Endoscopic nephrolithotomy for the removal of complicated nephroliths in dogs and cats: 16 kidneys in 12 patients (2005–2017)

Brian Petrovsky 1Department of Diagnostic Imaging and Interventional Radiology, The Animal Medical Center, 510 E 62nd St, New York, NY 10065.

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Allyson C. Berent 1Department of Diagnostic Imaging and Interventional Radiology, The Animal Medical Center, 510 E 62nd St, New York, NY 10065.

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Chick W. Weisse 1Department of Diagnostic Imaging and Interventional Radiology, The Animal Medical Center, 510 E 62nd St, New York, NY 10065.

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Erinne Branter 1Department of Diagnostic Imaging and Interventional Radiology, The Animal Medical Center, 510 E 62nd St, New York, NY 10065.

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Demetrius H. Bagley 2Department of Urology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107.

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Kenneth E. Lamb 3Lamb Statistical Consulting LLC, West Saint Paul, MN 55118.

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Abstract

OBJECTIVE

To describe techniques and outcomes for dogs and cats undergoing endoscopic nephrolithotomy (ENL) for the removal of complicated nephroliths.

ANIMALS

11 dogs and 1 cat (n = 16 renal units) with complicated nephroliths that underwent ENL via a surgically assisted ENL approach (12 renal units) or a percutaneous nephrolithotomy approach (4 renal units) between December 2005 and June 2017.

PROCEDURES

Data were obtained from the medical records regarding preoperative, operative, and postoperative findings. Follow-up information on complications and outcomes was also collected.

RESULTS

Indications for nephrolith removal included massive calculi displacing parenchyma (n = 7), recurrent urinary tract infections (5), and ureteral outflow obstruction (4). Median nephrolith diameter was 2.5 cm (range, 0.5 to 5.7 cm). Nephrolith composition differed among patients; calcium oxalate was the most common type (n = 7 [including 2 mixed nephroliths containing ≥ 60% calcium oxalate]). Following ENL (median duration, 180 minutes), 15 of 16 renal units were completely nephrolith free. Procedure-related complications included renal puncture-associated hemorrhage requiring a blood transfusion (n = 1), renal capsule tear (1), and ureteral puncture (1); all were managed without adverse consequence. Five of 12 patients remained alive at the final follow-up (median, 557 days after ENL), and none died from the procedure.

CONCLUSIONS AND CLINICAL RELEVANCE

ENL as performed was safe and effective in removing complicated nephroliths in a renal-sparing manner for the patients in this study. This procedure requires technical training and could be considered for the treatment of complicated nephrolithiasis in dogs and possibly cats.

Abstract

OBJECTIVE

To describe techniques and outcomes for dogs and cats undergoing endoscopic nephrolithotomy (ENL) for the removal of complicated nephroliths.

ANIMALS

11 dogs and 1 cat (n = 16 renal units) with complicated nephroliths that underwent ENL via a surgically assisted ENL approach (12 renal units) or a percutaneous nephrolithotomy approach (4 renal units) between December 2005 and June 2017.

PROCEDURES

Data were obtained from the medical records regarding preoperative, operative, and postoperative findings. Follow-up information on complications and outcomes was also collected.

RESULTS

Indications for nephrolith removal included massive calculi displacing parenchyma (n = 7), recurrent urinary tract infections (5), and ureteral outflow obstruction (4). Median nephrolith diameter was 2.5 cm (range, 0.5 to 5.7 cm). Nephrolith composition differed among patients; calcium oxalate was the most common type (n = 7 [including 2 mixed nephroliths containing ≥ 60% calcium oxalate]). Following ENL (median duration, 180 minutes), 15 of 16 renal units were completely nephrolith free. Procedure-related complications included renal puncture-associated hemorrhage requiring a blood transfusion (n = 1), renal capsule tear (1), and ureteral puncture (1); all were managed without adverse consequence. Five of 12 patients remained alive at the final follow-up (median, 557 days after ENL), and none died from the procedure.

CONCLUSIONS AND CLINICAL RELEVANCE

ENL as performed was safe and effective in removing complicated nephroliths in a renal-sparing manner for the patients in this study. This procedure requires technical training and could be considered for the treatment of complicated nephrolithiasis in dogs and possibly cats.

The incidence of complicated, or problematic, nephrolithiasis in dogs and cats has increased over the past decade, but such cases remain fairly uncommon.1–3 A complicated nephrolith is typically considered one that may cause partial or complete UPJ obstruction, resulting in progressive hydronephrosis; renal parenchymal loss due to nephrolith growth, deforming the pelvis and renal calices; intractable pyelonephritis despite appropriate medical management; and pain.4 The invasiveness and morbidity associated with nephrolith removal provoke some controversy as to whether nonobstructive nephroliths compromise renal function and, if so, when and how they should be removed. Nephroliths may predispose patients to worsening kidney injury, although confirmation of this relationship can be difficult.

Advancements in the field of human endourology such as ESWL, retrograde ureteropyeloscopy and laser lithotripsy, and PCNL have almost eradicated the need for open renal surgery to treat ureterolithiasis or nephrolithiasis.5–7 Great efforts have been made to find a technique that is as renal sparing as possible, with the understanding that renal trauma is probable with any intervention.8,9 The trend is similar in veterinary medicine, where interest in various management options is increasing among clients and clinicians.4 Some reported data for humans and cats suggest that the presence of nephroliths (vs no nephroliths) is associated with a faster progression of renal disease and a worse long-term outcome.6,10–12 Consequently, nephrolith removal has been encouraged for humans with evidence of early-stage CKD, particularly when the nephroliths are large and displacing renal parenchyma.6,11 Whether removal should be encouraged for veterinary patients with early-stage CKD is still unclear.

Cats with nephroliths are generally not treated unless the stones move into the ureter, resulting in obstructive ureterolithiasis. Given the high incidence of renal azotemia in cats,13–16 the decrease in GFR associated with surgical nephrotomy is a major concern.17 One study13 showed that cats with nephroliths and CKD do not have a different rate of disease progression than cats with CKD but no nephroliths.13 A more recent report10 of symmetric dimethylarginine and renal function in cats with and without nephrolithiasis suggested that the progression of renal disease is significantly more profound in cats with versus without nephrolithiasis; most nephroliths in that study were composed of calcium oxalate, and survival time of cats with nephrolithiasis was shorter. What remains unclear is whether nephroliths are a marker for more aggressive renal functional loss or the cause of renal disease progression. Verification that they are the cause would support the removal of uncomplicated nephroliths. The presence of nonobstructive nephroliths in cats with CKD is currently not considered an indication for stone removal. Regardless, it would be important to identify the safest, most renal-sparing approach to nephrolith removal, when necessary, prior to making more aggressive recommendations for any species.

Before the availability of minimally invasive treatment options, nephrolithotomy was typically performed surgically by means of open nephrotomy, pyelotomy, or salvage ureteronephrectomy techniques.2,18–20 In small animals, these procedures have been associated with various clinical complications, including hemorrhage, decreasing renal function, nephrolith or edema-induced ureteral obstruction, and urinary leakage.2,20 In humans, minimally invasive treatment options for complicated nephrolithiasis are the standard recommendation.18 Percutaneous nephrolithotomy is typically reserved for nephroliths > 1.5 cm, those composed of cystine, and those not easily accessible with retrograde ureteropyeloscopy (caudal pole nephroliths).18 Indeed, the American Urologic Association Guidelines states that “percutaneous nephrolithotomy should be the first treatment used for most patients” because ENL has the least effect on GFR and yields the highest nephrolith-free rates of all available options.17,21

Percutaneous nephrolithotomy has been evaluated in humans and is considered highly renal sparing, compared with ESWL, laparoscopically assisted nephrotomy, and traditional nephrotomy,11,22–25 likely because of the lack of nephron transection and only minimally isolated trauma involved. This standard of care has allowed the veterinary profession to reconsider their approach to nephrolith management. According to the 2016 American College of Veterinary Internal Medicine consensus statement,4 the current recommendation for removal of complicated nephroliths is to spare as much of the kidney as possible. For patients with associated renal compromise, selection of the most renal-sparing option should be considered a priority, and in the authors' experience, most dogs and cats with nephrolithiasis have some degree of renal compromise.

Endoscopic nephrolithotomy involves intracorporeal lithotripsy with removal of stone fragments through a renal-access sheath. The tract created in the renal parenchyma and into the renal pelvis results in renal parenchymal dilation and spreading of the nephrons, rather than transection, causing minimal trauma.11,23–25 In humans, reported advantages include prevention of ureteral obstruction from fragmented nephroliths, high subsequent stone-free rates for large nephroliths, prevention of the need for multiple procedures, minimal effect on GFR, and improved visibility and access to remove nephroliths through a small stoma. Endoscopic nephrolithotomy is performed with a combination of fluoroscopic and endoscopic guidance and can be performed by use of a PCNL approach with ultrasonography or a laparoscopically or surgically assisted approach. For veterinary patients, owners are not often willing to maintain a nephrostomy tube for a few weeks during healing after PCNL, so SENL is considered more appealing.

In humans, the PCNL technique, first reported in 1976,26 is highly (85% to 100%) effective in removing all clinically relevant stone fragments (> 3 mm), given that endoscopic calyceal inspection is superior to open nephrotomy for the visual identification and removal of fragments.17 Research has shown that both ESWL and PCNL have minimal effects on the GFR in humans with clinical nephrolithiasis, and ENL is the best procedure for children to preserve overall renal function when all methods of nephrolith removal are considered.25 We have modified the pediatric PCNL procedure further to treat complicated nephroliths in veterinary patients by using a nephrostomy tube-free approach, which has also been reported in pediatrics.27 The objective of the study reported here was to describe the technique and clinical use of a renal-sparing fluoroscopy- and endoscopy-guided nephrolithotomy procedure for dogs and cats.

Materials and Methods

Case selection criteria

Electronic medical records of the veterinary teaching hospital of the University of Pennsylvania and The Animal Medical Center in New York, NY, were searched to identify any dog or cat with complicated nephrolithiasis in which a PCNL or SENL approach to ENL was performed by the authors (ACB and CWW) between December 1, 2005, and June 30, 2017. Patients were considered to have complicated nephrolithiasis if at least one of the following conditions was recorded: partial or complete UPJ obstruction resulting in progressive hydronephrosis, renal parenchymal loss due to a large renal pelvic stone, and intractable pyelonephritis despite appropriate medical management with the presence of a large nephrolith.

Medical records review

Information was collected from the medical records regarding medical history, patient signalment, clinical signs, diagnostic imaging (abdominal ultrasonography or abdominal radiography) results, clinicopathologic findings (CBC, serum biochemical analysis, coagulation profile, urinalysis, stone analysis, and urine bacterial culture), procedure reports, treatment methods, procedure and hospitalization time, intraoperative and perioperative complications, and short-term (< 30 days) and long-term (> 30 days) outcomes. Follow-up data were obtained through serial reevaluations and included clinical signs; physical examination findings; and urinalysis, urine bacterial culture, serum biochemical, and diagnostic imaging (abdominal ultrasonography and abdominal radiography) results. All owners were contacted to assess postoperative recovery and short- and long-term management approach. They were also asked about their overall satisfaction with the procedure on the basis of an 11-point scale (0 = disappointed, 5 = do not feel the procedure had a positive or negative impact, and 10 = extremely satisfied), apparent systemic health of the animal at the time of contact, nephrolith prevention technique used, whether the nephrolith or UTI had recurred, and survival status of the animal at the time of contact, including time of and reason for death or euthanasia, when applicable.

Procedures

Each dog and cat had ENL performed via a PCNL or SENL approach while anesthetized; choice of anesthetic protocol was based on clinician preference. The entire abdominal region was clipped of hair and aseptically prepared in a routine manner. The vulva or prepuce and perineal region were aseptically prepared and flushed with a dilute chlorhexidine solution.

PCNL—For the PCNL approach, the patient was positioned in lateral recumbency, contralateral to the affected kidney. The PCNL was performed by use of ultrasonographic, fluoroscopic, and endoscopic guidance. With ultrasonographic guidance, the affected renal pelvis was accessed through the greater curvature of the kidney by use of an 18-gauge, 15-cm-long renal-access trocar needlea until the nephrolith was touched or urine was obtained in the hub of the needle (Figure 1). Then, with fluoroscopic-guidance, an antegrade pyeloureterogram was performed by infusion of a 50% mixture of iodinated contrast material.b Next, a 0.035-inch-diameter, angle-tipped, hydrophilic guidewirec was advanced through the renal-access needle, around the nephrolith, in an antegrade direction down the ureter, into the urinary bladder, and out the urethra and vulva or prepuce. This allowed through-and-through guidewire access to be obtained.

Figure 1—
Figure 1—

Photographs showing performance of PCNL in a male dog with complicated nephrolithiasis positioned in left lateral recumbency. The head is to the left of the image. A—Ultrasound guidance (arrow) is used during renal puncture. B—Once renal access is obtained with the needle, a guidewire (red arrows) is advanced from the renal pelvis, down the ureter, into the bladder, and out the urethra. The prepuce is indicated (yellow arrow). C—The introducer sheath (yellow arrow) is advanced over the inflated balloon (white arrow), into the renal pelvis in an antegrade fashion. D—The renal tract is dilated for the access sheath with a balloon insufflator. E—The nephroscope is advanced through the introducer sheath (arrow) for performance of intracorporeal lithotripsy. F—A PCNL tube (arrow) is placed after the procedure.

Citation: Journal of the American Veterinary Medical Association 255, 3; 10.2460/javma.255.3.352

Subsequently, with fluoroscopic guidance, a 5F open-ended ureteral cathetera was advanced over the guidewire in a retrograde manner up the ureter to the level of the UPJ. A renal-access sheathd,e was then loaded behind the uninflated balloon-dilation catheterf,g (Figure 1) in an antegrade manner on the wire. The ultimate size of the nephroscope that would be used determined the inner diameter of the selected sheath. The size of the balloon was chosen on the basis of the size of the selected sheath to provide sufficient dilation to achieve a smooth transition. The balloon was advanced over the guidewire, through the skin, and into the renal pelvis abutting the nephrolith. Dilation of the renal-access tract was performed with the balloon-dilation catheter by use of an insufflation device.h The sheath was then advanced in an antegrade manner over the inflated balloon and into the renal parenchyma until it was touching the nephrolith. The sheath remained in place while the balloon-dilation catheter was uninflated and removed, keeping the through-and-through guidewire in place.

The endoscopei-k was advanced through the sheath until the nephrolith was visible (Figures 1 and 2). A dual-action ultrasonic and pneumonic lithotriptorl was advanced through the working channel of the nephroscope, and the nephrolith was fragmented, removed, or both by use of a combination of endoscopic suction and various stone-retrieval basketsm-q or graspersr-u (Figure 3). In most instances, the dual-action lithotriptorl was used through a 22F nephroscope, and a combination of suction and stone graspers was used for fragment retrieval. In some instances, a Hol:YAG laser lithotriptorv with a 400-μm laser fiber was used, at 7 Hz and 0.6 J, followed by basket retrieval of fragments with endoscopic guidance. If the nephrolith was smaller than the renal-access sheath, the stone basket, grasper, or both were used to remove the stone en bloc without fragmentation. Endoscopy and fluoroscopy were used to monitor the nephrolith location and the size of the fragments during the procedure and to ensure that all fragments were removed from each renal calix and the entire renal pelvis prior to completion of the procedure. After complete stone removal was confirmed, a second through-and-through guidewire was passed from the access sheath, down the ureter, into the bladder, and out the urethra. Then, the open-ended catheter was used to flush sterile saline (0.9% NaCl) solution up the ureter, into the renal pelvis, and out of the renal-access sheath and to thoroughly flush away any blood clots, fragments, or debris.

Figure 2—
Figure 2—

Images obtained during performance of ENL by use of an ultrasonic-electrohydraulic lithotriptor in a female dog with a large nephrolith of mixed composition (5% calcium oxalate, 80% struvite, and 15% calcium phosphate) that did not dissolve with medical treatment. A—A dorsoventral abdominal radiographic image reveals a large nephrolith (arrow) in the left kidney prior to the procedure. Notice discrete layers within the nephrolith. B—An endoscopic image shows nephroscopy being performed through a sheath with the lithotriptor through the working channel of the endoscope, which is in contact with the large nephrolith (arrow). C—An endoscopic image obtained during lithotripsy shows the large stone broken into fragments (black arrow). Notice the guidewire (red arrow) within the renal pelvis (safety wire) that has been introduced down the ureter. D—A dorsoventral abdominal radiographic image obtained after left ureteral stent placement (arrows) shows the stent traveling from the renal pelvis, down the ureteral lumen, and into the urinary bladder. This image, obtained immediately after the procedure, confirms that the urinary tract is now stone free.

Citation: Journal of the American Veterinary Medical Association 255, 3; 10.2460/javma.255.3.352

Figure 3—
Figure 3—

Endoscopic images obtained during ENL with basket retrieval in 3 dogs. A—The stone basket is shown grasping a 5-mm nephrolith. B—The stone basket is shown grasping a 3-mm nephrolith at the UPJ. C—The safety wire and a second wire for the ureteral stent after nephrolith removal are visible, as is a clean ureter free from stones proximally.

Citation: Journal of the American Veterinary Medical Association 255, 3; 10.2460/javma.255.3.352

Finally, the guidewire was advanced up the ureteral catheter in a retrograde manner and coiled inside the renal pelvis. An appropriately sized double-pigtail ureteral stentw,x was then placed from the renal pelvis, down the ureter, and into the urinary bladder (Figure 2), as described elsewhere.20,28

After stent placement, the through-and-through guidewire was pulled back into the renal pelvis and coiled. Then, a 6F locking-loop nephrostomy tubey was placed over the guidewire into the renal pelvis as described elsewhere22 (Figure 1). The nephrostomy tube was secured in place with a pursestring suture and a finger-trap pattern. The abdomen was wrapped with a stockinette,z and the tube was secured, capped, and covered.

SENL—For the SENL approach, the procedure was performed similarly to that described for the PCNL approach, with laparotomy performed to allow renal access and closure (Figure 2). No ultrasonography was used for access because direct puncture with fluoroscopic visualization of the nephrolith was successful. In addition, the renal-access site was closed primarily with 3-0 or 4-0 polydioxanone sutureaa in a horizontal mattress suture pattern. No nephrostomy tube was used, and a double-pigtail ureteral stent was placed, as described for the PCNL approach.

Postprocedural management

Once patients had recovered from anesthesia, each received analgesics as chosen by the attending clinician for 1 to 3 days as needed. Antimicrobials were selected on the basis of results of urine bacterial culture and antimicrobial susceptibility testing. For patients without a positive culture result, enrofloxacin (10 mg/kg [4.5 mg/lb], PO, q 24 h for 14 days) was typically used to help prevent biofilm formation on the stent.29

For patients in which PCNL was performed, the nephrostomy tube was allowed to gravity drain into a closed urine collection system for 24 hours and was then capped and wrapped before discharge from the hospital. The nephrostomy tube was left in place for 4 weeks, and urine was obtained from the tube for analysis and bacterial culture once a week until the tube was removed. All patients underwent focal urinary tract ultrasonography and abdominal radiography prior to discharge from the hospital to ensure no evidence of uroabdomen was present and to assess the dimensions of the renal pelvis and ureters as well as the presence of any residual nephrolith debris.

Follow-up

Urine bacterial culture, hematologic evaluation (CBC and serum biochemical analysis), abdominal radiography, and urinary tract ultrasonography were recommended to be performed at 1, 2, 4, and 6 weeks and 2 months after the procedure and then every 3 to 6 months thereafter. Nephrostomy tubes were removed 4 weeks after placement by means of fluoroscopic guidance over a guidewire. The ureteral stent was typically removed endoscopically once there was evidence that the patient was nephrolith free.

Follow-up ultrasonography was recommended, and changes in renal pelvis size, renal parenchymal diameter, and overall kidney size were assessed (Figure 4). This was accomplished by measuring the kidney and renal pelvis in the sagittal plane and comparing the measurements with those obtained before ENL. All patients were placed on an aggressive stone prevention regimen on the basis of the results of nephrolith composition analysis. This regimen included an appropriate diet, chelating-alkalinizing agents (potassium citrate) when indicated, and, when appropriate, an enzyme inhibitor (allopurinol).

Figure 4—
Figure 4—

Ultrasonographic images showing the change in renal parenchyma thickness and renal pelvis diameter in a female dog before (A) and after (B) performance of ENL. The white line indicates the length of the kidney in the sagittal plane, and the yellow line indicates the length of the renal pelvis in the sagittal plane. The difference between these lengths is the renal parenchymal thickness.

Citation: Journal of the American Veterinary Medical Association 255, 3; 10.2460/javma.255.3.352

Statistical analysis

Univariate time-to-event analyses were performed by means of Kaplan-Meier product-limit estimation. Median survival time was compared between patients with IRIS stage 1 or 2 kidney disease and those with IRIS stage 3 or 4 kidney disease. Comparisons of ultrasonographic renal parenchymal measurements before and after ENL were performed with the paired t test. All analyses were performed with the aid of statistical software.bb Values of P < 0.05 were considered significant.

Results

Animals

The medical record search revealed 11 dogs and 1 cat (16 renal units) that had undergone ENL to treat complicated nephrolithiasis. All identified patients were included in the study. The 1 included cat was a spayed female domestic shorthair cat weighing 6 kg (13.2 lb). The dogs consisted of 7 spayed females, 3 castrated males, and 1 sexually intact female, with a median age of 7 years (range, 3 to 13 years) and body weight of 8 kg (17.6 lb; range, 2.5 to 26.6 kg [5.5 to 58.5 lb]). This group included 3 Bichon Frises, 1 Yorkshire Terrier, 1 French Bulldog, 1 Lhasa Apso, 1 Pug, 1 Maltese, 1 Miniature Schnauzer, 1 longhaired Dachshund, and 1 mixed-breed dog.

Concurrent medical problems included left-sided heart murmur (n = 3 dogs); dental disease (2 dogs); CKD (1 dog and 1 cat); a combination of UTI, untreated extrahepatic portosystemic shunt, mast cell tumor disease, and brachycephalic airway syndrome (1 dog); keratoconjunctivitis sicca secondary to trimethoprim sulfamethoxazole administration (1 dog); conjunctivitis, C6-T2 intervertebral disk disease, tracheal collapse, and hypertension (1 dog); thrombocytosis and hyperadrenocorticism (1 dog); portovenous hypoplasia without a macroscopic portosystemic shunt (1 dog); history of renal cell carcinoma with subsequent nephrectomy (1 dog); and recurrent cystolithiasis (1 dog).

Urinary history and findings

Concurrent urinary tract disorders were recorded for 3 patients. In addition to CKD, the cat had bilateral ureteral obstruction, for which one side was treated with a ureteral stentv and the other was treated by ENL owing to a contralateral ureterolith at the UPJ. One dog had undergone ureterotomy of the ipsilateral ureter and pyelolithotomy of the contralateral kidney to treat bilateral ureteral obstructions 3 years previously. This same dog also had its spleen removed for unknown reasons at the time of that initial surgery. Additionally, 1 dog had ESWL performed on the contralateral kidney 2 weeks prior to undergoing ENL, and that procedure resulted in a ureteral obstruction necessitating the placement of a SUB devicecc in the kidney at the same time when ENL (by means of the SENL approach) was performed on the other kidney.

Reasons for ENL in all patients included massive nephroliths with worsening azotemia (n = 8), recurrent UTI (5), and ureteral-outflow obstruction from the nephrolith (3). Six dogs and 1 cat were treated for documented (n = 4) or presumptive (3) UTIs of different durations (median, 88 days; range 45 to 365 days). The number of antimicrobial treatment courses as prescribed by the referring veterinarian ranged from 1 to 4 (median, 1), and none had resulted in resolution of the UTI. Every patient had been fed at least 1 type of veterinary prescription diet prior to the ENL procedure, including a stone-neutralizing diet (n = 6),cc renal-friendly diet (3),dd urate-prevention diet (2),ee acidifying stone-dissolution diet (2),ff and home-cooked diet formulated by a board-certified veterinary nutritionist (1). This prescription diet recommendation was based on the presumptive composition of the nephrolith, which was inferred from a combination of signalment, radiographic appearance of the nephrolith, results of urinalysis and urine bacterial culture, or prior history of nephroliths or other stones with a known composition. Four dogs had at least 1 previous cystotomy performed (1 had 2 cystotomies performed) to remove cystoliths, the composition of which included calcium oxalate (n = 2) and cystine (1). The cystoliths removed from 1 dog had not been submitted for qualitative and quantitative analysis.

At initial evaluation, 6 patients (5 dogs and 1 cat) had evidence of renal azotemia (serum creatinine concentration ≥ 1.4 mg/dL for dogs and ≥ 1.6 mg/dL for cats),30 with a median urine specific gravity of 1.016 (range, 1.009 to 1.020; reference range, > 1.030 for dogs and > 1.035 for cats), median serum creatinine concentration of 1.4 mg/dL (range, 0.7 to 9.1 mg/dL; reference range, 0.5 to 1.5 mg/dL), and median BUN concentration of 22.5 mg/dL (range, 6 to 106 mg/dL; reference range, 9 to 31 mg/dL). Median PCV and serum total protein concentration were 41% (range, 16% to 45%; reference range, 40% to 55% for dogs and 30% to 46% for cats) and 6.2 g/dL (range, 4.6 to 8.8 g/dL; reference range, 5.5 to 7.5 g/dL), respectively.

Five patients (4 dogs and 1 cat) had at least 1 positive result of urine bacterial culture before undergoing ENL. Recovered bacteria included Pseudomonas spp, Klebsiella spp, Enterococcus faecalis, Staphylococcus spp, and Escherichia coli. All 4 dogs received antimicrobial treatment on the basis of results of antimicrobial susceptibility testing for at least 2 weeks prior to ENL (range, 2 to 52 weeks). No coagulation abnormalities were detected in any patient.

Diagnostic imaging results

Abdominal ultrasonography was performed for all 12 patients (23 renal units; 1 patient had only 1 kidney). Detected abnormalities in all 16 renal units included large nephroliths (median size in the transverse by sagittal plane, 2.5 × 2.5 cm; range 0.4 to 4.6 cm × 0.4 to 5.7 cm) and were characterized as nonobstructive nephrolithiasis in 12 renal units and obstructive nephrolithiasis in 4 renal units. Renal pelvic dilation was noted in 4 renal units. The contralateral renal units in all 7 patients that underwent unilateral ENL also had evidence of smaller nephroliths that were not considered complicated at the time of ENL. Of 12 patients, 10 had bilateral nephrolithiasis. Of 23 renal units evaluated, 4 had evidence of chronic nephropathy that had been ultrasonographically determined on the basis of a small, thin, irregular cortex, with decreased corticomedullary distinction and loss of normal renal architecture. Five renal units for which ENL was performed had ipsilateral ureteroliths, 4 of which were obstructive, and 4 contralateral renal units had evidence of ureteroliths, 2 of which were obstructive. Concurrent cystoliths were noted in 5 dogs. The treated kidney had a median length in the sagittal plane of 3.4 cm (range, 1.9 to 5.7 cm) in dogs and a length of 3 cm in the cat. Median diameter of the renal pelvis in the transverse plane was 1.55 cm (range, 0.2 to 3.24 cm) and included the occupying nephroliths. Median thickness of the renal cortex in the same plane prior to ENL was 0.5 cm (range, 0.3 to 0.8 cm).

All 12 patients underwent abdominal radiography, and findings for the urinary tract were consistent with the ultrasonographic findings. Computed tomography was performed for 1 dog, revealing that the right renal pelvis was minimally dilated (< 2 mm) and 2 stones were present in the cranial (4 × 4 × 4 mm) and caudal (7 × 5 × 3 mm) poles of the renal calices. This dog also had evidence of small stones within the renal parenchyma.

Procedures

The SENL approach to ENL was used for 12 renal units (7 dogs and 1 cat), and the PCNL approach was used for 4 renal units (4 dogs). Four bilateral SENL procedures (8 renal units) were performed, 2 of which were staged 1 to 1.5 months apart. Two dogs had the bilateral SENL performed during the same anesthetic event.

Sizes of the renal-access sheaths used were 24F (n = 11), 18F (2), 12F (2), and 15F (1). The balloon-dilation catheters used matched the size of the sheath. For patients in which a 24F sheath was used, a 22F integrated nephroscope with a dual ultrasonic and electrohydraulic lithotriptorl was used for lithotripsy. For patients in which an 18F sheath was used, an ultrasonic lithotriptorgg was used with a 16F nephroscope or a 2.7-mm rigid cystoscope with a 400-μm fiber for the Hol:YAG laser lithotriptor. For patients in which a 15F sheath was used, a 2.7-mm, 30° rigid cystoscope was used with a stone-retrieval basket for en bloc removal of the nephrolith. For patients in which the 12F sheath was used, a 1.9-mm, 30° rigid cystoscope was used with a stone-retrieval basket. The dual ultrasonic lithotriptor was used for 11 renal units, the ultrasonic lithotriptor for 1 renal unit, a basket or grasper alone for 3 renal units, and a Hol:YAG laser lithotriptor for 1 renal unit.

Additional procedures performed at the time of ENL included esophagostomy tube placement and stem cell harvesting of falciform and omental fat (n = 1), esophagostomy tube placement (1), liver biopsy with ameroid constrictor placement for a splenocaval portosystemic shunt (1), and SUB device placement in the contralateral kidney after the development of a ureteral obstruction from ESWL (1). Postoperative abdominal radiography or ultrasonography was performed in all patients within 24 hours after ENL. One of 16 renal units had 2 small stone fragments noted in the ureter; 1 renal unit had debris in the renal pelvis that was nonshadowing and suspected to be a blood clot with some air but was deemed of no clinical importance owing to the placement of a ureteral stent.

No conversion to traditional surgery or a salvage procedure (eg, nephrectomy) was necessary for any patient. Median procedure time for ENL by any approach was 180 minutes (range, 90 to 270 minutes). Unilateral PCNL procedures (n = 4) required a median of 195 minutes (range, 120 to 270 minutes) for completion, and unilateral SENL procedures (n = 8) required a median of 180 minutes (range, 90 to 210 minutes). Bilateral SENL was performed in 2 patients in 1 session, for a total procedure time of 158 or 240 minutes. Median hospitalization time for all patients was 48 hours (range, 48 to 144 hours).

Nephrolith composition analysis

Representative nephrolith samples from all patients were submitted for composition analysis. Composition included mixed compounds (n = 7 renal units), calcium oxalate monohydrate (5), xanthine (2), and cystine (2). For the nephroliths of mixed composition, 2 were composed of 60% calcium oxalate monohydrate and 40% calcium phosphate; 1 of 55% struvite, 40% calcium apatite, and 5% calcium oxalate monohydrate; 1 of 80% struvite and 20% calcium phosphate; 1 of 70% calcium phosphate and 30% struvite; 1 of 75% calcium phosphate, 10% calcium oxalate, and 15% uric acid; and 1 of 95% calcium oxalate and 5% urate.

Complications

The smallest dog (3.1 kg) for which PCNL was performed had a proximal ureteral puncture during initial ultrasound-guided renal access. This was ameliorated after guidewire access was obtained across the ureter in a retrograde manner by means of cystoscopy. In this same patient, during balloon dilation of the renal tract, some bleeding was noted with associated hypotension, and 1 unit of packed RBCs was administered. The balloon-dilation catheter and sheath were used to stop the bleeding, and conversion was not needed; thus, a percutaneous approach was maintained. After nephrolith removal, a ureteral stent was placed across the ureteral puncture without consequence. On recovery from anesthesia, the dog regurgitated and aspirated the contents and had evidence of pneumonia on follow-up radiography, but its recovery was ultimately not affected.

In another dog, through-and-through antegrade guidewire access was difficult to obtain because of the size of the massive nephrolith in the renal pelvis, so access was obtained in a retrograde manner by means of cystoscopy. This was successful. In 1 kidney, the renal-access point was expanded from 24F to 30F during stone fragment removal, although the original nephrolith was > 5 cm in diameter (150F [3F = 1 mm]). This access point was closed routinely with 2 mattress sutures at the completion of the procedure, without complication. In 1 kidney, the nephroliths could be retrieved in full, but a large embedded cluster of ureteroliths could not. Instead, ESWL was used to fragment the ureteral stones 2 days later around the ureteral stent, and the renal and ureteral unit was then left stone free.

In the cat, the contralateral (left) kidney had a stent previously placed to address a ureteral stricture. The SENL approach was used to address a nephrolith in the UPJ of the right kidney, which allowed for decompression of that kidney. The right kidney had persistent ureteral and renal pelvic dilation 2 weeks after the procedure; therefore, a SUB devicehh was placed, after which the hydronephrosis resolved.

Clinicopathologic findings

Median preoperative and postoperative PCV was 41% (range, 16% to 45%) and 25% (range, 18% to 38%), respectively. Four of 16 patients required at least 1 blood transfusion before (n = 1), during (1), or after (2) ENL owing to clinically progressive anemia. All affected patients were dogs, one of which was anemic (preoperative PCV, 16%) and required the transfusion before ENL. No patients died of anemia or blood loss. In all patients, PCV returned to preoperative values within the first 4 weeks after ENL, and none required hormone supplementation.

Prior to ENL, the IRIS stage of kidney disease was determined for all patients, revealing that 1 was nonazotemic (unremarkable serum creatinine concentration and urine specific gravity), none had stage 1 disease, 7 had stage 2 disease, 2 had stage 3 disease, and 2 had stage 4 disease. Improvement in serum creatinine concentration after ENL was documented for all patients. Median (range) serum creatinine concentration before ENL was 1.4 mg/dL (0.7 to 9.1 mg/dL) and 1.3 mg/dL (0.5 to 8.3 mg/dL) 3 months after the procedure. At the time of the last follow-up, which occurred a median of 557 days (range, 4 to 2,490 days) after ENL, the median creatinine value was 1.5 mg/dL (range, 0.7 to 8.3 mg/dL). An increase or decrease in creatinine concentration was defined as an amount representing at least 25% of the baseline value; consequently, evidence of a mild transient increase in serum creatinine concentration was identified immediately after ENL in 3 patients (median increase, 0.8 mg/dL; range 0.2 to 2 mg/dL), and a decrease was identified in 4 patients (median decrease, 1.7 mg/dL; range, 0.5 to 3.2 mg/dL). Stabilization of serum creatinine concentration at the time of hospital discharge was identified in 5 patients (median change between before and after ENL, 0.3 mg/dL; range, 0 to 0.3 mg/dL).

Findings of hematologic evaluation, urine bacterial culture, and urinalysis performed 2 to 6 weeks and 3 to 6 months after ENL were all within reference limits, with no evidence of progressive azotemia, anemia, or postprocedural UTI. Evidence of improvement in pyelectasia was noted in 11 of 13 renal pelvises for which results of follow-up abdominal ultrasonography were available for review. Focused urinary tract ultrasonography revealed that before ENL, median renal pelvis size in the transverse plane, including the nephroliths, was 15.5 mm (range, 2 to 32.4 mm), whereas after hospital discharge and at the time of last follow-up, median pelvis size was 7.7 mm (range, 2.8 to 18.2 mm) and 4 mm (range, 1 to 18 mm), respectively. The change in renal parenchyma thickness after stone removal was monitored, and significant (P = 0.004) improvement (ie, increase from before ENL) was observed in the thickness of the parenchymal tissue in all patients (Figure 4). Five dogs (5 renal units) had evidence of stone recurrence during the follow-up period, including nephroliths (n = 2), cystoliths (2), or ureteroliths (1). Of these 5 dogs, median time until stones were noted was 150 days (range, 14 to 720 days). None of the 4 dogs treated by PCNL had positive bacterial culture results for urine collected from the indwelling nephrostomy tube while it was in place.

All ureteral stents (n = 15) were removed 1 to 20 weeks after ENL by cystoscopic guidance (12), fluoroscopic guidance (2), or a small keyhole cystotomy during the contralateral SENL (1). No immediate complications were associated with stent removal. One ureteral stent placed in a dog with xanthine stones was removed at 4 weeks after ENL, revealing that the stent had become encrusted with stone material. Another ureteral stent was found to be mildly encrusted in the renal pelvis at the time of removal 6 weeks after ENL (cystine calculi composition). Both encrusted ureteral stents were removed without complications. No complications (eg, dysuria, UTI, hematuria, or stent migration) were noted to have been caused by the ureteral stents. No other surgical complications were reported.

Outcomes

Resolution of complicated nephrolithiasis was achieved for all patients (16 renal units), with no evidence of recurrence of complicated nephroliths in any patient (15 renal pelvises) that survived for > 1 month. In 1 dog, crystalline and cellular debris obstructed the ureter 2 months after ENL and 1 month after stent removal, and the obstruction resolved after performance of retrograde ureteropyelography and endoscopic replacement of a ureteral stent. The material was flushed out of the passively dilated ureter and identified as cellular debris and a blood clot, rather than a discrete stone. The hydronephrosis resolved following stent replacement, and the owner elected to have the stent retained long-term with careful monitoring.

Two dogs were euthanized because of CKD 73 and 557 days after ENL, and necropsy revealed stones in the lower, not upper, urinary tract. These stones were not obstructive and were not submitted for analysis. Another dog had a suspected small nephrolith noted via ultrasonography 3 years after treatment, but this nephrolith was not deemed complicated and was no longer evident when ultrasonography was repeated a year later. The dog never had evidence of another problematic stone. One dog had recurrent calcium oxalate cystoliths, but on the last follow-up 11 years after ENL, the dog was still alive and doing well with no nephrolith recurrence. All 11 dogs received preventative diets appropriate for their documented stone type after ENL; the cat received a kidney-friendly diet because of persistent severe azotemia.

Median time from ENL to final follow-up was 557 days (range, 4 to 2,490 days); 5 of 12 patients (5 dogs) were still alive when the study concluded. Of the 6 dogs and 1 cat that died or were euthanized, the cause of death was progressive CKD (n = 4; median time to death, 103 days; range, 60 to 557 days), intractable seizures after portosystemic shunt attenuation (1), cognitive decline > 1,456 days after a PCNL procedure (1), and neurologic dysfunction due to a brainstem tumor at 268 days after a PCNL procedure (1). No patient died of persistent complicated nephrolithiasis or complications associated with ENL. Patients grouped at initial evaluation as nonazotemic or IRIS stage 1 or 2 had a significantly longer median survival time (1,007 days) than those with IRIS stage 3 or 4 (102 days; Figure 5). Overall, resolution of complicated nephrolithiasis was achieved in all renal units for which long-term follow-up was available (10/12 patients; 14/16 renal units). The 2 patients without long-term follow-up information included the 1 dog with intractable seizures and the cat, which had developed progressive azotemia and was euthanized 2 months after ENL.

Figure 5—
Figure 5—

Kaplan-Meier survival curves for II dogs and I cat with IRIS kidney disease stage 0 to 2 (blue line; n = 8) or 3 to 4 (red line; 4) before treatment for complicated nephrolithiasis by means of ENL (PCNL or SENL approach). Median survival time differed significantly (P < 0.05) between these 2 groups.

Citation: Journal of the American Veterinary Medical Association 255, 3; 10.2460/javma.255.3.352

Owners of 4 dogs treated by the SENL approach and 1 dog treated by the PCNL approach answered a follow-up questionnaire a median of 485 days (range, 28 to 1,001 days) after ENL and scored their satisfaction with the outcome of the ENL procedure as 10 of 10. All owners considered the outcome good, and all would consider this procedure again if necessary. For dogs treated by the SENL approach, the amount of postoperative care that owners were required to provide was reportedly minimal, whereas for the dog treated by the PCNL approach, postoperative care was viewed as more difficult because of the dog's temperament. However, once the tube had been removed from that dog and the dog was less restricted, its overall quality of life was reportedly excellent. Owners of the 4 patients with high serum creatinine concentrations that died or were euthanized because of CKD expressed the desire to have had ENL performed earlier in the course of disease if it could have helped preserve renal function for a longer period.

Discussion

Results of the present study supported the use of ENL as a safe, effective, and renal-sparing treatment option for complicated nephroliths in dogs and cats that can ultimately result in a high stone-free rate. Awareness is increasing of nephrolithiasis in veterinary patients, the potentially adverse impact that kidney stones can have on renal function,6–10,12 and the impaired function that traditional surgery can have on a diseased kidney.7 Our study provided evidence of the effectiveness of a renal-sparing option for clinically affected dogs and cats—an option that has been considered an important therapeutic technique in human medicine for decades.18 Indeed, findings indicated that use of ENL led to successful resolution of complicated nephroliths in all renal units in which the procedure was performed, with 1 patient having 2 small stone fragments (< 2 mm) in the ureter after the procedure. These fragments ultimately passed around the ureteral stent. Improvement in renal pelvis size was observed in all kidneys for which follow-up ultrasonography was performed, and chronic UTIs resolved in all patients that underwent nephrolithotomy for that reason, despite small stones remaining in the contralateral kidney. Additionally, no patient had recurrence of complicated stone disease during the follow-up period (> 6.5 years for some).

Other therapeutic options reported for the treatment of complicated nephrolithiasis in dogs and cats include ureteronephrectomy, nephrotomy, pyelotomy, and ESWL. In a retrospective review of information on 140 dogs with nephroliths or ureteroliths treated by ESWL, the most common complication was ureteral obstruction by nephrolith fragments passing down the ureter, which occurred in approximately 10% of dogs.22,31 In addition, approximately 30% of dogs require > 1 treatment to become stone free.22,31 Extracorporeal shockwave lithotripsy has been used in many dogs over the past 2 decades, but this technique is not currently recommended for the treatment of larger (> 1 to 1.5 cm) nephroliths in dogs nor is it recommended for the treatment of nephroliths in cats owing to the small diameter of the ureters and failure of stone-fragment passage as well as the potential risk for renal parenchymal trauma or bleeding.4,22,31 The concurrent placement of a ureteral stent at the time of ESWL decreases the incidence of ureteral obstruction after ESWL, but stone size and technical availability are still considered limitations of this technique, and stone-free rates are far less than with ENL for larger stone burdens.4,32

Patients in the present case series had nephroliths larger (median diameter, 2.5 cm) than the limits for ESWL. Treatment recommendations for those patients were in compliance with the American College of Veterinary Internal Medicine consensus recommendations.4 One patient (a dog) had ESWL performed on the contralateral kidney with concurrent ureteral stent placement to address a 1.5-cm calcium oxalate nephrolith. Those procedures resulted in ureteral obstruction from accumulation of a large burden of stone debris in the ureter and within the stent, resulting in exchange of the stent for a SUB device, and the affected renal unit was never observed to be stone free. The same dog had undergone SENL of the contralateral kidney to remove a 1.5-cm nephrolith during the same time the SUB device was placed, and the SENL procedure was successful, resulting in a nephrolith-free kidney.

In humans, open surgical removal of stones, even when performed laparoscopically, is typically avoided.7 This approach is generally reserved for kidneys with complex anatomic abnormalities or after a failure of renal-sparing options such as ESWL, PCNL, or retrograde ureteroscopy and laser lithotripsy.18,19,27 The effects of nephrotomy on renal function are of concern given that many patients undergoing nephrotomy have impaired renal function (eg, renal insufficiency, acute kidney injury, or CKD) prior to surgical intervention. In a study33 involving healthy dogs that underwent nephrotomy, a significant reduction in GFR was observed during the immediate postoperative period. A study34 involving healthy young cats showed a 10% to 20% reduction in the mean single-kidney GFR after unilateral nephrotomy, compared with GFR in the untouched contralateral kidney, but this reduction was not considered clinically important. Some healthy research animals had a more marked reduction (up to 50%) in GFR after nephrotomy.34 Another study2 involving healthy dogs revealed an unremarkable GFR after bisectional and intersegmental nephrotomies. It is important to emphasize that healthy kidneys have a hypertrophy mechanism to maintain a normal GFR after damage, and once that mechanism is exhausted, as would be expected in a patient with CKD or chronic urolithiasis, the iatrogenic renal damage could be more clinically important.6,20 More than 30% of adult cats will develop renal azotemia and associated CKD in their lifetime, resulting in a > 75% loss of overall renal function.34 This population of cats with CKD likely cannot tolerate a further 10% to 20% decrease in GFR associated with nephrotomy, and so less invasive and more renal-sparing alternatives would be ideal.

The main risks of ENL include hemorrhage, ureteral perforation, and urine leakage from the renal-access tract. Use of a balloon dilator, as in the study reported here, is believed to be more efficient and safer to block any hemorrhage.35,36 During dilation, if the renal-access tract bleeds, the balloon can provide a tamponade effect until the bleeding ceases. Balloon dilation of the tract allows distention of a plane of parenchyma through the puncture site, which stretches the renal tissue without transecting it and thus allows for preservation of nephrons, and is the reason this procedure is hypothesized to have minimal to no effect on renal function.36,37

The decision in the present study to consider an SENL approach over a PCNL approach, while maintaining a renal-sparing method through an open abdomen, was done in an effort to close the renal tract created during lithotripsy and select the ideal angle for the most effective nephrolith removal. The SENL approach appeared to improve overall client satisfaction without affecting patient recovery and maintaining the same effect on renal access. It also prevented urine leakage, postoperative bleeding, and the need for an externalized nephrostomy tube, which requires postoperative maintenance and can lead to associated UTI or be inadvertently removed at home. The owners whose dogs had SENL performed reported that the animals required minimal postoperative care, and the hospitalization times were no different between PCNL and SENL (48 hours).

The efficiency and successfulness of ENL depend on the technologic characteristics and effectiveness of the lithotripsy device. In the study reported here, a dual ultrasonic lithotriptor was used for 12 of the 16 renal units. This device is larger than the Hol:YAG alternative, making the required renal-access sheath larger (24F vs 14F to 15F). Despite the larger size of the stoma, the authors consider the dual ultrasonic device to be the lithotriptor of choice. This device is comprised of an ultrasonic handpiece with a dual high-frequency-low-frequency coaxial concentric probe (2.77-mm-diameter inner probe and 3.75-mm-diameter outer probe).38 It can penetrate and fragment all stone types without causing trauma to the renal pelvic tissue. In addition, there is a large working channel to the endoscope that accommodates suction during the procedure so that the stone fragments can be easily aspirated, avoiding the need for manual retrieval and thereby enhancing the efficiency of the procedure.38 The dual ultrasonic lithotriptor also penetrates uroliths in significantly less time than other lithotriptors,39 and its use was associated with no adverse events or mechanical malfunctions in the patients of the present study.

The Hol:YAG laser lithotriptor was used in 1 patient of the present study. Because of the small diameter of the laser fiber (400 microns), a traditional cystoscope can be used, allowing for a smaller renal-access sheath to accommodate the endoscope (12F to 18F). This laser will fragment all urolith types effectively, but each fragment will need to be manually removed with a retrieval grasper or basket, which is a tedious process and adds to total anesthesia and surgical times. The laser can also cause substantial renal pelvic damage if the laser fires into the tissue inadvertently, which can result in renal bleeding. A large amount of sediment is also created, which can easily pass down the ureter, resulting in a ureteral obstruction.40 It is therefore important that copious ureteral lavage be performed before the procedure is completed. Regardless of these disadvantages, the outcome was successful for the 1 patient treated with a Hol:YAG laser device in the present study.

The final option used for nephrolith removal in the study reported here was manual stone retrieval. This approach is typically reserved for uroliths that are small enough to fit through the access sheath en bloc and allows basket and grasper retrieval of the urolith without fragmentation. Three renal units were treated by manual stone retrieval in the present study, and no procedural complications were noted, but the affected patients had the smallest of all nephroliths in the study.

Most (10/12) of the patients in the present study had bilateral nephroliths. The decision to perform staged ENL versus bilateral ENL typically depends on many factors, including patient comorbidities, anesthetic risk, intraoperative complications, owner willingness to travel, and additional financial burden associated with staged procedures. Typically, we recommend a staged procedure to reduce anesthesia and surgery times for patients with bilateral disease. However, in the circumstances of the study, a bilateral approach was used for 2 patients and a staged approach for 2 patients. No complications were noted during the bilateral SENL procedures, although the median procedure time was 225 minutes, which was higher than that of unilateral SENL (180 minutes).

Every dog in the present study had a ureteral stent placed after ENL for a period ranging from 1 to 20 weeks. These stents were placed to protect the ureter from any debris from the renal pelvis passing into the ureter and resulting in a ureteral obstruction. Blood clots, mineral debris, and fibrin can accumulate and result in a ureteral obstruction. Ureteral stents are reportedly well tolerated by dogs and can effectively induce passive ureteral dilation.41 The stents were removed in a minimally invasive manner in all dogs without complication. Partial ureteral obstruction occurred in only 1 renal unit in which a stent had been placed, and this was noted 6 weeks after ENL. Removal of the cystine-encrusted stent resolved this partial obstruction.

The goal of nephrolithotomy is complete removal of the nephrolith. In human medicine, the single-procedure stone-free rate for PCNL is higher than that for ESWL, for comparably sized nephroliths.42,43 Higher postoperative stone-free rates decrease the need for secondary or salvage procedures. Given this goal of complete nephrolith removal, the present study had a higher stone-free rate (15/16 [93%] renal units) than that reported for ESWL (approx 85%) in veterinary medicine.31

Once patients were free of nephroliths in the study reported here, preventative measures were taken on the basis of nephrolith composition, including regular follow-up imaging, hematologic analysis, and urine bacterial culture as well as appropriate dietary management and chelation treatment. Interestingly, 5 patients had nephroliths removed because of chronic UTI, and afterward only 1 patient had a documented UTI, which was noted 4 years after ENL and deemed not recurrent. This finding may have suggested that nephrolith removal should be considered for dogs with chronic UTI and concurrent nephrolithiasis.

The median duration of follow-up for the patients of the present study was 557 days, and 5 of 12 patients remained alive at the time of last follow-up. Four of 7 patients died of suspected renal-related problems during the study period, but none of these deaths were considered associated with the nephrolith. What remains unknown is whether the progression of renal disease was due to the presence of the nephroliths prior to ENL, the ENL procedure, or CKD. Patients with IRIS stage 1 or 2 kidney disease at the time of diagnosis had a significantly longer median survival time (1,007 days) than those with stage 3 or 4 kidney disease (102 days). For comparison, previously reported median survival times for dogs with kidney disease are 400 days for those with stage 1 disease, 200 to 400 days for those with stage 2 disease, 110 to 200 days for those with stage 3 disease, and 14 to 80 days for those with stage 4 disease,44,45 suggesting some benefit of ENL for dogs with stage 1 or 2 and stage 4 disease. However, whether such a benefit exists would need to be explored further, particularly given the small sample size of the present study.

Limitations of the present study included the small number of dogs, inclusion of only 1 cat, retrospective nature of data collection, and differences in nephrolith composition among included patients. Without information regarding pre- and postoperative GFR, the renal-sparing nature of ENL could not be conclusively determined. One advantage of the study was that the same clinicians performed all procedures and managed all patients, so each case was more standardized than a traditional retrospective study might allow.

To the authors' knowledge, the present study represented the first in which ENL was evaluated for the treatment of nephrolithiasis in dogs and cats. With good long-term success achieved for many patients, ENL appeared to be a safe and effective procedure as an alternative to traditional surgery for complicated nephrolithiasis in dogs and possibly cats, although more research would be required to substantiate these findings for cats given that only 1 cat was evaluated. Proper training in the equipment used for ENL is recommended prior to attempting these procedures, and additional prospective studies are required to evaluate the effects of ENL on GFR in cats and dogs. Further investigation into the safety and usefulness of ENL by the SENL and PCNL approaches would be necessary prior to routine recommendation for stones that are not clearly problematic.

Acknowledgments

No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.

Presented in part in abstract form at the American College of Veterinary Internal Medicine Forum, Seattle, June 2013; and the ACVS Symposium, San Antonio, Tex, October 2013.

ABBREVIATIONS

CKD

Chronic kidney disease

ENL

Endoscopic nephrolithotomy

ESWL

Extracorporeal shockwave lithotripsy

GFR

Glomerular filtration rate

Hol:YAG

Holmium:yttrium-aluminum-garnet

IRIS

International Renal Interest Society

PCNL

Percutaneous nephrolithotomy

SENL

Surgically assisted endoscopic nephrolithotomy

SUB

Subcutaneous ureteral bypass

UPJ

Ureteropelvic junction

UTI

Urinary tract infection

UVJ

Ureterovesicular junction

Footnotes

a.

Cook Medical, Bloomington, Ind.

b.

Omnipaque injection, Amersham Health Inc, Princeton, NJ.

c.

Weasel Wire 0.035-inch hydrophilic angle-tipped guidewire, Infiniti Medical LLC, Menlo Park, Calif.

d.

Renal-access sheath set (18, 24, and 30F), Cook Medical, Bloomington, Ind.

e.

Peel-Away introducer sheath, Cook Medical, Bloomington, Ind.

f.

Amplatz renal dilator set, Cook Medical, Bloomington, Ind.

g.

Ultraxx nephrostomy balloon, Cook Medical, Bloomington, Ind.

h.

Bard Medical, Covington, Ga.

i.

OES Pro nephroscope (30° lens), Olympus America, Southborough, Mass.

j.

Rigid endoscope (2.7 mm; 30° lens), Richard Wolf, Vernon Hills, Ill.

k.

Rigid endoscope (2.7 mm; 30° lens), Karl Storz Endoscopy, Culver City, Calif.

l.

Cyberwand dual ultrasonic lithotriptor, Olympus Medical, Southborough, Mass.

m.

Reusable 3-wire helical retrieval baskets, Hobbs Medical, Stafford Springs, Conn.

m.

4-wire basket with 3-ring handle, Olympus Medical, Center Valley, Pa.

o.

4-wire foreign body basket, Medi-Globe, Tempe, Ariz.

p.

6-wire foreign body basket, Medi-Globe, Tempe, Ariz.

q.

Falcon rotatable retrieval basket, US Endoscopy, Mentor, Ohio.

r.

Foreign body retriever-grasper with forked jaws, Medi-Globe, Tempe, Ariz.

s.

Caesar grasping forceps, Cook Medical, Winston-Salem, NC.

t.

4-prong reusable retrieval forceps, Hobbs Medical, Stafford Springs, Conn.

u.

Pentapod grasping forceps, Olympus America, Center Valley, Pa.

v.

Odyssey 30-W Hol:YAG laser, Convergent Laser Technology, Alameda, Calif.

w.

Double-pigtail ureteral stents (2.5, 3.7, and 4.7F), Infiniti Medical LLC, Menlo Park, Calif.

x.

InLay stent (4.7F), Bard Medical, Covington, Ga.

y.

Infiniti Medical LLC, Menlo Park, Calif.

z.

Surgilast tubular elastic dressing retainer, Derma Sciences Inc, Princeton, NJ.

aa.

PDS plus antibacterial suture, Ethicon US, Cincinnati, Ohio.

bb.

SAS, version 9.4, SAS Institute Inc, Cary, NC.

cc.

Urinary SO diet, Royal Canin, St Charles, Mo.

dd.

Hill's prescription diet k/d, Hill's Pet Nutrition Inc, Topeka, Kan.

ee.

Hill's prescription diet u/d, Hill's Pet Nutrition Inc, Topeka, Kan.

ff.

Hill's prescription diet s/d, Hill's Pet Nutrition Inc, Topeka, Kan.

gg.

Storz Calcuson, Karl Storz Endoscopy, Culver City, Calif.

hh.

NorfolkVet, Skokie, Ill.

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