History
A 3-year-old 23.9-kg (52.7-lb) mixed-breed spayed female dog was evaluated because of chronic vulvar discharge and tenesmus of 5 months’ duration. The signs were first observed 4 weeks after routine ovariohysterectomy. The dog was bright, alert, and responsive. Body condition score was 4 on a scale from 1 to 5, and vital parameters were within reference range. A large mass in the caudal aspect of the abdomen was palpated, which elicited mild signs of pain from the dog. A moderate volume of serosanguineous vaginal discharge was also present. No external vulvar lesions were present. The dog was mildly anemic, mildly hyperproteinemic (8.3 g/dL; reference range, 5.4 to 8.2 g/dL), mildly hypoalbuminemic (2.4 g/dL; reference range, 2.5 to 4.4 g/dL), and hyperglobulinemic (5.9 g/dL; reference range, 2.3 to 5.2 g/dL). Amylase activity was high (1,403 U/L; reference range, 200 to 1,200 U/L). These abnormalities were not considered clinically relevant. Radiographs of the abdomen were made (Figure 1).
Lateral (A) and ventrodorsal (B) radiographic images of the mid to caudal aspect of the abdomen of a 3-year-old spayed female dog with chronic vulvar discharge and tenesmus of 5 months’ duration.
Citation: Journal of the American Veterinary Medical Association 247, 11; 10.2460/javma.247.11.1237
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
There is a 7-cm-long, 6-cm-diameter, well-defined, ovoid soft tissue mass in the caudal aspect of the abdomen causing cranial displacement of the urinary bladder and dorsal displacement and compression of the descending colon (Figure 2). Cranial displacement of the urinary bladder and dorsal displacement of the colon are most consistent with a mass of uterine or vaginal origin. A uterine origin where the mass tapered caudally to communicate with the vagina was confirmed by results of a subsequent abdominal ultrasonographic examination. Ultrasonographic findings indicated that the mass was solid and not cavitary or cystic.
Same radiographic views as Figure 1. A—Notice the mass in the caudal aspect of the abdomen (black arrow), dorsal displacement and compression of the descending colon (arrowhead), and cranial displacement of the urinary bladder (white arrow). B—Notice that the mass is on midline summating with the vertebral column on the ventrodorsal view (arrow).
Citation: Journal of the American Veterinary Medical Association 247, 11; 10.2460/javma.247.11.1237
On the basis of radiographic findings, the differential diagnoses for the mass were a uterine remnant abscess, uterine remnant pyometra, and neoplasia, such as leiomyosarcoma, leiomyoma, or transmissible venereal tumor. An intersex anomaly, such as an enlarged retained testicle, might also cause this appearance, but there were no outward signs of an intersex anomaly. The mass appeared solid on ultrasonographic examination; therefore, pyometra and uterine remnant abscess were considered less likely.
Treatment and Outcome
Fine-needle aspiration of the abdominal mass was performed under ultrasound guidance, and the cytologic findings were characteristic of a transmissible venereal tumor. The owner elected not to treat the dog. Four weeks later, the dog's clinical condition had deteriorated. The mass had increased in size and was compressing the urethra and descending colon more extensively. The dog was constipated, and the urinary bladder was markedly distended. Given the dog's declining condition, the owner elected to have the dog euthanatized. At necropsy, there were multiple firm, raised, sessile, encapsulated, and pedunculated masses within the vestibule, vagina, and uterine stump. The largest mass, within the caudal aspect of the abdomen, measured 6.5 × 9.5 × 4 cm and was associated with fibrous adhesions with the greater omentum, urinary bladder, vagina, and descending colon.
Comments
In the dog of the present report, the use of radiography facilitated identification of the mass and determination of its size, location, radiopacity, and margination; radiographic findings helped to establish the mass as the cause of the patient's clinical signs due to the associated mass effect. The localization of the mass caudal and dorsal to the urinary bladder in a female dog, being most unusual, was particularly important. On ultrasonographic evaluation, the mass was of medium echogenicity, compatible with a mass (as opposed to a fluid-filled lesion), and characterization of its echogenicity features, vascularity, and communication with the vagina greatly refined the list of differential diagnoses. Also, ultrasonography allowed for assessment of the entire abdominal cavity to rule out further associated pathological changes, such as local lymphadenopathy, other organ involvement, or ascites.
Masses in the caudal portion of the abdomen that result in cranial displacement of the urinary bladder are extremely rare in female dogs, compared with male dogs, where prostate gland enlargement commonly causes cranial displacement of the urinary bladder. In this scenario, masses from the uterine body or vagina would be the most likely source. Enlargement of the entire uterus, as with pyometra, does not cause such isolated cranial displacement of the urinary bladder as seen in the dog of the present report, as the enlarged uterus migrates cranial to the urinary bladder. In the authors’ experience, infection or pyometra of the uterine remnant is typically smaller than the mass in this patient. Uterine muscle tumors are rare and usually occur in older dogs.1 Only 1 report2 of transmissible venereal tumor of the uterine remnant is found in the literature, but the imaging findings were not described.
Transmissible venereal tumor is common in tropical and subtropical regions but occurs in nontropical urban areas as well. It occurs in dogs of any breed, age, or sex, although it is most common in dogs that are sexually mature and between 2 and 5 years of age. It can affect most organs, including the oral and nasal mucosa, dermis, rectum, and intra-abdominal organs.3–5 However, it most commonly affects the external genitalia. Tumors of the external genitalia originate as papules and progress to ulcerated, nodular masses. Vaginal discharge is a common clinical sign of transmissible venereal tumor that owners typically mistake for estrus. The disease is transmitted only through direct contact with infected cells; therefore, this dog most likely acquired the tumor through sexual activity prior to being spayed.
In conclusion, masses in the caudal aspect of the abdomen displacing the urinary bladder are rare in female dogs, and the most likely origin is a mass involving the uterine remnant or vagina.
1. Klein MK. Tumors of the female reproductive system. In: Withrow WS, Vail M, Page R, eds. Withrow and MacEwen's small animal clinical oncology. 5th ed. Philadelphia: WB Saunders Co, 2012; 610–618.
2. Musal B, Tuna B. Surgical therapy of complicated uterine stump pyometra in five bitches: a case report. Vet Med Czech 2005; 11: 558–562.
3. Oduye OO, Ikede BO, Esuruoso GO, et al. Metastatic transmissible venereal tumour in dogs. J Small Anim Pract 1973; 14: 625–637.
4. Rogers KS, Walker MA, Dillon HB. Transmissible venereal tumor: a retrospective study of 29 cases. J Am Anim Hosp Assoc 1998; 34: 463–470.
5. Mukaratirwa S, Gruys E. Canine transmissible venereal tumour: cytogenetic origin, immunophenotype, and immunobiology. A review. Vet Q 2003; 25: 101–111.
