Comparison of Miniaturized Percutaneous Nephrolithotomy and Standard Percutaneous Nephrolithotomy in Secondary Patients: A Randomized Prospective Study

Abstract

Aim:

We aimed to compare the efficacy and safety of mini-percutaneous nephrolithotomy (mPNL) and standard PNL (sPNL) in a group of patients who had a history of PNL and/or open renal surgery (secondary patients).

Materials and Methods:

The study included 148 patients who underwent secondary PNL between November 2016 and September 2018. The patients with kidney stone ≥2 cm were included in the study. Patients were randomly divided into two groups as mPNL and sPNL. For both groups, demographic data, stone characteristics, and operative and postoperative data were recorded prospectively. Data were analyzed at 95% confidence interval and considered significant when p value was <0.05.

Results:

A total of 148 (76 mPNL, 72 sPNL) patients with a history of PNL and/or open surgery were included in the study. The mean duration of operation was longer in mPNL (106.9 vs 91.2 minutes, p = 0.016). The mean duration of fluoroscopy in mPNL was shorter (4.4 vs 5.3 minutes, p = 0.021). The tubeless procedure was higher in the mPNL (21.1% vs 2.8%, p = 0.001). The hemoglobin drop was less in mPNL (0.7 vs 1.4 g/dL, p = 0.011). Duration of nephrostomy and hospitalization was longer in sPNL (p = 0.001 and p = 0.005, respectively). The success rate in the mPNL group was higher compared with the sPNL group; however, this difference was statistically insignificant (75.0% vs 72.2%, p = 0.558).

Conclusion:

mPNL is superior to sPNL in terms of hemoglobin drop, duration of fluoroscopy, applicability of a tubeless procedure, and duration of nephrostomy and hospitalization among secondary patients. Duration of operation was found to be longer for mPNL. Success rate was higher in the mPNL group, although not statistically significant.

Introduction

Treatment of stones in the urinary system has always constituted a major part in the practice of urology. While the incidence of urinary system stone disease in the past is unknown, studies indicate an increasing prevalence in the near future due to some factors such as the increasing rate of obesity and resulting metabolic changes, increased dehydration, and increased vitamin D due to global warming.^1

–4

Thanks to the unprecedented advances in optic systems in the last 25 years, the requirement for classical open surgical treatment for renal stones has dropped to a rate of 4%.⁵ Instead, modern methods such as percutaneous nephrolithotomy (PNL) and flexible ureterorenoscopy are widely used at present.

PNL surgery has been reported to be the gold standard for the treatment of renal stones larger than 20 mm in the European Association of Urology (EAU) guidelines.⁶ Although the efficacy and safety of PNL for renal stones have been proven, percutaneous kidney access comes with some problems. Need for transfusion due to postoperative hemorrhage has been reported to be 5%–18%.^7

–11 Some of this bleeding leads to resistant hematuria and 0.3%–1.4% of them require angioembolization.¹² Complications of conventional PNL are more prominent especially in the group of patients with a prior surgical treatment (secondary patients) and who have residual stones, since multiple access to the kidney is required and duration of operation is longer in this group of patients.

First defined by Jackman and colleagues in 1988, the mini-PNL (mPNL) procedure is based on the principle of performing a smaller sized dilation of the kidney using smaller instruments.¹³ mPNL is described as the procedure carried out by forming a ≤18 renal parenchymal tract in the EAU guidelines.¹⁴ Studies have shown a decrease in the rates of hematuria and hemorrhage requiring transfusion with this procedure due to the decreased area of parenchymal injury.¹⁵ In addition, it is easier to access other calices through the lower calix and the pelvicaliceal system is less traumatized as a natural result of the use of smaller instruments.

Secondary patients are a group of patients who had a history of PNL and/or open renal surgery. In general, treatment is difficult in those cases due to high stone load, presence of stones in more than one calix, or difficulty in accessing the kidney. Increased necessity for multiple access through the kidney and access to the other calices from a single-entry site is a challenging problem. We suggest that mPNL might be more advantageous in this complex group of patients compared with the standard method. A limited number of studies have been published in the literature comparing standard PNL (sPNL) and mPNL methods in secondary patient groups. In this randomized prospective study, we aimed to compare the efficacy and safety of sPNL and mPNL methods in patients to undergo a secondary procedure.

Materials and Methods

This prospective study was performed after obtaining an approval from the ethics committee. All the steps of the study were planned and performed according to the Helsinki Declaration of the World Medical Association (Haseki Training and Research Hospital, date: 24.02.2016 number: 305). Sample size was calculated using the GPower version 3.1.9.2 (Kiel, Germany) program and had the following settings: the type-1 error (α) was set to 0.05 and the power (1−β) to 0.8. Calculations based on these values produced a minimal sample size of 52 cases for each group. The study design and workflow are summarized in the consort flow chart (Fig. 1).

FIG. 1.

The study design and workflow.

The study included 148 patients who underwent secondary PNL (patients with a history of PNL and/or open renal surgery) between November 2016 and September 2018. Patients with urinary system anomalies, skeletal tract abnormalities and coagulopathy, pregnant patients, and pediatric patients (<18 years old) were excluded from the study. Patients were randomly divided into two groups as mPNL and sPNL. Randomization was performed by flipping a coin. For both groups, demographic data (age, gender, body mass index [BMI], and history of extracorporeal shockwave lithotripsy or surgery) and stone characteristics (size, lateralization, localization, and opacity) were recorded prospectively.

All patients were evaluated by urinalysis, urine culture, complete blood count, creatinine level, and coagulation tests. Patients with urinary tract infection were treated with appropriate antibiotherapy. Before the operation, sterile urine culture was obtained from all patients. As antibiotic prophylaxis, a second-generation cephalosporin was administered before the operation. All patients were evaluated preoperatively with noncontrast computed tomography (NCCT). When calculating the stone size, the longest measured dimension was recorded in millimeters (mm). In case of multiple calculi, the sum of the greatest dimension of each stone was calculated.

After the placement of a 5F ureteral catheter, access to the posterior calix was performed under C-arm fluoroscopy (Sire Mobil Compact, Siemens) using an 18-gauge needle (Boston Scientific Corporation, Natick, MA) while the patient was in the prone position. The tract was dilated using a high-pressure balloon dilator (NephroMax TM Microvasive; Boston Scientific Corporation) or Amplatz dilators. After dilatation, a 16.5F/20F sheath for mPNL or a 30F sheath for sPNL was placed under fluoroscopic guidance. Nephroscopy was performed with a 12 or 14F rigid nephroscope (Karl Storz, Tuttlingen, Germany) for mPNL and 26F rigid nephroscope (Karl Storz) for sPNL.

Fragmentation of the stone was accomplished using a pneumatic (Vibrolith^®; Elmed, Ankara, Turkey), ultrasonic (Swiss Lithoclast^®; EMS, Nyon, Switzerland), or holmium YAG laser lithotripter. Stone fragments were removed using a basket, bipod, or tripod grasping forceps. Big fragments were collected after fragmentation. Little fragments that could not be collected were taken out by water pressure and left to spontaneous passage. At the end of the operation, a 14F nephrostomy tube or 4.8F Double-J (Boston Scientific Corporation) catheter was placed. Operations were terminated without placement of a tube (neither a Double-J catheter nor a nephrostomy tube) unless residual stones or perioperative complications were present. Operative data (duration of operation, duration of fluoroscopy, dilator type, localization of access, access sheath size, lithotripter type, nephrostomy, and Double-J stent placement) were recorded prospectively.

All patients were assessed with complete blood count and creatinine level tests postoperatively. The kidney, ureter and bladder X-ray (KUB) was obtained on the 1st operative day. The nephrostomy tube was removed on the 2nd postoperative day. If a Double-J stent was placed during the initial operation, the catheter was removed 2 weeks after the operation. All patients were evaluated with an NCCT 3 months after the operation to determine the final stone-free status. Patients with complete clearance of stones and with residual fragments smaller than 4 mm were accepted as stone free. Postoperative data (duration of nephrostomy, duration of hospitalization, hemoglobin drop, increase in creatinine level, complications, and stone-free rate) were recorded prospectively. Clavien–Dindo classification was used to record complications.

The Statistical Package for the Social Sciences version 20 (SPSS IBM Corp.; Armonk, NY) program was used in the analysis of the data. Independent t test was used to compare independent groups, Pearson correlation test to examine the relationship between variables, and Pearson chi-square, chi-square, and Fisher exact tests to compare categorical data. Quantitative data are expressed as mean ± standard deviation values in tables. Categorical data were expressed as n (frequency) and percentages (%). Data were analyzed at 95% confidence interval (CI) and it was considered significant when p value was <0.05.

Results

A total of 148 (76 mPNL, 72 sPNL) patients with a history of PNL and/or open surgery were included in the study. No difference was found between the two groups in age, gender, BMI, history of surgery, stone size, and localization of the stones (p ≥ 0.05). The characteristics of patients and stones are shown in Table 1.

Table 1.

Demographic Data and Stone Characteristics

	mPNL	sPNL	p
Number of patients	76	72
Sex (female/male)	26/50	24/48	0.910
Age (year)^a	47.0 ± 13.9	46.7 ± 14.2	0.838
body mass index (kg/m²)^a	28.6 ± 5.4	28.4 ± 5.6	0.708
Previous SWL or surgery, n (%)
SWL	10 (13.2)	9 (12.5)	0.905
URS	11 (14.5)	7 (9.7)	0.377
PNL	62 (81.6)	58 (80.6)	0.874
Open surgery	24 (31.6)	23 (31.9)	0.962
Stone opacity (opaque/nonopaque)	71/5	68/4	0.707
Stone location, n (%)			0.196
Lower calix	4 (5.3)	3 (4.2)
Middle calix	0	1 (1.4)
Upper calix	0	1 (1.4)
Pelvis	4 (5.3)	0
Multiple calix	68 (89.5)	67 (93.1)
Stone size (mm)^a	32.6 ± 8.1	33.1 ± 10.9	0.563
Hydronephrosis (mild/severe)	52/24	47/25	0.685
Operation side (right/left)	40/36	35/47	0.124

Mean ± standard deviation.

mPNL = mini-PNL; PNL = percutaneous nephrolithotomy; sPNL = standard PNL; SWL = extracorporeal shock wave lithotripsy; URS = ureterorenoscopy.

The mean duration of operation was longer in mPNL (106.9 vs 91.2 minutes, p = 0.016). However, the mean duration of fluoroscopy in mPNL was shorter (4.4 vs 5.3 minutes, p = 0.021). Dilatation type, Amplatz sheath size, and lithotripter type were significantly different between the two groups (p = 0.001). Although there was no difference between the two groups in terms of perioperative Double-J placement (15.8% vs 18.1%, p = 0.713), the rate of the tubeless procedure was higher in the mPNL group (21.1% vs 2.8%, p = 0.001). The operational data are shown in Table 2.

Table 2.

Operative Data

	mPNL	sPNL	p
Number of patients	76	72
Duration of operation (minutes)^a	106.9 ± 38.8	91.2 ± 33.2	0.016
Duration of fluoroscopy (minutes)^a	4.4 ± 3.2	5.3 ± 3.1	0.021
Dilatation type (Amplatz/balloon)	76/0	51/21	0.001
Amplatz sheath size (F), n (%)			0.001
16.5	35 (46.1)	0
20	41 (53.9)	0
30	0	72 (100.0)
Access localization, n (%)			0.475
Lower calix	43 (63.2)	49 (68.1)
Middle calix	8 (10.5)	4 (5.6)
Upper calix	6 (7.9)	9 (12.5)
Multiple calix	14 (18.4)	10 (13.9)
Intercostal access, n (%)	11 (14.5)	10 (13.9)	0.919
Lithotripter type, n (%)			0.001
Ultrasonic	0	51 (70.8)
Pneumotic	0	17 (23.6)
Laser	76 (100.0)	4 (5.6)
Double-J placement, n (%)	12 (15.8)	13 (18.1)	0.713
Tubeless procedure, n (%)	16 (21.1)	2 (2.8)	0.001

Mean ± standard deviation.

Complications and postoperative outcomes are summarized in Table 3. There was no difference between the two groups in terms of complications (p ≥ 0.05). The hemoglobin drop was less in mPNL (0.7 vs 1.4 g/dL, p = 0.011). Duration of nephrostomy and hospitalization was longer in sPNL (p = 0.001 and p = 0.005, respectively). The success rate in the mPNL group was higher compared with the sPNL group, although not statistically significant (75.0% vs 72.2%, p = 0.558).

Table 3.

Complications and Postoperative Outcomes

	mPNL	sPNL	p
Number of patients	76	72
Postoperative Double-J placement, n (%)	6 (7.9)	6 (8.3)	0.922
Fever, n (%)	0	2 (2.8)	0.235
Blood transfusion, n (%)	2 (2.6)	4 (5.6)	0.433
Angioembolization, n (%)	1 (1.3)	1 (1.4)	1.000
Pleural effusion, n (%)	1 (1.3)	2 (2.8)	0.612
Hemoglobin drop (g/dL)^a	0.7 ± 1.3	1.4 ± 1.5	0.011
Increase in creatinine (mg/dL)^a	0.55 ± 3.78	0.04 ± 0.46	0.158
Clavien–Dindo classification, n (%)			0.880
0	60 (78.9)	55 (76.4)
1	7 (9.2)	6 (8.3)
2	1 (1.3)	3 (4.2)
3a	2 (2.6)	2 (2.8)
3b	6 (7.9)	6 (8.3)
4	0	0
Duration of nephrostomy (hour)^a	47.8 ± 42.8	61.8 ± 38.3	0.001
Duration of hospitalization (hour)^a	64.3 ± 36.5	75.5 ± 34.0	0.005
Success, n (%)	57 (75.0)	52 (72.2)	0.558

Mean ± standard deviation.

Discussion

PNL is a frequently used procedure in the treatment of large renal stones. Parallel to the advances in minimally invasive surgery over the years, the size of the PNL instruments has become smaller. Renal dilatation used to be performed by 24–30F instruments in sPNL, while the size of the instruments has decreased finally to 4.5F using mPNL, ultra-mPNL, super-mPNL, and micro-PNL. The superiority of any of the above procedures to the others especially in terms of complications and success rates is yet to be evaluated.

When compared with primary patients, patients with secondary renal stones form a special patient group with challenges in treatment. It is vital to ensure surgical success to avoid recurrent surgery and complications in this group of patients. Failure to treat these patients with a single operation is due to various factors such as the complex anatomical localization of the stones, the inability to access all of the stones, and perioperative complications. Therefore, it is crucial to determine the size of PNL in patients to undergo a secondary procedure. There are few studies in the literature on the PNL method in patients with a secondary procedure. To our knowledge, there is no prospective randomized study on this subject. The aim of the present study was to compare sPNL and mPNL procedures in patients with a secondary procedure.

Duration of operation in mPNL was found to be significantly longer compared with the conventional procedure (p = 0.016). While lithotomy was performed by laser alone in mPNL, ultrasonic or pneumatic lithotripter was used in 94.4% in the standard procedure. Besides, as the diameter of the sheath of access is decreased, the stone needs to be crushed and collected more to be completely removed out of the body. All of these factors have extended the duration of operation in mPNL. In a prospective study, Knoll and colleagues compared 50 patients who underwent sPNL and mPNL.¹⁶ Duration of operation was 59 ± 2 minutes in mPNL and 49 ± 2 minutes in sPNL with no significant difference between the groups. However, in a comparative study by Giusti and colleagues on 134 patients, mPNL operation was found to be significantly longer compared with the standard operation (p < 0.001).¹⁷ Thus, mPNL is considered disadvantageous in terms of the duration of operation.

The duration of fluoroscopy was found to be significantly shorter in mPNL (p = 0.021). Although this seems surprising, as Amplatz dilatation was mainly used in both groups, it is likely that dilatation at a smaller scale was completed in a shorter time. Studies on this subject have generally compared duration of operation without taking into account the duration of fluoroscopy. On the contrary, in a randomized prospective study by Erbin and colleagues on 97 patients, no significant difference was found between mPNL and sPNL in terms of the duration of fluoroscopy.¹⁸ While our study contradicts with the literature in this aspect, it is quite valuable when the potential effects of radiation on urologists are considered. If Amplatz dilatation is preferred instead of balloon dilatation, mPNL seems to have a shorter duration of fluoroscopy compared with the standard procedure, resulting in an advantage for mPNL. Nevertheless, further research involving more patients is necessary.

Evaluation of hemoglobin drop in the present study revealed a significantly lower drop in mPNL compared with the sPNL (p = 0.011). mPNL resulted in a lower rate of hemorrhage requiring transfusion, although not statistically significant. These results might be associated with the fact that trans-parenchymal dilatation in mPNL is at a smaller scale. A study by Cheng and colleagues involving 187 renal units compared mPNL and sPNL. Both hemoglobin drop and hemorrhage requiring transfusion were found to be in significantly lower rates in mPNL (p < 0.05).¹⁹ In a meta-analysis by Zhu and colleagues involving eight studies, hemoglobin drop and blood transfusion rates were found to be significantly lower in the mPNL procedure (95% CI).²⁰ Decreased hemorrhage in mPNL facilitates the application of a tubeless procedure at the end of the operation. Similarly in the present study, the number of patients undergoing a tubeless procedure in mPNL was found to be significantly higher compared with sPNL (p = 0.001). As a result, it could be concluded that lesser dilatation leads to lesser hemorrhage.

Long-term postoperative resistant hematuria is among the rare and feared complications. In our study, one patient in each group underwent angioembolization with no significant difference between the groups (p = 1). The rates of angioembolization were found to be 1.3% and 1.4% in the two groups, respectively, and are both higher than the rates reported in the literature (0.5%).^9,12 Access to the kidney is complicated due to the damaged caliceal anatomy due to complex stones that are present in most patients and prior open surgery, and thus, more than one access might be needed. These factors might have resulted in this condition.

While hemorrhage requiring transfusion occurred in fewer patients in mPNL, there was no significant difference between the two groups (p = 0.43). In the study by Cheng and colleagues, although parallel to hemoglobin drop, transfusion rates were also significantly lower in mPNL.¹⁹ The reason for different results obtained in the present study might be the characteristics of the patients included in the study, namely secondary patients. In a review by Tepeler and colleagues, it was stated that PNL was not a surgical procedure performed through a natural orifice translumenal endoscopic surgery (NOTES) despite the use of smaller instruments, and thus, mPNL and micro-PNL could minimize the risks but not completely eliminate them.²¹ Consequently, it should be kept in mind that there is a risk for hemorrhage requiring transfusion and angioembolization in all types of PNL.

Duration of postoperative nephrostomy and hospitalization was found to be shorter in mPNL compared with the standard procedure (p = 0.001 and p = 0.005, respectively) in the present study.¹⁹ In a meta-analysis by Zhu and colleagues involving eight studies, five studies showed shorter duration of hospitalization in mPNL.²⁰ The study by Giusti and colleagues also revealed a shorter duration of hospitalization in mPNL compared with sPNL.¹⁷ This might be due to the use of tubeless procedures more frequently, expectation of less hemorrhage, and more minimal kidney trauma in mPNL.

Surgical success in patients with a secondary procedure is associated with the choice of the surgical procedure. mPNL was more effective compared with sPNL, although not statistically significant (75% and 72.2%, respectively, p = 0.558). In the literature, surgical success has been reported to be higher in both groups compared with the present study. The patient group in our study mostly consisted of patients with multiple caliceal stones and this might have led to the decrease in success for both groups. In the study by Knoll and colleagues, patients with solitary renal stones were analyzed. While mPNL was found to yield more success compared with the sPNL, the difference between the groups was statistically insignificant (96% and 92%, respectively).¹⁶ The involvement of patients with solitary stones seems to be the factor for increased success.

In the study by Cheng and colleagues, the patients were grouped according to stone localization, and mPNL was found to have a significantly better success rate in patients with multiple caliceal stones.¹⁹ The multivariate analysis in a study by Kokov and colleagues evaluating 146 mPNLs revealed that the only independent determining factor affecting the success rate was stone size.²² In patients with a secondary procedure, there are usually residual stones in more than one calix. The tiny instruments used in mPNL facilitate access to different calices, through which the mucosa of the pelvicaliceal system is less traumatized. Considering the mean stone size about 3 cm in the present study, mPNL could be considered an effective and reliable procedure for patients to undergo a secondary procedure.

To our knowledge, our study is the first prospective and randomized study to compare mPNL and sPNL in patients with a secondary procedure. On the contrary, our study has some limitations and shortcomings. In our clinic, mPNL was performed using two different nephroscopes. Postoperative evaluation of the patients was performed without the use of a pain scale. Two dimensional calculation for stone dimensions was not used. Besides, our study involved relatively few patients. Clearer results may be obtained through larger series involving more patients.

Conclusion

In patients with a secondary procedure for renal stones, mPNL is superior to sPNL in terms of hemoglobin drop, duration of fluoroscopy, applicability of a tubeless procedure, and duration of nephrostomy and hospitalization. Rates of hemorrhage requiring transfusion or angioembolization are similar with those in sPNL. Duration of operation was found to be longer in mPNL. Success rate was higher in the mPNL group, however, the difference was statistically insignificant.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Abbreviations Used

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