Urinary Techniques - Kidney and Ureter
Ureteral Stenting
Ureteral stenting is performed for a variety of disorders to divert urine from the renal pelvis into the urinary bladder. This technique can be useful in patients with ureteral obstruction and due to ureterolithiasis, ureteral or trigonal obstructive neoplasia, following ureteroscopy, percutaneous nephrolithotomy, ureteral stone retrieval (basket retrieval or via laser lithotripsy), for post-operative ureteral anastomosis, ureteral tears, ureteral spasm, or ureteritis. In addition, the presence of the ureteral stent may result in subsequent passive ureteral dilation to permit passage of previously obstructive ureteroliths, or allow passage of the flexible ureteroscope for appropriate ureteral intervention. This technique is currently under investigation for use in veterinary patients with ureterolith-induced obstructions, particularly in cats (Figure 1). Ureteral stenting is also ideal in patients with nephroliths or ureteroliths that are undergoing ESWL to aid in fragment passage following treatment. (Figure 2).
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Urinary ureteral stent in cat
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Figure 1. A. Dorsoventral abdominal radiograph of a 6.5 kg dog with bilateral ureteroliths and nephroliths following double pigtail ureteral stent (white arrow is right; yellow arrow is left) and nephrostomy tube (white arrowhead) placement. B. Lateral radiograph of same dog showing one pigtail in the renal pelvis (yellow arrow) and one pigtail in the baldder (black arrow) of the ureteral stent and the nephrostomy tube in the right kidney (white arrowhead). |
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Figure 2. A. Nephroureteral stent. B. Double pigtail ureteral stent. C. Locking loop pigtail catheter |
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Figure 3. Lateral abdominal fluoroscopic image of a 6.5kg dog with TCC-induced obstruction of the left ureter. A. Percutaneous pyelocentesis with an 18 gauge catheter and contrast ureteropyelogram showing hydronephrosis (white asterisk) and hydroureter (white arrows). Black arrow = colonic marker catheter. B. Antegrade placement of an 0.035” angled hydrophilic guidewire and catheter (white arrows) across the obstruction and out the penis. C. Retrograde ureteral dilation with a 6Fr ureteral dilator placed over-the-wire (white arrows). D. Indwelling multifenestrated 4.7Fr x 12 cm ureteral stent (white arrows) from the renal pelvis (white asterisk) to the urinary bladder (UB) for decompression. |
Percutaneous Nephrolithotomy (PCNL)
Nephrolithiasis or proximal ureteral obstructions secondary to ureteroliths can result in progressive renal insufficiency, intractable pyelonephritis, ureteral colic, and hydronephrosis. If the stone is small enough it may pass, however others require surgery to relieve the obstruction or avoid permanent nephron damage. Nephrotomies, pyelotomies or ureterotomies can be prolonged, invasive, and complicated surgeries, potentially resulting in significant morbidity. In people, percutaneous nephrolithotomy is considered the standard-of-care for nephroliths too large to be treated with ESWL or retrograde ureteroscopy with laser lithotripsy, and has recently been performed successfully in clinical veterinary cases. This minimally invasive procedure aims to minimize morbidity, and preserve as much renal function as possible (FIGURE 4).
| Figure 4. Lateral fluoroscopic image of a dog with bilateral nephroliths. A. Following percutaneous nephrostomy and through-and-through guidewire and safety guidewire access (white arrows), an access sheath (black arrow) is placed up to nephrolith (white asterisk). B. A nephroscope with ultrasonic lithotripter (white arrow) is placed within sheath and the nephrolith is fragmented (black arrow heads) and fragments are removed. C. Fluoroscopic image displaying a stone-free kidney. D. Nephroureteral stent (white arrows) placement following lithotripsy. |
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| Figure 5. 7 year FS Yorkshire Terrier. Nephroscopic image of calcium oxalate nephrolith within the renal pelvis. This is the endoscopic image in the dog of Figure 4 B |
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Percutaneous Nephrostomy Tube Placement
Ureteral obstructions secondary to ureteroliths or malignancy can result in severe hydronephrosis and/or life-threatening azotemia when present bilaterally or in animals with concurrent renal insufficiency. Some patients can be managed with supportive care until a ureterolith passes, others may require surgery to avoid permanent damage and/or hemodialsysi to stabilize the patient prior to a prolonged anesthesia. Ureterotomies can be relatively prolonged and complicated surgeries in these often debilitated patients. One possibility is to place a nephrostomy tube percutaneously in order to quickly relieve the obstruction, and determine whether adequate renal function remains before prolonged anesthesia for ureteral surgery is performed. (Figure 3)
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Figure 6: Lateral abdominal fluoroscopic image of a cat with bilateral hydronephrosis. A. An 18 gauge catheter is percutaneously placed in the renal pelvis and contrast pyelogram is performed. B. Stiffened 0.035” guidewire advanced into the renal pelvis. C. Pigtail drainage catheter within renal pelvis following removal of the guidewire. D. Bilateral percutaneous nephrostomy tubes in place. |
Cystoscopic-Guided Ectopic Ureter Laser Ablation
Ectopic ureters are a common congenital anatomic deformity in dogs with the ureteral orifice being positioned distal to the bladder trigone within the ureter, vagina, vestibule or uterus. Over 95% of dogs with ectopic ureters transverse intramurally and are candidates for the minimally invasive procedure. Endoscopic repair of ectopic ureters is a common procedure in people, and has been performed in over 20 dogs successfully at 4 institutions in the United States. This is done with the use of fluoroscopy, cystoscopy and a diode or holmium:YAG laser. This procedure is performed on an out-patient basis at the time of cystoscopic ectopic ureter diagnosis avoiding the need for more than one anesthetic procedure for fixation. Overall, surgical fixation of ectopic ureters reports results of continued incontinence with concurrent medical intervention in anywhere from 40-71% of cases due to concurrent sphincter mechanism incompetence of the urethra (SMI).Mayhew, McLaughlin Thus far, in the author’s experience, continence has been maintained with (80%) or without (60%) concurrent medications (phenylpropanolamine) with this procedure, though more cases are needed with longer follow-up to accurately compare the procedures. (Figure 7)
Ureteroscopy for Idiopathic Renal Hematuria
Idiopathic renal hematuria (Figure 8) is a rare condition in which a focal area of bleeding in the upper urinary tract results in long term hematuria, iron deficient anemia (chronically) and the potential for clot formation, or calculi due to blood clots, resulting in ureteral colic or signs of lower urinary tract disease. In people, the presence of a hemangioma or vascular malformations have been visualized ureteroscopically, which is cauterized through the working channel of a ureteroscope. This has also been performed in a small number of dogs to date.
| Figure 8. Dorsoventral abdominal fluoroscopic image of a dog with unilateral idiopathic renal hematuria. A. A cystoscope (white arrow) is used to place a cone-tipped catheter in the most distal aspect of the ureter in order to perform a retrograde contrast ureteropyelogram. B. An angled-tipped hydrophilic 0.035” guidewire (black arrows) is advanced through the scope and up the ureter and into the renal pelvis. The “J-hooked” distal ureter is apparent (white arrow-head). C. The cystoscope is removed over-the-wire and a ureteral dilator (white arrows) is advanced over the wire under fluoroscopic guidance. D. The ureteral dilator is removed and the ureteroscope (white arrows) is advanced over-the-wire. E. Once evaluation for cautery or stone retrieval is complete the guidewire (white arrow-heads) is replaced through the working channel. F. A single pig-tailed locking-loop ureteral stent is placed over the guidewire (black arrow-heads). The loop is locked in place in the renal pelvis, with the distal end exiting the urethra to provide temporary patency. |
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ESWL for Nephro/Ureterolithiasis
Extracorporeal shock-wave lithotripsy is another minimally invasive alternative for the removal of upper tract calculi in the renal pelvis, or ureters. ESWL uses external shockwaves that is passes through a water medium directed under fluoroscopic guidance in 2 planes. The stone is shocked anywhere from 1000-2500 times at different energy levels to allow for implosion and powdering of a stone. The debris is then left to pass down the ureter into the urinary bladder over a 1-2 week period. This procedure can be performed safely in nephroliths smaller than 5 mm, and ureteroliths smaller than 3 mm. In larger stone burdens an indwelling double pigtail ureteral stent is placed prior to ESWL to aide in stone debris passage. For stones of larger sizes PCNL is recommended (Figure 9).
Urinary Bladder and Urethra
Laser lithotripsy is an innovative technique involving the intracorporeal fragmentation of uroliths, which is assessed using a rigid or flexible cystoscope or ureteroscope. The first report of holmium laser lithotripsy was in 1995 in human medicine (Denstdet, 1995). The holmium:YAG (yttrium, aluminum, garnet) laser is a sold-state pulsed laser that emits light at an infrared wavelength of 2100 nm. (Wollin) The energy is absorbed in less than 0.5 mm of fluid, making it safe to fragment uroliths in tight locations, as within the urethra, ureter, renal pelvis or urinary bladder, with limited risk to urothelial damage (Wollin). It combines both tissue cutting and coagulation properties, as well as the ability to fragment stones upon contact. (Wollin)
Small diameter fibers (200, 365, 550 microns) are guided through the working channel of small diameter flexible or rigid cystoscopes/ureteroscopes. Although the various commercial models of lithotriptors vary slightly, the pulse duration of the holmium laser ranges from 250-750 microseconds, the pulse energy from 0.2-4.0 J/pulse, and the frequency from 5-45 Hz, averaging a power from 3.0-100 W. The power that one chooses is based on the application one is using it for.
The laser energy is focused on the urolith surface, directed via cystoscopy. Pulsed laser energy is absorbed by water inside the urolith, resulting in a photothermal effect, which causes urolith fragmentation. The holmium laser effect on the calculus is by a vapor bubble. The vapor bubble is created when the pulse of laser energy traveling through water from the tip of the fiber is trapped within a bubble (Moses effect). If the fiber tip is 5 mm or more away from tissue, the vapor bubble collapses, the water absorbs the energy and no impact is made. As the fiber tip is advanced less than 5 mm from the calculus, the vapor bubble comes in contact with and impacts the stone. The closer the fiber tip is to the target, the larger the effect. The stone is fragmented until the pieces are small enough to be removed normograde through the urethral orifice, either via voiding urohydropropulsion or with the assistance of a stone basket. This process is useful for ureteral, cystic and urethral calculi (Figure 10, Figure 11). All stone types are able to be fragmented using laser lithotripsy.
Other urologic applications for laser lithotripsy include incision of urethral and ureteral strictures; ablation of superficial transitional cell carcinoma/prostatic adenocarcinoma within the urethral lumen, laser ablation of urinary polyps (Figure 12) Bladder polyps are common findings in dogs and can be associated with chronic, recurrent urinary tract infections, cystolith formation, and are often misinterpreted for cystic neoplasia. Using cystoscopy and baskets or laser lithotripsy the polyps can be removed without surgical intervention by cauterizing the stalk.
Urethral Stenting for Malignant Obstructions
Malignant obstructions of the urethra can cause severe discomfort, dysuria and life-threatening azotemia. Greater than 80% of animals with transitional cell carcinoma (TCC) of the urethra, and/or prostatic carcinoma experience dysuria and approximately 10% developing complete urinary tract obstruction. Chemotherapy and radiation therapy has been successful in slowing tumor growth but complete cure is uncommon. When signs of obstruction occur, more aggressive therapy is indicated. Placement of cystostomy tubes, transurethral resections, and surgical diversionary procedures have been described but are invasive and potentially associated with an undesirable outcome due to manual urine drainage, associated morbidity, frequent urination, and infection. Placement of self-expanding metallic stents using fluoroscopic guidance through a transurethral approach can be a fast, reliable, and safe alternative to establish urethral patency in both males and females with an 86% good to excellent palliative outcome. Urethral stenting may also be useful in patients with benign urethral strictures, or reflex dysynnergia, when traditional therapies have failed or when surgery is refused or not indicated. All animals that died after stent placement were due to reasons other than urinary obstruction, most of which being distant metastatic disease (Weisse).
A contrast cystourethrogram is performed and transurethral retrograde or antegrade guidewire access across the malignant narrowing is obtained. Measurements of the normal urethral diameter and the length of obstruction are obtained (Fig. 13A) and an appropriately sized self expanding metallic urethral stent (SEMS) is chosen (approximately 10-15% greater than the normal urethral diameter and 1cm longer than the obstruction on both the cranial and caudal ends). The stent is deployed under fluoroscopic guidance and a repeat contrast cystourethrogram is performed to document restored urethral patency (Figs. 13B and 13C).
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Figure 13: Lateral abdominal fluoroscopic image of a dog with prostatic and urethral Transitional Cell Carcinoma. A. Contrast cystourethrogram demonstrating extravasation of contrast into prostatic tissue and contrast attenuation due to urethral narrowing at the level of the prostate. (3) 2cm marker catheter placed within the rectum for measuring purposes. (4) Urethral diameter measurement taken caudal to the diseased urethral. B. Partial SEMS deployment during fluoroscopic visualization. C. Contrast cystourethrogram immediately following complete stent deployment demonstrating restored urethral patency. |
Transurethral Submucosal Collagen Implantation
Collagen injection via urethroscopic guidance has been performed for USMI at many institutions. This procedure is indicated if medical management for SMI has failed, is contraindicated, or not tolerated. Overall success of the procedure is excellent, though the average maintenance of continence following this procedure is reported at 17 months, with re-injections being common thereafter. Barth
Using a rigid cystoscope the urethra is cannulated and an area just caudal to the bladder trigone is identified within the urethra. A collagen heuber needle with syringe is inserted into the working channel of the cystoscope, being preloaded with the collagen material. A submucosal injection is made placing a bled into the urethral lumen. This is done in 3-4 areas, creating a new narrowing within the urethral lumen. (Figure 14).
Antegrade Urethral Catheterization
Urethral catheterization is typically a fairly simple and routinely performed procedure in veterinary patients primarily used to monitor urine output, establish urine drainage in patients that are recumbent or have mechanical/functional urethral obstructions, or to provide urethral patency following urethral or urinary bladder surgery. Occasionally, standard retrograde catheterization can be difficult in very small (female) patients, female patients with obstructive tumors, or feline patients with urethral tears following attempts to de-obstruct blocked cats or secondary to trauma. Antegrade urethral catheterization performed under direct fluoroscopic visualization can be performed rapidly, easily, and safely in patients in whom attempts at routine retrograde catheterization have failed.
Under general anesthesia cystocentesis is performed using an 18g over-the-needle catheter, and contrast is injected to define the urinary bladder and urethra (Fig. 15B). Under fluoroscopic guidance, a guidewire is advanced antegrade into the bladder and down the urethra until exiting the penis or vulva (Fig. 15C). A urinary catheter (open-ended or pig-tail) is advanced over-the-wire in a retrograde fashion into the urinary bladder (Fig. 15D) and the guidewire is removed (Fig. 15E). The urinary catheter is secured in place in a routine fashion.
| Figure 15: Lateral abdominal fluoroscopic image of cat with an iatrogenic urethral tear secondary to traumatic catheterization. A. Retrograde contrast urethrogram demonstrating misplaced tomcat catheter (black arrows) and peri-urethral contrast extravasation (white asterisk). Contrast within the normal urethra (white arrows). B. Percutaneous cystocentesis with 18 gauge over-the-needle catheter (white arrow) and contrast cystourethrogram. C. Angled hydrophilic 0.035” guidewire (black arrows) advanced through catheter (white arrow) and down urethra. D. Urinary catheter (white block arrows) advanced retrograde over guidewire (black arrow) and into urinary bladder (UB). E. Urinary catheter (white block arrow) placement following removal of guidewire and cystocentesis catheter. |
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Percutaneous Cystostomy Tubes
Cystostomy tubes are regularly placed during surgery to manage veterinary patients with urinary obstructions or to divert urine away from a traumatized urethra. Occasionally, these patients are severely debilitated and even a relatively short period of general anesthesia would be dangerous. A variety of cystostomy tubes and techniques are available to place these tubes quickly and safely with a percutaneous approach in order to establish urine drainage and/or diversion. Locking-loop drainage catheters have been used for such purposes in veterinary patients. These tubes can be placed via palpation alone, or with fluoroscopic or ultrasound guidance.