Overview

• Ovarian remnant syndrome is the presence of behavioral and/or physical signs of an estrous cycle in a female dog or cat having previously undergone ovariohysterectomy.
• Caused by the presence of functional residual ovarian tissue.
• Ovarian remnant syndrome is reported to be responsible for 17% of all post-OHE complications.

Signalment

• Female dog and cat; more common in cat.
• No breed predisposition or geographic distribution.
• Signs of an estrous cycle usually occur months to years after OHE but can begin within days after surgery.

Signs

Causes & Risk Factors

• Failure to remove both ovaries completely.
• No correlation with age at OHE, difficulty of surgery, obesity of patient, or experience of surgeon.
• Presence of anatomically abnormal ovarian tissue (fragmentation into the broad ligament) is possible, more common in queens.
• Supernumerary ovary (rare).
• Experimentally, functionality returns to ovarian tissue removed from its vascular supply and replaced into or onto the lateral abdominal wall, mesentery, or serosal surface.

Differential Diagnosis

• Inflammation or infection of the genitourinary tract.
• Vaginal hemorrhage due to foreign body (grass awn).
• Trauma.
• Uterine stump granuloma secondary to local pathology (foreign body reaction to suture material or grass awn).
• Neoplasia of a remnant portion of the tubular tract (uterine stump leiomyoma or leiomyosarcoma).
• Neoplasia of an ovarian remnant (granulosa cell tumor, carcinoma, luteoma, functional teratoma).
• Neoplasia of the urinary tract (transitional cell carcinoma).
• Vascular anomalies of the genitourinary tract.
• Coagulopathy.
• Exogenous estrogen administration (as for sphincter incompetence associated with urinary incontinence).
• Exposure to human transdermal hormone replacement therapy (most commonly small lap dogs).
• Endogenous extraovarian source of estrogen: adrenal pathology (rare).

CBC/Biochemistry/Urinalysis

• Usually normal.
• Chronic blood loss anemia if vaginal hemorrhage is profound; uncommon unless concurrent ovarian neoplasia, follicular cysts, coagulopathy, or other systemic disease.
• Pancytopenia is possible from estrogen toxicity.
• An inflammatory leukogram and isosthenuria can occur subsequent to uterine stump pyometra.

Other Laboratory Tests

• Observation of behavioral and physical signs of estrus together with vaginal cytology and/or measurement of serum progesterone or estradiol concentrations confirming the presence of functional ovarian tissue.
• Vaginal cytology: vaginal mucosal cornification is a bioassay for elevated plasma estradiol concentrations (see Breeding, Timing).
• Vaginal cytology (bitch): epithelial cell cornification is generally >90% during estrus (superficial and pyknotic or anuclear cells).
• Vaginal cytology (queen): epithelial cell cornification ranges from 10% to 40%; clearing (absence of debris and clumping of cells) occurs in 90% of smears during estrus.
• Serum progesterone (bitch): a serum progesterone concentration >2 ng/mL (measured 1–3 weeks after behavioral estrus) is consistent with functional luteal tissue. GnRH (50 µg IM), hCG (400 IU IV), or hCG (1,000 IU “1/2 IV, 1/2 IM”) can be used to attempt to induce ovulation or luteinization for diagnostic purposes; serum progesterone concentration is measured 2–3 weeks later. Note: pathologic ovarian tissue may not be responsive to either hormone.
• Serum progesterone (queen): ovulation and/or luteinization is stimulated most commonly by coital stimulation during behavioral estrus, and serum progesterone concentration is measured 2–3 weeks later; post-stimulation serum progesterone concentrations >2 ng/mL are consistent with adequate coital stimulation and functional luteal tissue. GnRH (25 µg IM) can be used to attempt to induce ovulation or luteinization for diagnostic purposes; serum progesterone concentration is measured 2–3 weeks later. Pathologic ovarian tissue may not be responsive.
• Serum estradiol: peak levels triggering behavioral estrus range from 20 to >70 pg/mL; serum estradiol concentrations are confirmatory to the diagnosis of ovarian remnant syndrome based on vaginal cytology.
• Luteinizing hormone assay (Witness LH, Zoetis): the LH assay should be positive (>1 ng/mL) in a gonadectomized dog due to lack of pituitary feedback from a gonad. When a positive result is obtained, consider repeating in 24 hours to rule out detection of the 12–24h LH surge in an intact, estrual bitch (should have representative vaginal cytology with superficial cells predominating). If both are positive, then the dog has been gonadectomized. A negative test (<1 ng/L) is found with intact dogs unless performed at the moment of the LH surge during estrus. The assay is licensed for use in the bitch, but likely is applicable in male dogs, toms and queens, provided that the queen is exposed to 14 hours of light/day. Note: exogenous estrogen exposure in a gonadectomized dog can cause the LH to become misleadingly negative.
• Anti-müllerian hormone (AMH) testing: A positive test in a bitch >6 months of age supports the presence of ovarian tissue (SpayCheck^®; offered by multiple endocrine laboratories in cases with a negative AMH but convincing clinical evidence supporting remnant syndrome. Some investigators advise obtaining a progesterone to identify persistent luteal structures lacking AMH).
• Cytology of vulvar discharge can be suppurative if a uterine stump granuloma or pyometra exists.
• Provocative adrenal testing (pre- and post-ACTH administration).

Imaging

Diagnostic Procedures

• Exploratory laparotomy-removal of residual ovarian tissue confirms and resolves the problem.
• Identification of residual ovarian tissue is facilitated by the presence of follicles or corpora lutea; schedule procedure during times of elevated progesterone or during behavioral estrus. Unlike a routine ovariohysterectomy, this laparotomy is facilitated by hormone influence.
• Histopathology-always submit visible ovarian tissue; if no visible ovarian tissue is identified, submit all residual tissue at the ovarian pedicles. This helps confirm the diagnosis and screens for malignancy. Submit revised uterine stump tissue for aerobic and anaerobic cultures and histopathology (hormone influence, inflammatory response, malignancy).

Drug(s)

• Progestational or androgenic compounds to suppress follicular ovarian activity-not recommended because of undesirable side effects (mammary neoplasia, diabetes, undesirable behavior, hepatopathy, dermatopathy).
• Immunocontraception or GnRH agonist (Suprelorin, Peptech Animal Health Pty Limited, Australia; Virbac, Vienna) administration will offer a viable alternative or adjunctive therapy to laparotomy when perfected and commercially available in the United States.

Possible Complications

• Removal of functional luteal tissue may induce transient signs of pseudopregnancy in dogs and cats postoperatively (see False Pregnancy).
• The use of oral antiprolactin agents (cabergoline) can be considered for pseduopregnancy.

Expected Course and Prognosis

• Successful removal of remnant ovarian tissue should result in cessation of clinical signs of estrus/diestrus.
• Adjunctive therapy for pyometra (systemic antibiotics, supportive care) as indicated.
• Adjunctive therapy for functional ovarian neoplasia as indicated.

See Also

• Breeding, Timing
• False Pregnancy

Abbreviations

• ACTH = adrenocorticotropic hormone
• GnRH = gonadotropin-releasing hormone
• hCG = human chorionic gonadotropin
• LH = luteinizing hormone
• OHE = ovariohysterectomy

Authors Autumn P. Davidson and Tomas W. Baker

Consulting Editor Sara K. Lyle