Keys to ureteral stenting: A case study

In the first of new series for DVM Newsmagazine, this case-study approach to radiology is offered to showcase the many possibilities in managing medical cases through imaging. This case involves multiple uroliths obstructing a cat's ureter and kidney.

Initial findings

• Signalment: 10-year-old female spayed domestic shorthaired cat

• Presenting complaint: Decreased appetite, vomiting and weight loss for about two weeks and one episode of hematuria

• Pertinent history: Mild azotemia with creatinine between 2.5 and 3.1 mg/dl for about two years

• Medications: Prescription Diet k/d (Hill's Pet Nutrition), famotidine (2.5 mg every 24 hours)

• Physical examination findings: Quiet and alert; body condition score 4/9; renomegaly (right) and a left small kidney (about 2.5 to 3 cm); no pain on abdominal palpation

Figure 1: A lateral radiograph of the patient in this case. Note that the left kidney is larger than the right and that multiple stones are inside the left ureter and both renal pelves.

Diagnostic evaluation

• Complete blood count: Mild normochromic normocytic nonregenerative anemia (24%)

• Serum chemistry profile: Blood urea nitrogen 108 mg/dl; creatinine 5.6 mg/dl; phosphorus 12 mg/dl; potassium 4.7 mEq/L; sodium 147 mEq/L

• Urinalysis: Urine specific gravity 1.015; no white blood cells; 10 to 20 red blood cells/hpf; no crystals, no bacteria seen; pH 6.5

• Abdominal radiographic examination: See Figure 1

• Abdominal ultrasonographic examination: See Figures 2A & 2B

• Urine culture: Negative

• Blood pressure: 130 mm Hg systolic

Problem list

• Chronic renal- and acute post-renal azotemia

• Multiple ureteroliths and associated ureteral obstruction due to stone disease

• Nephrolithiasis

Figures 2A & 2B: Abdominal ultrasonograms of the left kidney documenting severe hydronephrosis (12 mm diameter) and hydroureter with multiple stones in the ureteral lumen that are shadowing.

Presumptive diagnosis

Left ureteral obstruction secondary to ureterolithiasis with associated chronic kidney disease (small right kidney and history of renal azotemia).

Treatment options

• Multiple ureterotomies

• Ureteral reimplantation

• Ureteral stenting

Treatment decisions

Because of the sheer number of stones in this patient's ureter and kidney, traditional ureteral surgery was not considered the best option. Serial ureterotomy procedures would be necessary, resulting in a high risk for stricture, leakage or reobstruction. Removal of all of the stones in the ureter would be impossible, making the chance for reobstruction high.

Figure 3A: A retrograde ureteropyelogram obtained during the ureteral stent placement. This was done via cystoscopy. A wire and catheter were advanced up the ureteral opening inside the urinary bladder, and then, using fluoroscopy contrast, the ureter was imaged by a retrograde contrast ureterogram. Notice the numerous stones and filling defects inside the ureteral lumen and the dilated and tortuous ureter and dilated renal pelvis.

This led to the decision to place a ureteral stent inside the lumen of the ureter to bypass all of the stones without the need for stone removal (Figures 3A & 3B). This was accomplished with a combination of cystoscopy, fluoroscopy and abdominal surgery.

Figure 3B: The patient with the ureteral stent in place. The stent goes from the renal pelvis to the urinary bladder and curls inside the pelvis and bladder to prevent stent migration. Notice that the contrast has drained from the kidney, showing renal pelvis decompression with the ureteral stent.

Outcome

This patient was discharged from the hospital four days after ureteral stent placement and with a creatinine concentration of 3.1 mg/dl. She has been followed for the past two years, with radiography, ultrasonography, bloodwork and urine cultures performed every three to six months. Her creatinine concentration has been stable at 2.5 mg/dl with no evidence of renal pelvic dilation and no urinary tract infections. She has been asymptomatic for multiple ureteral and kidney stones.

Discussion

Ureteral stenting can be performed for various disorders to divert urine from the renal pelvis into the urinary bladder. This stent is a polyurethane-type of material that's soft and biocompatible. It's an indwelling catheter that has a double pigtail shape, allowing the proximal pigtail loop to curl inside the renal pelvis. The shaft travels through the entire ureteral lumen, with the distal loop sitting inside the urinary bladder. These loops prevent stent migration and allow the entire ureter to be protected from obstruction.

This technique can be useful in patients with ureteral obstruction due to ureteral stones, ureteral or trigonal obstructive cancer, ureteral strictures or stenosis, ureteral tears, ureteral spasm and ureteral inflammation as well as for postoperative ureteral anastomosis or trauma. In addition, the ureteral stent's presence results in subsequent passive ureteral dilation, which can permit passage of a previously obstructive ureterolith or allow passage of urine around the stones and the stent.

A feline ureter is normally 0.3 to 0.5 mm in diameter, and after a ureteral stent is in place from a few days to about two weeks, the ureter diameter can reach 1.5 mm.

This technique is currently being performed on a regular basis in veterinary patients at The Animal Medical Center for various causes of ureteral obstruction such as ureterolith-induced obstructions, ureteral strictures, obstructive neoplasia and congenital ureteral anomalies. This is a common procedure in our practice, as ureterolith-induced obstruction in cats has seemingly become more common during the past five to 10 years and is a serious dilemma therapeutically.

A feline ureteral stent has been created to fit more appropriately in a feline ureter, as the commercially available human stents are far too large for cats. Ureteral stenting is also ideal in patients with nephroliths or ureteroliths that are undergoing extracorporeal shockwave lithotripsy to aid in fragmentation and passage of stone debris after treatment. To date, we have placed about 170 ureteral stents in both dogs and cats for various causes, and the most mature stent has remained indwelling for more than four years.

Interventional radiology and interventional endoscopy

For patients with newly diagnosed or worsening azotemia or with worsening urine specific gravity, further evaluation of the urinary system with radiologic imaging is highly recommended. Abdominal radiography and abdominal ultrasonography are best when used in combination for the characterization of renal insufficiency, particularly for the diagnosis of ureteral obstruction. Stones can be missed on an ultrasonographic examination, and stone number, size and location often are more obvious on radiographs. Ultrasonography is ideal for documenting hydroureter and hydronephrosis, which will aid in therapeutic planning.

For more case studies and to see how interventional radiology and interventional endoscopy can benefit patients, visit amcny.org/interventional-radiology-endoscopy.

Dr. Berent is the director of Interventional Endoscopy Services in the Department of Diagnostic Imaging at The Animal Medical Center in New York City. Dr. Weisse is the director of Interventional Radiology Services in the Department of Diagnostic Imaging at The Animal Medical Center in New York City.

Suggested reading

• Berent A, Weisse C, Bagley D, Casale P. Ureteral stenting for benign and malignant disease in dogs and cats, in Proceedings. Am Coll Vet Surg, October 2007.

• Berent A, Weisse C, Bagley D, et al. Ureteral stenting for obstructive ureterolithiasis, in Proceedings. Am Coll Vet Intern Med, 2009.

• Hubert KC, Palmer JS. Passive dilation by ureteral stenting before ureteroscopy: eliminating the need for active dilation. J Urol 2005;174(3):1079-1080.

• Uthappa MC, Cowan NC. Retrograde or antegrade double-pigtail stent placement for malignant ureteric obstruction? Clin Radiol 2005;60(5):608-612.