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Ureteral obstruction

Possible treatment options for ureteral obstruction include medical management, ureterotomy (conventional surgery), ureteral stent placement, and subcutaneous ureteral bypass placement (SUB). 

Ultrasound of ureteral obstruction

Longitudinal ultrasound image of an obstructed cat kidney showing hydronephrosis.
Transverse ultrasound image of an obstructed cat kidney showing hydronephrosis.

Surgical correction is typically associated with ureteral stricture, and leakage and there is a high rate of recurrence. Ureteral stent placement can be difficult in cases where the obstruction is proximal. Subcutaneous ureteral bypasses (SUB) were developed to serve as an artificial ureter. The main advantages are the low complication rate when compared to the other available options. However, SUBs require continuous management. SUBs need to be flushed 2-4 times per year to make sure they are still patent and that infections are not present given the direct connection between the bladder and kidney. Occasionally, they need to be replaced or leak urine. Fortunately, this is an uncommon occurrence. 

Given the lack of success in medical management, complications of ureterotomy, and technical difficulties with stent placement, we recommend a SUB placement. SUB has also a lower re-obstruction rate when compared to conventional surgery or ureteral stent placement. However, SUBs require to be flushed periodically to make sure it does not get obstructed. Long-term complications of SUB placement include obstruction, infection, and dysuria (from SUB catheter rubbing on bladder wall). Dysuria is more common in bilateral SUB placement cases.

Overall, stones are the most common cause of ureteral obstruction (65-80%) followed by ureteral strictures (20%), circumcaval ureteral blockage, bloodstones, infection, and tumors. 

Ureteral obstruction may be partial or complete. Complete ureteral obstruction requires emergent treatment because of the risk of permanent damage to the kidney. Following complete unilateral ureteral obstruction, renal blood flow gradually declines and by two weeks post obstruction, renal blood flow is only 20% of normal. The complete function of the affected kidney can return to normal if the obstruction is relieved within a few days. Once an obstruction has been present for two weeks, permanent damage occurs and although function will improve after the obstruction has been relieved, it remains less than 50% of normal in previously healthy animals. In animals with pre-existing renal disease (which is the case based on a slightly elevated creatinine in the past), this damage may be even more severe. Partial obstruction also requires immediate medical attention. In these cases, renal damage still occurs although the damage is slower and less severe. Recovery from partial obstruction is more complete even with delayed intervention. Experimentally, after 4 weeks of partial obstruction, the function returned to normal once the obstruction was relieved.

Options to relieve ureteral blockage include: 
Medical therapy

Hospitalization with intravenous fluids and other medications. This will not help in patients with strictures (20% of cases). Short-term (less than 1 week) mortality is high at 30%. Kidney function failed to improve in 87% of patients within 1 week to 1 month. Only 7.7% had documentation of stone passage. 

Ureteral surgery to relieve the blockage

This is the option that was mostly done in the past but has been less used due to newer techniques with fewer risks and side effects. Uroabdomen leakage occurs in 6-15% of cases. Mortality to discharge from hospital is approximately 21%. Re-obstruction occurs 40% of the time within 1 year.

Ureteral stenting 

Ureteral stenting with a double pig-tail stent has been reported and can be considered. Stents are placed into the ureter via surgery in cats. Success appears to be very good in dogs but the procedure is technically challenging in cats due to the small size of the feline ureter. The perioperative complication rate with stents is lower than with ureteral surgery (10-14%) but long-term complications, are high with dysuria (discomfort during urination) in 17-35% of animals, urinary tract infections in about 20%, recurrent obstruction in 22% and stent migration (movement) in 5% being the most common possibilities.

Lateral view radiographs of ureteral stent in a dog.
Subcutaneous ureteral bypass (SUB)

The newest technique to treat ureteral obstruction is the subcutaneous ureteral bypass (SUB™) system. Developed in 2009 based on a bypass device used in humans, the SUB device has shown improved outcomes and decreased complications in cats when compared to ureteral stents. Complications are rare but include leakage (<5%) in the immediate post-operative period from the tubes or port, kinking of the device (<3%), and obstruction of the SUB (previously 24.5%; now 12.7%) with debris/stones/blood clots. The rate of postoperative obstruction is decreased with regular flushing of the device. Discomfort during urination, which is the most common long-term complication seen with the double pigtail stent, is rare after SUB placement (5%). Regular postoperative maintenance of the SUB is necessary. The device should be flushed every 3 to 6 months to confirm the patency of the device. 

SUB placement in a cat with a unilateral ureteral obstruction

SUB flush during surgery

Longitudinal ultrasound image of a previously obstructed cat kidney. The hydronephrosis is completely resolved.

Ultrasound post-SUB placement

Transverse ultrasound image of a previously obstructed cat kidney. The hydronephrosis is completely resolved.

Other possible, but less likely short-term complications and risks, include anesthetic death, hemorrhage, leakage of urine into the abdomen, infection, and dehiscence of sutures, among others. Additionally, it is possible that the creatinine will not go back to baseline. This is because we don’t know how long the kidneys may be partially obstructed. If the blockage was acute or recent, there is a greater chance that the kidney values will go down to where they were before, however, the longer the blockage has been present, the less likely the kidney will be able to go back to acceptable function. Therefore, some animals will have only 50% or less of improvement in the kidney values, which may still be too high for a good quality of life. Animals in which the kidney values do not improve significantly usually do not have an acceptable quality of life and humane euthanasia is often elected shortly after the procedure. However, a lot of animals will have kidney function restored to a point that they are able to go back to normal life. Unfortunately, it is impossible to know which case we are dealing with since we do not have more recent blood work. 

If the patient does well in the short term, the long-term maintenance of the SUB is routine flushes to try to avoid infection and the formation of stones/minerals into the SUB tubes. SUB flush will happen 1 week after the placement, then 1 month, and every 3-4 months thereafter. Long-term complications include dislodgment of the port or tubes, reobstruction, tube migration, kinking of the tube, and infection. Depending on the complication, surgery may need to be done to correct it.

Unfortunately, aside from attempting to relieve the kidney obstruction, there is not much it can be further done and a quality of life decision will have to be made soon if you elected to forgo the surgery. 

Extensive research has been done to evaluate SUB devices and excellent results were reported for a series of 137 cats that had SUB placement for ureteral obstruction. Over 93% of the cats survived to discharge. Renal pelvis dilation resolved and improvement in kidney values was seen. In one study, kidney values dropped 77.3% between admission and discharge from the hospital. Cats with more severe renal disease have worse long-term survival, but because it is impossible to know how much previous damage a kidney has, there is no way to know how the animal will do after the procedure. Owner satisfaction following the SUB procedure is high (>90%). SUB placement has become the treatment of choice for cats with ureteral obstruction.

Radiographs of subcutaneous ureteral bypass (SUB)
Radiographs of subcutaneous ureteral bypass (SUB)

Individual glomerular filtration rate post-SUB placement

In this cat, the majority of the kidney function is coming from the kidney that has the SUB.
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