Indwelling ureteral stents have been used for years in people to treat ureteral obstructions, but only recently have they begun to emerge as a treatment option in veterinary medicine for ureterolithiasis, ureteral stricture, ureteral trauma, and trigonal tumors. In people with ureteral malignancy, ureteral stents provide palliative treatment and help preserve kidney function. In the past, dogs with urothelial neoplasia had limited treatment options once ureteral obstruction was diagnosed.

In a recent study, researchers evaluated the use of indwelling, double-pigtail ureteral stents in dogs with ureteral obstruction secondary to trigonal malignancy. These stents are multifenestrated catheters with a pigtail loop on each end. One loop is positioned in the renal pelvis with the length of the catheter in the ureteral lumen, and the other pigtail is positioned within the urinary bladder. Urine can then pass from the kidney and into the bladder through and around the stent.

Study design
In this retrospective analysis, case files between January 2006 and January 2009 from the Mathew J. Ryan Veterinary Hospital of the University of Pennsylvania and the Michigan State University Veterinary Teaching Hospital were reviewed to identify dogs with ureteral obstruction secondary to carcinoma of the bladder, prostate, or urethra. Patients were included if they had evidence of ureteral obstruction based on ultrasonographic evidence of ureteral dilatation to the level of the ureterovesicular junction (UVJ) and if a double-pigtail stent had been placed to alleviate the obstruction.

The stent placement procedure was similar for all dogs. Briefly, the dog was placed in lateral recumbency with the affected kidney facing up. After surgical prep, an 18-ga renal access needle was inserted through a skin incision over the kidney for antegrade ureteropyelography. Contrast solution was injected, and fluoroscopy was used to insert a guide wire into the ureter, down through the bladder, and out through the urethra. This wire was then used to place the stent. A double-pigtail ureteral stent was advanced in a retrograde fashion so that, ultimately, one loop was curled in the renal pelvis and the other in the bladder to alleviate the obstruction. The duration of the procedure as well as any complications were recorded for each patient.

Twelve patients met the inclusion criteria and were included in the study. Nine of these patients had transitional cell carcinoma, two had prostatic carcinoma, and one had an undifferentiated carcinoma. Procedure-related complications were documented in one patient because of migration of the stent as well as disruption of the renal pelvis during placement. These complications were successfully managed. The stents were well-tolerated by all patients based on the absence of any pain, dysuria, hematuria, or pollakiuria, and no deaths were reported as a result of stent placement or urinary tract obstruction.
Fifteen stents were placed overall since three dogs had bilateral stent placement. In the authors’ experience, cystoscopic-guided retrograde ureteral stent placement is less invasive than antegrade placement, and patients may often be discharged the day of the procedure. Some risks are associated with the procedure such as ureteral perforation, iatrogenic pyelonephritis, and stent migration, but these risks may be outweighed by the potential benefits.

Results
Overall, the authors found that stent placement was an effective and safe procedure in these patients and resulted in a median survival time of 285 days (range = 10 to 1,571 days) from the time of diagnosis and 57 days from the date of stent placement (range = 7 to 337 days). Previous studies have shown that in clinically normal dogs, renal function diminishes rapidly and irreversibly in the face of ureteral obstruction, and any possible recovery may take weeks to months. Patients with malignancy may not have time to allow for slow recovery once the obstruction is relieved, so early and aggressive intervention, such as with ureteral stent placement, may yield a better outcome. Although the median survival time between the two groups did not differ significantly, it is interesting to note that the patients with no clinical signs at the time of the initial examination survived a median of 240 days, while those with systemic signs of illness on initial examination had a median survival time of 52 days.

All patients that had azotemia before stent placement showed improvement in their blood urea nitrogen and creatinine concentrations after the procedure. Ultimately, two dogs were lost to follow-up, but in the remaining 10 patients, abdominal ultrasonography showed improvement in the degree of hydronephrosis and hydroureter after stent placement.

In people, ureteral stents may need to be exchanged if they are in place for long periods, but in veterinary patients with neoplasia, this is unlikely to be necessary. If needed, stent exchange can be done fluoroscopically or endoscopically. None of the stents in this study became occluded because of tumor invasion, but the authors recognize that routine postmortem or imaging examinations were not performed.

The patients with the longest survival times shared four traits

• An absence of azotemia at the time of the initial examination
• No urethral stent required in addition to the ureteral stent
• No evidence of metastatic disease
• Body condition score ≥ 4 on a scale of 1 to 9.

It important to note, however, that the small sample size may affect these findings. Patients with transitional cell carcinoma treated only with piroxicam have a survival time of about 181 days, while those treated with a combination of piroxicam and chemotherapeutic drugs have a survival time of 150 to 300 days. Theoretically, the authors hypothesized  that stent placement in conjunction with piroxicam and chemotherapy would provide the longest survival times of all. Preservation of renal function early in the course of the disease through stent placement would lessen systemic signs of illness and, therefore, improve prognosis.

Postobstructive diuresis after stent placement can develop, which may in turn lead to some degree of dehydration. For this reason, the authors discuss delaying the administration of any chemotherapeutic drugs or NSAIDs until seven to 10 days after this procedure. Three patients in this study died because of chemotherapeutic-induced toxicosis after stent placement, and it is possible the diuresis and dehydration may have played a role.

A more accurate assessment of survival times will require future prospective studies since this study was limited because of its retrospective nature, small sample size, and variable treatment and follow-up protocols, which likely affected survival times in this population.

Berent AC, Weisse C, Beal MW, et al. Use of indwelling, double-pigtail stents for treatment of malignant ureteral obstruction in dogs: 12 cases (2006-2009). J Am Vet Med Assoc 2011;238(8):1017-1025.