Ureteral stent placement
Ureteral obstruction can be treated medically with fluid diuresis and medications to relax the ureter, by removing the kidney, removing the ureteral calculi via surgery, fragmenting via shock-wave lithotripsy, by stenting the ureter, or by placing a subcutaneous ureteral bypass to allow drainage of the kidney. Surgical removal of the kidney is undesirable because it automatically removes 50% of the potential kidney function. This kidney function could be important in the future, especially if chronic kidney disease were to develop. Medical treatment rarely works.
One study showed that only 7.7% of patients had documented passage of the calculi. Also, this does not work in large calculi. Surgical removal of the calculi is associated with 15% chance of reobstruction to due calculi or stricture at the surgical site. This is undesirable, especially for stone formers (patients that are likely going to continue to form new stones). Fragmentation via shock wave lithotripsy can be considered, but ureteral stenting prior to shock wave lithotripsy is recommended to lower the chances of calculi fragments obstructing the ureter. Subcutaneous ureteral bypass (SUB) has been considered the treatment of choice for ureteral obstruction in cats. Ureteral stenting can typically be done endoscopically, avoiding abdominal surgery. This makes it more desirable than a SUB placement in dogs.
Ureteral stenting is a minimally invasive way to bypass the obstruction. It is achieved by passing a tube in the ureter that connects the kidney to the bladder. This tube has many holes that allows the passage of the urine. This is typically done endoscopically, but can occasionally be done percutaneously in patients that have a mass obstructing the bladder/ureteral junction (vesiculo-ureteral junction - UVJ). The anatomy and obstruction type plays an important role in stenting. Successful stenting is approximately 90% in females and 70% in males.
Minimally invasive ureteral stent placement approaches
Cystoscopic ureteral stent placement
Percutaneous cystolithotomy ureteral stent placement
Perineal approach cystoscopic ureteral stent placement
Percutaneous ureteral stent placement
Cystoscopic ureteral stent placement
This is the preferred method for ureteral stent placement in female dogs that have a ureteral obstruction from a stone.
Percutaneous cystolithotomy ureteral stent placement
A small incision is made into the abdomen to expose the bladder. Then, a rigid cystoscope is introduced into the bladder and used to pass the ureteral stent. This method is used for dogs that have a concurrent bladder and/or urethral stones.
Perineal approach cystoscopic ureteral stent placement
An artificial urethra is created by passing a peel away sheath directly from the perineal region into the bladder. This method is used in male dogs with ureteral stones.
Percutaneous ureteral stent placement
Ultrasound guidance is used to pass a guide wire percutaneously into the ureter from the kidney. A ureteral catheter is typically used over the guide wire to traverse the mass in the trigone region. This method is used in dogs that have a mass in the trigone obstructing the ureteral vesicular junction.
Outcome and possible complications
Recovery is very quick given the non-invasive nature of the placement. Most dogs do very well with the ureteral stent. Possible complications of stenting includes ureteral perforation (<1%), leakage (<1%), or ureteral tear (<1%), but fortunately these are rare. Post-operative complications includes hematuria (up to 20%), dysuria (<2%), persistent obstruction (<2%), proliferative tissue at UVJ (5-25%), reobstruction (9%), migration (6%), encrustation (2%), stent fracture (<2%).