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Abstract

Practical relevance:

Interventional radiology and interventional endoscopy (IR/IE) uses contemporary imaging modalities, such as fluoroscopy and endoscopy, to perform diagnostic and therapeutic procedures in various body parts. The majority of IR/IE procedures currently undertaken in veterinary medicine pertain to the urinary tract, and this subspecialty has been termed ‘endourology’. This technology treats diseases of the renal pelvis, ureter(s), bladder and urethra. In human medicine, endourology has overtaken traditional open urologic surgery in the past 20–30 years, and in veterinary medicine similar progress is occurring.

Aim:

This article presents a brief overview of some of the more common IR/IE procedures currently being performed for the treatment of urinary tract disease in veterinary patients. These techniques include percutaneous nephrolithotomy for lithotripsy of problematic nephrolithiasis, mesenchymal stem cell therapy for chronic kidney disease, sclerotherapy for the treatment of idiopathic renal hematuria, various diversion techniques for ureteral obstructions, laser lithotripsy for lower urinary tract stone disease, percutaneous cystolithotomy for removal of bladder stones, hydraulic occluder placement for refractory urinary incontinence, percutaneous cystostomy tube placement for bladder diversion, urethral stenting for benign and malignant urethral obstructions, and antegrade urethral catheterization for treatment of urethral tears.

Evidence base:

The majority of the data presented in this article is solely the experience of the author, and some of this has only been published and/or presented in abstract form or small case series. For information on traditional surgical approaches to these ailments readers are encouraged to evaluate other sources.

Novel Endourologic Procedures – What is the Appeal?

The relatively common incidence of upper and lower urinary tract obstructions (stones, strictures, tumors, etc), troublesome uroliths and refractory incontinence, combined with the invasiveness and morbidity associated with many of the traditional surgical techniques, and the lack of therapeutic options at times, makes the use of novel endourologic procedures extremely appealing. For decades, such procedures have been considered the standard of care in human medicine. Over the past 5–10 years the reality of such possibilities in small animal veterinary medicine has also been demonstrated, and these procedures are moving to the forefront of veterinary urology.

New Approaches to Kidney and Ureteral Conditions

Nephrolithiasis

Nephroliths are rarely problematic in cats. Complicated nephroliths are those that result in progressive renal insufficiency, intractable pyelonephritis, intermittent ureteral outflow obstructions, progressive hydronephrosis, chronic pain or chronic hematuria. If the stone is small enough it may pass. However, in cats a ureteral obstruction could easily develop. Nephrotomies, pyelotomies or salvage ureteronephrectomies can be prolonged, invasive and complicated surgeries, potentially resulting in significant morbidity and a progressive decline in glomerular filtration rate (GFR).^1

–6 These procedures do not prevent future obstruction as a result of stone recurrence or fragment passage, and over 98% of upper tract stones in cats are composed of calcium oxalate, making stone dissolution of little value.^7

–11

Complications can be severe and life-threatening after traditional surgery, including hemorrhage, decreased renal function, postoperative ureteral obstruction by remaining fragments, and uroabdomen.^1

–6 In a study of normal cats, the GFR decreased by 10–20% after a nephrotomy; while this was considered clinically insignificant in normal cats,^4,5 in a clinical patient with maximally hypertrophied nephrons, the significance could be dramatic. Therefore, feline patients with an already compromised GFR from chronic stone disease, and a 30% chance of developing renal azotemia with age, may develop a clinically significant decline in renal function after nephrotomy and cannot tolerate a 10–20% further decline in GFR.^12,13 Most would agree that a nephrotomy should be avoided when possible, especially in patients with existing renal disease or contralateral stone disease.^4,5

Figure 1

Some of the equipment used in veterinary endourology

In humans, minimally invasive options are considered the treatment of choice for nephrolithiasis. These procedures include extracorporeal shock-wave lithotripsy (ESWL) for nephroliths <1–2 cm and percutaneous nephrolithotomy (PCNL) for nephroliths >1–2 cm. Open surgery and laparoscopy are rarely necessary and are usually considered only after other, less invasive options have failed or been determined inappropriate.⁶ Human studies have shown ESWL and PCNL to have minimal effects on GFR of clinical stone-forming patients, particularly when compared with traditional surgical nephrotomy.^14,15 These procedures, particularly PCNL, have been found to be highly effective in removing all stone fragments.¹⁴ ESWL is not typically used for feline nephroureterolithiasis because the fragments are rarely less than 1 mm, and the feline ureter is 0.3–0.4 mm in diameter, creating a high risk of subsequent ureteral obstruction.¹⁶

In humans, PCNL is typically considered for large or impacted nephroliths (>15–30 mm).¹⁴ In small animals, PCNL (Figure 2), or surgically assisted endoscopic nephrolithotomy (SENL), is considered for cats in the author’s practice when a complex nephrolith is determined. PCNL/SENL was recently reported in nine dogs and one cat.¹⁷ Although not commonly necessary in cats, due to the low incidence of problematic nephroliths, these procedures can be done if needed. A combination of nephroscopy and fluoroscopy allows access into the renal pelvis and guides nephroscopic intracorporeal lithotripsy (electrohydraulic, ultrasonic, and/or holmium: YAG laser lithotripsy) or nephroscopic stone basketing. In feline patients this is often performed with surgical assistance so that the mobile kidney can be manually stabilized and the access point can be closed primarily, avoiding the need for a temporary nephrostomy tube.

Figure 2

Images of a cat before, during and after PCNL for problematic nephrolithiasis. (A) Endoscopic image showing a lithotripter probe (asterisk) inserted through the working channel of the nephroscope breaking down a large nephrolith (arrow). (B) Lateral radiograph revealing large nephroliths bilaterally (arrow). (C) Endoscopic image of one of the large nephroliths after it has been broken into multiple pieces. A guide wire (arrow) is seen within the renal pelvis. (D) Same view as ‘C’ under fluoroscopic guidance (black arrow = guide wire, white arrows = nephrolith fragments). (E) Nephroscopic image after the stone has been removed, showing a clean renal pelvis (asterisk indicates the lithotripter). (F) Fluoroscopic image confirming stone removal. (G) Ventrodorsal radiograph showing the nephrolith (arrow) before PCNL. (H) Ventrodorsal radiograph after PCNL, with a ureteral stent in place (arrows)

Idiopathic renal hematuria

Idiopathic renal hematuria 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, venous rupture, angioma or vascular malformations has been visualized ureteroscopically in the renal pelvis, which is typically cauterized or lasered through the working channel of a ureteroscope. This is possible in animals over 15–20 kg, so not practical to consider for feline patients.

In smaller veterinary patients fluoroscopic-guided catheter-directed sclerotherapy using povidone–iodine and liquid silver nitrate has been investigated to chemically cauterize the bleeding lesion. This has been effective in about 85% of dogs to date,¹⁸ and is still being investigated in cats.

Chronic kidney disease

One of the biggest challenges facing veterinary nephrology is improving the outcome of kidney disease in cats. Therapeutic strategies should aim to prevent disease progression and treat the underlying condition, but this is not possible in most cases currently. In veterinary medicine, we often treat the clinical signs while progression ensues.

Mesenchymal stem cells (MSCs) are multipotent cells that reside in various tissues of the body such as fat and bone marrow. They are attractive candidates for renal repair because nephrons are of mesenchymal origin and stromal cells are of crucial importance for signaling, which can lead to the differentiation of both nephrons and collecting ducts. In animal models, stem cell therapy has been shown to have many potential benefits in tissue recovery, regeneration and differentiation of damaged cells. This occurs by various mechanisms including the release of chemical mediators for their trophic effects (paracrine effects of growth factors and cytokines), angiogenic effects, anti-apoptosis, anti-fibrosis and anti-inflammatory effects. In various animal studies, MSCs were shown to markedly accelerate glomerular recovery, most likely related to paracrine growth factor release.¹⁹ The highest engraftment rates were seen when the cells were selectively delivered into the renal artery, when compared with intravenous delivery.²⁰

Currently there is a fully funded, randomized placebo-controlled study under way that is investigating the use of autologous MSCs in feline patients with IRIS stage 3 chronic kidney disease. This study, which is comparing the delivery of these cells intravenously and intra-arterially (Figure 3), using fluoroscopic guidance, is following the patients over 3 years, assessing systemic signs, blood pressure, GFR, and biochemical, ultrasonographic and radiographic parameters. To date, over 95 treatments have been performed in both dogs and cats with kidney disease and the results have been promising.

Figure 3

Fluoroscopic digital subtraction image of a left renal arteriogram during superselective intra-arterial MSC infusion

Ureteral obstructions

Cause and traditional therapy

Ureterolithiasis is the most common cause of ureteral obstructions in cats,^7,8,10,11 with ureteral strictures²¹ and trigonal neoplasia following.²² Over 98% of feline ureteroliths are composed of calcium oxalate;^7,8,10,11 since these stones will not dissolve medically, they need to pass spontaneously, remain in place, or be removed. Traditionally, once medical management failed (see page 56), partial obstructions were monitored and left in place due to the high risk/benefit ratio of attempted surgical removal. This would not be the case in human medicine.

Following a ureteral obstruction in normal healthy dogs, studies have shown that ureteral pressures increase immediately, resulting in dramatic changes in both renal blood flow and GFR.^23,24 The longer the ureter was obstructed, the more permanent damage was found to have occurred (GFR was permanently diminished by 35% after 7 days of obstruction, by 54% after 14 days, and after 40 days there was no return of function). These studies were in normal dog models without any pre-existing azotemia, chronic interstitial nephritis or chronic obstruction. Extrapolation to our feline patients, which are likely to have already maximized and exhausted their renal hypertrophy mechanisms, are commonly azotemic at the time of unilateral obstruction diagnosis,^8,11 and typically have stones present in their contralateral kidney,^10,11 would certainly seem to support aggressive and timely intervention. Indeed, with more experience it has become clear that management of partial obstructions dramatically improves renal function and should be considered, particularly if safer therapeutic options are available.

In the past, traditional intervention for ureterolithiasis was accomplished surgically via ureterotomy, neoureterocystostomy, ureteronephrectomy and renal transplantation. In 2005, Kyles et al reported two retrospective studies in a large number of cats.^7,8 There were high rates of procedure-associated complications (over 30%) and mortality (18%), but surgical outcomes were considered superior to medical management alone.^7,8 This study was from two universities that had extensive expertise with ureteral surgery. The morbidity and mortality may be higher in environments where operating microscopes and microsurgical experience are not as readily available.

Many of the associated complications with surgery are due to site edema, recurrence of obstruction from stones that pass from the renal pelvis to the surgery site, stricture formation, and ureterotomy-associated or nephrostomy tube-associated urine leakage.^7,8 Of the cats that had long-term imaging follow-up, 40% had evidence of ureteral stone recurrence. Of these cats with recurrence of their ureteral obstruction, 85% had evidence of ipsilateral nephrolithiasis at the time of the first surgery. The number of animals that did not have stone recurrence with prior nephrolithiasis was not evident in that study. Chronic kidney disease is common at the time of diagnosis, with 75–97% of cats being azotemic with a unilateral obstruction; persistent, yet improved, azotemia is also common, though can progress slowly over years.^7,8,10,11

Over the past decade the number of stones found in the obstructed feline ureter has increased from one to four,¹¹ with over 60% of patients in this more recent study not being considered good traditional surgical candidates. In the same study over 86% of cats had evidence of ipsilateral nephrolithiasis, making the risk of ureteral reobstruction high.

Feline ureteral strictures were recently reported in 10 cats,²¹ and may develop secondarily to a previous surgery of the ureter for stone disease, as a result of a stone lodging in the ureteral mucosa, as a congenital abnormality, as an idiopathic process, and possibly associated with a circumcaval (retrocaval) ureter. Most ureteral strictures were found to occur in the very proximal ureter (<2.5 cm from the renal pelvis),²¹ and this is also the author’s clinical experience. With the cat’s ureteral lumen being 0.3–0.4 mm in diameter, this can be a very challenging fixation with traditional surgery, particularly in a potentially unstable patient.

The ‘ideal’ treatment

A treatment that results in immediate decompression and stabilization of the kidney, while concurrently allowing patency to be established quickly and effectively, for a ureteral obstruction of any cause (stone, stricture, debris, blood stones/clots, neoplasia, etc), is the ideal. The use of IR/IE techniques, either minimally invasively or with surgical assistance, has aided in circumventing the complications of traditional ureteral surgery alone (perioperative leakage, stricture, reobstruction, etc), particularly in cases that are not considered good surgical candidates. IR techniques have allowed successful and efficient stabilization of the patient regardless of the cause of ureteral obstruction, while decreasing renal pelvic pressure and stopping the cycle of pressure-induced nephron damage and loss.

In human urology, developments in ureteroscopy, ureteral stenting, lithotripsy and laparoscopy have almost eradicated the need for open ureteral surgery (see box below).⁶

Case work-up and therapeutic decision making

In feline patients azotemia is common at the time of diagnosis, even with a unilateral obstruction (83–97% of cats).^7,8,10,11 The degree of azotemia at presentation does not appear to be associated with outcome if successful decompression occurs.³⁰ Bilateral ureteral obstructions occur in about 20–25% of cats.^{7,8,10,11,30,31} Radiopaque calculi are typically visible in patients with calculi-induced obstructions, making radiographic evaluation mandatory during a work-up. This helps to determine stone size, number, location and the presence of concurrent nephrolithiasis, but does not replace the need for an ultrasound examination.

Ultrasound is ideal for the documentation of hydroureter, hydronephrosis and the precise location of the most proximal obstructive lesion. If hydroureter is present and very proximal, with no evidence of a shadowing stone at the junction of normal and abnormal ureter, then a ureteral stricture may be the cause of the obstruction. In a recent study,²¹ 60% of cats with a ureteral stricture had evidence of periureteral hyperechoic tissue at the stricture site on ultrasound examination. Ureteral strictures are most commonly seen on the right side and associated with a circumcaval ureter. Identifying concurrent nephroliths and other ureteroliths is vital in deciding which interventional option (traditional surgery, ureteral stenting, subcutaneous ureteral bypass) is best for an individual patient. Another key piece of information is the exact diameter of the dilated renal pelvis.

Traditional surgical intervention techniques including ureterotomy, neoureterocystostomy, ureteronephrectomy and renal transplantation are discussed elsewhere. It is important to realize that a ureteronephrectomy is not ideal in any stone-forming patient, especially in those with concurrent renal azotemia (50–97% cats).^{7,8,10,11,30,31} In a recent study, 97% of cats were azotemic at the time of diagnosis of ureteral obstruction, even when unilateral.¹¹ Persistent azotemia is a common problem, even after a successful intervention (40–70% of cats), but it is often minor and remains stable for years.^10,11,30,31

Newer minimally invasive options

Percutaneous/surgically assisted locking-loop pigtail nephrostomy tubes

Ureteral obstructions secondary to ureteroliths or malignancy can result in severe hydronephrosis and/or life-threatening azotemia when presenting bilaterally, or in animals with concurrent renal insufficiency/ failure. Fixation procedures can be relatively prolonged and complicated in these debilitated patients, with an unclear outcome in terms of residual renal function. One option is to place a nephrostomy tube to quickly relieve the obstruction and determine whether adequate renal function remains before prolonged anesthesia for a permanent fixation (Figure 4). A locking-loop pigtail catheter is recommended to decrease the risk of inadvertent tube removal or urine leakage.

Figure 4

Placement of a locking-loop nephrostomy tube. (A–E) Fluoroscopic images showing a locking-loop pigtail catheter being placed within the renal pelvis over a guide wire using the modified Seldinger technique. (A) Renal access needle (arrow) within the renal pelvis, allowing for a pyelogram to be performed. (B) Guide wire (white arrows) advanced through the needle and into the renal pelvis. (C) The locking-loop catheter (red arrows) placed over the guide wire (white arrow) as it is curled within the renal pelvis. (D) The catheter (red arrows) being locked within the pelvis. (E) Drainage of the contrast within the renal pelvis. (F) The nephrostomy catheter externalized through the body wall

Historically, nephrostomy tubes have met with resistance due to high complication rates (over 50%). With the advent of these sturdy, multi-fenestrated tubes, which form a loop that will lock the catheter in the renal pelvis, these complications seem to have declined dramatically. The author and colleagues recently reported on the use of the locking-loop pigtail catheter in 20 patients.³² These catheters were deemed to be safe, effective and well tolerated. Typically, in cats, this is a surgically assisted procedure performed with fluoroscopy (in dogs it is carried out percutaneously using ultrasound and fluoroscopic guidance).

Ureteral stenting

Double pigtail ureteral stents have many benefits recognized in human medicine (see right).^25
–28,33 More recently, these benefits have been documented in veterinary medicine,^{10,11,17,18,22,30} based on the placement of ureteral stents in more than 125 feline ureters for various indications in the author’s practice.

The use of double pigtail ureteral stents has been investigated as an alternative to traditional surgery in cats, and the result has been immediate ureteral decompression, renal stabilization, a decreased risk of ureteral leakage/ uroabdomen, and a decreased rate of ureteral obstruction recurrence.¹¹ There are currently veterinary ureteral stents available designed for use in cats (2.5 Fr). Once experience is obtained, stent placement is highly successful. The main concerns with stents are typically seen months to years after placement and include dysuria, stent migration, stent occlusion (most common with ureteral strictures) and stent encrustation. These are not usually life-threatening complications, and are relatively easy to address on an outpatient basis.

Figure 5

Ureteral stent placement in a feline patient with ureteroliths causing a left ureteral obstruction. (A) Antegrade renal pelvis access using a renal access needle (black arrow). (B) Antegrade ureteropyelogram through the renal access needle (black arrow), documenting hydroureter and hydronephrosis and the path for guide wire passage. (C and D) A guide wire (white arrows) has been advanced through the needle, into the renal pelvis and down the ureter. (E) The ureteral stent (red arrow) being advanced over the guide wire (white arrow), through the lumen of the ureter and into the renal pelvis. (F) The proximal loop of the ureteral stent (red arrow) coiled within the renal pelvis. (G) Fluoroscopic image of the entire ureteral stent (red arrows) showing one loop within the renal pelvis and the other loop within the urinary bladder as the shaft travels down the entire length of the ureter. (H) Lateral radiograph of the stent in place; note the numerous ureteroliths (red arrows)

In over 150 cats stented to date in the author’s practice, the success in placement (either endoscopically or surgically) has been 95%. In a recent study of 40 feline ureteral stents placed for benign ureteral obstructions,¹¹ over 60% of the cases were considered poor surgical candidates based on stone number and/or location, stricture location, concurrent number of nephroliths and patient stability. There was a median of four stones per ureter and 86% of cats had concurrent nephroliths. About 25% of cats had a ureteral stricture (with or without a stone). In 95% of cases, a significant improvement in azotemia was seen post-procedure. The perioperative mortality rate was 7.5%, with no deaths attributable to surgical complications or the ureteral obstruction. The short-term (<1 month) complication rate was 9%, and included ureteral stent misplacement, a ureteral tear, and urine leakage at the concurrent ureterotomy site. These were fixed with stent repositioning and closed suction drain placement, respectively. The long-term (>1 month) complications were less severe, including dysuria (35%, with 4% persistent), stent migration (6%), ureteral stent reaction (3%), and scar tissue formation around the stent (11%).

Scar tissue formation is typically associated with a concurrent ureterotomy or a previous stricture and can occur 3–6 months post-stent placement (median 68 days). Fifty-seven percent of all cases that developed scar tissue had a previous stricture in their ureter at the time of stent placement. These strictures have also been associated with a circumcaval ureter.¹¹ For cats with strictures causing ureteral obstruction, placement of a SUB device is recommended, rather than a ureteral stent, to avoid the risk of reobstruction.³¹ The risk of long-term dysuria is very rare after SUB placement (<2%), which is another reason why SUBs have been used more commonly than ureteral stents in cats in the author’s practice over the past 3 years.

This preliminary data would suggest that ureteral stenting in cats is safe and effective, resulting in immediate decompression of the renal collection system. Few major procedural or perioperative complications have occurred, but the learning curve has been steep. In cats, any complications were not typically life-threatening and could be managed medically with time. The equipment has dramatically improved over the past 4 years, making stent placement less complicated and more successful.

In the long term, stent exchange or manipulation may be necessary if a ureteral reaction, stricture-induced stent occlusion or stent migration occurs, and all owners should be prepared for ‘stent upkeep’. Because of the management issues associated with feline ureteral stents, which are tolerable but can be expensive, the author currently recommends the SUB device for cats when possible.

SUB device

The biggest limitation to nephrostomy catheters is the externalized drainage, requiring careful management and hospitalization to prevent infection and dislodgement.³² The development of an indwelling SUB device using the combination of a locking-loop nephrostomy catheter and cystostomy catheter (Figure 6) means that the device can remain indwelling long term.³¹ In humans, a similar device has been shown to reduce complications associated with externalized nephrostomy tubes and improve quality of life when used as a long-term treatment.²⁹ The use of a SUB device has recently been described in 25 cats and two dogs.³¹

Figure 6

Fluoroscopic images during placement of a SUB device in a cat. The patient is positioned in ventrodorsal recumbency. (A) Nephrostomy access (white arrow) with a ureteropyelogram documenting hydronephrosis and proximal hydroureter. (B) Guide wire (red arrow) coiled within the renal pelvis. (C) Nephrostomy catheter (black arrow) advanced over the guide wire (red arrow) and to be coiled within the renal pelvis as seen in image (D). Note the black marker that indicates the last hole of the loop, ensuring the entire loop is within the renal pelvis. (E) Fluoroscopic image of the entire SUB device showing the nephrostomy catheter and cystostomy catheter (white arrow) connected to the subcutaneous shunting port. (F) Contrast study through the shunting port confirming patency of both the nephrostomy and cystostomy catheters

The author has performed subcutaneous ureteral bypass in over 100 cat ureters to date for various reasons. Initially this technique was reserved for proximal ureteral strictures or ureteral stent failures, but more recently the SUB device is often considered the first choice for all causes of feline ureteral obstruction(s) in the author’s practice. The procedure requires fluoroscopic guidance and is performed with surgical assistance.

Of the >100 SUB devices placed, all have been well tolerated. Patency of the device has been evident in over 90% of cats over a median of 2.5 years. Six devices were found to have become obstructed with stone debris, four of which needed replacement; the remaining two were treated with serial flushing. The main procedure-related complication encountered was leakage at the nephrostomy tube site, and this was circumvented by changes in the device design, and has not occurred in over 2 years in the author’s practice. With the new design, 97% of patients have survived to discharge, with no deaths attributable to ureteral obstruction or procedure-associated complications.

There are far fewer long-term issues with the SUB device than the ureteral stent or traditional surgery in cats, when appropriately managed. Because of the subcutaneous shunting port, the device is currently flushed with a special needle (Huber) every 3 months to prevent occlusion and the urine sampled for culture. With the advent of this recommendation, occlusions have been minimized.

The biggest risk postoperatively in all cats with ureteral obstructions is the development of either congestive heart failure from fluid overload or pancreatitis. Overall, the postoperative mortality rate with traditional surgery is 21%, while with stents it is documented to be 7.5% and, with SUBs, 5.6% (see Table 1, page 63), making these very viable alternatives for treatment of feline ureteral obstructions.

Table 1

Reported outcomes of various ureteral interventions in cats

Procedure	Operative findings	Postoperative outcome (<1 week)	Short-term outcome (1 week to 1 month)	Long-term outcome (>1 month)	Follow-up
Medical management of ureteral obstruction^7,8 • Diuresis • Mannitol therapy • α-adrenergic blockade • Data on stones only • Will not help for the ~20% of strictures		Mortality (to discharge) 33%⁸	Failure of renal function improvement (87%)⁸	If survived to discharge 30% had an improvement in azotemia⁸	13% had response to medical management, with 7.7% documentation of stone passage⁸
Traditional ureteral surgery (n = 153,^7,8 47³⁹) • Ureterotomy/ reimplantation/ ureteronephrectomy/ renal transplantation^7,8 • Ureterotomy/ reimplantation³⁹ • Data on stones only	Uroabdomen leakage (6%³⁹–15%⁸) Presence of abdominal effusion postoperatively (34%)³⁹	Persistent ureteral obstruction (7%)⁸ due to stricture, edema, persistent stonesFailure of renal function improvement (17%)⁸ Second surgery required during hospitalization (13%)^8,39 Other⁸ CHF (3%), septic peritonitis (2%), pancreatitis (1%), pyelonephritis (1%) Mortality (to discharge) 21%^8,39 (25% with ureterotomy/ reimplant; 18% if include transplantation and ureteronephrectomy)⁸	Failure to improve renal function (17%)⁸ Mortality (within 1 mo) 25%⁸	Reobstruction (40%)⁸ – ~1 y later – 50% mortality	Follow-up: 1 to >2000 d Major issue is postoperative complications: leakage, reobstruction, stricture formation and long-term obstruction recurrence. Few cases were followed up long term (~50%)⁸ Mortality (peri-operative) 21%
Ureteral stent^{10,11,30,40,41} (n = 79,⁴⁰ 92⁴¹) • Data on 71–79% stones, 21–28% strictures, 1% obstructive pyelonephritis	Ureteral penetration with guide wire (17%) (little clinical consequence; no uroabdomen)Leakage if concurrent ureterotomy needed (6.7%)Eversion of ureteral mucosa during stent passageUreteral tear during stent passage (3.8%)	Fluid overload during post-obstructive diuresis (17%) Concurrent pancreatitis (6%) Failure for creatinine to improve (5%) Mortality (to discharge) 7.5%⁴⁰ due to non-urinary causes (pancreatitis or CHF)	Inappetence (temporary) (25%) Dysuria (self-limiting 7–14 d) <10%⁴⁰ Stent migration (3%)⁴⁰	Dysuria (38%)⁴⁰ –nearly all respond to prednisolone and/or prazosin (persistent 1.6% post- steroid therapy)UTI (30% postop versus 34% pre-op)⁴⁰Reobstruction (over 3.5 years) (19%)^40,41 – Stricture (58% of strictures occluded the stent) – Adhesions around ureter from ureterotomy – Obstructive pyelonephritis – Proliferative ureteritis Chronic hematuria (18%)⁴⁰ Stent migration (6%)⁴⁰ Ureteral reflux (<2%)⁴⁰	Follow-up: 2 to 1278 d MST = 498 d; for renal cause of death >1250 d – 21% of cats died of renal-related causes – Only predictor of long-term survival was the 3 mo post-creatinine³⁰ Major issue is need for stent exchange in 27% of cases due to migration or occlusion of ureter and dysuria due to ureteral stent location in urinary bladder Mortality (peri operative) 7.5%(none related to surgical complications)
SUB device^10,30,31,41 (n = 61,⁹ 71⁴¹) • Data on 20% strictures (± stones), 76% stones, 4% obstructive ureteritis	Kinking of catheters (<5%) Inability to place SUB (<1%)	Leakage (5%)⁴¹ – resolved with new device Fluid overload (<5%)^10,41 Blockage of system (5%)^10,41 (blood clot, purulent material, device failure) Failure for creatinine to improve (4%)^10,41 Mortality (to discharge)5.6%⁴¹	Dysuria <2%^10,41 Inappetence ~25% (temporary) Seroma 1%	UTI (15%; 35% pre-operative)¹⁰ Reobstruction (7%)⁴¹ (0% strictures; 10% of stone cases) Dysuria (<2%)^10,41	Follow-up: 2 d to 4.5 y MST = 762 (circumcaval ureters) and 963 (stones or strictures, noncircumcaval)⁴¹ Major issues are device occlusion (10%) which requires serial flushing or exchange (usually due to stone accumulation), kinking and leakage (less of an issue with proper training) Mortality (peri operative) 5.6% (none related to surgical complications)

CHF = congestive heart failure, d = days, mo = months, y = years, UTI = urinary tract infection, MST = median survival time

New Approaches to Urinary Bladder and Urethral Conditions

Bladder and urethral stones

Laser lithotripsy

Laser lithotripsy is an innovative technique involving the intracorporeal fragmentation of uroliths using a laser fiber under cystoscopic guidance (Figure 7).¹⁶ This procedure is typically considered for female cats that are large enough to accommodate a rigid cystoscope. A new prototype male cat cystoscope has been used with a small working channel that accepts a small (200 micron) laser fiber.

Figure 7

A bladder stone being broken into two pieces during Hol:YAG laser lithotripsy under cystoscopic guidance. (A) Laser fiber touching the shell of the intact stone. (B) Once the laser is turned on the stone shell starts to crack. (C) The two pieces of stone prior to removal

The laser energy is focused on the urolith surface, directed via cystoscopy. As the fiber tip is advanced to within 5 mm of the calculus, the vapor bubble comes into contact with and impacts the stone. The closer the fiber tip is to the target, the greater the effect. The stone is fragmented until the pieces are small enough to be removed in a normograde manner through the urethral orifice, either via voiding urohydropropulsion or with the assistance of a stone basket.

Laser lithotripsy is useful for renal, cystic and urethral calculi in cats and, potentially, any type of stone may be fragmented using the process. However, since there are various other minimally invasive endourologic procedures that are considered more effective and less traumatic to the urethra for the removal of urinary bladder stones (eg, percutaneous cystolithotomy, PCCL [see below]), laser lithotripsy is less commonly performed in cats with bladder stones in the author’s practice.

Percutaneous cystolithotomy

The most common procedure performed in the author’s practice for the retrieval of cystic/urethral calculi is the new minimally invasive technique of PCCL. Enabling a combination of cystic and urethral stone retrieval in any size, sex or species, the technique is very easy to perform in cats.³⁴

This procedure is considered the treatment of choice for children with a large burden of bladder stones.³⁵ Stones are identified with cystoscopic visualization through a small incision in the bladder apex, and a stone retrieval device is used to remove all cystic or urethral calculi. This avoids excessive urethral passage, which can be traumatic in narrow lumen urethras. In people, a suprapubic cystostomy catheter is left in place for 24 h, and a urethral catheter is left in place for 48 h, for a seal to form in the bladder without primary closure. For humans with large stone burdens in the bladder, a PCCL (± lithotripsy) procedure is recommended over transurethral lithotripsy, and has been shown to be safe, minimally invasive and effective. It was this procedure that the PCCL technique in veterinary patients was modeled on.

In cats, PCCL is performed via a 1 cm ventral midline skin incision over the bladder apex. Once the bladder is digitally palpated it is secured with three stay sutures and brought to the skin. A trocar is advanced into the bladder lumen. A rigid cystoscope is passed through the trocar into the urinary bladder for stone removal with an endoscopic stone basket (Figure 8). This maintains bladder distension during saline infusion for ultimate visibility. The entire mucosal surface of the bladder, the ureterovesicular junction and the pelvic urethra are visualized, and stones within the urethra can be removed. During this procedure the bladder can be explored carefully for polyps or masses, which are removed with the laser or biopsied if necessary. Once the scope and trocar are removed the incision is closed primarily. This procedure permits excellent bladder and urethral exploration and ureteral access if needed, and minimizes bleeding, irritation and the risk of leaving stone fragments behind. The literature reports that in 20–30% of traditional cystotomy surgeries stone fragments will be left behind, versus under 3% with this procedure.³⁴

Figure 8

Endoscopic images during a PCCL procedure in a cat with calcium oxalate stones. (A) A collection of stones in the trigone of the bladder seen using antegrade cystoscopy. (B) Removal of the final stone, which was lodged within the urethra, using a stone retrieval basket

PCCL has rendered the need for urethrotomy for stone disease in veterinary patients virtually obsolete. It is considered an outpatient procedure and is significantly faster to perform than lithotripsy, regardless of stone size, type or number.

Refractory urinary incontinence

Hydraulic occluder placement

Refractory urinary incontinence is a rare finding in feline patients. When all anatomical anomalies have been fixed or ruled out with appropriate imaging and testing, and bladder voiding function is deemed appropriate, an artificial urethral sphincter, or hydraulic occluder, can be considered. This is a silicone ring that is placed around the proximal urethra, about 2–3 cm caudal to the bladder trigone. The ring is attached to actuating tubing which, in turn, is connected to a port that is placed under the skin on the ventral abdominal wall. By infusing saline into this port the silicone ring around the urethra will tighten; the extraluminal compression decreases the urethral luminal diameter, resulting in outflow resistance and improved continence.

This procedure has been performed in only three feline patients to date in the author’s practice, but has been successful in improving continence. The device is typically placed using a small surgical approach to the caudal abdomen.

Malignant urethral obstruction

Urethral stenting

Malignant obstructions of the urethra can cause severe discomfort, dysuria and life-threatening azotemia. Transitional cell carcinoma is the most common tumor of the trigone and urethra in cats. Chemotherapy and non-steroidal anti-inflammatory 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 in dogs, but are invasive and potentially associated with an undesirable outcome. Placement of a SEMS (see page 52) under fluoroscopic guidance can be a fast, reliable and safe alternative to establish urethral patency (Figure 9). This technique, which is an outpatient procedure, has been performed in over 150 canine patients in the author’s practice, but only a dozen or so feline patients. Urethral stenting has also been useful in patients with benign urethral strictures when traditional therapies (balloon dilation) have failed, or when surgery is refused or not indicated. Benign urethral strictures may, however, resolve with urethral balloon dilation alone, and this has been performed in a small number of cats as well.

Figure 9

Fluoroscopic images showing urethral stent placement in a male cat with a transitional cell carcinoma. Access was obtained via an apical approach similar to that used for PCCL. (A) Cystourethrogram showing the area of proximal urethral narrowing, allowing for measurement of the normal urethral diameter for stent sizing. A marker catheter is within the colon to help adjust for magnification. (B) A urethral stent placed over the guide wire on its delivery system advanced in an antegrade manner. (C) Deployment of the urethral stent. Note it is opening from caudal to cranial because it is placed in an antegrade manner (versus a retrograde manner used for female cats, or dogs). (D) The stent opened after deployment, confirming urethral patency

Using fluoroscopic guidance a cystourethrogram is performed to determine the urethral diameter and obstruction location and length. Then an appropriately sized balloon (if balloon dilation alone is to occur) or SEMS is chosen. In feline patients this is typically 5–6 mm diameter x 20–40 mm length. Recently, 10 cats were evaluated after urethral stent placement and the outcomes were considered good to excellent.³⁶ About 25% of cats had some degree of urinary incontinence after stent placement.

Percutaneous cystostomy tube placement

Cystostomy tubes are placed to bypass a urethral obstruction or ‘buy time’ while a urethral/trigonal lesion is healing. This might be secondary to malignant neoplasia (trigonal or urethral), proliferative/granulomatous urethritis, urethral strictures, urethral tears or urethral stones that are difficult to remove surgically. There is some thought that percutaneous cystostomy tubes may hold a place in the treatment of blocked male cats, rather than irritating the urethra with a transurethral urinary catheter. With the advent of urethral stents (see earlier), the use of cystostomy tubes has declined for treatment of structural urethral obstructions and should be considered a more temporary fix.

Cystostomy tubes can either be placed percutaneously or surgically. With the locking-loop pigtail catheter, percutaneous cystostomy tube placement has become a relatively fast and easy technique when necessary (Figure 10).

Figure 10

Percutaneous cystostomy tube placement. (A) The locking-loop pigtail catheter when it is straight on its stylette. (B) Once the stylette is removed the catheter coils in a pigtail shape and can be locked with a string to prevent dislodgement. (C) Fluoroscopic image obtained after cystostomy catheter placement in the bladder of a cat

Cystostomy tubes are commonly associated with secondary infections (at least 86% in one study),³⁷ due to the external nature of the tube. Additionally, complications with the tubes have been reported in as many as 49% of patients, involving inadvertent tube removal, eating of the tube by the patient, fistulous tract formation and mushroom tip breakage during removal. This is not ideal in circumstances where chemotherapy (for malignant obstructions) or immunosuppressive therapy (for immune-mediated disease [proliferative urethritis]) is being used.

Antegrade urethral catheterization

Urethral catheterization is a simple procedure used commonly in feline patients. Occasionally, standard retrograde catheterization can be difficult in very small (female) patients, female patients with obstructive tumors, or feline patients with urethral tears following trauma or attempted serial catheterizations for urethral obstruction. Urethral tears are most commonly seen in male cats, and are usually the result of vehicular trauma or attempts to unblock the patient.

Antegrade urethral catheterization can be rapid, easy and safe in such cases.³⁸ This procedure accesses the urethra through a cystocentesis (bladder puncture), in an antegrade manner, using a guide wire under direct fluoroscopic visualization (Figure 11). Once the wire is through and through, an appropriately sized urethral catheter can be advanced over the guide wire in a retrograde manner into the urethra and bladder. This is ideal for male cats with urethral tears, because the tear is usually longitudinal and made in a retrograde manner. Longitudinal urethral tears will usually heal within 5–10 days without surgical intervention, and the catheter should be maintained for that length of time.

Figure 11

Fluoroscopic images showing percutaneous antegrade urethral catheterization. (A) Cystocentesis performed using a catheter (black arrows), allowing for a cystourethrogram. (B) A guide wire (white arrows) through the bladder catheter (black arrows), aiming down the urethra in an antegrade direction. (C) Once the wire is through and through, a catheter (black arrows) is advanced over the wire in a retrograde manner. Images courtesy of Chick Weisse

Key points

Endourology has made dramatic progress in feline medicine in the past decade. With experience and device development, patients with previously ‘non-treatable’ disease, or those considered poor surgical candidates, are now being treated routinely and effectively.

Ureteral obstructions cause a dramatic decline in renal function over a short period of time and present veterinarians with a significant clinical challenge.

Misdiagnosis is a common problem. All cats with an acute onset of azotemia should be evaluated for a ureteral obstruction prior to a presumptive diagnosis of chronic interstitial nephritis or chronic kidney disease.

Newer interventional treatment options like the SUB device and double pigtail ureteral stents have decreased the morbidity and mortality when compared with traditional surgery.

Most of these procedures should only be performed after appropriate training and by those with interventional experience.

In the author’s experience, fewer than 5% of feline nephroliths are considered problematic, with the majority not requiring intervention.

Future use of mesenchymal stem cell therapy for the treatment of chronic kidney disease is of great clinical interest, and results to date have been promising.

Footnotes

Funding

The author received no specific grant from any funding agency in the public, commercial or not-for-profit sectors for the preparation of this article.

Conflict of interest

The author is an advisor for Infiniti Medical and Norfolk Vet Products.

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New techniques on the horizon

Abstract

Practical relevance:

Aim:

Evidence base:

Novel Endourologic Procedures – What is the Appeal?

New Approaches to Kidney and Ureteral Conditions

Nephrolithiasis

Idiopathic renal hematuria

Chronic kidney disease

Ureteral obstructions

Cause and traditional therapy

The ‘ideal’ treatment

Case work-up and therapeutic decision making

Newer minimally invasive options

Percutaneous/surgically assisted locking-loop pigtail nephrostomy tubes

Ureteral stenting

SUB device

New Approaches to Urinary Bladder and Urethral Conditions

Bladder and urethral stones

Laser lithotripsy

Percutaneous cystolithotomy

Refractory urinary incontinence

Hydraulic occluder placement

Malignant urethral obstruction

Urethral stenting

Percutaneous cystostomy tube placement

Antegrade urethral catheterization

Key points

Footnotes

Funding

Conflict of interest

References