Percutaneous Nephrolithotomy in Children

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Percutaneous Nephrolithotomy in Children

Adam S. Howe,¹ Jordan S. Gitlin,¹ & R. John D’A. Honey²

¹ Department of Pediatric Urology, Cohen Children’s Medical Center, Zucker School of Medicine at Hofstra/Northwell, Long Island, NY, USA

² Department of Surgery, University of Toronto, Toronto, ON, Canada

Introduction

Rupel and Brown reported on the first pediatric patient having a renal calculus removed via a nephrostomy tract in 1941 [1], but it was not until 1985 that Woodside et al. presented the earliest series of percutaneous nephrolithotomy (PCNL) in children [2]. In this study, seven patients aged 5–18 years old were treated successfully using adult‐sized instruments and equipment. Over the years, the development of smaller nephroscopes and instruments, along with advancements in the form of more efficient energy sources, have resulted in PCNL replacing open surgery for treating both adults and children with large stone burdens, with PCNL monotherapy having stone‐free rates approaching 90% [3–5]. Most recently (2015) Lee et al. found PCNL in pediatric patients to be safe and efficacious compared to a matched adult cohort, with similar rates of second‐look nephroscopy, length of stay, and complications [6]. There was, however, a higher requirement for a second access tract in the pediatric cohort (15.4%) compared to adults (4.52%). The authors postulated that this was because the small access tracts used in the pediatric cohort made it more difficult to clear the stone burden and another tract was necessary in order to accomplish this without placing too much torque on the tract [6]. PCNL has even been performed successfully in children who have had previous PCNL or open pyelolithotomy, with stone‐free rates of 79.17% and only 4.2% requiring blood transfusion [7].

Indications

Although there are no absolute indications for PCNL in children over any other treatment modality by any current consensus, relative indications include a large stone burden (>2 cm) in the upper urinary tract, lower pole stones larger than 1 cm, an anatomic abnormality which impairs drainage and stone clearance, certain metabolic abnormalities such as cystinuria, or known struvite stone composition [8]. Proper diagnosis is essential as staghorn calculi may be confused with nephrocalcinosis, a condition most often managed nonsurgically [9]. The most recent American Urological Association (AUA) guidelines for treatment of stones in children recommend that PCNL and extracorporeal shock‐wave lithotripsy (ESWL) are reasonable treatment options for total renal stone burdens larger than 2 cm. They also recommend that a low‐dose, noncontrast computed tomography (CT) scan be obtained prior to PCNL (having the patient in the prone position during CT can be helpful for surgical planning). For patients with questionable function of the renal unit with stones, the panel recommends that a functional study such as a DMSA or MAG3 nuclear renal scan be performed to ascertain if alternative treatment (e.g. nephrectomy) is needed [10].

Risks

PCNL carries many risks, such as failure to remove all stone fragments, bleeding either immediately post operative, requiring blood transfusion, or delayed renal hemorrhage (both of which may require angioembolization), urine leak requiring stent placement, injuries to adjacent organs (most commonly bowel), inadvertent entry into the chest cavity (pneumothorax, hemothorax, urothorax), and sepsis. A preoperative urine culture should be checked two to three weeks prior to surgery and treated if positive. Broad‐spectrum intravenous antibiotics should always be given at the time of the procedure even if the cultures are negative. The AUA guidelines also recommend that a complete blood count including platelet count be obtained before PCNL [10].

Pediatric concerns

Although PCNL has been shown to be safe and effective in the adult population, it is not as well established in pediatric populations. Historically, urologists were reluctant to perform this operation in children due to the concerns about parenchymal damage and subsequent insults to renal function from the large adult‐size instruments. In the early days of PCNL, smaller/pediatric equipment did not exist. Figure 27.1 demonstrates how the smaller body types of children (Figure 27.1a) have less distance from collecting system to skin (along with total body surface area) than adult patients (Figure 27.1b). Major surgical complications such as bleeding and sepsis when there are fewer invasive options, along with increased radiation exposure from prolonged fluoroscopy, are other considerations that make pediatric providers hesitant to perform PCNL. In addition, there is increased potential for hypothermia along with its sequelae (e.g. coagulopathy) and hyponatremia (e.g. seizures, coma) due to prolonged exposure to irrigation. To decrease the risk of hypothermia, warm isotonic solutions should be used for irrigation, along with warming the operating room, proper draping, monitoring of body temperature throughout the case, and limiting operative times to less than 90 minutes. Warm saline should be used for irrigation whenever feasible, although this would have to be switched to warm water or glycine if an electrosurgical procedure is performed, despite the risk of dilutional hyponatremia.

Image described by caption. — **Figure 27.1** (a) CT scan of a 9‐year‐old male showing a skin‐to‐collecting system distance of 2.5 cm, compared to (b) that of a 44‐year‐old woman with a skin‐to‐collecting system distance over three times longer (8.5 cm). This demonstrates how the spinal needle should not be inserted as deep during access in younger patients.

Patient positioning

The procedure is almost always performed under general anesthesia. The patient is first placed in dorsal lithotomy position and an open‐ended ureteral catheter is advanced to the level of the proximal ureter (Figure 27.2a). The ureteral catheter size chosen will vary depending on the size of the patient. Figure 27.3 shows the smaller sized ureteral catheters which can be used in children. In the smallest of children, a 3 Fr open‐ended catheter is used. The ureteral catheter is left in place with the proximal end within the ureter, and a Foley catheter is placed alongside this for bladder drainage. The patient is then faced prone, with the flank elevated 30° for percutaneous access. Care must be taken to protect and cushion all body parts [11]. If the patient is large enough, they may be placed in the prone position initially with flexible cystoscopy used for ureteral catheterization. This modification obviates the need for repositioning and will aid in decreasing surgical and anesthesia time. Certain patients within the pediatric population who are prone to urinary stone disease offer a special set of challenges in performing PCNL. These patients include those who are wheelchair‐ or bed‐bound, and patients with spina bifida. Patients with spina bifida can have existing spinal hardware which may restrict spinal mobility, impede percutaneous needle placement, and hinder radiographic imaging during the case.

In this patient population, latex‐free catheters should be used. Many of these patients may also have limb contractures which makes positioning difficult, and care must be taken to place the extremities in the most comfortable position without excessive flexion and tension on the joints. The risk of pneumothorax is increased with scoliosis, kyphosis, or lordosis due to altered renal anatomy [12]. Patients who are paraplegic or quadriplegic have been shown to have worse outcomes after PCNL, as Danawala and Singh showed, with these patients being three times as likely to suffer a complication from the procedure than nonparaplegic/quadriplegic patients [13]. Supine PCNL has also been reported, with patients placed in a modified supine position with flexion of the ipsilateral hips and shoulder. Desoky and colleagues were able to achieve stone‐free rates of 90.9% with a mean operative time of 65 minutes in 22 children with renal pelvic stones of 2–3 cm [14], while Gamal et al. achieved stone‐free rates of 92.5% in 27 children with an operative time of 41 minutes [15]. One patient in each study encountered bleeding that required a blood transfusion.

Access and tract dilation

A ureteral catheter is placed via the bladder, and is injected with contrast for retrograde pyelography to define the collecting system. Ultrasound guidance can also be used to assist with access to the collecting system, which normally lies in the posterior axillary line. A rotating C‐arm is used for biplanar fluoroscopic visualization of the collecting system in the anterior–posterior and oblique positions throughout the procedure. The most optimal tract is determined using the “bullseye” technique (Figure 27.2b). Ideally this would be posterior, and yield direct access, with the shortest distance to the stone, especially when a calyceal diverticulum and/or infundibular stenosis are present. However, for more complex stones or lower pole stones, upper pole access is advantageous as this provides access to both the lower pole calyces, renal pelvis, and ureter [16]. Caution must be taken as this location for access carries increased risk of pneumothorax.

A 21 gauge spinal needle is used to access the desired calyx with return of urine confirming correct placement (Figure 27.2

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