Ureteral Obstruction: To Stent or Not To Stent
Natasha Stanke, DVM, DACVS-SA
Ureteral obstruction is a rarely diagnosed condition of small animals. Ureteral calculi can occasionally be noted on abdominal radiographs of otherwise healthy patients. In these rare instances the calculi are considered incidental findings and patient monitoring is advised. The most common clinical presentation of a life-threatening ureteral obstruction involves a “big kidney, little kidney” situation in which a formerly obstructed kidney has become nonfunctional and atrophied and the remaining kidney has hypertrophied to take over function. In this instance, acute obstruction of the functional kidney’s ureter results in life-threatening azotemia. Rarely, simultaneous bilateral ureteral obstruction can also cause life-threatening azotemia. Clinical signs of azotemia include anorexia, vomiting and lethargy.
Presumptive diagnosis of ureteral obstruction can be made based on abdominal radiographs demonstrating “big kidney, little kidney” with or without radio-opaque ureteral calculi with concurrent elevation in renal values on serum chemistry. Definitive diagnosis can be made by abdominal ultrasonographic visualization of ureteral obstruction, ureteral dilation proximal to the obstruction, and hydronephrosis. Diagnosis can also be made by contrast radiography or CT, however contrast agents should be used with caution in the face of urinary obstruction due to the high risk of exacerbating renal dysfunction.
Medical treatment options generally involve improving azotemia via peritoneal dialysis or hemodialysis, encouraging passage of the calculi (with medications such as amitriptyline), and pain control. In rare cases, passage of the ureteral calculi can resolve the life-threatening obstruction; however, in the majority of cases surgical intervention is necessary. Stabilization of patients prior to anesthesia is recommended, though surgical intervention is generally necessary to resolve azotemia.
Surgical treatment options include ureterotomy or ureteral resection and anastomosis, ureteral stenting, subcutaneous ureteral bypass (SUB), and urinary diversion such as nephrostomy tube. Ureterotomy or ureteral resection and anastomosis are not recommended without concurrent ureteral stenting due to the high risk of post-surgical ureteral obstruction with blood clot, inflammation or stricture. Ureteral stenting can be performed minimally invasively utilizing fluoroscopy, however open surgical placement allows removal of calculi for diagnostic and therapeutic purposes. Additionally, open surgical stenting also allows evaluation of the ureter and resection of severely damaged tissue. Currently available ureteral stents are flexible, hydrophilic, fenestrated, double-pigtail catheters that maintain their position within the renal pelvis and urinary bladder. Potential complications of ureteral stenting include post-operative urine leakage from the surgical site, post-operative stent displacement, persistent stranguria and recurrent calculi.
Patients are usually monitored in the hospital for multiple days following surgery. Renal values typically normalize in the first 24 hours following surgery and patient status improves accordingly. In some cases persistent azotemia may occur due to underlying renal dysfunction. If uroliths are identified and removed at the time of surgery, submission for stone analysis is necessary to guide medical management to reduce the risk of future stone recurrence. When diagnosed promptly and treated aggressively, cases of ureteral obstruction can have a good long-term prognosis.