Contemporary Minimal Invasive Surgical Management of Stones in Children

Abstract

Although urinary tract stone disease is less common in the pediatric age group than in adults, the increasing incidence of this problem in the last two decades, higher rate of recurrences and the difficulty of interventions make the this population very special for urologists from certain aspects. Continuity of normal renal functional status, complete stone elimination and prevention of stone recurrence are the most important parameters of treatment strategies for urologists. It has been well indicated that management and prevention of stone disease may cause serious morbidity along with a considerable financial cost. When compared with adult ones, based on the well documented metabolic derangements in approximately fifty per cent and anatomical abnormalities in approximately one third of the patients, pediatric stone formers require a detailed urological and metabolic evaluation. In order to plan the best surgical treatment, anatomical characteristics of the urinary system, the presence of obstruction and infection and the location as well as the size of the stone(s), must be taken into consideration. Anatomical and metabolic abnormalities should be treated in an effective manner on time. In addition to a vigorous medical treatment to alkalinize the urine and increase urinary citrate levels in certain cases; adequate fluid intake to increase urine volume and necessary lifestyle changes should be strongly recommended. With respect to the endourological stone management, all available alternatives can be performed in an effective and safe manner in these cases based on the technological advances, improvements in surgical instruments and most importantly experience gained from the adult population. Today, minimal (non) invasive management options for pediatric stones include extracorporeal shock wave lithotripsy (ESWL), semirigid ureteroscopy (URS), retrograde intrarenal surgery (RIRS), percutaneous nephrolithotomy (PCNL), laparoscopic, robot-assisted laparoscopic and open surgery. While URS, RIRS, PCNL, and laparoscopic procedures require more expertise, SWL is still the first most practicle, non-invasive choice for the vast majority of pediatric stones with its highly effective and safe nature resuting in higher stone-free rates. Open surgery always remains as an alternative treatment option for large and complicated stones with anatomical abnormalities.

1. Introduction

The incidence of pediatric nephrolithiasis has increased by 6–10% annually over the past 20 years [1]. Changes in lifestyle, dietary content, climate conditions along with the defined comorbidities seem to be the main factors on this aspect. Approximately 1–3% of all urinary tract stone patients treated are pediatric patients and 17% of these cases are under the age of 14. In a study, it has been reported that while the disease is more common in boys in the first 10 years of life, girls were found to be affected commonly in the second 10 years of life [2]. The incidence seems to be variable and while it is less common in developed countries such as the USA and Northern Europe, the disease has been reported to be endemic in developing countries such as India, Pakistan, Iran and Turkey, and in far eastern countries [3, 4, 5]. Considering the chemical composition of stones in the pediatric age group in developed countries, the stones are often in the form of calcium oxalate and calcium phosphate which are usually located in the upper urinary tract. In underdeveloped countries however, due to the high consumption of grain and rice as a possible etiological cause, bladder stones are more common with compositions of ammonium acid urate and uric acid.

On the other hand, published data has clearly shown that the recurrence rate of pediatric stone disease is quite high. Therefore, it is utmost important to determine the underlying metabolic as well as anatomical problems that may cause stone formation when developing rational and effective treatment strategies. Anatomical abnormal conditions such as ureteropelvic junction stenosis, megaureter, ureteral cyst and urethral valve are the main causes of stasis and stone formation in these cases. Concerning the metabolic aspect of the disease, hypercalciuria, hypocitraturia, hyperoxaluria, hyperuricaciduria, cystinuria and hypomagnesuria are the most commonly identified risk factors causing stone formation in children. Last but not least, endemic factors and recurrent urinary tract infections are the other most important underlying causes to be considered [6, 7].

2. Minimal invasive surgical management

Pediatric urinary tract stone disease is prone to recurrence, so all necessary precautions should be taken to reduce the recurrences. Additionally, minimal invasive surgical options need to be performed tor ender these cases stone free reduce the possible negative effects of surgery on the growing kidneys. Surgical treatment is recommended for ureteral stones unlikely for spontaneous passage and that of symptomatic kidney stones [8]. Surgical treatment of pediatric stone patients has become more effective and safe with the development of miniature endourological devices in parallel with technological developments and the increase in the endourological surgical experience of urologists. The same minimally invasive surgical methods are used in pediatric patients as in the adult population. Commonly used minimally invasive methods are ureteroscopy (URS), shock wave lithotripsy (SWL) and percutaneous nephrolithotomy (PCNL). Although patients are at risk of anesthesia and radiation during the application of these methods, they are considered minimally invasive compared to more invasive surgeries such as open or laparoscopic surgery performed in patients with anatomical anomalies.

As in adults, the aim of treatment in pediatric patients is to achieve the highest SFR without the least number of procedures and complications. The equipment, localization and size of the stone(s), anatomical factors, comorbidities and the experience of the surgeon must be taken into consideration when choosing the type of the procedure.

There is still no consensus on the definition of stone-free status after these procedures an Tasian et al. defined stone-free as “resolution of symptoms by clearance of the offending stone on imaging after ureteroscopy, shock wave lithotripsy, percutaneous nephrolithotomy or spontaneous stone passage” [9]. However, in clinical practice, there is no established consensus on the size stone fragments give clinical symptoms and spontaneous passage in pediatric patients [10].

3. Extracorporeal shock wave lithotripsy (ESWL)

The minimally invasive ESWL method works on the principle of high-energy shock waves generated from the electrodes in the lithotripsy device. There are three types of shock wave generators. Electrohydraulic generators use evaporation bubbles, electromagnetic generators use magnetic fields and piezoelectric generators work on the principle of vibration of crystals when current flows through them [10, 11]. This method, which allows kidney stones to be broken into small pieces that will allow spontaneous passage, was introduced into clinical use in the 1980s and has proven its effectiveness and reliability over time. Since it is minimally invasive and effective, it has become the first choice for stone treatment in pediatric patients. Initially, its use in pediatric patients was delayed due to concerns about adverse consequences that may develop after administration due to organ development in children [12]. Over time, these concerns disappeared, and SWL began to be widely used in pediatric stone patients. SWL has been the first choice in the treatment of pediatric stone diseases because of the positive effects such as less stone-skin distance and better dilatation of the ureters allowing shorter and spontaneous stone passage in children [13].

SWL has more effective aspects in children than adults. In children, shock wave energy attenuation is less due to the short stone-skin distance. In addition, since the water content of the tissues between the body surface and the kidney tissue in children is higher than in adults, the acoustic impedance is low, which is very convenient for the transmission of energy.

The undesirable aspect of SWL is that several sessions may be required and some patients may need additional interventions to ensure stone-free status. Contraindications for its application are coagulation dysfunction, active urinary tract infection, extreme obesity, skeletal malformations and hemangioma located close to the stone. In the light of the literature data, the SFR seems to be high in renal pelvis and calyx stones up to 2 cm. However, as the stone size increases, lower success rates could be anticipated in cases with calcium oxalate monohydrate and cystine stones or in difficult access situations due to the anomalies of urinary tract [14].

Approximately 80% of stones seen in pediatric patients can successfully be treated with SWL. While short-term stone-free rates are 57–97%, there are different studies reporting that this rate is 57–92% in the long-term [15, 16, 17].

Because of the relative hardness of cystine stones and their resistance to high energy shock waves, SWL is not considered as the first choice in the treatment of these calculi [18]. As mentioned above, kids with a history of anatomical abnormalities are not ideal candidates for SWL because stone-free rates are as low as 12.5% in such patients [19]. Although general anesthesia is usually performed in young children, in older children sedation could be sufficient to relieve possible discomfort during the SWL procedure [20, 21].

Hematuria resulting from local trauma caused by the application shock waves is the most common complication after SWL. Haematuria usually resolves spontaneously within 1 week [22, 23]. In addition, renal colic, steinstrasse, subcapsular haematoma, perirenal haematoma, intestinal perforation, hepatic haematoma, splenic rupture, abdominal aortic rupture, pneumothorax, urinothorax and acute necrotising pancreatitis are possible complications of SWL [14]. Care should also be taken in terms of the potential risk of hypertension. A population-based retrospective study found that SWL for the kidney stones was associated with a 40% higher risk of hypertension, and patients treated with SWL had twice the risk of hypertension than those without kidney stones [24, 25]. Similar data is highly limited in children but the potential risk of hypertension should always be taken into account given the long life expectancy. Although potential hypertension and loss of renal function have been seriously discussed, no significant morphological and functional changes were detected in long-term evaluations of children treated in different series. However, it should not be forgotten that pediatric patients should be completely stone free in a short time with a reasonable number (up to 2000) of high energy shock waves [26, 27].

Ureteral stones sizing less than 5 mm tend to pass spontaneously at a rate of 98%. Very successful results are obtained with SWL in the treatment of impacted ureteral stones larger than 5 mm [11, 20, 28]. Compared with adults in terms of anatomy and elasticity of the ureter, pediatric patients pass stone fragments more easily and ureteral stent placement is rarely needed. Alternative surgical procedures such as PNL or RIRS should be considered in cases where the stone size is large and a ureteral stent may be needed.

In conclusion, available evidence-based data suggest that SWL is an effective and safe treatment alternative in the majority of pediatric stones.

4. Ureteroscopy (URS)

As an highly effective and safe management option, URS, has been easily adopted and applied in adult patients. However, it took a reasonable time period to be applied in children due to the lack of experience, the small size of the body and concerns about intraoperative complications. URS was first applied to distal ureteral stones in children in 1988, and a stone-free rates of 86–100% has been reported [29]. Parallel to technological developments, with the introduction of thinner and more flexible ureteroscopic instruments and efficient use of Holmium: YAG laser, this procedure has begun to be used and preferred not only in distal and middle ureteral stones but also in the upper ureteral ones. Literature data showing similar or even better results than adult case applications in terms of treatment efficacy and complication rates of URS [30, 31]. Concerns about damage to the ureteral and urethral mucosa related to the use of thick-calibrated (11.5 Fr-8.5 Fr) instruments have disappeared with the clinical introduction of thinner (4.5/6 Fr, 6/7.5 Fr and 8/9.8 Fr) caliber instruments. Therefore, currently complications arising from the use of larger instruments are very rare. There are two types of ureteroscopic instruments in different calibers for the removal of ureterla and kidney stones namely, semi-rigid and flexible. When these two models are compared, the semi-rigid model appears to have a larger working channel, better water flow and greater durability. With the cautious use of semi-rigid model, the entire ureter and even the pelvic system (in a very careful approach in limited cases) can be accessed. The flexible model is more suitable for upper ureteral stones particular in kinked ureters due to its bendable tip [32].

SWL or URS is recommended for pediatric upper urinary tract stones which do not pass with follow-up or medical expulsive therapy, or who have a very low probability of spontaneous passage. Published data on this aspect demonstrated that, the SFR is 78% for stones >10 mm and 95% for stones <10 mm when treated with URS. Compared to SWL, this rate is 73 and 87%, respectively [8].

URS treatment of upper ureteral stones requires advanced endoscopic skills and the risk of ureteral trauma is very high, especially during the removal of large and impacted stones. For lower and middle ureteral stones, stone-free rates are satisfactory ranging between 87.5 and 100% in different studies [11, 31].

In recent years, URS has also gained popularity in the management of pediatric ureteral stones and has become widely used for stones <15 mm. It should be kept in mind that the procedure is not complication free despite the surgical experience gained and widespread use of the fine and less traumatic instruments. In general, complication rates in children are similar to the rates noted in adults [33]. Potential complications include ureteral avulsion, ureteral perforation, hematuria, infection, and ureteral stricture. If ureteral perforation occurs, the procedure should be terminated and a ureteral stent placed. If a ureteral avulsion occurs, which is a very rare but very serious complication, extensive, judicious approaches including open repair will be required. In a study, the complication rate of URS in children was reported as 7.1% [34]. There are certain concerns about the role and necessity of ureteral dilatation and complications such as urethral stricture and vesicoureteral reflux may occur after this maneuver. However, studies have shown that such risks have not been increased [35].

5. Retrograde intrarenal surgery (RIRS)

Similar to adult patients, the main goal of the treatment for pediatric kidney stones is to achieve a stone-free kidney with the least number of interventions resulting in the least morbidity. As a result of the marked developments in the ureteral access sheat, guide wire, nitinol basket and holmium laser fiber technology used in endoscopic surgery the application rates of RIRS in pediatric stone patients has also increased. Recent data have shown that RIRS can be performed also in pediatric renal stones larger than 2 cm [36]. At the same time, the use of natural orifice approach to reach the stone and the high success with low morbidity increased the popularity of RIRS. This makes RIRS more effective and safe in the treatment of pediatric kidney Stones when compared with PNL.

Currently the EAU guidelines recommended RIRS as another treatment method in addition to SWL and PCNL for the minimal invasive and relatively safe treatment of kidney stones [37]. Initially, the indications for RIRS were limited to lower calyx stones, stones smaller than 1.5 cm and Stones resistant to SWL. However, these limitations in RIRS indications have decreased due to the recent accumulated experience and the ease of application provided by the advances in surgical instruments. RIRS is an acceptable treatment option in kids where SWL was found to be unsuccessful for pediatric kidney stones smaller than 2 cm. Because of its relatively low morbidity in pediatric kidney stones larger than 2 cm, it is also an alternative treatment option to PCNL in experienced hands. Li et al. treated 55 pediatric patients with upper ureteral and kidney stones with RIRS and reported a stone-free rate of 94% [38]. In a study Resorlu et al., have compared 106 patients with kidney stones undergoing mini-PCNL and 95 patients undergoing RIRS based on the SFR obtained and reported outcomes were 86 and 84%, respectively [39]. Despite similar SFR, RIRS appears to be safer because of less radiation exposure, fewer complications, instrumental administration through the natural orifice urinary tract which minimizes well the extent of possible trauma to tissues.

RIRS can be applied effectively and safely also in certain problematic cases such as the ones with non-opaque stones, SWL resistant stones, anatomical abnormalities, lower calyceal calculi, musculoskeletal deformities as well as obesity.

In summary based on the safe applications and successful outcomes in experienced hands, RIRS could be regarded as an effective and safe method in the treatment of pediatric kidney stones. However, it should be kept in mind that that uncorrected bleeding disorder, uncontrolled urinary tract infection, severe urethral stricture, narrow ureter, large and complex stones, anatomical abnormalities that make retrograde access difficult and previous endoscopic failures are absolute contraindications for this particular procedure.

6. Percutaneous nephrolithotomy (PCNL)

PCNL in pediatric kidney stone treatment was first performed in 1985 [40]. The EUA guidelines for stones recommend PCNL for the treatment of complex (staghorn or partially staghorn), kidney stones larger than 2 cm, lower calyx stones larger than 1 cm, kidney and ureteral stones that have failed SWL and RIRS [14]. Although PNL has been widely used in adult patients, it took a certain time period to become widespread in pediatric patients due to concerns regarding the indications and large sized instruments used at first. However, the miniaturization of the tools used as a result of technological advances paved the way for widespread use of PNL in children. In their original study Jackman et al. emphasized that the 24 Fr sheath used in pediatric patients is actually equivalent to the use of a 72 Fr sheath in adults [41] which certainly justifies the initial concerns discussed above. Taking the certain level of damage induced in the kidney parenchyma, miniaturization of instruments has resulted in the limitation of severe complication such as bleeding and shortened the operative times.

The patient’s age and stone volume are very important factors in selection of appropriate instruments. Although definitions vary according to the size of the instruments used, they are generally defined as mini (16/22 Fr), super-mini (14/16 Fr), ultra-mini (10/13 Fr) and micro (4.85 Fr). This miniaturization of the instruments has enabled them to be used in pediatric patients of all age groups. This has made PCNL an alternative as an option in the treatment of smaller stones that are candidates for SWL or RIRS. It also increases tubeless PCNL experiences, resulting in reduced pain and reduced hospital stays. Decreased calibration of instruments brings with it limitations such as reduced image quality, difficulty in removing stone fragments and higher intrarenal pressure. However, the introduction of vacuum-assisted evacuation sheaths can help solve these problems and shorten operation times [42].

Mini-PCNL is a modified PCNL procedure using a smaller (14–20 Fr) channel. Zeng et al. treated 20 children with kidney stones with mini-PCNL and reported a SFR of 95% [43]. Mini-PCNL has advantages such as reduction in bleeding, postoperative pain and hospital stay, and reduction in treatment costs.

Zeng et al. designed a new miniaturized endoscopic system called super-mini PCNL (SMP) to further optimize the PCNL technique. It was designed with a two-layer metal structure with 12 or 14 Fr nephroscope options associated with a new irrigation suction sheath concept [44]. This new design can prevent the possible rise in intrarenal pressure, improve image quality and improve stone fragment removal by continuous aspiration of the dust and fragments as they form during the procedure.

Desai et al. proposed a new PCNL procedure, which they called ultra-mini PCNL. The aim here was to increase the efficacy and safety of mini-PCNL and to reduce complications. In this definition, 11 or 13 Fr sheath, 7.5 Fr nephroscope and 3 Fr telescope are used [45]. There are indications for the use of this modality as an alternative to SWL or RIRS in SWL-resistant stones, renal diverticulum stones, lower calyx stones that are not suitable for RIRS or medium-sized kidney stones. Dede et al. reported a stone-free rate of 87.1% for kidney stones managed with ultra-mini PCNL. They reported that no patient required blood transfusion and the safety of the operation was increased due to the low intrarenal pressure during the procedure [46].

Last but last least, another version of mini-PCNL was described as micro-PCNL by Desai et al. With the help of 4.8 Fr tract size, the procedure is performed in a single step with the careful use of an “all-seeing” needle [47]. This system has been advised to be performed in both pediatric and adult patients with relatively smaller (1–2 cm) stones. This modality seems to have some advantages such as no tract dilatation, less bleeding, less exposure to radiation, shorter operation time and less complications. However, the modality has been found to have certain disadvantages where the quality of vision was found to be not clear enough and expensive nature of the applications. Patients regarded to be unsuitable for SWL due to anatomical abnormalities may be a good indication for micro-PCNL.

7. Laparoscopic surgery

Laparoscopic procedures can be used in the treatment of pediatric renal and ureteral calculi, but since the data reported in the literature are very limited, large series are needed. Therefore, laparoscopic and robot-assisted pyelolithotomy, nephrolithotomy or ureterolithotomy may be an option only in selected patients with large renal pelvic and ureteral calculi. The EAU stone guidelines suggests that laparoscopic or robot-assisted intervention may be considered for complicated renal anatomy, calyceal diverticulum, megaureter or after a failed endoscopic intervention [14].

8. Cystolithotomy

Bladder stones, which are reported to be an endemic pathology in underdeveloped and developing countries, are also seen after augmented bladder or continent urinary diversion. The treatment principles of bladder stones are like upper urinary tract stones. Alternative methods such as transurethral, percutaneous suprapubic lithotripsy or suprapubic cystolithotomy are available in the treatment of bladder stones, which are generally seen as single and hard chemical structures. The biggest drawback of transurethral treatment options is the damage that may occur, especially in the male urethra [48].

9. Conclusions

The main goal of pediatric kidney stone management is to protect the renal function as much as possible, achieve the highest SFR in a single session (if possible) and prevent further recurrences. While planning the most rational treatment option, stone and the patient related factors need to be very well evaluated. The individual experience of the surgeon is also another highly important parameter that should be taken into account for successful and complication free outcomes particularly in this specific population.

Although data showing that SWL and URS are equally effective and safe alternatives in the minimal invasive treatment of stones sizing 1–2 cm, similar to the clinical applications in adult patients, SWL is still considered to be the first treatment option for such kidney stones. PCNL remains the most effective method for the treatment of large and complicated pediatric kidney Stones sizing larger than 2 cm. Further data indicating the exact role of laparoscopic and robot-assisted pyelolithotomy and even RIRS methods are certainly needed.

Well-designed, randomized studies are still needed to understand better the exact role and judicious use of RIRS and that of different miniaturized PCNL methods.

Conflicts of interest

The authors declare no conflict of interest.

Funding support

None.