Over the past 3 decades, minimally invasive stone surgery has completely overtaken open surgical approaches to upper tract pediatric urolithiasis. Progressing from least to most minimally invasive, extracorporeal shock wave lithotripsy, ureteroscopy, and percutaneous nephrolithotomy are the surgical methods of today for kidney and ureteral stones. The choice of treatment modality is individualized in children, considering patient age, stone size, number, location, and anatomic and clinical contributing factors. The purpose of this article is to review these techniques for pediatric upper urinary tract stones and summarize outcomes and complications.
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In children, the choice of stone treatment modality is individualized, considering patient age, stone size, number, location, and anatomic and clinical contributing factors.
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When surgical intervention is warranted for pediatric urolithiasis, extracorporeal shock wave lithotripsy (ESWL) and ureteroscopy (URS) provide effective, safe, minimally invasive outpatient options for less complex cases, each with inherent advantages and disadvantages.
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When faced with complex stone disease, percutaneous nephrolithotomy (PCNL) with or without adjunctive ESWL is useful but carries higher risks.
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Given that stone disease is increasing in children in the United States and, if left untreated, can lead to loss of a kidney or renal function, it is comforting to know that minimally invasive treatments performed by pediatric urologists expert in urolithiasis surgery are effective.
Introduction
As in adults, the vast majority of urinary stones in children become symptomatic or detected when present within the upper urinary tract (kidneys and ureters). Although a stone may sit in the upper urinary tract for weeks to years, renal colic only ensues when the stone moves to a location that partially or completely obstructs the flow of urine, causing stretch of the kidney, renal pelvis, and possibly ureter. Stones typically become obstructing in 3 locations within the ureter, namely, the ureteropelvic junction (UPJ), the ureterovesical junction (UVJ), and where the ureter crosses the common iliac vessels. Rarely, stones are trapped within the kidney in a renal calyx behind a narrow infundibulum or a calyceal diverticulum ( Fig. 1 ). Staghorn calculi, which partially or completely fill renal calyces and renal pelvis, require surgical therapy because they are unable to pass. Otherwise, for simple renal or ureteral stones, a trial of stone passage may be permitted depending on the size of the stone. Whereas hydration, antiemetics, and analgesics were previously all that was offered during renal colic episodes not complicated by urinary tract infection (UTI), now α 1A -adrenergic receptor antagonists, such as tamsulosin, are administered to selectively relax distal ureteral smooth muscle in adults and children. Although not Food and Drug Administration approved for use in children, one recent prospective randomized pediatric trial has shown off-label use of α 1A -blockers to have significant efficacy, increasing stone passage rates, decreasing days until stone passage, and providing pain relief during passage of stones less than 12 mm.
If 14 days of α 1A -antagonist therapy have not resulted in stone passage, if pain is uncontrolled, if UTI occurs, or if vomiting prevents medication efficacy, then surgical intervention for stone removal is typically required. Fortunately, several surgical approaches are available ( Table 1 ) that are minimally invasive, relatively safe, and efficacious; the choice of which approach to use is dictated by the scenario of each patient.
| ESWL | Ureteroscopy | PCNL | |
|---|---|---|---|
| Typical use | Simple renal or ureteral stones <1–2 cm | Simple renal or ureteral stones <1–2 cm | Staghorn or multiple larger stones |
| Anesthesia | General | General | General |
| Service | Outpatient | Outpatient | Inpatient (2–6 days) |
| Site of entry into body | None, waves pass through skin to stone (extracorporeal) | Through the urethra, bladder, and ureter to the ureter/kidney stone | Tubes are passed through the flank skin into kidney (percutaneous) |
| Stone removal rate | 44%–95% | 50%–100% | 70%–90% |
| Need for second surgery | Low-moderate | Low | Moderate–high (planned second PCNL typically done at same hospitalization) |
| Success depends on spontaneous stone fragment passage | Totally | Partially | ∼None |
| Need for ureteral stent postoperatively | Very low | High (usually for 3–5 days postoperatively and removed in office) | High (usually removed before discharge) |
| Need for nephrostomy tube postoperatively | None | None | High |
| Complications | 0%–18% (Pain, bleeding, sepsis, retention, ureteral obstruction, UTI, ureteral stricture) | 0%–8% (Renal colic, gross hematuria, febrile UTI, ureteral stricture, ureteral perforation or ureteral avulsion) | 0%–30% (Self-limited urine leak, urine leak requiring stent, fever, hematuria requiring transfusion, colon injury, perforation, sepsis, vascular injury, pneumothorax, and hydrothorax) |
| Possibility of adjacent organ injury | Very low | None | Low (lung, colon) |
| Need for blood transfusion | None | None | <5% |
| Days off from school/work | Up to 7 | Up to 14 | Up to 20 |
Extracorporeal shock wave lithotripsy
ESWL is a noninvasive, outpatient technique for the surgical approach to kidney and ureteral stones. Beginning in 1986, ESWL has been routinely used in children and is now widely accepted despite lack of Food and Drug Administration approval for pediatric use. The joint European Association of Urology (EAU)/American Urological_Association (AUA) Nephrolithiasis Guideline Panel’s “2007 Guideline for the Management of Ureteral Calculi” states, in reference to recommendations for the pediatric patient: “…Treatment choices should be based on the child’s size and urinary tract anatomy. The small size of the pediatric ureter and urethra favors the less invasive approach of ESWL.” Thus, ESWL remains a first-line treatment option for most pediatric upper tract urinary calculi.
ESWL Technique
Modern-day lithotriptors use an external generator to create pulses of energy that are subsequently generated into shockwaves. These shockwaves are transmitted through a flexible treatment head covered with gel (for acoustic coupling) that is compressed against the patient’s body. Shockwaves travel through the body and are focused at the target (stone), wherein collective force is created to break up the stone. Breakage is accomplished by cavitation, the formation and subsequent collapse of bubbles at the surface of the stone. If successful stone shattering occurs, stone fragments must then be spontaneously passed through the urinary tract and voided per urethra. Unfortunately, spontaneous stone fragment passage is variable.
ESWL is performed using fluoroscopy, ultrasonography, or a combination of fluoroscopy and ultrasonography to localize and target the stone 3-D, thereby correctly positioning the treatment head on the skin to focus the shockwaves on the stone ( Fig. 2 ). Anesthetic requirements may be minimized in adults undergoing ESWL, with some tolerating the procedure with only intravenous sedation. Pediatric cases, however, require general anesthesia because patient movement can shift the stone off target, losing stone fragmentation efficacy if not readjusted back on target.
For the majority of ESWL cases, there is no associated UTI and the size of the stone (stone burden) is low. For the remaining cases, however, consideration should be given to placement of a ureteral stent, an internal tube spanning from the renal pelvis to the bladder for urine drainage ( Fig. 3 ). The EAU/AUA Nephrolithiasis Guideline Panel states, “routine [ureteral] stenting is not recommended as part of ESWL,” based on Panel consensus and level III evidence. When treating staghorn stones with ESWL monotherapy, one group reported similar stone-free outcomes in stented versus nonstented children (78% vs 79%); however, unstented children were found to have more major complications (21% vs 0, P = .035) and longer hospital stays (6.4 vs 4.6 days, P = .022) than stented children. Nevertheless, surgeons may elect to place stents before ESWL in specific scenarios, such as sepsis, obstruction, solitary kidney, and anomalous anatomy, or to facilitate retrograde pyelography for stone localization.
ESWL Outcomes
There is wide variation in reported success rates after ESWL, because some investigators declare that stone fragments less than 4 mm to 5 mm after ESWL are “clinically insignificant residual fragments” and thus success has been achieved, whereas others require complete absence of fragments to be deemed stone-free. Afshar and colleagues evaluated children with small residual fragments (<5 mm) after ESWL and concluded that these fragments were clinically significant, increasing risk for adverse clinical outcomes (either growth of the fragment or clinical symptoms) compared with children who were rendered completely stone-free (odds ratio 3.9; 95% CI, 1.5–9.6). Moreover, use of different imaging modalities (potentially underestimating stone burden) and variable timing at post-ESWL imaging (potentially not allowing all fragments to pass spontaneously) may contribute to variable reporting of success.
Overall stone-free rates for ESWL in children range from as low as 44% after a single session to 95%. Retreatment rates (additional ESWL sessions) have been reported to occur in 10% to 54%.
Children have been shown to have a greater propensity for passing stone fragments after ESWL than adults (95% vs 79%, P = .086). This may be attributed to the shorter length and greater elasticity of the pediatric ureter. Additionally, multiple studies have demonstrated that successful ESWL outcomes are achieved regardless of stone location, including isolated lower pole stones.
As opposed to adults, body mass index does not seem to negatively correlate with stone-free status in children. Skin-to-stone distance (SSD) as measured on noncontrast CT scan has been shown predictive of outcome after ESWL in adults, with SSD greater than 10 cm more likely to fail treatment. The authors’ multicenter study evaluated SSD in children, concluding that on univariate analysis SSD was a statistically significant predictor of success but was not significant on multivariate logistic regression.
Certain stone types, including brushite, cysteine, and calcium oxalate monohydrate, are known to be resistant to ESWL due to their hardness. Thus, knowledge of stone composition or suspicion of stone composition based on preoperative CT Hounsfield units may contribute to decision making for treatment. The authors’ multicenter study identified stone attenuation of less than 1000 Hounsfield units on noncontrast CT scan as a significant predictor of success with ESWL in children, independent of stone size. Total stone diameter has also been shown the only factor to independently predict stone-free status after ESWL, with age, gender, body mass index, and number and location of stones not predictive.
ESWL Complications
Complications after ESWL in children, tabulated from meta-analysis, include bleeding (5%), pain (18%), retention (2%), sepsis (4%), stricture (1%), ureteral obstruction (2%), and UTI (2%).
The process of cavitation as well as shear forces, although beneficial for stone fragmentation, can cause damage to surrounding tissues. Animal studies have shown that a slower delivery of shock waves significantly decreases renal tissue injury. A prospective study by Fayad and colleagues involved obtaining baseline technetium dimercaptosuccinic acid (DMSA) scan and glomerular filtration rate (estimated using diethylene triamine pentaacetic acid [DTPA]) and comparing with studies obtained 6 months after ESWL. In their cohort, no patient developed renal scarring or statistically significant decrease in renal function. Reisiger and colleagues also showed that treatment with ESWL did not impact renal growth in children.
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