The efficacy and parenchymal consequences of extracorporeal shock wave lithotripsy in infants

Authors


Dr H.B. Lottmann, Paediatric Urology Dept, Fondation Hôpital Saint-Joseph, 185 rue Raymond Losserand, 75674 Paris Cedex 14, France. E-mail: uro.inf@worldnet.fr

Abstract

Objectives To determine the efficacy of extracorporeal shock-wave lithotripsy (ESWL) in young children and to evaluate, using renal scintigraphy, any possible adverse effects on renal parenchyma.

Patients and methods From January 1991 to October 1998, 19 infants (aged 5–24 months) underwent ESWL for kidney urolithiasis using a Sonolith 3000 (14 kV, Technomed Corp, Lyon, France) or a Nova (14–20 kV, Direx Medical Systems, Paris, France) lithotripter. The treatment and its effects were evaluated using a physical examination, conventional imaging (plain abdominal X-ray and ultrasonography) and renal scintigraphy 24 h before ESWL and again at least 6 months after the last session of treatment.

Results Ten children were rendered stone-free by ESWL after one session and 18 after two sessions. At the follow-up (8 months to 8 years, mean 36 months) no hypertension was recorded and no acquired parenchymal damage was detected with conventional imaging. No scars or significant variation of differential function attributable to ESWL were identified on renal scintigraphy.

Conclusion ESWL is clearly effective for treating infant urolithiasis. There were no renal parenchymal lesions associated with ESWL, even in previously damaged kidneys or after the treatment of staghorn calculi. A long-term follow-up (assessing blood pressure) is mandatory and renal scintigraphy before and 6 months after ESWL in infants is recommended to confirm these results in a larger series.

Introduction

Since its introduction by Chaussy et al. in 1980 [1] ESWL has considerably modified the management of upper urinary tract lithiasis and has become the therapeutic option in most cases [1]. With a follow-up of nearly 20 years this technique is considered to be efficient, noninvasive and safe for adults and children [2–5]. However, although the efficacy of ESWL is clearly established, its safety for the renal parenchyma, particularly in very young patients whose kidneys are actively growing, has not yet been confirmed. The consequences of extracorporeal shock waves on renal parenchyma remain unclear [6, 7]; renal damage after ESWL has been reported in adults [8]. Thus there may be a rational reluctance to treat very young patients using this method. A preliminary report evaluating potential long-term renal parenchymal damage using DMSA renal scintigraphy before and after ESWL in 15 children (aged 9 months to 15 years) indicated that the technique was safe [9]. The purpose of the present study was to evaluate prospectively the efficacy and potential adverse effects of ESWL in a series of very young patients (< 2 years old at the time of treatment).

Patients and methods

From January 1991 to October 1998, 19 infants (two girls and 17 boys) were treated for renal stones. All children were < 2 years old (5–24 months, mean 15), with a mean (range) weight of 10.3 (6.8–14) kg and a mean height of 77 (61–89) cm. Only one patient was asymptomatic (the renal stone was an incidental finding on plain X-ray); in the 18 remaining patients, acute pyelonephritis led to the diagnosis of renal stone (the main micro-organisms being Proteus mirabilis and Escherichia coli). The evaluation before treatment comprised an abdominal plain X-ray, IVP, VCUG and renal ultrasonography. In all, 24 stones (22 renal and two ureteric) were treated, with a mean (range) size of 14.4 (6–25) mm (multiple in one patient and bilateral in another), comprising 15 left and seven right renal stones (including three complete and four incomplete staghorn calculi), 11 pelvic and four calyceal stones. Two patients also had an associated stone in the pelvic ureter. In 16 patients the stones were visible on a plain X-ray but were poorly calcified in seven; in 3 patients, the stone was located by renal ultrasonography and IVP only. At the time of treatment all the patients had a normal serum creatinine level and blood pressure, and sterile urine; 12 patients were taking antibiotic treatment and seven were not. An abnormality of the urinary tract was detected in six infants; three had low-grade VUR, one a megaureter, one renal malrotation and one a horseshoe kidney.

Renal 99mTc-DMSA scintigraphy was performed 24 h before treatment according to the following protocol:6 h after an intravenous injection with 1 µBq/kg of 99mTc-DMSA, a posterior, lateral and two oblique posterior views were obtained using a gamma camera equipped with a low-energy, high-resolution parallel collimator. Additional pinhole views of each kidney were taken. The scintigrams were assessed qualitatively two independent observers using 128 × 128 or 256 × 256 matrix digitized images; the relative renal uptake was determined after background and depth correction. All the infants underwent a complete metabolic evaluation; only one had an isolated elevated urinary Ca++/creatinine urinary ratio and the rest were normal.

Fifteen infants were treated using a Sonolith 3000 (Technomed Corp, Lyon, France, 14 kV) and four with a Nova (Direx Medical Systems, Paris, France, 14–20 kV) lithotripter, under general anaesthesia with an endotracheal tube. A specially designed device was used to reduce the size of the opening above the generator so that the infants could be positioned safely. Their lungs were protected by applying thick colloidal foam to the skin during treatment; when fluoroscopy was used to target the stone, their gonads were also protected againstX-rays. The infants were also protected against acoustic damage using a headset ( Fig. 1). All the patients received antibiotic prophylaxis (50 mg/kg ceftriaxone injected 1 h before the session).

Figure 1.

The positioning of the patient during treatment with the Nova lithotripter.

For the 15 patients treated with the Sonolith 3000, the stone was targeted using only ultrasonography, by a paediatric radiologist and urologist. For the four patients treated with the Nova system, the stone was targeted fluoroscopically by a trained technician and the paediatric urologist. The number of impacts per session and the total number of sessions were recorded for each patient. A maximum of 3000 shocks was delivered per session and there was a minimum (range) interval of 1 (1–5 months) between sessions. A JJ stent was inserted before treatment in two infants (21 and 24 months old) to prevent steinstrasse. All the patients received an adequate intravenous fluid load during treatment and 0.5 mg/kg of frusemide at the end of each session, to provide optimal conditions for the elimination of stone fragments. Immediately after each treatment the abdominal cavity and urinary tract of the patient was assessed with ultrasonography.

The evaluation after treatment comprised a physical examination, including the measurement of blood pressure, urine culture, an abdominal plain X-ray and renal ultrasonography 24–48 h after each session. This evaluation was repeated 1, 3 (in case of residual fragments only) and 6 months after treatment, and then annually. During the 48 h after treatment, urine and stone fragments were collected, and analysed by crystallography and chemically. A 99mTc-DMSA renal scan was also taken 6 months after the last session of treatment, using the same protocol as before. The scans were compared to identify any acquired parenchymal lesions or assess any significant variation in differential function.

Results

A single ESWL session was sufficient to clear the stones in 10 patients and two sessions were necessary in the remaining nine. The latter group included the infant with a bilateral kidney stone, one with a unilateral renal and ureteric stone, and three of the seven with a staghorn calculus. One patient was treated in two sessions because the first session had to be interrupted after 400 shocks as there was a technical problem with the lithotripter.

The mean (range) total number of shocks delivered per session was 2100 (400–3000) and the total number of shocks per treatment was 1250–6000, when multiple sessions were used. At 1 or 3 months after ESWL, 18 infants were stone-free; only one patient had small residual fragments after 6 months and remained under regular follow-up.

Incidents occurring during treatment were the technical problem with the lithotripter in one patient and one episode of haemoptysis with no radiological consequences, which did not curtail the session. There was no detectable lesion of the treated kidney or surrounding organs on ultrasonography immediately after ESWL. One of the two girls developed steinstrasse and acute pyelonephritis, which required the insertion of a ureteric stent for 4 days and appropriate intravenous then oral antibiotic therapy for 15 days. No infant developed significant pain and all were able to leave hospital after 2 days (these two days being necessary to collect urine samples and fragments, and because some patients lived far from the hospital). For the infants treated in two sessions the mean (range) total hospital stay was 4.5 (4–6) days. All the patients had a cutaneous ecchymosis where the shock waves penetrated the body; 13 patients had temporary haematuria that resolved within a few hours.

During the follow-up (8 months to 8 years, mean 36 months) there was one recurrence in the girl with hypercalciuria, which was re-treated with good fragmentation (and a short follow-up), and one patient had remaining small residual fragments. All the patients who had a UTI before treatment had sterile urine afterward. To date, no child has developed hypertension and no acquired parenchymal lesions have been detected with conventional imaging.

The stones were predominantly ammonium phosphate in eight patients, calcium phosphate in eight, calcium oxalate in one and silicate in one (subsequent to long-term treatment for gastro-oesophageal reflux with a pectin/cellulose/silica gel). No fragments were collected from one patient.

The results of the DMSA renal scans before and after ESWL were classified as: both normal ( Fig. 2) in 12 infants; showing pre-existing parenchymal lesions not modified by ESWL (four patients); unexplained changes in differential function associated with a stable absolute uptake on the treated side and an increase in absolute uptake on the contralateral side (one patient). No scars or significant changes in differential function attributable to ESWL were detected in the patients 6 months after treatment. Two infants have not yet been assessed by renal scintigraphy.

Figure 2. a,.

Plain X-ray showing bilateral renal stones in a 16-month-old infant treated in two sessions. b, the DMSA renal scans before and after ESWL, showing no abnormality.

Discussion

ESWL is the first option for the treatment of most renal or ureteric stones [5, 10–12]. The present study, in which ESWL was successful in 10 of 19 patients after one session and in 18 after two sessions, confirms the efficacy of this technique in infants to be similar to that in our previous series of older children (13 of 15 after 1–4 sessions) [9].

In 1989, Nijman et al.[13] reported a success rate of 79% at 6 months after ESWL in a series of 73 children. Myers et al.[14], in a multicentre study involving 446 children treated for renal (238) or ureteric (208) stones reported a 68% success rate after one session and 78% after several sessions (with multiple sessions used in 7–35% of the patients, depending on the treating centre).

Most authors consider ESWL to be particularly well suited for use in children because the stones are relatively soft in this age group and the urinary tract is compliant, which allows relatively large fragments to be eliminated easily [7, 10–12, 14]. The present study, to our knowledge the largest reported consecutive series of infants treated at a single institution with ESWL, confirms these features, as most of the treated stones were large (mean 1.5 cm) and poorly calcified. Even staghorn calculi in this age group can be treated in one or two sessions, in contrast to those in older children where, in our experience with the same lithotripter (Sonolith 3000), up to four sessions may be necessary to treat a complete staghorn calculus. The remaining stones needed a combination of ESWL and percutaneous or open surgery [9]. In the first two patients with large stones in the present series, a JJ stent was inserted to prevent steinstrasse, but this procedure was not beneficial, particularly in boys, in whom there is a potential risk of a secondary urethral stricture, and it requires additional general anaesthesia to remove the stent. We have abandoned this procedure and inform the parents of the potential need to insert a ureteric stent or a percutaneous nephrostomy if there is future obstruction; this occurred only once.

ESWL in patients < 2 years old requires general anaesthesia with an endotracheal tube; the stone should be targeted by ultrasonography to avoid excessive irradiation, the opening above the generator reduced with an adapter and the lungs protected with foam [6, 15]. One of the present patients had haemoptysis but it was impossible to determine if it was secondary to the shock waves or to the insertion of the endotracheal tube. Finally, the child should also be protected against acoustic damage during ESWL; an unpublished report suggests temporary deafness in unprotected young children.

Although there remains some reluctance to use ESWL in children or infants, no major renal parenchymal lesion secondary to ESWL, whatever the lithotripter used, has been reported in children [3, 5, 9–12]. However, the effect of shock waves, particularly delivered to an actively growing kidney, remains uncertain. Potentially small lesions in infants could lead to a major parenchymal defect in adulthood. In an animal study, Kaji et al.[16] reported no significant reduction in renal growth or renal function after ESWL. They noted a potential risk of hypertension in adulthood, as there was a significant increase in blood pressure in the treated animals and several histological changes (tubular atrophy, interstitial fibrosis, glomerular destruction or capsular thickening). These changes were proportional to the number of shocks delivered. However, the shocks were not delivered to a stone, but directly to the renal parenchyma, and the energies used in that study (26–29 kV) were much higher than the mean energies used in clinical practice (10–20 kV). Nonetheless, adequate targeting, a limited number of impacts per session and low energies are important factors in sparing the renal parenchyma. ESWL always induces some parenchymal contusion and most patients have haematuria for a few hours after treatment. Recently, Goel et al.[17], in a series of 50 children, reported two intrarenal, three perirenal and one subcapsular haematoma after ESWL, all resolving spontaneously. These parenchymal trauma have been detected using urinary assay of α2-macroglobulin, a urinary marker of renal haematoma [18]; however, the variations in this marker are transient.

In the present study, potential functional and morphological lesions after ESWL were assessed by DMSA renal scans; this method is accepted as the ‘gold standard’ for diagnosing renal scarring after pyelonephritis. As only those lesions persisting after 6 months are considered definitive, the renal scan was assessed after this delay. Short-term reversible parenchymal defects were reported by Saussine et al.[8] in a series of 25 adults; they detected a focal defect in 40% of patients 10 days after ESWL and in only 10% 3 months later. Dumont et al.[19] noted a reduction in DMSA uptake by the treated kidney in 59% of patients 48 h after ESWL, which resolved in all after 6 months. Picramenos et al.[20] assessed DMSA scans before and at 1 and 3 months after ESWL in a series of 12 children treated with a Dornier HM4 (18 kV) lithotripter: they found no significant or permanent variation in differential function. The present results confirm these data; similarly, in a previous series of 15 children (aged 10 months to 15 years) treated with the Sonolith 3000 lithotripter, there were no significant changes in renal uptake [9]. The only abnormalities detected consisted in an insignificant variation in the differential function that was stable or resolved on further renal scans.

Thus ESWL appears to be particularly suitable for treating renal or ureteric stones in infants. To better evaluate each type of lithotripter and to define the parameters (e.g. energy, number of shocks per session, interval between sessions) outside which ESWL might harm the renal parenchyma, a DMSA renal scan should be taken routinely both before and at least once (at ≈6 months) after ESWL. A lifelong follow-up of blood pressure is also recommended.

Authors

H.B. Lottmann, MD, FEBU, FEBPS, Paediatric Urologist.

F. Archambaud, MD, Nuclear Medicine Physicians.

O. Traxer, MD, Resident in Paediatric Urology.

B. Mercier-Pageyral, MD, Radiologist and Ultrasonographer.

B. Helal, Nuclear Medicine Physicians.

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