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Compendium September 2011 (Vol 33, Issue 9)

Clinical Snapshot: Abdominal Mass in a Shelter Dog

by Lisa C. Pinn, DVM, Lynn M. Milewski, DVM, Aaron M. Jackson, DVM, DACVS

    Case Presentation

    A 6-year-old, 18.5-lb (8.4-kg), female Pekingese of unknown reproductive status presented to River Trails Animal Hospital, Riverwoods, Illinois, with marked, primarily left-sided, abdominal distention; the dog appeared otherwise bright, alert, responsive, and healthy. The dog was obtained by a local animal shelter 48 hours before presentation, and previous medical history was unknown. The body condition score was 4 out of 9, and a large, left-lateralized, mid-abdominal mass was noted on abdominal palpation. Other abnormalities included ocular changes (bilateral pigmentary keratitis, nuclear sclerosis, and centrally located immature cataracts), grade 3/4 dental disease, mild pelvic limb muscle atrophy, hypertrophied vulva with no visible discharge, and a poor, dry haircoat. Vaginal examination was unremarkable.

    A complete blood count revealed a mild inflammatory leukogram (white blood cells, 19.4 × 103/µL [reference range, 6.0 × 103/µL to 17.0 × 103/µL]; neutrophils, 16.3 × 103/µL [reference range, 3.5 × 103/µL to 12.0 × 103/µL]). Serum biochemical analysis was unremarkable. Abdominal radiography revealed a soft tissue opacity with well-defined margins indicative of a mass within the mid-ventral abdomen (FIGURE A and FIGURE B).

    1. What are the limitations of the radiographs? Do those limitations affect the differential diagnosis?

    2. What other diagnostic tests could be conducted before devising a treatment plan?

    3. What are the possible origins of the abdominal mass?

    4. Given the dog’s situation, what would be the most effective and least expensive treatment option?

    Answers and Explanations

    1. The lateral radiograph (FIGURE A) does not include the ventral abdominal wall. The dog’s sternum is positioned to the left on the ventrodorsal view (FIGURE B), which may have exaggerated lateralization of the mass to the left. Despite improper positioning, the abdominal mass is still easily identified and the physical examination confirmed left lateralization.

    2. Thoracic radiography would demonstrate the presence or absence of metastatic disease in the lungs. Additional imaging modalities (e.g., abdominal ultrasonography, magnetic resonance imaging, computed tomography) could be useful in determining the exact location, organ of origin, size, and local invasiveness of the mass. Testing of a fine-needle aspirate of the mass might have further classified the mass as inflammatory/infectious, hyperplastic, or neoplastic. Aspiration was not performed because of the potential complications associated with seeding the abdomen with infectious and/or neoplastic cells.

    3. Based on the location of the mass and signalment of the patient, the most likely organs of origin were considered to be uterine (unilateral closed pyometra, unilateral pregnancy, granuloma, neoplasm), splenic (neoplasm, hematoma), ovarian (granuloma, neoplasm), or cervical (granuloma, neoplasm).

    4. Due to financial constraints, the shelter declined further diagnostic imaging. An exploratory celiotomy was approved because the cost–benefit ratio for exploratory surgery was considered superior to that of other diagnostic procedures (i.e., the potential to surgically remove the mass and provide a cure). While not performed, fine-needle aspiration might have been beneficial; this procedure is inexpensive and might have demonstrated that the mass was benign. This information would have supported the decision to perform an exploratory celiotomy with a chance for a good prognosis.

    ***

    Treatment

    Exploratory celiotomy revealed a firm, white, spherical mass approximately 16.5 × 16.5 × 16.5 cm in size, weighing 1.5 kg. The mass was attached to the proximal one-third of the left side of the cervix by a 1 × 1–cm stalk of white, thick, fibrous, tubular tissue. The mass was adhered dorsally to the colon and ventrally to the urinary bladder and shared a common blood supply with the urinary bladder. The dog was intact with a normal uterus, uterine horns, and multiple cystic follicles on normal-sized ovaries.

    A routine ovariohysterectomy was performed first. The body of the uterus was ligated proximal to the cervix, leaving the cervix and the growth intact initially. The adhesions and blood supply of the mass were then broken down and ligated. The proximal half of the uterus was removed with the stalk, allowing complete excision of the mass and its area of attachment. Dissection of the mass revealed an outer lining of thick muscular tissue surrounding an inner solid mass of muscular tissue.

    Diagnosis: Cervical Fibroleiomyoma

    On histologic examination, the mass was composed of background mesenchymal stromal cells admixed with bundles of well-differentiated smooth muscle cells. No histologic indices of malignancy were noted in the stromal or smooth muscle components. Histopathologic diagnosis was a fibroleiomyoma.a The origin of the fibroleiomyoma was determined surgically to be the cervix.

    Fibroleiomyomas are a subset of leiomyomas with a large portion of the tumor composed of fibrous stromal tissue. Leiomyomas are mesenchymal tumors of smooth muscle that are typically round, firm, white, and encapsulated.1,2 Less than 3% of canine neoplasms are leiomyomas.1 Approximately 85% of canine leiomyomas are found in the female reproductive tract, especially the vagina, vestibule, and vulva.1 Canine female reproductive tract leiomyomas are most common in patients between 5 and 16 years of age, and boxers appear to be predisposed.1,3

    Clinical signs associated with leiomyomas typically pertain to the site of origin, with vaginal leiomyomas often seen protruding into the vulva or causing perineal swelling.1,3 The presentation in this case was as an abdominal mass due to the cervical location of the tumor; fewer cases of cervical leiomyomas are reported compared with those associated with the vagina and vulva.1  Studies using Ekar rats demonstrated that the growth of uterine leiomyomas depends on steroid hormone, including excessive amounts of estrogen.4 Estrogen and progesterone receptors have been identified in smooth muscle tumors of the canine female genital tract.5 Repeated exposure of myofibroblasts to androgens, especially estrogen, contributes to the remodeling of the smooth muscle of the tubular genital tract, leading to the development of leiomyomas.4,5 Surgical removal combined with ovariohysterectomy is considered curative.1,4

    Follow-Up

    Two weeks after surgery, the dog had recovered fully and was adopted by a new family through the shelter.

    What Can Be Learned From This Case?

    Abdominal masses are a relatively common finding on physical examination, especially in older dogs. Radiography alone often does not allow a definitive diagnosis, and additional diagnostic imaging and exploratory surgery are often needed. In this case, the financial situation prohibited further imaging, but an exploratory celiotomy was allowed. Exploratory surgery alone provided not only a diagnosis but also a cure. While advanced imaging is useful—and often indispensible—exploratory surgery can still be used as a diagnostic tool, especially when finances are a consideration.

    References

    1.Kang TB, Holmberg DL. Vaginal leiomyoma in a dog. Can Vet J 1983;24(8):258-260.

    2. Mikaelian I, Labelle P, Doré M, Martineau D. Fibroleiomyomas of the tubular genitalia in female beluga whales. J Vet Diagn Invest 2000;12(4):371-374.

    3. Radi ZA. Vulvar lipoleiomyoma in a dog. J Vet Diagn Invest 2005;17(1):89-90.

    4. Walker CL. Role of hormonal and reproductive factors in the etiology and treatment of uterine leiomyoma. Recent Prog Horm Res 2002;57:277-294.

    5. Millán Y, Gordon A, de los Monteros AE, et al. Steroid receptors in canine and human female genital tract tumours with smooth muscle differentiation. J Comp Pathol 2007;136:197-201.

    References »

    NEXT: Feline Focus: Feline Pediatrics: How to Treat the Small and the Sick

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