Current Concepts

Interventional Endourology

MaryAnna Labato, DVM, DACVIM (SAIM)

Endourology is the branch of urologic surgery concerned with closed procedures for visualizing or manipulating the urinary tract. The techniques are typically reserved for disorders of the urethra, urinary bladder, ureters and the pelvis of the kidney. In human medicine endourology has advanced tremendously over the past 20-30 years; however, in veterinary medicine the discipline is just starting to develop.

Some of the more commonly performed procedures in veterinary medicine include urethral stenting for the treatment of neoplasia and strictures, nephrostomy tube placement, ureteral stenting, percutaneous nephrolithotomy and cystoscopic–guided laser ablation of ectopic ureters and urethral transitional cell carcinomas. Additionally, lasers and shock wave lithotripsy may be used for the treatment of upper and lower urinary tract calculi.

 EQUIPMENT 

Various flexible and rigid endoscopes are used for traditional endourologic procedures.  Rigid cystoscopy is commonly performed in female dogs and cats for urethral and bladder access.  It is also possible in some animals to approach the ureters in this manner. Flexible ureteroscopes are used for urethral and bladder access in male dogs and for ureteral access in animals of acceptable sizes ( >15-20 kg). Rigid nephroscopes are used for percutaneous procedures of the kidney. Intracorporeal lithotripters (ultrasonic, pneumatic and electrohydraulic types) and the holmium:YAG laser are available for these procedures. The diode laser is used for endoscopic tissue resection, allowing for effective tissue cutting and tissue coagulation with limited bleeding. Extracorporeal shock-wave lithotripsy (ESWL) also has great application for small to moderate size nephroliths and ureteroliths.

Stents are commonly used in the urinary tract to treat obstructions in the urethra or ureter. A urethrane soft double pigtail ureteral catheter is the classic indwelling ureteral stent. A NITINOL ( Nickel and Titanium alloy from the Naval Ordinance Laboratory) self expanding metallic stent  (SEMS) is used for urethral obstructions.

For many of the more commonly performed procedures it is useful to have available either a C-arm fluoroscopy unit or an ultrasound machine to assist with guidance of the instruments and catheters. The C-arm Fluoroscopy unit is portable and permits various tangential views without moving the patient. Ultrasonography is useful for percutaneous nephrostomy and cystostomy tube placement. Guidewires and catheters of an assortment of sizes and shapes are needed for each procedure.

PROCEDURES

Urinary Bladder and Urethra

Laser Lithotripsy is a technique involving the intracorporal fragmentation of uroliths.  The laser tip is guided through the working channel of small diameter rigid or flexible cystoscope or ureteroscope. As the tip is advanced to within 5 mm of the urolith, the vapor bubble comes in contact with and impacts the stone. The stone is fragmented until the pieces are small enough to be removed normograde through the urethral orifice either via voiding uropropulsion or a stone basket. This process is useful for renal, ureteral, cystic and urethral uroliths; however, it is easiest to perform for urethral and cystic calculi. All stone types can be fragmented using laser lithotripsy. Laser lithotripsy should not be performed on male dogs < 7 kg or male dogs with large numbers of bladder stones.  In those cases, laparascopic-assisted lithotripsy is a more appropriate minimally invasive procedure.  Lithotripsy is a reasonable alternative to surgery in female dogs, female cats and male dogs with urethral stones. It is important to inform owners that urethral calculi in the male dog may end up in the bladder, requiring cystotomy, as dislodgement and retrograde movement of the urolith is a possibility. Cystoscopic stone basketing, (when a small basket device passes through the cystoscope that we use to scoop up the stone that we visualize and then remove it in the carrying basket that we have scooped it into) is an alternative if the stones or stone fragments are small enough to pass through the dilated urethra.

Antegrade Urethral Catheterization 

Urethral catheterization is typically a fairly simple procedure that is routinely performed for patients for whom attempts at routine retrograde catheterization have failed. It is important to note  there are circumstances when this techique may become problematic such as with very small female patients or patients with a urethral mass or a urethral tear.  In these cases, the technique can be performed under direct fluoroscopic visualization.

Urethral Stenting for Obstruction

Over 80% of animals with transitional cell carcinoma or prostatic adenocarcinoma experience dysuria, and approximately 10-30% develop complete urethral obstruction.  Chemotherapy, radiation therapy and laser ablation may be successful in shrinking the mass or slowing its growth, but complete cure is uncommon. When obstruction occurs, placement of self-expanding metallic stents using fluoroscopic guidance through a transurethral approach can be a fast and reliable way of establishing urethral patency. The procedure is successful in relieving obstruction in >85% of cases. Stents can also be used to treat urethral strictures.

Cystoscopic-Guided Ectopic Ureter Laser Ablation

Ectopic ureters are a common congenital anatomic deformity in dogs in which the ureteral orifice is located distal to the bladder trigone, in the urethra, vagina, vestibule or uterus. Most ectopic ureters in dogs transverse the bladder intramurally and are candidates for this minimally invasive procedure. Endoscopic repair of ectopic ureters is done with fluoroscopy, ultrasonography, cystoscopy and a diode or holmium;YAG laser.  The abnormal tissue that separates the ureter from the urethra or genital tract is divided longitudinally with the laser from distal to proximal, ending at the level of a normal ureteral termination, so that urine can enter the bladder rather than bypassing it (figure 1). The procedure can be performed in female and male dogs and female cats. Surgical repair of ectopic ureters eliminates incontinence in 30-60% of cases, with failures the result of concurrent urethral sphincter mechanism incompetence (USMI), short urethral syndrome, or an intrapelvic bladder. Laser ablation has similar results, but has the advantage to of being able to be performed at the time of diagnosis and even on an outpatient basis.


Figure 1 – Video demonstrating laser ablation of an ectopic ureter in a dog.

Ureteral Stenting

Figure 2

Figure 2 – Placement of a ureteral stent in a cat. The guidewire for the stent has been passed through the renal cortex, into the renal pelvis, down the ureter, and into the bladder.

Figure 3

Figure 3 – Postperative radiograph of a ureteral stent in a dog, demonstrating the stent’s pigtails in the renal pelvis and bladder.

Ureteral stenting is performed for a variety of disorders to divert urine from the pelvis of the kidney into the urinary bladder. This technique is performed in patients with ureteral obstruction secondary to ureterolithiasis, ureteral or trigonal obstructive neoplasia, strictures, or tears. The presence of a stent results in passive ureteral dilation ( over 2 days to 2 weeks) which may permit the passage of previously obstructive ureteroliths. Stents have a pigtail at either end to maintain their positioning in the bladder and renal pelvis, and come in a range sizes suitable for any dog or cat (figures 2 and 3).

Extracorporeal Shock-Wave Lithotripsy (ESWL) 

ESWL is a minimally invasive alternative for the removal of calculi in the renal pelvis or ureters. The technique uses external shockwaves that pass through a water medium directed in two planes, using fluoroscopic guidance. The urolith is shocked anywhere from 1000-3500 times at different energy levels, causing implosion and powdering of the stone. The debris is then left to pass down the ureter into the urinary bladder over a 1-2 week period. It may take months for full stone clearance and the procedure may need to be repeated.  ESWL can be performed safely for nephroliths larger than 4 mm and smaller than 10 mm.  For larger stones an indwelling double pigtail ureteral stent may be placed prior to ESWL to aide in debris passage via ureteral dilation.

Percutaneous Nephrostomy Tube Placement and Percutaneous Nephrolithotomy (PCNL)

Nephrostomy tubes are locking loop pigtail catheters that may be placed percutaneously to decompress an obstructed kidney and to manage azotemia before proceeding to a prolonged definitive procedure. PCNL can be used to treat renal pelvis or proximal ureteral stones too large to treat with ESWL.