Interventions for Ureteral Obstructions in Dogs and Cats
Ureteral obstructions can be benign or malignant, with the majority that occur in dogs and cats being secondary to ureterolithiasis. There are other documented causes, including ureteral strictures/fibrosis, neoplasia (transitional cell carcinoma), and dried/solidified blood clots. In cats, 98% and in dogs, 50% of the stones in the ureters and kidneys are calcium oxalate, making them resistant to medical dissolution. Once an obstruction occurs, there is a decrease in renal function. The longer the obstruction is present, the greater the loss of renal function and less chance to reverse the damage. A previous study showed a 54% decrease of GFR after 14 days of a ureteral obstruction.
The clinical signs associated with ureteral obstructions are often vague and include vomiting, diarrhea, decreased appetite, lethargy and weight loss. Azotemia is more common in cats compared to dogs, however the degree of azotemia is not prognostic in appropriately treated animals. Diagnosis is achieved with the combination of abdominal radiographs and abdominal ultrasound (approximately 90% sensitive for ureteral stones in cats).
The diagnosis and management of ureteral obstructions has been improving with increased access to ultrasound in the diagnostic investigation of azotemia in dogs and cats. Traditional surgical techniques (e.g. nephrectomies and ureterotomies) are associated with high complications rates and increased morbidity and mortality. Recurrence of benign obstructions (stones) is also common following ureterotomies. Due to the potential irreversible loss of function and morbidity associated with traditional surgical techniques, early and minimally invasive therapy is warranted. New treatment modalities including pigtail stents and sub-cutaneous ureteral bypasses (SUBs) are now available for both dogs and cats.
Ureteral double pigtail stents are used to divert urine from the renal pelvis to the bladder through the ureter. The placement of the stent facilitates the passage of urine via passive dilation of the ureter around the stent and bypassing the obstruction. Typically in people these are temporary (<3 months) management practices, however, they have been used in dogs and cats for months to years (>4). In some dogs, they can be placed endoscopically, however in small dogs and cats they need to be placed with abdominal surgery. Complication rates are around 20% for stents, and include stent occlusion, dysuria, stent migration, and re-obstruction. Typically due to small size (<0.4 mm) of the feline ureter, I recommend SUBs in all cats.
Sub-cutaneous ureteral bypasses devices consist of a locking loop catheter placed in the kidney and a second catheter placed in the apex of the bladder: The two catheters are connected with a vascular access port under the skin. Essentially a SUB is creating an artificial ureter, which we can access in the future with a specialized needle. The size of patient is not a factor affecting the decision to place a SUB. Complication rates are around 10% for SUBs and include kinking of the catheter, obstruction (stone/stone debris), hematuria, recurrent infections, and dysuria. SUBs need to properly maintained, and every 3 to 6 months, they require ultrasound guidance.
The use of ureteral stents and sub-cutaneous ureteral stents are beneficial to our patients, resulting in decreased morbidity and mortality. These procedures allow the veterinary internal medicine team to preserve and potentially reverse renal damage leading to better outcomes.