Veterinary Society of
Surgical Oncology

PATHOPHYSIOLOGY

General Considerations

  • vaginal and vulval tumors are the 2nd most common canine reproductive tumor and account for 2.4%-3.0% of all canine tumors
  • majority of vaginal and vulval tumors are benign:
  • leiomyoma and fibroma in cat
  • leiomyoma and lipoma in dog
  • Leiomyoma

  • 86% of vaginal and vulvar tumors are benign smooth muscle tumors (i.e., leiomyoma and fibroma)
  • majority of leiomyomas arise from vestibule of vulva rather than vagina
  • extraluminal and intraluminal forms have been described:
  • extraluminal present with a slow-growing perineal mass
  • intraluminal are attached to vestibular or vaginal wall by variably sized pedicle and can be multiple
  • mucosa is generally intact but ulceration may occur with exposure and irritation
  • leiomyoma may be hormone dependent:
  • leiomyoma has not been diagnosed in dogs ovariectomized < 2 years
  • 15% local tumor recurrence rate in intact and 0% in dogs following ovariohysterectomy
  • mean age 10.8 years
  • breed predisposition: Boxer
  • incidence of leiomyoma higher in nulliparous bitches
  • 33% associated with cystic endometrial hyperplasia, ovarian cysts, and mammary gland tumors
  • Lipoma

  • lipoma can arise from perivascular or perivaginal adipose tissue and attach to tuber ischii
  • lipoma can lie within pelvic canal and are usually well-circumscribed and relatively avascular
  • mean age 6.3 years
  • Transmissible Venereal Tumor

  • transmissible venereal tumors occurs in 4-5-year-old dogs with increased risk in free roaming dogs
  • cell origin of transmissible venereal tumors is unknown, but an undifferentiated round cell tumor of reticuloendothelial origin is most likely
  • transmissible venereal tumors have a common origin as chromosomal aberrations are constant and highly specific
  • virus particles have been identified in transmissible venereal tumors
  • however, viral etiology is unlikely as the disease cannot be transmitted by cell-free filtrates
  • transmissible venereal tumors are transmitted by contact with genital mucous membranes during coitus
  • transmissible venereal tumors appear as multiple tumors along the mucosal lining of the vagina and vestibule
  • Other

  • benign tumors: sebaceous adenoma, fibrous histiocytoma, benign melanoma, myxoma, and myxofibroma
  • malignant tumors: leiomyosarcoma, ADC, SCC, TCC, HSA, OSA, MCT, and epidermoid carcinoma
  • carcinoma of bladder or urethra may present with palpably enlarged urethral papilla
  • CLINICAL FEATURES

    Clinical Signs

  • duration of clinical signs longer for extraluminal compared to intraluminal leiomyoma
  • intraluminal leiomyoma often presents as mass extruding between vulval lips, particularly during estrous
  • other clinical signs include vulval bleeding or discharge, enlarging vulvar mass, dysuria, hematuria, tenesmus, excessive vulval licking, and dystocia
  • lipomas usually present with a slowly growing mass impinging on adjacent structures
  • Diagnosis

  • vaginoscopic examination, retrograde vaginography, and urethrocystography may delineate mass
  • ultrasonography, FNA, and histopathology
  • Treatment

    Medical Management

  • local tumor recurrence rate is high for dogs with transmissible venereal tumor and surgery is not recommended
  • transmissible venereal tumors are very response to chemotherapy and radiation therapy
  • chemotherapy: vincristine 0.5-0.7 mg/m 2 IV 4-8 times ± doxorubicin
  • Surgical Management – Benign Tumors

  • exploratory celiotomy for ovariohysterectomy (due to hormonal dependence and local tumor recurrence)
  • conservative surgical resection
  • wide resection probably not required if ovariohysterectomy performed concurrently
  • dorsal episiotomy may be required to provide adequate visualization and ensure complete resection
  • dorsal episiotomy indicated for extraluminal vaginal and vulvar tumors as tumors are usually well-circumscribed and poorly vascularized resulting in good probability of complete excision
  • perineal approach or pubic split is rarely required
  • Surgical Management – Malignant Tumors

  • malignant infiltrative vaginal tumors treated with complete vulvovaginectomy and perineal urethrostomy
  • sternal recumbency in perineal stand with perineum elevated
  • urethra catheterized
  • fusiform skin incision performed around vulva
  • deeper tissues sharply dissected from labia and vestibule
  • constrictor vestibuli and constrictor vulvae muscles are dissected from the vestibule
  • dorsal labial branches of the ventral perineal artery are ligated or bleeding controlled with electrocautery
  • catheterized urethra identified and dissected free from encircling constrictor vestibuli muscles
  • From: Bilbrey SA, et al: Vulvovaginectomy and perineal urethrostomy for neoplasms of the vulva and vagina. Vet Surg 18:450-453, 1989.

  • vagina dissected with transection of ischiocavernosus and ischiourethralis muscles
  • dissection continued cranially between paired levator ani muscles to level of cervix
  • vaginal branches of vaginal and uterine arteries and veins ligated
  • vagina transected immediately caudal to cervix in intact bitches or cervix and uterine stump removed in spayed dogs
  • deep tissues closed to reduce dead space
  • perineal urethrostomy performed with transected urethra tractioned caudally, distal end spatulated, and closed in 2 layers with final layer mucosa to skin
  • From: Bilbrey SA, et al: Vulvovaginectomy and perineal urethrostomy for neoplasms of the vulva and vagina. Vet Surg 18:450-453, 1989.

    Prognosis

  • complete surgical excision is usually curative
  • guarded to poor prognosis with ADC, TCC, and SCC due to high local tumor recurrence and metastatic rates
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