Minipercutaneous Nephrolithotomy in the Management of Large and Complex Renal Calculi in Children: How Effective Is It?

Introduction

With an evident increase in the incidence over the past two decades, surgical management of pediatric stone disease always posed specific challenges for urologists due to the common underlying metabolic and anatomical abnormalities causing higher stone recurrence rates in this specific population. Based on this well-known fact, minimal or (if possible, noninvasive) treatment options need to be inevitably preferred to render all these cases completely stone free and preserve the function of growing kidney as well. To accomplish this task, similar to adult cases, in addition to the stone related (location, size, and density)-factors, renal anatomical characteristics, and the presence and the degree of obstruction should be well evaluated to select the most appropriate management option for an effective outcome. ^{1 –4} More importantly, a detailed metabolic evaluation-based medical management with appropriate agents seems to be of paramount importance to limit the possible high risk of new stone formation. ¹

Concerning the minimal invasive management of pediatric stones, because of the marked advances in instrument technology and the experience gained so far in adult cases, currently safe and effective application of all available endourologic procedures is possible in these cases. Regarding the advantages and disadvantages of these treatment modalities, while extracorporeal shockwave lithotripsy (ESWL) still seems to be the first choice for most upper tract calculi, excellent stone-free rates (SFRs) with minimal morbidity could be obtained also with other methods such as ureteroscopic lithotripsy (URS) and percutaneous nephrolithotomy (PCNL), which certainly require adequate experience. ^{2,3,5 –7}

Among these treatment options, currently PCNL is the treatment of choice in the management of large (>2 cm) and complex renal stones. Following the first report of percutaneous stone surgery for upper tract stones in 1976 in adults, this method began to be applied also in children because of the experience gained. The first pediatric PCNL outcomes were reported by Woodside and associates in 1985 and adult-sized instruments (28F–30F) have been used in the removal of large stones for a long period of time. ^{8 –10} Taking the higher risk of complications associated with the creation and use of large-sized tracts into account (mainly bleeding), endourologists aimed to decrease the degree of invasiveness in terms of the extent of the renal parenchymal trauma induced mainly by using smaller tract sizes to limit. ¹¹

This concept with effective application has facilitated the use of PCNL in the pediatric population with its highly efficient and safer nature.

Currently, SFRs after a single mini-PCNL session vary between 86% and 98% in children with large stones. Even higher success rates could be obtained with the additional retrograde intrarenal surgery/ESWL procedures in a combined manner. ^5,9,12,13

Although the use of smaller instruments reduced the degree of invasiveness, certain complications can occur during and after these procedures. Similar to adult cases again, hemorrhage is the most common complication requiring blood transfusion in about 10% of the patients operated. ¹⁴ Reported data indicated that operative time, sheath size, puncture site, and complexity of the stone(s) (partial staghorn, staghorn) were the statistically significant parameters affecting complication rates in such cases. ⁵ Among the miniaturized PCNL techniques applied, mini-PCNL (15F–24F), ultramini PCNL (11F–15F), and micro-PCNL (<11F) have all increased the maneuverability of the nephroscope to a greater extent in the smaller kidneys of kids. ¹⁵ Consequently, these methods seemed to provide high SFRs with acceptable complication rates in experienced hands as a good alternative to ESWL and other minimally invasive interventions particularly in large and complex calculi in children.

Finally, effective and safe use of high-power laser energy with such miniaturized instruments resulted in the effective management of pediatric staghorn, partial staghorn, and in even cystine stones. ^{14 –17}

In the present study, we aimed to evaluate the efficacy and safety of mini-PCNL application in the management of complex (partial-complete staghorn) pediatric stones.

Patients and Methods

From May 2017 to April 2021, a total of 41 children (25 boys, 16 girls) underwent mini-PCNL for renal stones in two different centers and the institutional medical records were reviewed in a retrospective manner. Of all the 41 procedures, 34 were done by author 1, the remaining were done by three different surgeons.

All children had large/complex (staghorn-partial staghorn) renal calculi, the majority of which have been found to be resistant to two sessions of ESWL therapy (five cases) or difficult to be tackled by flexible ureteroscopy (fURS). Regarding the exclusion criteria, while children with coexistent pelviureteric junction obstruction or primary obstructive megaureter requiring other additional surgical procedures were not included, kids with other renal abnormalities (such as horseshoe kidney, duplex kidney, malrotated kidney) were all included into the study program. Children with obstructive renal functional deterioration requiring appropriate diversion first (Double-J stenting/percutaneous nephrostomy) were also not included in our study group as the mini-PCNL procedure was the primary surgical procedure in our trial. Lastly, kids with urinary tract infection (UTI) were treated with the culture test-based appropriate antibiotic regimen and underwent the mini-PCNL procedure as soon as the urine became clear.

In addition to a detailed history, serum biochemistry, complete blood count, urine analysis, and urine culture tests were performed before the intervention. Radiological evaluation was made by using plain abdominal radiography (kidney, ureter, and bladder radiograph [KUB]), urinary ultrasound (USG), a noncontrast computed tomography (NCCT). Stone size and density were calculated on NCCT (or KUB for size in some cases with opaque stones) images, and the longest diameter was accepted as the size of the stone. In the case of multiple stones in the kidney, the sum of the longest diameter of all stones was assessed.

Results

A total of 41 procedures were performed in 26 boys and 15 girls (male/female = 1.73). While the age of the kids ranged from 2.5 to 10 years (mean 6.74 ± 2.76), mean size of the stones was 16.28 ± 3.43 mm (range 11–24) with a mean stone density value of 816 HU (range 550–1350). Nineteen cases had staghorn stones (46.3%), 16 cases had partial staghorn (39.1%), and 6 cases had multiple stones (14.6%). Mean body mass index value was 15.2 kg/m² (range 14.6–18). Of the 41 patients, 15 patients (36.5%) had bilateral stones. However, most of these patients had small renal stones in the opposite kidney, which did not require any intervention.

While renal anatomy was normal in 14/41 cases (34.1%), malrotation of the kidney was present in 9 (21.9%), duplex system in 9 cases (21.9%), horseshoe kidney in 7 (17.1%), ectopic kidney in 1 (2.5%), and solitary kidney in 1 (2.5%) case. Regarding the presentation of the patients, majority of them had pain (63.4%), six cases had hematuria (14.6%), failure of ESWL in seven cases (17.1%), and two cases (4.9%) had recurrent infection. Mean HU value of the stones in cases was 816.1 (range 550–1350 HU). Although no hydronephrosis was present at sonographic examination in 46.3% of the cases, severe hydronephrosis has been noted in 2 (4.9%) cases. Urine culture revealed no growth in 36 cases (87.8%), and UTI was present in the remaining cases, which was treated with an appropriate antibiotic regimen in accordance with the culture-sensitivity test outcome. Patient and stone characteristics are summarized in Tables 1 and 2.

Although majority of the cases (33/41, 80.4%) were treated with a single tract, a second tract was needed only in 19.6% of the cases. Puncture site has been decided depending on the stone configuration and pelvicaliceal anatomy. Although middle calix has been preferred in most of the cases, lower calix punctures have also been made when needed. Available flexible scope was not used since mini-PCNL enabled us to reach all the relevant calices for disintegration and irrigation during the procedure.

Evaluation of the success rates in terms of complete stone clearance on postoperative day 1 revealed that while 73.2% (30/41), residual fragments have been noted in 11 cases (26.8%) (1 stone in 7 cases and 2 stones in 4 cases). Size of the residual fragments ranged from 2 to 7 mm (mean 4.3). Of those children, 10 cases required fURS for stone removal, and in 1 case, placement of Double-J was adequate for spontaneous passage. During a 3-month follow-up, however, the SFR increased to 100% without any residual fragment left inside the treated kidneys. Double-J stent was placed for 2 weeks and removed after this period, with spontaneous passage of the fragment. Procedure-related parameters are summarized in Table 3.

Supracostal and infracostal renal punctures were performed in 10 (24.3%) and 31 (75.7%) children, respectively. Mean operative time (from the time of puncture to the placement of NT) was 56.15 minutes (range 30–90). While the pretreatment mean hemoglobin value was 13.57 ± 1.12, this value decreased to 13.02 ± 1.14 after treatment. Although the difference was statistically significant (t (39) = 9.182, p < 0.001), values remained in the normal reference range of the hospital laboratory. On the contrary, while the pretreatment median creatinine value of the patients was 47.65 μmol/L (30–100), this value increased to 51.00 μmol/L (29–106) postoperatively, and the difference was statistically significant (z = −3.927, p < 0.001), being in the normal reference value range of the hospital laboratory (Table 4).

Lastly, regarding the complications, a total of nine cases (22%), children, had fever after the procedure. For seven of these children with fever, additional oral antibiotic application was adequate for spontaneous recovery without any special management. This problem was classified as grade 2 according to the Clavien grading system. ¹⁸ No significant difference was found between children with supracostal and infracostal puncture with respect to the complications. No case required blood transfusion, and mean hospital stay was 3.1 days (2–5 days).

Discussion

Management of pediatric stones has changed considerably as a result of both the technological advancements enabling the use of smaller instruments and, more importantly, the experience gained in the adult population. All available endourologic treatment alternatives, namely, ESWL, PCNL, URS, or a combination of these modalities, can be performed effectively in the majority of pediatric cases with stones. ^{2,8,19 –21} Similar to adult cases, the efficacy and the safety of all these procedures could be affected with both stone (location, composition, and size)- and patient-related factors (body mass index, anatomy of the collecting system, and the presence of obstruction with or without infection).

Concerning the minimal (none) invasive management of pediatric stones, although ESWL is being performed as the preferred modality in the majority of small/medium-sized kidney stones, PCNL is the most appropriate treatment choice for larger and complex pediatric calculi. Currently experienced endourologists perform this technique in this specific population as monotherapy or in combination with other approaches to remove larger stone burdens. Despite the compulsory but cautious use of adult-sized large instruments in the majority of the earlier series as reported in the literature, advances in the technology, miniaturization of instruments, and the availability of more efficient energy sources for intracorporeal lithotripsy have revolutionized PCNL management of calculi in children. With the clinical introduction and effective use of smaller nephroscopes, miniaturized techniques, namely, mini-, ultramini, and supermini procedures, began to be performed in the percutaneous removal of larger/complex stones in children.

Currently, the highly efficient use of the Ho:YAG laser with such smaller nephroscopes during PCNL is possible for the excellent disintegration (pulverization) of all calculi in children. ^{9,22 –24} Based on all these facts, the mini-PCNL procedure began to be preferred as a rational and less invasive treatment option in children with a large/complex stone burden to avoid repeated ESWL sessions under anesthesia and that of open surgery, which may be more harmful to the growing kidneys of these cases.

Published data so far on this aspect clearly demonstrate that PCNL is a safe and highly effective method for maximal clearance of stone burden in cases with large and complex (staghorn) stones, which definitely requires a certain level of experience. Use of these smaller instruments particularly under USG guidance (if there is enough experience) will let the procedure be safe and efficiently performed enough particularly in experienced hands. ^{2,16,20,25 –27} In terms of PCNL efficacy, SFRs of 90% (ranging from 67% to 100%) with no significant complications have been reported in many series. ^{23,24,28 –30}

Although PCNL has been performed effectively in pediatric relatively larger stones (>2 cm) with acceptable complication rates, in the light of the experience gained in adults again, more and more complex stones such as partial/complete staghorn began to be treated in skilled hands. Regarding this issue, in an original study focusing on the role of mini-PCNL in children with large and complex staghorn stones, the authors have reported an SFR of 78% along with a high rate of severe (17%) complications. ¹⁶ Outcomes of some other studies also revealed varying SFRs and complication rates of 58% to 94% and 13% to 42%, respectively. ^9,13,16

Although some authors have suggested that the overall complication rate could be significantly correlated to procedure time, the number of access tracts and stone size were also found to be factors affecting the outcomes. ^31,32 We performed a single tract in the majority of our cases, which certainly limited the degree of invasiveness and the stone size did not affect our success rates. A systematic review of eight studies evaluating the efficacy of mini-PCNL application in kids showed that the overall pooled SFR was 97% with 19% rate of complications. The mean transfusion rate reported across the studies was 3.3%. ³³

Concerning the use of mini-PCNL procedure in children again, while Bodakci et al reported an SFR of 81.2% at the end of the first postoperative week in 48 infant mini-PCNL procedures, ³⁴ by performing mini-PCNL in 67 renal units of 56 children aged <3 years, USG-guidance, Xiao et al reported an SFR to be 92.5% during the hospital discharge. ³⁵ On the contrary, however, in their retrospective study including 46 pediatric patients, Brodie et al reported a complete stone clearance rate of 76%, with no intra/postoperative blood transfusion or mortality rate. The size of the Amplatz sheath used was 16F or less. ³⁶ An SFR of 76.9% was reported in a prospective study of Daw et al and this value increased to 85% and 92.3%, respectively, after application of ESWL and other additional procedures. ³⁷

Related to the complication rates noted, contradictory outcomes have been reported in some series in the literature. By using nephrostomy tracts ranging from 18F to 30F for pediatric PCNL, Zeren et al reported an SFR of 87%, postoperative fever rate of 30%, and transfusion rate of 24%. ²³ Guven et al performed PCNL with only one nephrostomy tract among infants with complicated renal stones. They found a significant reduction in hemoglobin levels when the tract was larger than 20F. ³¹ In addition, Yan et al found that mini-PCNL monotherapy (tract size 14F–16F) cleared 85.2% of stones, with no children requiring blood transfusions. ³⁸ Zeng et al described their experience with children in 331 renal units, showing a stone clearance rate of 80.4% and blood transfusion rate of 3.1%. ³⁹

Some certain operative-related parameters have been evaluated for the possible correlation with the outcomes of PCNL procedure in children. Among these factors, stone-related factors, operational duration, presence and degree of hydronephrosis, and tract size were the most commonly evaluated ones. Related with this issue, studies by Ozden, Desai and Manohar have shown the extent of hemoglobin decrease with mean values of 1.6, 1.9, and 2.2 g/dL, respectively, in pediatric patients undergoing PCNL for difficult caliceal and staghorn calculi. ^27,32,40 They observed that the decrease in hemoglobin was related to the number and size of the nephrostomy tracts. Patients with several nephrostomy tracts experienced a statistically significant increase in blood loss and transfusions.

Last but not least, by performing pediatric mini-PCNL, in their original study, Zeng et al reported a mean operative time of 73.6 ± 20.2 minutes, which has been found to be shorter compared with adults. ³⁹ This may be explained by the results of Falahatkar et al, who found a significant correlation between operative time and the number of nephrostomy tracts, amount of stone burden, and position of the calix for access (upper>lower>middle calix). ⁴¹

Evaluation of our findings demonstrated that while 73.1% of the pediatric cases operated in our group were stone free after the first session of single-tract mini-PCNL, all of them (100%) were completely stone free after 3 months. As all cases had partial/complete staghorn stones, stone-related factors (burden and location) did not affect the stone-free status of the children in our study. In addition, the presence and degree of hydronephrosis was found to have no significant affect on the final outcomes of the mini-PCNL procedure although it has facilitated to get access into the collecting system and shortened the operation time. Similar to the data reported in the literature concerning the outcomes of mini-PCNL in kids, SFRs of our series seemed to be higher than some studies performed mainly in infants.

As important parameters evaluated regarding the effect of the procedure on the risk of bleeding and change in renal functional status, although evaluation of the changes both in hemoglobin and serum creatinine levels did show statistically significant change after the procedure, these values remained in the normal reference range of the hospital laboratory values. Last but not least, depending on the experience of our team, no severe complication was noted apart from minor ones (mostly fever) which did not affect the clinical course of the postoperative convalescence period.

In the light of our present findings and the data reported so far in the literature, we may say that although pediatric renal calculi sizing up to 20 mm may be treated with ESWL as the first option, larger and complex stones such as partial/total staghorn ones could be managed well with the mini-PCNL technique, even through a single tract, in experienced hands with an acceptable SFR and a complication rate. This approach will give the chance of being extremely minimal invasive for the growing kidneys of this specific population. Our success rates might be slightly lower than the data reported in the literature but taking the complex nature of these stones requiring sometimes multiple procedures under anesthesia and also the limited information available in the literature into account, we believe that our current outcomes will be contributive to the existing published data so far.

Our study is not free of limitations. First, the retrospective nature of the study design may represent an important drawback. On the contrary, the number of the cases operated may seem to be limited, but taking the rarity of the disease in this specific population along with the limited number of cases referring with complex partial-complete staghorn into account, we believe that data obtained in our current series will be contributive enough to the existing data in the literature.

Conclusions

Mini-PCNL with Ho:YAG laser intracorporeal lithotripsy through a single tract can be performed in a safe and effective manner to remove complex kidney stones (staghorn, partial staghorn) with high SFR and low complications rates in children. However, a second tract may always be needed in some cases based on the stone- and anatomy-related factors. We believe that an adequate experience is the key point in achieving such effective outcomes particularly in children with complex renal calculi.

Ethical Approval

All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.