Case Study: Percutaneous Nephrolithotomy

By Allyson Berent, DVM, DACVIM and Chick Weisse, VMD, DACVS

• Signalment: 3 year old spayed female Bichon frise
• Presenting complaint: Recurrent urinary tract infections and intermittent hematuria
• Past pertinent history: 2 years of recurrent intermittent dysuria, hematuria and pollakiuria with 3 documented urinary tract infections consisting of Staphylococcus spp.
• Previous diagnostics performed:
  1) Urinalysis: USG 1.021, pH 8.0, too numerous to count cocci bacteria/hpf, 10-20 WBC/hpf, 5-10 RBC/hpf, protein 3+
  2) Urine culture: Staphylococcus intermedius >100,000 colonies
  3) CBC: WNL
  4) CHEMISTRY PANEL: BUN 38 mg/dL, Creatinine 2.1 mg/dL (slightly elevated)
• Previous medications: Clavamox (15 mg/kg PO BID 14 days) 4 different treatments periods.
• Progression: Each course of antibiotics improved the dysuria and hematuria. These signs recurred within 1-4 weeks after discontinuation of antibiotics.
• Physical examination: Bright, alert, good body condition. Slightly hooded vulva
• Problem list:
  1) Recurrent urinary tract infections
  2) IRIS stage 2 CKD (elevated creatinine with low specific gravity)
• Differential diagnoses:
  1) Pyelonephritis
  2) Possible urolithiasis (suspected struvite)
• Further diagnostics:
  • Abdominal Radiographs: Figure 1
  • Abdominal Ultrasound: large nephrolith in each kidney measuring 3.5 cm on Left and 2.8 cm on Right. Small bladder stones (<2 mm)
• Diagnosis:
  1) Bilateral Staghorn Nephrolithasis: Suspected struvite stones
  2) Cystolithiasis
• Treatment decisions:
  Based on the positive Staphylococcus urine culture with staghorn stones in both renal pelvis’ and an elevated urine pH, the cause of the azotemia is likely associated with chronic pyelonephritis that is associated with struvite nephrolithiasis. Typically, if stones are made of struvite, or magnesium ammonium phosphate, they can be medically dissolved with the use of a dissolution diet (either acidifying or neutralizing) and appropriate antibiotic therapy. This must be followed strictly for effective dissolution. For nephroliths this can take 3-9 months for appropriate dissolution. Many struvite nephroliths contain some calcium apatite or a calcium oxalate shell, and they will then not dissolve well. Radiographs and a urine culture should be taken every month to confirm no bacterial growth and the stones are not getting larger. If by 3 months the stones are not getting smaller then removal may be necessary.

  This patient was followed for 5 months with serial negative urine cultures and radiographs. The nephroliths did not change in size and minimally invasive removal was elected with the use of staged bilateral percutaneous nephrolithotomy (PCNL) scheduled 6 weeks apart. With the use of intracorporeal ultrasonic lithotripsy (Figure 3) the stones were able to be successfully removed without complication, avoiding a nephrotomy.

• Outcome:
  The left side was treated first and the entire stone was able to be removed through a small sheath using nephroscopy and lithotripsy. A ureteral stent was then placed prophalactically to prevent any edema or fragments from obstructing the ureter. (Figure 4) Six weeks later the same was done on the right side. Four weeks after both kidneys were completed the patient had a cystoscopy performed for bilateral ureteral stent retrieval. Over the course of the following 1.5 years there were no recurrent urinary tract infections, no uroliths detected on serial radiographs or ultrasound and the creatinine improved to 1.2 mg/dL. The dog was maintained on a neutralizing stone diet.
• Discussion:
  Urolithiasis is a common clinical problem in small animal veterinary patients. In the past, nephroliths were treated medically, via dissolution, or removed by surgical nephrostomy, nephrectomy or pyelotomy. Management of calculi can be challenging in small animals as the incidence of stone recurrence in dogs and cats is high. Many canine and feline nephroliths remain static in size and clinically silent for years. Some controversy still exists as to whether non–obstructive kidney stones worsen underlying kidney disease. Their removal is typically recommended if the stones are growing, if there is a partial or complete ureteropelvic junction (UPJ) obstruction resulting in progressive hydronephrosis, renal parenchymal loss, worsening renal function, chronic hematuria, pain, or recurrent infections.

  In small animals, traditional surgical interventions are met with complications that can be severe and life-threatening. Nephrotomy has been associated with severe hemorrhage, decreased renal function, remaining nephrolith fragments causing ureteral obstructions, and urinary leakage. In a study of normal cats, there was a 10-20% decrease in the GFR of the ipsilateral kidney after a nephrotomy. This was clinically insignificant in normal cats, but in a clinical patient, who has maximally hypertrophied the remaining nephrons due to prior nephrolith induced damage, the significance could be dramatic. Therefore, patients with an already compromised GFR from chronic stone disease, may develop a clinically significant decline in renal function. Also, knowing that over 30% of adult cats will develop chronic kidney disease in their lifetime, resulting in a 67-75% decline of renal function, they can not tolerate a 10-20% further decline in GFR from a nephrotomy. Hence, this procedure should ultimately be avoided whenever possible. Similar studies have not been done in clinical dogs to date, only normal dogs without exhausted hypertrophy mechanisms, which would not be considered clinically equivalent to our patient population.

  In humans the treatment of choice is typically minimally invasive in nature consisting of ESWL for nephroliths smaller than 2cm and percutaneous nephrolithotomy (PCNL) for nephroliths larger than 2 cm. Open surgery and laparoscopy is usually considered necessary after other less invasive options have failed or have been deemed inappropriate, and is rarely necessary. These, and many other human studies have shown ESWL and PCNL to have a minimal effect on the GFR of clinical stone forming patients, particularly when compared to traditional surgical nephrotomy. These procedures, particularly PCNL, has been shown to be highly effective in removing all stone fragments, as endoscopic calyceal inspection is superior for visualization and fragment retrieval.

  In small animals, if extracorporeal shockwave lithotripsy (ESWL) fails, is not available, there are cystine stones (EWSL resistant), or the stone is larger than 15 mm, then a PCNL is considered. PCNL has been performed in a handful of canine patients to date, as well as a feline patient. Typically, this is done using a combination of ultrasonographic, endoscopic and fluoroscopic guidance. Patient size is less of a factor for PCNL than for ureteroscopy, as the smallest canine patient that had successful PCNL was only 3.1 kg.

  Typically, for PCNL, the renal pelvis is accessed through the greater curvature of the kidney with ultrasound guidance using a renal access needle. Subsequently, using fluoroscopic guidance, a sheath (12-30 french) and balloon dilation catheter combination is advanced through the renal parenchyma into the renal pelvis over a guidewire, onto the offending nephrolith. A mini-PCNL approach using an 18 or 24 French access kit is used. Once the sheath is in the renal pelvis, a nephroscope is used to identify the stone(s). If small enough, a stone-retrieval basket is used to remove the stone. If the stone(s) are larger than the sheath then intracorporeal lithotripsy is used for stone fragmentation (ultrasonic, electrohydraulic or Hol:YAG laser). (Figure 2). This is all guided using fluoroscopic (Figure 3) and endoscopic guidance. Once the stones are small enough to fit through the sheath, they are removed and a locking-loop nephrostomy tube (5 or 6 french) is left in place to allow the small hole to seal and form a nephropexy.

  Surgical assisted nephroscopic lithotripsy is performed by using a rigid endoscope during an open laparotomy, resulting in excellent magnification of the renal pelvis for stone retrieval. The same procedure as above (PCNL) can be performed via laparotomy, rather than percutaneously, termed nephroscopic guided lithotripsy. The greater curvature of the kidney is punctured with a renal puncture needle and a pyelogram is performed. A guidewire is then advanced into the renal pelvis using fluoroscopic guidance and a balloon dilation catheter, pre-loaded with a matching sheath, is advanced over the wire onto nephrolith. The balloon is dilated and the sheath slides right over the balloon with a smooth transition. The balloon is withdrawn and the scope is inserted through the sheath for stone removal. By using a balloon/sheath combination there is very little risk of hemorrhage as this creates a tamponade effect and the renal parenchyma is spread apart with the balloon, not cut with a scalpel blade, making renal damage dramatically less then that with a nephrotomy. If this is done surgically then a nephrostomy tube is not necessary as the hole can be closed by directly suturing the renal capsule to prevent leakage. Because a balloon is used to dilate the renal parenchyma, minimal nephron loss occurs and the tissue is compressed via balloon dilation rather than being incised. This is now being performed routinely on canine kidneys in the authors’ practice to date and has been highly successful.

  Unlike a nephrotomy, these minimally invasive procedures do not require transient occlusion of renal vessels and results in a much smaller hole in the renal parenchyma than a nephrotomy. Placing sutures in the capsule and apposing the small incision can close the renal access point. Care must be taken to assess all areas of the renal pelvis and renal calyces, as small calculi can remain if concurrent fluoroscopy and contrast nephrography are not used concurrently. The authors recommend the use of concurrent fluoroscopy, as is recommended in human urology. (Figure 3)
  
  After the procedure a ureteral stent is placed to protect the ureter from any small fragments from causing an obstruction. (Figure 4). This is then removed 4-6 weeks later cystoscopically.

• IR/IE Tip:
  Nephroliths rarely cause a problem in canine or feline patients unless they results in recurrent urinary tract infections, progressive azotemia, pyelectasia or hydroureter. This is seen in about 10% of patients with nephroliths in the authors’ experience. When stones need to be removed the 3 main options currently considered in the authors practice are: 1) medical dissolution: for struvite or urate (if associated with a hepatic vascular anomaly) stones only, 2) Extracorporeal shockwave lithotripsy (ESWL): For any stone under 1.5 cm other than a cysteine stone, 3) Intracorporeal Nephrolithotripsy: For any stone >1.5 cm causing a clinical problem.

  Recurrent urinary tract infections should incite further investigation with advanced imaging like radiographs and ultrasound. If an alkaline urine pH with a urease producing bacteria is detected on urine culture and urinalysis then radiographs should be taken for evaluation of magnesium ammonium phosphate (struvite) stones.

***for more case examples and to see how interventional radiology and interventional endoscopy (IR/IE) can benefit your patients please visit: http://www.amcny.org/interventional-radiology-endoscopy

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LEGEND

Figure 1: Radiograph of a female dog with bilateral large staghorn nephroliths.
 

Figure 2: Endoscopic image during intracorporeal lithotripsy for removal of large struvite nephrolith. Notice the large yellow stone inside the renal pelvis. The lithotrite is fragmenting the stone into small pieces for removal.

Figure 3: Fluroscopy image during PCNL procedure. A) Patient with sheath (black arrow) inside kidney onto large nephrolith (white asterick). A safety guidewire is down the ureter (white arrows). B) :Nephroscope (white arrow) inside the renal sheath as the large nephrolith is fragmented (black arrowheads). C) Image after nephroliths is removed. D) Ureteral stent(white arrows) in place to protect the ureter.

Figure 4: Post operative radiograph of female dog after nephroscopic lithotripsy of the left nephrolith. Notice the double pigtail ureteral stent that was placed after stone removal for ureteral protection.

• References: more available upon request

  Raza A, Turna B, Smith G, et al. Pediatric urolithiasis: 15 years of local experience with minimally invasive endourological management of pediatric calculi. J of Urol. 2005;174: 682-685.

  Donner GS, Ellison GW, et al. Percutaneous nephrolithotomy in the dog: An experimental study. Vet Surg 1987; 16(6): 411-417.

  Al-Shammari AM, Al-Otaibi K, Leonard MP, et al: Percutaneous nephrolithotomy in the pediatric population. J of Urol 162: 1721, 1999

  Lennon GM: Double pigtail ureteric stent versus versus percutaneous nephrostomy: effects on stone transit and ureteric motility. Eur Urol 31(1):24, 1997