Ovarian Remnant Syndrome

Coby Richter, DVM, DACVS, discusses a case study of ovarian remnant syndrome and a vaginal mass in a Labrador retriever. Learn the evaluation, diagnostics, and treatment.

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Bogey, an eight year old spayed female Labrador retriever dog was referred for a vaginal mass which had appeared in the last 24 hours.

The owner noticed that the vulvar area seemed larger than normal over the past month and reported that Bogey had been mounted by two male dogs recently. When asked about other estrus behavior in this spayed female, the owner observed that Bogey periodically shows signs of breeding receptivity during the 6-7 years since she underwent routine ovariohysterectomy. The dog was otherwise healthy, active, and current on vaccinations and not on any medications.

Upon presentation, a 6 cm diameter pink, shiny ovoid mass was noted protruding from the vulvar lips without evidence of significant tissue necrosis or inflammation. Digital and vaginal speculum exam revealed the mass arising from the floor of the vestibule midway between the urethral orifice and the cervix. The base of the stalk palpated approximately 2 cm in width, and the cervix was open during exam. No other masses were visualized and no uterine discharge was seen. A serous pink vaginal discharge was present. The remainder of her physical exam was unremarkable. CBC, chemistry and urinalysis were all within normal limits. An abdominal ultrasound was performed revealing hypoechoic nodular foci (2.1 cm length) caudal and dorsal to the right kidney, a mildly fluid distended portion of the uterine body and mild sublumbar lymph node enlargement. Radiologist interpretation of these findings indicated a strong suspicion of ovarian remnant syndrome. There was no evidence of peritonitis.

 

The owners elected exploratory celiotomy with the goal of removing the nodular structure caudal to the right kidney as well as any abnormal uterine tissue. Following celiotomy, the vaginal mass would be excised providing Bogey was doing well under anesthesia. She was started on ampicillin-sulbactam (22 mg/kg IV q8 hours), maropitant (1mg/kg SQ once), Norm R for maintenance fluids and fentanyl CRI. Through a standard midline celiotomy approach, a cystic structure 20mm x 6 mm was identified near the caudal pole of the right kidney and was excised using a vessel sealing device. No abnormal tissue was identified caudal to the left kidney. A dark gray-purple 5mm cystic structure was found at the cranial end of the uterine stump with no evidence of perforation.  The uterus was double ligated and transected just cranial to the cervix allowing removal of the cystic structure and an additional 1.5 cm of uterine body. The remainder of the exploration was unremarkable and closure was routine following lavage and suction. The resected portion of uterus was cultured for aerobic and anaerobic growth.

 

Bogey was moved from dorsal recumbency to sternal recumbency with her hind legs supported via tape stirrups over the end of the surgical table. Towels were used to provide padding between quadriceps, pelvis and the table. Following rectal purse-string, routine prep and draping, a red rubber catheter (8F) was passed retrograde into the urethra and the bladder emptied via syringe. The catheter was left in place to aid in avoiding trauma to the urethra during mass excision.  Visibility was acceptable due to the size of the stalk, thus no episiotomy was necessary.  The mass was excised close to the base and at least 1.5 cm from the urethral orifice through the stalk. The defect was closed with absorbable suture resulting in good hemostasis. Recovery was uneventful and Bogey was discharged the following morning with one week of oral antibiotics as well as anti-inflammatory and pain medications. Her owners report that she did well once home with an uncomplicated return to normal activity.

 

The cystic mass removed from the vicinity of the caudal pole of the right kidney returned a histopathological diagnosis of cystic rete (adenomatous hyperplasia arising from the hilar area of the ovary). The vaginal mass returned a diagnosis of low grade leiomyosarcoma. Both sites showed clean margins histopathologically. Culture did not grow any pathologic bacteria.

 

Masses of the vestibule, vagina and vulva are reported to be benign in 74-82% of dogs presenting for this condition. The most common benign tumors (not including vaginal edema) in this location include leiomyoma, fibroma, fibropapilloma (polyps) and cysts. Of the malignant lesions in dogs, leiomyosarcoma is the most common followed by transmissible venereal tumor (TVT), transitional cell carcinoma (TCCA), and hemangiosarcoma. Other reported malignancies of this region include rhabdomyosarcoma, mast cell tumor, osteosarcoma and neuroendocrine tumors.

 

A typical diagnostic plan for canine vaginal mass should include complete physical exam, history, abdominal ultrasound, vaginoscopic exam and vaginal cytology. Retrograde vaginography or urethrocystography may be indicated to better define tumor extension. Computed tomography (CT) or magnetic resonance imaging may be useful for vaginal tumors where an ultrasound examination is difficult. A fine needle aspirate or incisional biopsy or traumatic catheterization is indicated prior to surgical excision. In the case of a pedunculated mass with no evidence of metastasis or local invasion such as Bogey, an excisional biopsy is worth discussion with the owner. As with any neoplasia, a histopathological diagnosis prior to surgical removal is always preferred. In this particular case, the owners elected a single anesthetic event to address the suspected ovarian remnant syndrome as well as the vaginal mass. Thoracic radiographs or CT imaging of the chest are also important to help guide anesthetic plans and prognosis.

 

Surgical excision of benign masses of the vagina and vulva is usually curative. Leiomyosarcomas excised with clean margins have a good prognosis, though referral to a veterinary oncologist was recommended for Bogey. Resection of other malignancies such as TCCA carries a guarded prognosis due to the likelihood of metastatic lesions and local invasion at the time of surgery. Leiomyomas and leiomyosarcomas are both believed to be hormone dependent, or at least affected by hormone activity. Staging procedures (removal of hormone source followed days or weeks later by mass excision) may be beneficial in some dogs.  There are reports of benign leiomyomas regressing completely after ovariohysterectomy, thus eliminating the need for a second procedure.  

 

Selected references:

  • Thomson and Britt. 2012 Reproductive system in Veterinary Surgical Oncology pp 341-363. Kudnig and Seguin editors.
  • Klein MK 2007. Tumors of the female reproductive system. Small Animal Clinical Oncology 4th ed. Withrow and Vail, editors.
  • Kydd and Burnie. 1986. Vaginal neoplasia in the bitch: a review of 40 clinical cases. J Sm Anim Pract 27:255-263.
  • Thacher C, Bradley RL: Vulvar and vaginal tumors in the dog: a retrospective study. J Am Vet Med Assoc 183:690–692, 1983

 

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