Introduction

Ureteral stenting is a well-described procedure in veterinary medicine to treat ureteral obstruction most commonly secondary to urolithiasis.¹ In humans, ureteroliths are considered an important factor in the development of pyonephrosis.^2–4 Since ureteral stenting was first reported in veterinary medicine,⁵ several manuscripts describing outcomes and complications have been published.^6–11 To our knowledge, this is the first description of a ureterocutaneous fistula as a complication of ureteral stent placement in a dog.

Case Report

A 7 yr old spayed female shih tzu presented for treatment of left ureterolithiasis with obstruction of the left ureter and left pyonephrosis. Evaluation by her primary veterinarian revealed increased blood urea nitrogen of 21.2 mmol/L (reference range 3.26–9.44 mmol/L) and creatinine of 265 µmol/L (reference range 57–137 µmol/L), and ultrasonography showed a left ureteral obstruction with left hydronephrosis. Coagulase-positive Staphylococcus was cultured from a urine sample acquired by ultrasound-guided pyelocentesis. She was treated with 9 mg/kg enrofloxacin^a orally q 24 hr, 14 mg/kg amoxicillin/clavulanate^b orally q 12 hr, and 0.1 mg/kg prazosin^c orally q 8 hr and was referred to our hospital.

On presentation 2 wk later, renal values were within normal limits and the only significant finding on physical examination was the presence of a systolic heart murmur grade 2/6. Abdominal ultrasonography revealed a severe left hydronephrosis with pelvic dilation (1.9 × 3.8 cm), ureteral dilation (6 mm), two ureteral calculi (4 mm), and a urinary bladder urolith (1 cm). The patient was anesthetized and retrograde fluoroscopic-guided cystoscopic ureteral stent placement was attempted but proved unsuccessful. An exploratory laparotomy was performed. Cystotomy allowed removal of the bladder urolith and access to the left ureterovesicular junction for retrograde ureteral stent placement. Passage of a 0.018 inch angled tip hydrophilic weasel guidewire^d was attempted as the first step in this procedure but was unsuccessful as it could not pass the obstruction caused by the distal ureterolith. A left distal ureterotomy was performed and the ureterolith was removed, which allowed passage of the guidewire retrograde from the ureterovesicular junction into the renal pelvis. The ureterotomy site was sutured and a ureteral stent (3.7-French × 70 cm)^e was placed retrograde over the guidewire under fluoroscopic guidance. The guidewire was removed allowing the proximal pigtail to curl in the renal pelvis and the distal pigtail in the urinary bladder. Postoperative abdominal radiographs showed satisfactory position of the ureteral stent (Figure 1A). Results of bladder urolith and ureterolith analysis revealed struvite calculi with no bacterial growth. One day later, an abdominal ultrasonography revealed a decrease in the size of the renal pelvis (1.2 × 2.7 cm) and a minor improvement in the size of the ureter (5.5 mm). The patient was discharged 3 days later with 9 mg/kg enrofloxacin^a orally for 4 wk, 14 mg/kg amoxiciline/clavulanate^b orally, 0.1 mg/kg of prazosin^c orally for 6 wk, and a dissolution diet^f. Antibiotic therapy was continued based on the urine culture results from the primary veterinarian despite negative culture results obtained at our hospital. Re-evaluations at 1 and 3 mo postoperative revealed proper positioning of the stent with a progressive decrease in the hydronephrosis. No bacterial growth was found on urine culture at these rechecks. The proximal left ureteral stone persisted at 3 mo despite antibiotic therapy and diet. It was recommended to continue with the urinary dissolution diet^f and to schedule a recheck appointment in another 3 mo, but the patient was then lost to follow-up.

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Three years and 6 mo from the last evaluation, the patient presented for investigation of a chronic suppurative wound on the left flank that had appeared 4 mo earlier. The primary veterinarian had treated a recent episode of hematuria, that was not investigated, with 10 mg/kg gabapentin^g orally q 12 hr. The flank abscess and fistula were treated by debridement, application of medical honey, and 8 mg/kg cefovecin^h subcutaneously every 2 wk. The wound did not resolve, and she was referred to our hospital.

On presentation, physical examination revealed a systolic murmur 5/6 and a fistula on the left flank with purulent discharge. Abdominal ultrasonography confirmed a left fistulous retroperitoneal tract with suspected involvement of the cranial aspect of the left ureter. There was severe hydronephrosis and pelvic dilation (1.8 × 1.7 cm) with hyperechogenic content and suspected pyonephrosis, ureteritis, and cystitis. Abdominal radiographs revealed fracture of the caudal aspect of the ureteral stent, the formation of a stone (17 × 14 mm) around the bladder pigtail, and multiple folds or partial fractures of the stent at different levels (Figure 1B). Echocardiography confirmed a chronic degenerative mitral and tricuspid valve disease grade ACVIM B2. Thoracic radiographs revealed a moderate cardiomegaly with no signs of cardiac failure. Biochemical profile and complete blood count were normal. The patient was anesthetized, and a contrast-enhanced computed tomography (CT) scan of the abdomen confirmed communication of the cranial aspect of the left ureter with the fistula (Figure 1C) along with degenerative/inflammatory changes in the left kidney. Given the presence of a uretero-cutaneous fistula with purulent discharge, the severe changes present in the left kidney and ureter, and absence of azotemia (blood urea nitrogen 9.43 mmol/L; creatinine 62 μmol/L; symmetric dimethylarginine 10 μg/dL [reference range 0–14 μg/dL]), a left ureteronephrectomy was recommended.

An exploratory laparotomy revealed inflammation and fibrosis of the left retroperitoneal space involving the left kidney and ureter (Figure 2A). A traditional open surgical technique for ureteronephrectomy was performed. The renal artery and vein and the distal ureter were ligated with 3-0 polydioxanone and transected. Careful dissection allowed isolation of the uretero-cutaneous fistula, and it was transected with minimal abdominal contamination. The region was debrided and flushed with sterile saline. The abdominal wall opening of the fistula was closed with a simple suture of 3-0 polydioxanone. Cystotomy allowed removal of the bladder urolith, and a full-thickness biopsy of the bladder wall was taken for culture. Lavage and closure of the abdomen was routine, and the cutaneous side of the fistula was debrided, flushed, and closed routinely. The left kidney and ureter were fixed in formalin for histopathological examination (Figures 2B, C).

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Recovery was uneventful, and the patient was discharged 2 days after surgery with 20 µg/kg of buprenorphineⁱ sublingual q 8 hr and 0.2 mg/kg of pimobendan^j orally q 12 hr. Histopathology revealed a left renal abscessation with severe loss of renal parenchyma and a multifocal ulceration of the proximal left ureter. The urolith analysis^k revealed a combined calcium phosphate and calcium oxalate stone. Culture results of the tissue revealed a Staphylococcus intermedius, and a treatment with 12.5 mg/kg amoxicillin/clavulanate^b orally q 12 hr was initiated for 15 days. Sixteen days after surgery, a serum renal biochemical profile revealed normal values except for a very mild increase in serum urea nitrogen (9.8 mmol/L; creatinine 63 µmol/L). Otherwise, the patient had a satisfactory recovery from the procedure with complete healing of the surgical wounds and resolution of the fistula and infection.

Following discharge, the patient was followed by the primary veterinarian for several episodes of cardiogenic pulmonary edema, and she was euthanatized 4 mo after surgery because of recurrent episodes nonresponsive to medical treatment. Blood tests performed during these visits revealed renal values within reference range, and no other clinical signs related to the urinary system were reported.

Discussion

To the authors’ knowledge, this is the first case report of a uretero-cutaneous fistula and secondary renal abscessation as a complication of ureteral stent placement in a dog. Previously reported complications following ureteral stenting in veterinary patients include urinary tract infections, pollakiuria, hematuria, ureteritis, tissue ingrowth, stent encrustation, stent occlusion, stent fracture, and stent migration.^1,6,9–14 A possible explanation for the uretero-cutaneous fistula formation is the partial fracture or bending of the stent, which may have caused friction of the stent with the ureter and contributed to inflammation and foreign body reaction. This situation has not been previously reported in veterinary patients; however, in humans, arterio-ureteral fistulas have been described after ureteral stenting and are frequently found between the ureter and the iliac artery, suggesting a friction between both structures during or after ureteral stenting.^15,16 Fracture of ureteral stents is also reported in the human literature, and potential causes such as prolonged time of exposure to urine, mechanical stress at the sites of fenestration, or encrustation have been discussed.^17,18 Owing to these issues, ureteral stents in people are considered temporary and usually removed after 4–6 wk. There is only one case report of a ureteral stent fracture in a cat in veterinary medicine,¹⁴ but the reason or site of stent fracture were not explained. In veterinary medicine, ureteral stenting has been shown to be an acceptable long-term treatment for ureteral obstruction in dogs and cats,¹ and its removal is not routinely recommended. The cause of stent fracture in our patient is not known. A possible explanation is that stone formation around the bladder pigtail weakened this portion of the stent, resulting in fracture.

Uretero-nephrectomy was the treatment of choice in our case following development of these complications. Alternative surgical techniques such as placement of a subcutaneous ureteral bypass or ureteral reimplantation could have been considered, but given the severe changes observed in the CT scan and the purulent nature of the content present in the ureter, as well as because of financial restrictions and lack of azotemia, these techniques were not considered the best course of action for this patient. Nephrectomy is a nonreversible procedure in which a correct assessment of the remaining kidney with glomerular filtration rate by scintigraphy should always be considered preoperatively. In our case, individual kidney glomerular filtration rate was not performed. The owner was warned that the procedure may lead to decreased renal function.

Medical management for calcium oxalate stones is crucial to prevent potential recurrence of ureteral obstruction in patients with a single kidney. Additional investigation through ionized calcium, phosphate, and triglycerides levels should have been done to identify the cause for recurrent calcium oxalate uroliths but was not performed at the time of surgery because of financial limitations, and ulterior investigation was truncated by the euthanasia of the patient.

Conclusion

Uretero-cutaneous fistula with renal abscessation is a rare complication of ureteral stenting in dogs but should be included as a differential in patients presenting with a cutaneous flank fistula and having a ureteral stent. Regular follow-up of patients with ureteral stents may help prevent this complication.