ROLE OF MICROPERC IN MINIMAL INVASIVE EXTRACTION OF Renal STONES IN CHILDREN

Abstract

Background

Microperc using all-seeing needle is associated with reduced tract-related morbidity.

Aim & Objectives

The purpose of this study was to examine the effectiveness and safety of microperc in children.

Patients & Methods:

From July 2010 to August 2014, a total of 17 children with renal stones underwent microperc at Muljibhai Patel Urological Hospital, Nadiad, India. Renal access was achieved through 4.85-Fr (16 gauge) all-seeing needle (PolyDiagnost, Pfaffenhofen, Germany). and fragmentation with 200 µm holmium:YAG laser fiber. The patient’s demographic data, clinical features, operating time, hemoglobin drop, stone clearance, complications (Clavien-Dindo), and length of hospital stay were prospectively studied.

Results

A total of 17 patients with a median age of 9 years were studied. The stone size ranged from 5.3mm to 24.9mm. The median operative time was 40 minutes. The median decrease in haemoglobin was 1.2 mg/dl. The stone-free rate at first postoperative day and at the first month after the procedure were 82.4% and 88.2% respectively. The mean hospital stay was 56.4 hours. None of the patients required blood transfusion. An overall success rate of 94.1% was achieved at median follow-up of 4 months. Comparing small size stones (< 1cm) and moderate size stone (1-3cm); the immediate clearance rates were 100% and 75% respectively (p=0.331). There was no statistically significant difference in the operating time (40 vs 43mins; p=0.592), haemoglobin drop (0.85 vs 1.25 g/dl; p=0.595) and the length of hospital stay. One patient in each group had conversion to miniperc to remove residual stone fragment. There was one minor intra-operative pelvic perforation (Clavien II). There were two postoperative complications in patients with moderate stone; one of the patients had right lower lobar pneumonia and the other had colic pain and both cases were managed conservatively (Clavien I).

Conclusion

This study has demonstrated that microperc is a safe and effective procedure in the extraction of small to medium size renal stones in children.

Introduction

The incidence of urinary stone disease in children is 1-2 %1. Recent evidence however showed rising incidence of nephrolithiasis in children2. The recurrence rate of paediatric urolithiasis is high due to the known association with urinary infection, anatomic and metabolic abnormalities. Complete clearance is therefore required in the management of urolithiasis in children in addition to eradication of urinary infection and appropriate correction of any underlying metabolic or anatomical abnormalities. Paediatric urolithiasis usually poses management challenges to the paediatric urologist because of the need to strike a balance between stone clearance and the morbidity related to the procedure3.

The options of management of paediatric urinary stones include shock wave lithotripsy (SWL), percutaneous nephrolithotomy (PCNL), retrograde intrarenal surgery (RIRS) and laparoscopic and/or robotic approach4. Although, current European Urological Association guidelines stipulated Shockwave lithotripsy as the first choice for treating most paediatric renal stones and percutaneous renal surgery for larger and complex stones5,the limitations of SWL are the relatively lower stone clearance rates and the need for multiple sessions6,7. While percutaneous nephrolithotomy (PCNL) has been accepted as a well-established minimally invasive procedure in children, the concerns with PCNL include the use of large instrument in pediatric kidneys, parenchymal damage and the associated effects on renal function, radiation exposure with fluoroscopy, and the risk of major complications especially bleeding4. Most of the complications associated with PCNL including bleeding, calyceal and infundibular tear, persistent urine leak and nephron loss have been attributed to the size of the tract8,9.

Micro-PCNL or “microperc” which is a minimally invasive PCNL technique was recently described as a major gains of miniaturization of instruments, limitation of tract size and advanced intra-corporeal lithotripters10. The procedure is performed by using a 16 G microperc needle in a single-step fashion10. The working hypothesis of the 'All-seeing needle' is that a perfect tract will reduce tract-related morbidity and may provide a new standard of obtaining renal access10. While the feasibility and safety of microperc have been reported in adult series10^-12, only a few case reports and case series have been published to document the efficacy and safety of this new modality in paediatric population6, 13.

The purpose of this study was to examine the effectiveness and safety of the single-step micropercutaneous nephrolithotomy (microperc) in children. We hypothesized that there is no difference in outcome of microperc for small and moderate size stone in children.

Patients & Methods

This prospective study analyzed the demographics, clinical features, management outcomes of children who had stone extraction using microperc technique. All the children below 18 year who had microperc minimal invasive extraction of renal stones from July 2010 to August 2014 at Muljibhai Patel Urological Hospital, Nadiad, India were included in the study. The study was approved by Institutional ethic review committee.

Technique:

The procedure was carried out under general anesthesia. In lithotomy position, through cystoscopy under fluoroscopic guidance, the ureter of the affected kidney was catheterized with a 5 Fr ureteric catheter.

The ureteric catheter was fixed to 10 Fr urethral catheters and the patient was turned to prone position with all pressure points were padded. The pelvicalyceal system was gently filled with saline injected retrogradely through the ureteric catheter to create a mild hydronephrosis. Under Ultrasound and/or fluoroscopy guidance an appropriate calyceal puncture was performed using the 16 G all seeing needle (PolyDiagnost, Pfaffenhofen, Germany). Once a proper puncture was achieved, the stylet was removed and a three-way connector was attached to the proximal part of the shealth to connect the laser probe and irrigation. The stone was fragmented by a 200 µm holmium: yttrium-aluminum-garnet laser fiber (LISA Laser, Pleasanton, California, USA) under direct vision with a 0.9 mm flexible microperc telescope as shown in figure 1. Vision was controlled to the optimum level using a surgeon controlled irrigation pump as required. In patient with renal calculi larger than 2cm, an 8Fr or 10Fr microshealth that allows for better manipulation was inserted over a guidewire. Double-J stent was placed if patient had residual fragments of stone considered significant. The procedures were done by two senior endourologists.

Figure 1. Showing 4.85 Fr ‘All seeing needle’, Telescope and Laser fibre assembled for renal access and stone fragmentation .

At the end of the procedure fragmentation and clearance were assessed by fluoroscopy. The patient was monitored for postoperative complications. Ureteric catheter was removed along with Foley catheter in first post-operative day. DJ stent was removed after 4weeks. The patients were re-evaluated with KUB and or Ultasound to assess the stone free rate at day 1 and 1-month follow up. Clearance was defined as no residual stone on KUB and ultrasound. All fragments less than 4 mm were considered clinically insignificant residual fragments (CIRF).

The patient’s demographic data, stone characteristics, stone fragmentation method, intraoperative assessment of stone fragmentation, complications (Clavien-Dindo), operating time, haemoglobin drop and hospital stay were prospectively studied. A complete stone-free status or CIRF at 1 month was accepted as the criterion for final clinical success.

Statistical analysis

Data were recorded prospectively in a database and the analysis was done using SPSS version 15.0 (SPSS Inc., Chicago, IL, USA). The Mann Whitney U-Test was used to compare continuous variable among groups. For categorical data, a chi-square test or fisher exact test was performed as appropriate. P-values less than 0.05 were accepted as significant.

Results

A total of 17 patients (14 males and 3 females) with a median age of 9 years (range 9months -18yrs) were studied. Stone was on the left side in 10(58.8%) patients. The stone locations were pelvis in 11(64.7%), lower calyx in four (23.5%), middle calyx 1(5.9%), and upper calyx 1(5.9%). Stone size ranged from 5.3mm to 24.9mm (mean 12.7± 4.7mm). Preoperative characteristics of the patients were as shown in Table 1. The operative time ranged from 30 to 90 min (mean 47.9± 17.1mm; median 40). Tract size was 4.85Fr in 8 patients, 8Fr (n=4) and 10Fr (n=5). The mean haemoglobin drop was 1.25 ± 0.85 g/dl (ranged 0-3.0; median 1.2 g/dl). Laser lithotripsy was used in 16(94.1%) patients while one patient had ultrasonic lithotripsy.

Table 1. Characteristic of the study population.

Charateristics	Value mean±SD (median; range)
Number	17
Male/ Female	14/3
Age	10.0±5.3(9; 9months-18)
Stone size(mm)	12.7±4.7 (11.4; 5.3-24.9)
Laterality(R/L)	7/10
Hounsfield units	1144.9±290.3 (1220; 486-1507)
Stone location
Pelvis	11
Lower calyx	4
Middle calyx	1
Upper calyx	1

Auxiliary procedures were needed for two patients (check nephroscopic in one and Miniperc in another patient with failed microperc). The stone-free rate at postoperative day 1 and at the first month thereafter was 82.4% and 88.2% respectively. The mean hospital stay was 56.4±18.4 (36-96) hours. None of the patients required blood transfusion. An overall success rate of 94.1% (including one (5.9%) case of clinically insignificant residual fragment rate) was achieved at median follow-up period of 4 months (range: 1-18).

Comparing small size stone (< 1cm) and moderate size stone (1-3cm), the immediate clearance was 100% and 75% respectively (p=0.331). There was no statistically significant difference in operating time (40 vs 42.5mins; p=0.592), haemoglobin drop (0.85 vs 1.25 g/dl; p=0.595), and length of hospital stay (48 vs 48 hours; p=0.109) as shown in Table 2. One patient with 7.5mm stone with narrow neck diverticulum in the middle calyx needed conversion to miniperc and another child with stone size of 24.9mm required miniperc to remove residual stone fragments. There was one minor intra-operative pelvic perforation (Clavien II) in a 6-year old child who was observed to have extravasation at the end of the procedure. The patient was managed without stent and was discharge home on postoperative day 2. There were two postoperative complications in patients with moderate size stones; a 9-month-old child had right lower lobar pneumonia and another patient experienced postoperative renal colic; both cases were managed conservatively (Clavien I).

Table 2. Comparison of the characteristics and outcome of small and moderate size calculi subjected to microperc extraction.

Characteristics	<1cm(n=5)	1-3cm(n=12)	ALL(n=17)	P value
Median operative time in minutes (mean± SD; range)	40	42.5	42.5 (47.9± 17.1; 30-90)	0.592
Median duration of hospital stay in hours(mean; range)	48	48	48 (56.4±18.4; 36-96)	0.109
Median Hemoglobin drop in g/dl [mean±SD; range]	0.85	1.25	1.2(1.25±0.85; 0-3.0)	0.495
Median tract size(Fr)	4.85	8	8	0.011
Stone clearance (n, %)
1st day	5(100)	9(75)	14(82.4)	0.331
1st month	5(100)	10(83.3)	15(88.2)	1
CIRF	0(0)	1(8.3)	1(5.9)
Conversion to miniperc (n, %)	1	1	2	0.512
Auxillary procedure (n, %)	0(0)	2(16.7)	2(11.8)	1
Check nephroscopy	0(0)	1(8.3)	1(5.9)
Miniperc	0(0)	1(8.3)	1(5.9)
Complications
Intraoperative complication	0(0)	1(8.3)	1(5.9)	1
Clavien II(Minor pelvic perforation)	0	1	1
Postoperative complications	0(0)	2(16.7)	2(11.8)	1
Clavien grade I(pneumonia)	0	1	1
Clavien grade I(renal colic)	0	1	1
Intraoperative Double-J stent (n, %)	0(0)	3(25)	3(17.6)	0.512
Postoperative Double-J Stent (n, %)	0	0	0	1
SD: standard deviation; n: Number; % :percentage

Discussion

The main finding of this study was that the immediate clearance rates of small stones was 100% with no significant morbidity. After the first pediatric series evaluating the use of percutaneous nephrolithotomy (PCNL) in children was reported by Woodside et al in 198514, further advances in access techniques and instrumentation facilitated the application of percutaneous nephrolithotomy in pediatric population15,16.

Reported stone-free rates range widely from 58% to 99% when PCNL was used as the sole therapy for stone extraction in children as shown in Table 317^-20. Salah et al in a review of PCNL in 135 children reported a success rate of 99%20. In a multicenter study of 140 PCNL in 130 children, Guven et al documented a stone free rate of 83%16. However, bleeding requiring blood transfusion has been a major concern of PCNL. Zeren et al., reported significant intraoperative hemorrhage requiring transfusion in 24% of patients in their study19. Lower transfusion rate of 8.5% was reported by Guven et al16. More recent studies however documented much lower rates of transfusion of less than five percent18,21.

Table 3. Comparison of percutaneous nephrolithotomy and microperc stone extraction in children.

Study	No. of patients/Renal units	Mean Age(Yrs)	Mean stone size	Maximum tract size	Conversion rate	Clearance(%)	Complications		Transfusion rate %
Paediatric percutaneous nephrolithotomy
Guven et al.,16	130/140	10.28	26.28mm	28	NA	83.9		27.9	8.5
Nouralizadeh et al., 18	20/24	3.1	33mm	26	NA	79.2		15.4	5
Zeren et al., 19	55/67	7.9	283mm2	30	NA	87		23.9	24
Salah et al., 20	135/138	8.9	507mm2	26	NA	99		9.6	1
Paediatric MicroPercutaneous nephrolithotomy(Microperc)
Hatipoglu et al., 6	37	8.4	14.8mm	4.85	3/37(8.1)	89.2		21.6	ND
Silay et al., 13	19	7.5	14.8mm	8	2/19(10.6)	89.5		15.7	Nil
Present study	17	9.96	12.7mm	10	2/17(11.8)	94.1		17.6	Nil
ND: Not documented; NA: Not applicable

Furthermore, study comparing the use of pediatric instrument and adult instrument for pediatric PCNL has shown a significant less mean haemoglobin drop of 0.71g/dl in those on whom pediatric instruments were used compared to haemoglobin drop of 1.53g/dl on those in whom adult instruments were utilized, p <0.00116. This has further strengthened the assertion that complications were more related to tract size and dilatation associated with PCNL.

Microperc as a form of minimally invasive percutaneous nephrolithotomy (PCNL) in which percutaneous renal access and stone fragmentation are achieved in a single-step using a 16 G needle is associated with less dilatation related complications. In the present study, microperc was used for 17 patients with mean stone size of 12.7mm in maximum diameter. The mean operating time was 47.9 minutes, lower than 63.6minutes reported in other series6,10^-13. This is an improvement on the learning curve when compared with the long operating time recorded in the reported first case of microperc stone extraction from this center10.

Bleeding which had been the major bane of PCNL was significantly lower in microperc. It had been postulated that bleeding occurred as a result of access creation, dilatation, or stone disintegration phase of PCNL22,23. Therefore, renal access achieved in a single step through the all-seeing needle with a 4.85Fr tract size minimized the risk. In some series, the mean hemoglobin drop associated with microperc ranged from 0.8 g/dl to 1.4 g/dl10,24,25. However, in a recent multicenter prospective trial of microperc in 19 children from four different centers, Silay et al reported a mean hemoglobin decrease of 0.1 mg/dl13. The need for blood transfusion or angioembolization was not indicated in those studies. In this study, blood transfusion was not required as the mean haemoglobin drop was 1.25mg/dl consistent with previous reports10,13.

The stone clearance rate reported with microperc from various workers ranged from 87% to 97%6, 10^-12. Desai et al in their first clinical report on 10 patients with the mean stone size was of 14.3 mm documented stone clearance rate of 90%10. Hatipoglu et al reported a stone clearance rate of 86.5% at 1-month and 89.2% at 3-months follow-up in a series of 37 children with a mean stone size of 14.8 mm (range 6-32mm)6,24. In a multicenter study of 19 children with mean stone size of 14.8mm, Silay et al. reported a clearance rate of 89.5% at 1-month follow up13. In the present study involving 17 patients with mean stone size of 12.7mm, the clearance rates at 1^st day and 1-month follow-up were 82.4% and 88.2% respectively. The result is comparable to some the findings of other workers6,13. We found no significant difference in the operating time [p=0.59], haemoglobin decrease [p=0.50], and median duration of hospital stay [p=0.65] between patient with small size renal stone and those with moderate size renal stone. However, 4.85 tract size was used for all the patients with small size stone compare to median tract size of 8Fr in children with moderate size renal stone[p= 0.01]. Moreso, three patients with moderate size renal stone had intraoperative placement of DJ stent while none had DJ stent in those with small size stone. This does not reach a statistical significant (p=0.51). Similarly, 2 patients needed auxillary procedure among those with moderate size stone while none of those with small size stone needed other procedures to extract the stones [p=1]. One patient with 7.5mm stone with narrow neck diverticulum in the middle calyx needed conversion to miniperc while another child with stone size of 24.9mm required miniperc to remove residual stone fragments.

Although, recent guidelines recommended shock wave lithotripsy (SWL) as the first line modality for stone <2cm in pediatric population5, but SWL is associated with high rate of re-treatment (27.9%-53.9%) and additional intervention to clear all the stones (7% to 33%)6,26,27. A recent analysis of 108 children with renal stones with average size of 11.3mm who undergone shockwave lithotripsy in Turkey showed that 31(28.7%) of the children required a repeat session of SWL6. Similarly, in a series of 170 children undergoing flexible ureteroscopy, 57% of them required passive dilatation of the ureter for 1-2 weeks before ureteroscopy could be done28. In this study, microperc was successful in 16(94.1%) at the first attempt except for an 11year old child with a stone size of 16.6mm who required miniperc to achieve complete clearance of the residual renal stones. Microperc is therefore safe and efficient in the minimal access extraction of renal stone in children and young adolescents.

The complication rate of 17.6% in the current study compares favourably with rates of 15.7% to 25.7% recorded in other studies6,11^-13. Most of the complications in microperc fall into the modified Clavien grade 1 group which are usually clinically insignificant, such as renal colic usually managed conservatively. These complications were due to principle of ‘break and leave’ employed in microperc which left stone fragments resulting in renal colic postoperatively. We recorded episodes of renal colic in a 14-year old boy who had microperc for 16mm stone. The patient was managed conservatively.

One of the limitations of microperc was the poor visibility due to blood clot or small bleeds which could lead to conversion to miniperc in some patients. The need for conversion to miniperc was 10% in a report from Turkey in the management of moderate sized calculi25. In this study, the conversion rate was 12% required to remove residual stone fragments. Another potential problem of microperc could be stone migration. Since microperc utilizes a tiny rigid instrument, retrieving a migrated stone fragment may be difficult. However, stone migration is low with careful holmium laser lithotrispsy in an undilated pelvicalyceal system. This study is limited by its non randomized design and the small sample size.

Conclusions

This study has shown that microperc is a safe and effective procedure for the extraction of renal stones in children.