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Signalment and history

A 6-year-old female spayed Golden Retriever presented for further evaluation of an abdominal mass found on annual examination. Two weeks prior to referral, the patient had undergone a brief ultrasound followed by an exploratory laparotomy as a clear organ of origin of the mass was undetermined on sonographic assessment. At surgery, the large mass was suspected to be arising from the left kidney. The patient was recovered without further intervention for referral.

Physical examination and bloodwork:

On presentation, the patient was bright, alert and responsive. Vital parameters were within normal limits. The abdomen was mildly tense on palpation with notable organomegaly on the left. The remainder of the physical examination was normal. No abnormalities were identified on complete blood count. The serum biochemistry profile revealed an elevated creatinine kinase (3184U/L, reference range: 40-255 U/L). An abdominal CT was performed to further evaluate the mass and for surgical planning.


Abdominal CT, precontrast.

Abdominal CT, immediately after injection of contrast.

Abdominal CT, four minutes following contrast administration.


  • The left renal pelvis is severely dilated with fluid (3.8 cm in a width). The cranial segment of the left ureter is moderately dilated and tortuous (up to 2.0 cm at the level of the renal pelvis). As the left ureter courses caudally, it is confluent with a very large (8.5 cm in diameter x 27 cm in length), tubular, sacculated and fluid-filled structure that is surrounded by a thick, soft tissue attenuating and mildly contrast enhancing wall. Contained in this fluid filled structure are numerous soft tissue attenuating polypoid nodules.
  • Following contrast administration, during the pyelogram phase, contrast pools in the left ureter as well as in the lumen of the large left tubular mass, confirming a ureteral origin. A normal left ureter inserting on the urinary bladder at the level of the trigone is not identified.
  • In peritoneal cavity is a mild amount of fluid and minimal amount gas. The ventral abdominal wall centered on the linea alba is a moderately thick, contains a mild amount of gas and is surrounded by numerous strands of soft tissue attenuation. A ground-glass to alveolar attenuation is present in the dependent aspect of the right middle and right caudal lung lobes, compatible with atelectasis. A mild amount of gas is contained in the subcutaneous tissues of the right lumbar dorsum, attributed to prior intramuscular injections.


  1. Severe left-sided hydronephrosis and hydroureter with numerous endoluminal nodules/masses.
  2. Mild peritoneal fluid.
  3. Recent abdominal laparotomy.

The left ureteral changes could represent of a benign process such as a paraureteral cyst, pyogranulomatous ureteritis with hydroureter, or fibroepithelial polyps causing a hydroureter. Alternatively, a neoplastic process such as a leiomyoma/sarcoma, hemangiosarcoma or urothelial carcinoma is also possible. The presence of peritoneal fluid could represent an inflammatory transudate/modified transudate, mild hemoabdomen or less likely uroabdomen such as due to rupture of the ureter.


  • Given the possible complications associated with ureteral resection and anastomosis (e.g., urinary leakage or ureteral stricture), a ureteronephrectomy was performed.

Histological diagnosis

  • The ureter is multifocally expanded by long papillary or polypoid like projections that are composed of fibrovascular stroma with variable amounts of haphazardly arranged smooth muscular bundles, lined by 1-5 cell layer thick urothelial epithelium. Some projections have abundant empty space supported by a fine meshwork of fibrovascular stroma, while others have dense collagen bundles. Occasionally the urothelial epithelium is expanded 2 – 3 times normal. In some polyps, there are large aggregates of foamy macrophages with adjacent cholesterol clefts. In the left kidney, there are a few aggregates of mononuclear cells (lymphocytes, plasma cells) in the interstitial space.
  • No bacteria were isolated on aerobic and anaerobic cultures.
  •  Conclusion
    Severe hydronephrosis and hydroureter with multiple fibroepithelial polyps


The most commonly reported benign tumors of the ureter include leiomyomas, transitional cell papilloma, fibropapilloma, and fibroepithelial polyps. Malignant ureteral neoplasms reported include hemangiosarcoma, leiomyosarcoma, transitional cell carcinoma, mast cell tumor, and spindle cell sarcoma.1, 2, 3, 4 Benign ureteral neoplasms are commonly located in the cranial segment of the ureter while malignant neoplasms are more likely to involve the caudal segment of the ureter.5, 6

Ureteral fibroepithelial polyps are rare in both human and veterinary medicine. They are thought to represent a benign neoplasm, hamartous condition, or a chronic inflammatory reaction. These benign lesions typically are polypoid and pedunculate and most commonly arise from the wall of the cranial ureteral segment. Ureteral fibroepithelial polyps are associated with urinary incontinence and urinary tract infections, and cause secondary hydronephrosis and hydroureter. The etiology of ureteral fibroepithelial polyps has not been established. Obstruction, infection, trauma, chronic irritation, hormonal imbalance and development defects are postulated as possible predisposing causes.6

Human studies have documented that ureteral fibroepithelial polyps more commonly occur in males (male: female ratio of 3:2), at the infundibulum of the proximal ureter, and on the left.4 Of the eight cases described in the veterinary literature4, 6, 7, 8, four occurred in male dogs, five were located within the cranial segment of the ureter, and five involved the left ureter. A predilection for lateralization to the left side may be similar to that described in the human literature, although this remains speculative considering the low number of cases reported in veterinary medicine.

Previously reported radiographic findings in the veterinary literature include a tubular soft tissue opacity extending in the right hemiabdomen from the first lumbar vertebra to the fifth lumbar vertebra.4 Antegrade pyelogram or intravenous excretory urography may reveal a contrast filled dilated renal pelvis and ureter with a large intraluminal ureteral filling defect.6 On ultrasonography, hydronephrosis and hydroureter secondary to the presence of an echogenic ureteral mass are common findings.6 Prior reports describe the use of nuclear scintigraphy to assess the renal function of individual kidneys to guide surgical management (ureteronephrectomy vs. nephron sparing surgery).6

Interesting features of the case presented include the absence of clinical signs or renal biochemical abnormalities expected with such an advanced disease process, the number of fibroepithelial polyps present within the ureter, and the severity of hydroureter.


  1. Seiler GS, Thrall D. Textbook of Veterinary Diagnostic Radiology. 6th ed. St Louis, MO: Elsevier; 2013:722–723.
  2. Deschamps JY, Roux FA, Fantinato M, Albaric O. Ureteral sarcoma in a dog. J Small Anim Pract. 2007;48:699–701.
  3. Guilherme S, Polton G, Bray J, Blunden A, Corzo N. Ureteral spindle cell sarcoma in a dog. J Small Anim Pract. 2007;48:702–4.
  4. Farrell M, Philbey AW, Ramsey I. Ureteral fibroepithelial polyp in a dog. J Small Anim Pract. 2006;47:409–12.
  5. Troiano D, Zarelli M. Multimodality imaging of primary ureteral hemangiosarcoma with thoracic metastasis in an adult dog. Vet Radiol Ultrasound. 2019;60(4):E38-E41.
  6. Reichle JK, Peterson RA, Mahaffey MB, Schelling CG, Barthez PY. Ureteral fibroepithelial polyps in four dogs. Vet Radiol Ultrasound. 2003;44:433–7.
  7. Burton CA, Day MJ, Hotston Moore A, Holt PE. Ureteric fibroepithelial polyps in two dogs. J Small Anim Pract. 1994;35:593–6.
  8. Hattell AL, Diters RW. Snavley DA. (1986). Ureteral fibropapilloma in a dog. J Am Vet Med Assoc. 1986;188(8):873.


The authors would like to thank:

  • Brigitte Brisson, DVM DVSc DACVS and Samantha Stine, DVM for case management and surgery.
  • Carmon Co DVM MSc and Brandon Lillie DVM PhD DACVP for histopathological analysis.
  • Trevor Morimoto, DVM DACVR for his assistance in the preparation of this case summary.

Left kidney (top) and ureter, post-operative.