Ovarian Surgery
Common indications for surgery of the equine ovary include:
- Ovarian mass, commonly unilateral
- Tumor
- Ovarian hematoma
- Ovarian abscess
- Ovarian cyst
- Bilateral ovariectomy to prevent estrus in riding mares of no breeding potential
- Bilateral ovariectomy to create a "jump mare"
Tumors of the equine ovary may arise from 3 tissues of origin:
- Epithelial cell: adenoma, adenocarcinoma, cystadenoma, carcinoma. These tumors are rare, but metastasize frequently.
- Germ cell: dysgerminoma (highly malignant), teratoma (incidental)
- Sex cord stromal tumor: granulosa cell tumor
Granulosa cell tumors (GCT)
GCT are the most frequently reported tumor of the equine ovary. Mares with GCT frequently present with the following complaints
from owners: nymphomania or continuous estrus (failure to cycle normally), anestrus, aggression or stallion-like behavior,
or perhaps no behavior change (rare), or simply failure to conceive. GCT are typically detected on rectal palpation as an
enlarged ovary with the contralateral ovary being much smaller in size or dormant. Transrectal ultrasound is used to confirm
ovarian enlargement by finding a characteristic loculated, cystic-like appearance of the ovary. It is important for the veterinarian
to confirm these findings on repeated palpations over a 6-8 week time frame. Hormonal assays play a critical role in the diagnosis
of GCT. Serum levels of testosterone, progesterone and inhibin are helpful in confirming a diagnosis of GCT. Most mares with
GCT tumors will show elevated levels of testosterone and inhibin, but not all. Of the mares with GCT, 87% and 54% will show
elevated levels of inhibin and testosterone, respectively. The Endocrinology Lab at UC Davis charges $50 for the GCT pane
(http://www.vetmed.ucdavis.edu/PHR/endolab.htm).
GCT have been reported in juvenile fillies and also bilaterally in adults, but this is rare. Unlike other tumors, GCT rarely
metastasize or appear on the contralateral lateral ovary following removal. Surgical removal of the ovary is the treatment
of choice, with mares returning to normal estrous behavior within 6-8 months.
Ovarian hematoma, abscess and cyst
Mares with ovarian hematomas may present with signs of either acute or chronic colic. Ovarian hematomas often occur following
ovulation due to the high level of anti-coagulant contained with follicular fluid. Once bleeding is initiated, the capsule
of the ovary is stretched, causing pain. In the acute stage, mares may show evidence of abdominal pain, stamping or shifting
of the hind feet and flag their tails. Transrectal ultrasound will show an enlarged ovary with either swirling hyperechoic
fluid or clotted blood. The decision to remove the ovarian hematoma is based upon the size of the ovary, degree of pain and
chronicity of the condition. Mares with smaller size hematomas may slowly resolve over time. Mares with larger hematomas that
are persistently painful may require ovariectomy. Ovarian abscesses are unusual, and caused by either hematogenous spread
of infection or secondary infection an ovarian hematoma. Mares may present with symptoms of chronic abdominal pain, peritonitis,
fever of unknown origin or failure to cycle normally. Once diagnosed, ovarian abscesses should be removed in case of rupture
with secondary peritonitis and adhesions formation. Ovarian cysts are generally diagnosed on transrectal ultrasound and are
removed when they repeatedly interfere with normal reproductive cycles.
