Congenital cysts are common in the dog, cat and horse. Cysts located within the ovary itself are known as intraovarian cysts, and cysts outside the ovary are known as paraovarian cysts, and this form is more common. Intraovarian cysts may be functional, but paraovarian cysts are normally an incidental finding.

Acquired

Follicular Cysts

These are also known as Cystic Graffian Follicles. Follicular cysts are thin-walled, fluid-filled cysts. Multiple cysts are often seen and they can grow quite large (greater than 2.5cm in the cow). They develop when the follicle fails to ovulate due to low levels of lutenising hormone (LH). Luteinization does not occur. This is known as Cystic Ovarian Disease (COD). Underlying causes include uterine infection, high milk yield and stress. They are seen in cattle and pigs, rarely in small animals but not at all in mares.

These cysts may secrete oestrogen which can alternate cyclic activity leading to anoestrus or nymphomania and changes in rest of reproductive tract, e.g. cystic endometrium and mammary hyperplasia in the large animal. Small animals are more likely to suffer from a persistent oestrus (and the associated clinical signs), and can ultimately suffer bone marrow suppression (causing anaemia and thrombocytopaenia) as result of high oestrogen levels.

Ultrasonographic findings (identification of a thin-walled fluid filled cyst) are combined with the history and clinical signs to make a diagnosis. Rectal examination can be used in large animals to make a presumptive diagnosis.

Treatment in large animals is the administration of chorionic gonadotrophin or GnRH. Prolonged progesterone treatment (PRID) can also be used. First-line treatment in small animals is the administration of HCG or progestagens, which should induce ovulation or luteinization and return the animal to normal cyclical activity. They can sometimes recur following treatment. Alternatively, definitive treatment is ovariohysterectomy.

Luteinised Cysts

The failure to ovulate due to inadequate or delayed LH release results in theca luteinisation. Luteinised cysts are firm and thick-walled cyts, consisting of a central cystic cavity surrounded by a thin layer of fibrous tissue and a thick layer of theca cells. They secrete progesterone. This can cause anoestrus and cystic ovarian disease in large animals and prolonged dioestrus, anoestrus, and pyometra in small animals.

In large animals rectal examination (palpation of a firm cyst) and ultrasonography (identification of a thick-walled cyst) are combined with the history and clinical signs to make a diagnosis. In small animals, persistently high levels of serum progesterone are diagnostic.

Treatment in large animals is a dose of prostaglandins to induce luteolysis and return the cow to cyclic activity or alternatively prolonged progesterone treatment (PRID). Treatment in small animals is ovariohysterectomy.

NB. In large animals, if the type of cyst cannot be identified, treatment with the following hormones can be attempted. |GnRH followed by prostaglandin administration approximately two weeks later, or the use of a PRID and prostaglandins.

Cystic Corpora Lutea

Cystic corpora lutea are a clinically normal feature that develop after ovulation. An ovulation papilla can be seen on the cyst surface.

They do not cause infertility and are of no clinical significance.

Others

These include tuboovarian cysts in cattle, cystic ovarian bursa, mesonephric duct remnant cysts.

Ovarian Cysts Learning Resources
Flashcards Test your knowledge using flashcard type questions	Small Animal Abdominal and Metabolic Disorders Q&A 08

References

Information by permission of Professor RW Else

Jeckel, S (2009) Pathology of the Female Genital Tract - Urogenital System RVC Course Notes

Noakes, D (2009) Infertility in the cow: Ovarian problems - Urogenital System RVC Course Notes

Tennant, B (1999) Self-Assessment Colour Review Small Animal Abdominal & Metabolic Disorders Manson

Tivers, M & Baines, S (2010) Surgical diseases of the female genital tract 1. Ovaries and uterus In Practice 2010;32:292-299