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
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.
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.
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
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.
- 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.