Hot Literature: Indwelling ureteral stents: a possible treatment for malignant ureteral obstruction
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.
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.
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
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.Link to abstract: http://avmajournals.avma.org/doi/abs/10.2460/javma.238.8.1017