Clinical Exposures: Post-traumatic perirenal urinoma associated with an intraureteral air gun pellet in a dog

Clinical Exposures: Post-traumatic perirenal urinoma associated with an intraureteral air gun pellet in a dog

This case hinged on the discovery of a stray air gun pellet in this stray dog, detected by excretory urography.

Urinomas, or uriniferous pseudocysts, are the result of chronic accumulation of urine within a fibrous sac in the retroperitoneal space.1 Urinoma development is due to urine extravasation from the kidney or ureter associated with trauma, surgical injury or urolithiasis.2-10 Urinomas are rarely reported in cats and are extremely rare in dogs; only two cases have been appeared in the literature.2-10 Urinomas may be periureteral or perirenal, though periureteral is more common. However, to our knowledge no report of a perirenal urinoma exists in the literature in dogs. This article describes the diagnosis, surgical treatment and long-term outcome of a dog with a perirenal urinoma associated with an intraureteral air gun pellet.

Case presentation

A 9-year-old, 24-kg mixed-breed female spayed dog was admitted to the Veterinary Centre of Thessaloniki with a 24-hour history of anorexia and depression for further investigation and treatment. The dog had been found as a stray and adopted by the owner three years previously, and since then the dog had had an indoor-outdoor lifestyle. No history of trauma was reported since adoption.

Clinical examination revealed the dog was in good general condition with an elevated temperature of 103.5 F (39.7 C) and mild pain on palpation of the cranial abdomen. A complete blood count and serum chemistry profile revealed leukocytosis (27 × 103/μl = reference range = 6 to 15 × 103/μl), mild hypokalemia (3.3 mmol/L; reference range = 3.7 to 5.8 mmol/L) and hyponatremia (128 mmol/L; reference range to 138 to 160 mmol/L).

An abdominal ultrasonographic examination showed an anechoic mass immediately caudal to the left kidney (compatible with a cystic lesion) and dilation of the left renal pelvis and the left ureter. No free abdominal fluid was detected. Fine-needle aspiration of the urinoma under ultrasonographic guidance revealed a clear yellow fluid. Analysis of the fluid revealed a specific gravity of 1.010 and creatinine concentration of 24 mg/dl (compared with a serum creatinine concentration of 1.1 mg/dl; reference range = 0.3 to 1.4 mg/dl), the presence of degenerate neutrophils and macrophages, and no microorganisms. The fluid was submitted for bacterial culture and sensitivity testing but no bacteria were evident. The analysis showed that the fluid was compatible with urine accumulated in the retroperitoneal space.

On excretory urography with intravenous infusion of iodine contrast, the left renal pelvis and ipsilateral ureter were found dilated; contrast medium was present in the retroperitoneal space caudal to the left kidney. An air gun pellet was also visualized in the left ureter (Figure 1).

Figure 1. A lateral excretory urography radiograph showing contrast media extravasation close to the left kidney, ipsilateral renal pelvis dilatation and hydroureter and an air gun pellet in the caudal abdomen. (Photos courtesy of Dr. Lysimachos Papazoglou)

Anesthesia was induced with intravenous (IV) midazolam (0.5mg/kg), followed by an intravenous bolus of fentanyl (5 μg/kg), and maintained with isoflurane in oxygen. Butorphanol was administered at a dose of 0.1 mg/kg intramuscularly every four fours for the first 24 hours after surgery and at a dose of 0.1 mg/kg intramuscularly every six hours for another two days after surgery.

The dog was fully monitored (cardiovascular and respiratory monitoring) throughout and after the surgical procedure. An exploratory midline laparotomy was performed, and a large thin-walled capsular structure was detected surrounding the hilus of the left kidney and firmly attached to the ventral sublumbar musculature on the left side. The left kidney adhered to the capsular structure. Most of the left ureter was dilated. The dilated ureter was traced from the renal pelvis to the bladder, and a foreign body compatible with an air gun pellet was found in the lumen 2 cm before the ureterovesical junction. The capsular structure was punctured, and about 70 ml of urine was retrieved by suction. The left renal hilus, part of the parenchyma and about 1.5 cm of the proximal ureter were covered with granulomatous tissue.

The left kidney was dissected free of the cystic adhesions, and a ureteronephrectomy was performed by ligating the renal vessels and the ureter just before the bladder wall with 2-0 polydioxanone suture (Figures 2 and 3).

Figure 2. An intraoperative photograph of the left kidney and ipsilateral ureter, which were dissected free after ligation of the renal vessels. A hemostat is pointing to the air gun pellet obstructing the ureter a few centimeters before the entry of the ureter to the bladder. Figure 3. The air gun pellet outside the ureter after ureteronephrectomy.The ventral capsular wall was partially removed, and omentalization of the capsular cavity was performed by attaching an omental leaf to the wall of the capsule with horizontal mattress sutures consisting of the same suture material. The abdominal cavity was lavaged with warm normal saline solution, and the laparotomy was routinely closed.

Histopathologic examination of the left kidney and ureter revealed a dilated renal pelvis and ureter and a severe pyogranulomatous infiltration involving the renal parenchyma, perirenal adipose tissue and the wall of the ureter, without penetration of the epithelium. The inflammatory infiltrate consisted of numerous degenerated neutrophils, macrophages, lymphocytes and plasma cells admixed with red blood cells, fibrin and cellular debris. Reactive fibroblasts created an emerging stroma, mainly in the periphery of the inflammatory infiltrate. The ureter’s lamina propria was thickened due to edema and infiltration by lymphocytes and plasma cells, and the transitional epithelium was infiltrated multifocally by leukocytes. Histopathologic examination of a section of the wall of the cyst revealed a fibrous reaction with no epithelial lining, consistent with a urinoma.

At re-examination one month after surgery, no abnormalities were noted. Telephone communication with the owner 10 months after surgery found that the dog continues to do well.


In this case, a urinoma was diagnosed in a dog based on the analysis of the fluid obtained from the retroperitoneum under ultrasonographic guidance, surgical findings and histopathologic examination. Although no history of trauma was reported and no entrance point to the kidney or ureter was detected at surgery or on histopathologic examination of the left kidney and ureter, the intraluminal air gun pellet found to obstruct the left ureter may have been responsible for creating the urinoma in this case. The pellet may have penetrated the renal parenchyma or pelvis or ureter within the renal capsule, resulting in urine extravasation and accumulation in the retroperitoneal space. The pellet also obstructed the left ureter, contributing to the maintenance of a persistent flow of urine to the retroperitoneal space.2 Traumatic ureteral obstruction is usually temporary and was never demonstrated; it is associated with intraluminal blood clots or extramural hematoma formation.4

This is the first case in which an intraluminal obstruction was shown to clarify the pathophysiology of urinoma formation. After extravasation, the urine caused inflammation, lipolysis, fat necrosis and long-term formation of a fibrous capsule with no epithelial lining that encased the urine.2-4

Diagnostic imaging of the abdomen in this case aided in identifying urine leakage and determining the cause and extent of the disease.10 Abdominal ultrasound proved valuable as it allowed for fluid aspiration and biochemical analysis to confirm the presence of urine in the retroperitoneal space. Differential diagnoses of the anechoic mass detected ultrasonographically included urinoma, localized ureteral dilation, hematoma, abscess or neoplasia.9 However, the cystic mass detected on ultrasound associated with renal and ureteral dilation and the absence of free fluid in the abdominal cavity led to the tentative diagnosis of urinoma.

Another case report found that ultrasound-guided percutaneous antegrade pyelography and computed tomography was also diagnostic for a urinoma formation associated with partial ureteral rupture in a dog.10 In our case, confirmation of the presence of urine in the cystic mass was made by analysis of the fluid obtained at aspiration. The fluid’s elevated creatinine concentration in contrast to the normal creatinine concentration in the serum led to the diagnosis of retroperitoneal urine collection.4 Excretory urography aided in identification of the cause of the urine accumulation. Demonstration of contrast extravasation immediately caudal to the kidney, the presence of pelvic dilation and hydroureter and the air gun pellet along the course of the left ureter helped in clarification of the cause of the condition and identification of the specific side of leakage in our study.

In the case presented here, the proximity of the extravasated contrast to the left kidney or renal pelvis was highly suggestive of a perirenal urinoma.3 However, the exact origin is unknown since there were no signs of trauma in the kidney or any other part of the urinary tract at the time of surgery. Perirenal urinomas have been reported in only two cats.2,3

Treatment of urinomas in dogs and cats is surgical. Options include placing a subcutaneous ureteral bypass system (SUB) or performing a ureteronephrectomy combined with omentalization of the urinoma.4-6,8-11 Renal function of the left kidney would have been evaluated by measuring the glomerular filtration rate or monitoring urine output by placing a nephrostomy tube. In case of a functional kidney, SUB would be a better option.8,11 In our case, ureteronephrectomy along with omentalization were elected because of the owner’s financial constraints. Omentalization of the cystic mass was considered beneficial to eliminate dead space after partial ablation of the mass.4,6


Perirenal urinoma should be included in the list of differentials of dogs presented with urinary tract trauma due to air gun pellet injury. Ultrasound-guided aspiration of the cystic mass and excretory urography aids in diagnosis. Ureteronephrectomy along with cystic mass omentalization provided a favorable outcome.


1. Mathews K. Ureters. In: Tobias KM, Johnston SA, eds. Veterinary surgery small animal. St Louis: Elsevier, 2012;1962-1977.

2. Geel JK. Perinephric extravasation of urine with pseudocyst formation in a cat. J S Afr Vet Assoc 1986;57:33-34.

3. Lemire TD, Read WK. Macroscopic and microscopic characterization of a uriniferous perirenal pseudocyst in a domestic short hair cat. Vet Pathol 1998;35:68-70.

4. Bacon NJ, Anderson DM, Baines EA, White RAS. Post-traumatic para-ureteral urinoma (uriniferous pseudocyst) in a cat. Vet Comp Orthop Traumatol 2002;15:123-126.

5. Moores AP, Bell AMD, Costello M. Urinoma (para-ureteral pseudocyst) as a consequence of trauma in a cat. J Small Anim Pract 2002;43:213-216.

6. Worth AJ, Tomlin SC. Post-traumatic paraureteral urinoma in a cat. J Small Anim Pract 2004;45:413-416.

7. Rossanese M. Partial ablation of a para-ureteral pseudocyst without ureteronephrectomy in a cat. Vet Rec Case Rep 2015. [Epub.]

8. Rossanese M, Murgia D. Management of paraureteral pseudocyst and ureteral avulsion using a subcutaneous ureteral bypass (SUB) in a cat. Vet Rec Case Rep 2015. [Epub.]

9. Tidwell AS, Ullman SL, Schelling SH. Urinoma (para-ureteral pseudocyst) in a dog. Vet Radiol 1990;31:203-206.

10. Specchi S, Lacava G, d’Anjou MA, et al. Ultrasound-guided percutaneous antegrade pyelography with computed tomography for the diagnosis of spontaneous partial ureteral rupture in a dog. Can Vet J 2012;53:1187-1190.

11. Berent AC, Weisse CW, Todd KL, et al. Use of locking-loop pigtail nephrostomy catheters in dogs and cats: 20 cases (2004-2009). J Am Vet Med Assoc 2012;241:348-357.