Canine Vaginal Leiomyoma Diagnosed by CT Vaginourethrography

Introduction

Vaginal tumors comprise a small percentage of canine neoplasms. In one study of 3,073 dogs with tumors, 85 (2.8%) had vaginal or vulvar tumors.¹ In other studies, that number ranges from 1.9% to 3%.^1,2 Most canine vaginal tumors are benign. In a study of 99 dogs with either vulvar or vaginal tumors, 72 (73%) were benign and 60 (83%) of those were leiomyomas, which included fibromas and polyps due to their similar histopathologic characteristics.^3,4 Other less common benign tumors included lipomas, nerve sheath tumors, fibrous histiocytomas, benign melanomas, myxomas, and myxofibromas.⁴

Vaginal leiomyomas are predominantly identified in intact female dogs, as this tumor type is suggested to have estrogen-dependent characteristics.^5,6 The mean age of canines diagnosed with leiomyomas is 10.8 yr.¹ Dogs with vulvar or vaginal tumors often do not present until the tumors are large and cause clinical signs, with the majority of tumors measuring 5–20 cm at time of diagnosis.¹ The most frequent clinical signs include vulvar discharge and a mass protruding from the vulva.⁴ Other clinical signs may include perineal swelling, stranguria, hematuria, tenesmus, and vulvar licking.^1,4 When benign, surgical resection of vaginal tumors is generally curative.⁵ Successful surgical outcome is associated with the proximity of the mass to the urethral orifice.^1,3,4 Due to the low occurrence of vaginal tumors, minimal publications exist that describe the diagnostic approach to vaginal masses.

Case Report

A 13 yr old 29.5kg spayed female Labrador retriever was evaluated for a 2-wk history of vulvar bleeding, which had decreased in frequency during a 2-wk course of oral amoxicillin trihydrate/clavulanate potassium^a. The patient had a history of recurrent urinary tract infections that responded to antibiotic therapy. The most recent infection was reported 1.5 yr prior to presentation.

On rectal examination, a mass was palpated and determined to be outside of the rectal lumen and within the ventral aspect of the pelvic canal. The mass was freely moveable and nonpainful. The mass could be palpated externally at the perineum following gentle digital manipulation and caudal traction via rectal examination. Digital vaginal examination was unremarkable. The remainder of the physical exam was unremarkable.

Complete blood count and serum biochemical analysis did not reveal abnormalities pertinent to the case. Urinalysis obtained by cystocentesis revealed a pH of 6.5, urine specific gravity of 1.034, 4+ protein, occasional red blood cells (< 10/high-power field), WBCs (< 5/high-power field), rare transitional epithelial cells, and a moderate amount of fat. Although no bacteria were identified on urinalysis, a urine culture was positive for Pseudomonas aeruginosa (> 100,000 colonies/mL), which was sensitive to multiple antibiotics.

Thoracic radiography was unremarkable. On survey abdominal radiographs (Figures 1A, B), an ill-defined soft tissue mass was present in the ventral pelvic canal, causing dorsal displacement of the rectum. The caudal abdomen was not included in the ventrodorsal survey radiograph. Radiographic differential diagnoses included a mass of vaginal, uterine, urethral, or adnexa/nonorgan associated origin. Multiple, small mineral opaque calculi were also identified in the urinary bladder.

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A complete abdominal ultrasound examination was performed to look for metastatic disease. Intrapelvic lesions are not routinely evaluated with ultrasound, as the pelvic canal cannot be evaluated through a transabdominal approach. Utilizing a perineal transcutaneous approach, only a small portion of the pelvic canal mass could be identified. To better evaluate the mass, transrectal ultrasound was performed. A solid, vascular, mixed echogenic mass (4 cm × 5 cm) was present ventral to the colon.

Computed tomographic^b (CT) examination of the pelvic inlet was performed in dorsal recumbency under general anesthesia to determine if the mass was resectable and to aid in planning the surgical approach for resection. Transverse images (2 mm) of the pelvis were acquired before and after IV administration of 74 mL Iohexol^c (880 mg I/kg). On sagittal reformations and oblique transverse images, a well-circumscribed 4.5 cm × 5.2 cm × 8 cm soft-tissue mass was present within the vagina that moderately and heterogeneously contrast-enhanced (Figures 2A, B). The mass extended from the midventral vaginal wall, filled the majority of the pelvic canal, and caused dorsal compression of the rectum and ventral displacement of the urethra. The mass did not extend beyond the vaginal wall. Incidentally, a nodule was identified within the dorsal superficial soft tissues.

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A CT vaginourethrogram was acquired after foley catheter placement and administration of 40 mL of a 33% solution of iohexol diluted with lactated ringers solution (117 mg I/mL) within the vestibule. On sagittal reformations and oblique transverse images, contrast medium surrounded the vaginal mass and better delineated its attachment to the ventral aspect of the vaginal wall (Figures 3A, B). The most caudal aspect of the mass was approximately 3 cm cranial to the location of the urethral orifice, making surgical excision without urethroplasty possible.

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For clinical interest, subsequent radiographs postCT and vaginourethrography were performed. Contrast medium within the urinary bladder, ureters, and kidneys was secondary to IV administration during routine CT examination. Positive contrast medium in the vagina delineated a large, smoothly marginated vaginal mass (Figures 4A, B). Contrast medium in the distal urethra confirmed the assessment of surgical resectability. The amended differential diagnoses for the vaginal mass included vaginal neoplasia, granuloma, or hematoma.

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The patient was placed under general anesthesia and a total vaginectomy was performed, as well as a cystotomy to remove the urinary bladder calculi. The vagina and vaginal mass were ligated 1 cm cranial to the vaginovestibular junction. The uterine stump, vagina, and vaginal mass were submitted for histologic examination. Microscopic evaluation revealed a well-circumscribed, noninfiltrative neoplasm that was composed of long spindle cells with a low mitotic rate and multifocal areas of hemorrhage and edema. The final diagnosis was a vaginal leiomyoma with complete surgical margins. Postoperatively, the patient recovered and continued to do well 6 mo postoperatively at the time of the last follow-up.

Discussion

In clinical practice, vaginal masses may be identified either on physical examination or suspected based on clinical history and signs. Survey radiographs and ultrasound are useful as a screening tool, but are of limited diagnostic value due to the intraplevic location of the vagina. Small animal imaging rarely includes transluminal (e.g., intravaginal, intrarectal) imaging, although it is common in production animals. Transrectal ultrasonography was attempted in this case and allowed visualization of the mass, but afforded minimal information regarding surgical options.

Cystoscopy and vaginourethrography are additional imaging modalities available to evaluate the vagina. Those diagnostic tools are helpful in localizing masses, strictures, and ectopic ureters, but are unlikely to provide the degree of anatomic information required for surgical planning.⁷ CT is a helpful diagnostic tool for vaginal disease as it allows localization of the anatomic site of origin due to multiplanar imaging capabilities and improved contrast resolution compared with radiographs.⁸ MRI is infrequently used in veterinary patients to characterize vaginal masses. Only a single case report of a vaginal rhabdomyosarcoma exists.⁹

In humans, vaginal leiomyomas are rare, with approximately 300 reported cases.^10,11 Almost all vaginal leiomyomas arise from the midline anterior wall.^10,11 Similar to dogs, vaginal leiomyomas are also estrogen-dependent, and women can present with urinary tract symptoms, including stranguria.^8,10 In humans, multiple diagnostic imaging modalities are used, including ultrasound, cystoscopy, CT, and MRI. Ultrasound and cystoscopy have similar limitations to those experienced in veterinary medicine, mainly the intrapelvic location precludes a thorough examination. Although CT is often used in human medicine to evaluate vaginal tumors, MRI is currently considered the gold standard for imaging, as leiomyomas can be differentiated from malignant vaginal tumors, such as leiomyosarcomas, based solely on their MRI characteristics. Leiomyomas are round, well-circumscribed, hypointense on T1- and T2-weighted MRI with homogeneous contrast-enhancement.¹¹ In contrast, malignant tumors are irregularly marginated, heterogeneous, hyperintense on T2-weighted images, and often show heterogeneous contrast-enhancement with areas of necrosis and hemorrhage.⁸

In this case report, full assessment of the vaginal mass and urethral orifice was accomplished through multiple complementary diagnostic imaging studies. At the authors’ hospital, CT is routinely used for surgical planning and was used in this case following survey radiography. Although the authors have not previously used MRI to evaluate canine vaginal masses, MRI may become a valuable tool in the future. Vaginourethrography was performed following CT out of clinical interest, to compare multiple imaging modalities in the diagnosis of this mass. Radiographically, intravaginal contrast medium outlined the margins of the mass and allowed visualization of the urethra. In retrospect, contrast radiography would have been sufficient to reach a definitive diagnosis as well as assess the position of the urethra relative to the mass. However, CT more exactly delineated the narrow attachment to the vaginal wall and its precise distance from the urethra, which was necessary for surgical planning. The authors found vaginourethrography to be a simple procedure that only required iodinated contrast medium and a foley catheter for delivery. Vaginourethrography also requires light sedation and can be performed in the vast majority of hospital settings.⁷ In addition to vaginal masses, vaginourethrography can be helpful in diagnosing either vaginal or vestibular clefts, stenoses, and strictures.⁷ The caudal abdomen was not included in the ventrodorsal survey radiograph, which should be included when reproductive, rectal, or lower urinary tract disease is suspected. However, this likely would not have changed the authors’ diagnostic methodology, as the intrapelvic location of this mass precluded a radiographic only diagnostic approach.

Conclusion

The authors of this study found routine CT, CT vaginourethrography, and multiplanar reconstructions most useful for studying the characteristics of the vaginal mass and assessing treatment options. CT, including contrast medium within the vagina, provided the best visualization of the ventral attachment of the mass, and its proximity to the urethral orifice was more accurately determined compared with contrast radiography and survey CT. To the authors’ knowledge, this is the first published case of CT vaginourethrography.