Urethral stenting for patients with malignant obstruction

Malignant urethral obstructions can cause life-threatening biochemical changes in veterinary patients. Most patients experience significant dysuria, and a small percentage develop complete urinary tract obstruction. Urethral stenting is an effective, minimally invasive out-patient procedure that can offer immediate relief of stranguria, as shown in the case below.

Initial findings

• Signalment: 8-year-old castrated male beagle (48.5 lb; 22 kg)

• Presenting complaint: Progressively worsening stranguria with near complete urinary obstruction

• Pertinent history: Four months ago, the dog had a suspected urinary tract infection that did not improve with antibiotic therapy; results of follow-up ultrasonography and examination of prostatic fine-needle aspirate confirmed urothelial carcinoma

• Medications: Piroxicam (5 mg orally once daily), misoprostol (50 µg orally b.i.d.); owner declined chemotherapy

• Physical examination findings: Quiet, alert and responsive; body condition score 5/9; multiple soft moveable subcutaneous masses; moderate bilateral hindlimb muscle atrophy; very large caudal abdominal structure consistent with distended urinary bladder; large, firm, lobulated, irregular prostate palpated on rectal examination; lumbar lymph nodes not palpable on rectal examination; urine dripping from prepuce

Diagnostic evaluation

• Heart rate: 140 beats/min

• Complete blood count: Mild stress leukogram

• Serum chemistry profile: ALT 79, AST 39, ALP 420

• Abdominal radiography: Enlarged, mineralized prostate; hepatomegaly

• Thoracic radiography: Unremarkable

• Abdominal ultrasonography: Soft tissue mass located at urinary bladder trigone and extending into and from proximal urethra; intrapelvic urethra not visualized; lumbar lymph nodes normal; no evidence of hydroureter or hydronephrosis; slightly enlarged hyperechoic liver; remaining structures unremarkable

• Urinalysis/urine culture: Pending

Treatment decisions

This patient was determined to have a complete or near complete urethral obstruction due to the progressive urothelial carcinoma. Emergency department personnel inserted an 8-F urethral catheter, and 400 ml of urine with marked hematuria was removed from the urinary bladder. The dog's rapid heart rate decreased after the bladder drainage.

Discussion with the owner included the following treatment options:

• Surgery (cystostomy tube)

• Chemotherapy (after urinary patency restored)

• Radiation therapy (palliative or full course) with periodic urinary catheterization (two or three times daily) until urethral patency

• Urethral stenting

Tumor extension into the trigone, as well as prostatic involvement, made complete surgical resection an unlikely option. Medical management (chemotherapy) was discussed, but an acute response permitting urination was unlikely. The owner declined radiation therapy due to the extent of the disease and the potential for significant side effects.

The owner chose urethral stenting, which is a rapid, effective, minimally invasive out-patient procedure shown to provide immediate relief of stranguria by rapid restoration of a patent urethra.

The surgical procedure

The patient was anesthetized and positioned in lateral recumbency. The urinary catheter that had been placed in the emergency room was removed. A 4-F angiographic marker catheter was placed within a 14-F red rubber catheter that was then advanced per rectum into the descending colon (Photo 1). This marker catheter was used to calculate radiographic magnification.

Photo 1: A lateral caudal abdominal static fluoroscopic image demonstrating a marker catheter in the descending colon (black block arrows) and a guidewire (white arrows) placed retrograde into the urethra and urinary bladder. (Photos courtesy of Drs. Berent and Weisse)

The prepuce was clipped, scrubbed and draped. All wire, catheter and stent manipulations were performed under fluoroscopic guidance. A 0.035-in, angled hydrophilic guidewire was placed transurethrally and advanced into the urinary bladder. An 8-F introducer sheath was advanced over the guidewire and secured to the prepuce with a single nylon suture.

Photo 2: A lateral caudal abdominal fluoroscopic image obtained during retrograde contrast urethrocystography demonstrating a normal penile urethra but a narrowed prostatic urethra (white arrows) with contrast extravasation into prostatic tumor. There’s also a filling defect in the dorsal bladder trigone (red arrows).

A 4-F Berenstein catheter was advanced over the wire, through the introducer sheath and into the urinary bladder. The guidewire was removed, a sample of urine was collected for culture and a 1:1 combination of iodinated contrast and sterile saline solution was injected until the urinary bladder was full.

Photo 3: A lateral caudal abdominal static fluoroscopic image demonstrating the stent delivery system placed over the guidewire and the compressed radiopaque stent (white arrows) placed across the malignant obstruction before stent deployment.

Urethrography was performed with the same contrast mixture through the introducer sheath to distend the urethra and define the extent and location of the urethral obstruction (Photo 2). Maximal urethral diameter was determined, and an appropriately sized, laser-cut, nickel-titanium alloy (Nitinol—NDC), self-expanding metallic stent was chosen. The Berenstein catheter was removed over the guidewire, and the stent delivery system was advanced over the guidewire across the urethral obstruction (Photo 3). The stent was deployed across the urethral obstruction, and repeat urethrography was performed through the introducer sheath to confirm urethral patency (Photo 4). A final radiograph was obtained and the guide wire and introducer sheath were removed.

Photo 4: A lateral caudal abdominal fluoroscopic image obtained during repeat retrograde contrast urethrocystography demonstrating the deployed stent (white arrows) and a patent urethra.

Outcome

The patient was discharged from the hospital the same day and experienced immediate resolution of the urethral obstruction. Discharge medications included a two-week tapering dose of enrofloxacin pending urine culture results.

Follow-up phone calls each week confirmed that the patient continued to do well. Initially, the dog occasionally dripped urine between normal strong urinations, but this resolved after the first week. A recheck examination was scheduled two weeks later with an oncologist to discuss further treatment options.

Discussion

Urothelial/transitional cell carcinomas are the most common lower urinary tract tumors encountered in dogs, often involving the trigone, urethra or prostate. More than 80 percent of these patients experience significant dysuria, and about 10 percent develop complete urinary tract obstruction.1,2 While chemotherapy has been demonstrated to result in improved survival times, substantial tumor responses are uncommon, complete cures are rare and tumor progression is typical.

Once signs of urinary obstruction occur, few good options exist. Cystostomy tube placement, transurethral resection and surgical diversion have been described, but these are either invasive or associated with significant morbidity, including the need for manual urine drainage, tube dislodgement, urinary tract infection, incontinence or surgical complications.3-6

More recently, transurethral placement of self-expanding metallic stents under fluoroscopic guidance has been described. These stents result in rapid and effective restoration of urethral patency and urine flow.7 The procedure is performed on an out-patient basis and helps the patient avoid the need for manual drainage and other surgery-associated complications.

A recent study reported good results after urethral stent placement in 41 dogs: a major incontinence rate of 25 percent (three-quarters of patients had minor or no incontinence) and median survival time of about 250 days if the patients received chemotherapy after stent placement.7 The cause of death in these patients is rarely due to repeat urinary obstruction; rather, the most common cause of death is secondary to tumor metastases and signs of systemic illness. These stenting techniques also have been effective in cats as well as for benign urethral strictures.

A video of the procedure can be viewed at amcny.org/node/342#Urethral_Stenting. The stenting procedure is fairly short, and patients are typically discharged from the hospital the same day. Medical management with antibiotics (short-term), nonsteroidal anti-inflammatory drugs and chemotherapy continue after stenting.

For more case studies and to see how interventional radiology and interventional endoscopy can benefit patients, visit amcny.org/interventional-radiology-endoscopy/IR-IE-procedures.

Dr. Berent is the director of Interventional Endoscopy Services in the Department of Diagnostic Imaging at The Animal Medical Center in New York City. Dr. Weisse is the director of Interventional Radiology Services in the Department of Diagnostic Imaging at The Animal Medical Center in New York City.

References

1. Norris AM, Laing EJ, Valli VEO, et al. Canine bladder and urethral tumors: a retrospective study of 115 cases (1980–1985). J Vet Intern Med 1992;6(3):145-153.

2. Knapp DW, Glickman NW, DeNicola DB, et al. Naturally-occurring canine transitional cell carcinoma of the urinary bladder. A relevant model of human invasive bladder cancer. Urol Oncol 2000;5(2):47-59.

3. Stiffler KS, McCrackin Stevenson MA, Cornell KK, et al. Clinical use of low-profile cystostomy tubes in four dogs and a cat. J Am Vet Med Assoc 2003;223(3):325-329.

4. Liptak JM, Brutscher SP, Monnet E, et al. Transurethral resection in the management of urethral and prostatic neoplasia in 6 dogs. Vet Surg 2004;33(5):505-516.

5. Stone EA, Withrow SJ, Page RL, et al. Ureterocolonic anastomosis in ten dogs with transitional cell carcinoma. Vet Surg 1988;17(3):147-153.

6. Weisse C, Berent A, Clifford C, et al. Evaluation of palliative stenting for management of malignant urethral obstructions in dogs. J Am Vet Med Assoc 2006;229(2):226-234.

7. Blackburn A, Berent A, Weisse C, et al. Urethral stenting in canine patients with urothelial carcinoma: a review of 41 cases (2004-2008), in Proceedings. Am Coll Vet Intern Med, 2010.