Management of Anteriorly Located Renal Caliceal Stones with Two Different Techniques (Mini-Percutaneous Nephrolithotomy vs Flexible Ureteroscopic Laser Lithotripsy): A Critical Comparative Evaluation of the Outcomes

Abstract

Purpose:

To evaluate the efficacy and safety of two different approaches, flexible ureteroscopic laser lithotripsy (fURS) and mini-percutaneous nephrolithotomy (mini-PCNL), for the minimally invasive management of anteriorly located caliceal stones in a location-based manner.

Materials and Methods:

A total of 93 patients with anterior caliceal stones (<15 mm) were treated with following two different modalities: fURS (n = 52, 55.9%) (Group 1) and mini-PCNL (n = 41, 44.1%) (Group 2). Demographic, per-operative, and postoperative parameters were comparatively evaluated in both groups.

Results:

The groups were similar in terms of their demographic data and stone characteristics (p > 0.05). Operation, fluoroscopy time, and hospital stay were significantly longer in Group 2 (p < 0.001). The perioperative complication and overall stone-free rates were similar between the groups (p = 0.44 and p = 0.53, respectively). However, when the stone-free rates were examined according to the calix groups, Group 2 was significantly more effective in terms of stone-free rates in the lower calix (52% vs 84%, p = 0.03). Although not statistically significant, more postoperative complications were observed in Group 2 (p = 0.09).

Conclusion:

Our findings demonstrate that although mini-PCNL may be performed well through a caliceal puncture to remove lower caliceal stones with a high stone clearance rate, the fURS approach may be safer and more rational for the removal of stones located in the middle and upper anterior calices.

Introduction

Urinary system stone is one of the most common urologic diseases within certain geographies, with a prevalence of as much as 20%.¹ Renal stones located in different parts of the collecting system, including anterior caliceal stones, constitute a considerable proportion of all renal stones.² Interventional treatment of such stones poses a challenge for endourologists because of their specific location and difficulty in reaching the stone site.³

Minimally invasive interventional management seems to be in demand when the stone size and anatomical characteristics of the involved kidney seem to play critical roles. Moreover, the removal of anterior caliceal stones has been found to be complicated because of the difficulties in anatomical access through these calices and the extraction and elimination of fragments.^4,5 Among the factors affecting the final outcome of the management size of the stone, its composition, any modifications in the renal collecting system, the clinician’s or patient’s preference, and the availability of adequate equipment and experience can be regarded as important ones to be considered well during decision-making phase.⁶

In this study, we aimed to report our experience with the management of anterior caliceal stones (<15 mm) using two different approaches as follows: flexible ureteroscopic laser lithotripsy (fURS) and mini-percutaneous nephrolithotomy (mini-PCNL).

Materials and Methods

After receiving approval from the local ethics committee, 813 patients who underwent retrograde intrarenal surgery (RIRS) and mini-PCNL for the treatment of upper urinary tract stones between 2019 and 2024 were retrospectively analyzed. Of these patients, 93 with isolated anterior calix stones were included in the study as follows: 52 patients underwent fURS (Group 1), and the remaining 41 patients underwent mini-PCNL (Group 2). Patients who had previously undergone extracorporeal shockwave lithotripsy (SWL) or operation for kidney stones, congenital kidney anomalies, solitary kidney, concomitant procedure, were under 18 years of age, had preoperative Double-J stent and/or nephrostomy catheter, and had stones outside the anterior calix were excluded from the study. Routine preoperative radiologic imaging, including abdominal unenhanced CT, and laboratory analyses, including serum creatinine levels, coagulation tests, urinalysis, and urine culture, were performed in all patients. All the patients underwent direct X-ray imaging on the 1^st postoperative day to evaluate the location of the Double-J or nephrostomy tube. In addition, the final stone clearance rate was evaluated using noncontrast CT imaging at the end of the 1^st postoperative month. Stone-free status was categorized into three grades based on postoperative CT scans (with 2 mm cuts). Grade A is no stone (0 mm) in the CT images, Grade B is the presence of <2 mm residual stones, and Grade C is a 2.1–4 mm residual stone. Additional procedures (fURS) were performed in patients who were not stone free. Renal stones with a length of less than 15 mm were selected as the stone measurement for evaluating a specific comparable group. Patients were randomly assigned to perform fURS vs mini-PCNL based on patient requests and the availability of the device during the operation. Written informed consent was obtained from all patients before the procedure. All patients with positive urine cultures were treated according to an antibiogram, and operation was performed under sterile urine. Second-generation cephalosporins were used for antibiotic prophylaxis, and all surgeries were performed under general anesthesia by a single experienced surgeon. The surgeon has more than 10 years of surgical experience, with an average of 250 endourology stone-related cases per year. Age, sex, body mass index (BMI), stone size, surgical side, stone density, presence of renal hydronephrosis, preoperative serum creatinine level, operation time, fluoroscopy time, hospitalization time, perioperative complication rates, postoperative hemoglobin loss, postoperative transfusion rates, narcotic analgesic requirement, number of secondary interventions, and stone-free rates were evaluated.

Surgical technique for RIRS (Group 1)

Standard cystoscopic procedures and ureteral visualization were performed using a 6F/8F rigid ureterorenoscope on the surgical side. A safety guidewire (0.035 inch) was routinely placed in the ureter. A 10/12-F ureteral access sheath (UAS) (Bi-Flex™, Rocamed, Monaco) was inserted over the guidewire and placed 1 cm below the ureteropelvic junction under fluoroscopic guidance. A disposable flexible ureteroscope with 9 Fr (HugeMed HU30; Shenzhen, China) was placed through the UAS. The kidney stone unit was fragmented and dusted using a Ho-YAG (50 Watt, Jena, Germany) device and a 272 µm laser fiber. When the stone fragments were smaller than the laser tip diameter, they were considered to have sufficient fragmentation and left for passive drainage. A Nitinol basket catheter was used in the presence of the large stone fragments. A 4.7-Fr Double-J stent was routinely placed in the urinary system and removed after 2–4 weeks in the office.

Surgical technique for Mini-PCNL (Group 2)

A standard cystoscopic procedure and 6-F ureteral catheter placement were performed under fluoroscopic guidance. Retrograde contrast material was administered to the kidney in the prone position, and 18-gauge Chiba needles were used to provide access. Before the procedure, the surgeon planned to reach the posterior calix at the level of the stone or directly to the anterior calix depending on the surgeon’s preference. The first kidney was assessed under fluoroscopy using the bull’s eye technique. Dilation was performed using fascial dilators. An 18/20F Amplatz sheath was placed in the kidney, and access to the kidney was provided using a 16 F Mini Nephroscope (Hawk, Hangzhou Hawk Optical Electronic Instruments, Zhejiang, China) through the sheath. Kidney stones were fragmented or pulverized using a 550 µm laser fiber Ho-YAG (50 Watt, Jena, Germany) laser device or pneumatic lithotripter (Vibrolith Plus, Orlando, USA). Stone fragments were removed using 4F forceps if necessary. The decision to insert a Double-J stent or nephrostomy tube was made based on the duration of the procedure, perioperative bleeding status, and surgeon’s preference.

Statistical analysis

In analyzing the data, descriptive statistics, including the mean, standard deviation, median, minimum, and maximum values, were used to characterize the variables. Frequency and percentage values were used to describe the categorical variables. The Student’s t-test was used to compare the means of two independent groups. Paired t-tests were used to compare the means of two repeated (pre–post) measurements. Chi-square test statistics were applied to evaluate the relationship between categorical variables. The statistical significance level was set at p < 0.05. Data analysis was conducted using the IBM SPSS version 25 statistical package program.

Results

A total of 93 patients were included in the study; 52 (55.9%) of these patients were in Group 1 and 41 (44.1%) were in Group 2. The mean age of all patient groups was 49.9 ± 15.3 years. Sixty-three (67.7%) patients were male, and 30 (32.3%) were female. The groups were similar in terms of age, sex, and BMI (p > 0.05). Although the operation time was 59.8 ± 11.2 and fluoroscopy time was 1.58 ± 0.97 minutes in Group 1, these times were calculated as 120.1 ± 13.5 and 4.85 ± 1.63 minutes, respectively, in Group 2. Operation, fluoroscopy time, and hospital stay were significantly longer in Group 2 (p < 0.001). In the mini-PCNL group, anterior access was achieved through the posterior calix puncture in 24 patients. In contrast, in 17 patients, direct anterior calix puncture and access were performed due to the perpendicular angulation of posterior calix. In addition, no significant differences were observed between the fURS and mini-PCNL groups in terms of stone location, hydronephrosis degree, stone density, and stone size (p > 0.05). Demographic and stone-related data and perioperative findings are summarized in Table 1.

Table 1.

Patient Demographics and Perioperative Findings of Flexible Ureteroscopic Laser Lithotripsy and Mini-Percutaneous Nephrolithotomy Patients

	fURS (Group 1) (n = 52)	Mini-PCNL (Group 2) (n = 41)	p-value
	Mean ± SD	Mean ± SD	p-value
Age	51.6 ± 16.1	47.7 ± 14.2	0.23^a
BMI (kg/m²)	24.10 ± 1.35	23.66 ± 1.13	0.09^a

	n (%)	n (%)
Sex			0.58^b
Female	34 (65.4)	29 (70.7)
Male	18 (34.6)	12 (29.3)
Stone Side
Right	24 (46.2)	20 (48.8)	0.84^b
Left	28 (53.8)	21 (51.2)	0.84^b
Degree of Hydronephrosis
Grade 0	37 (71.2)	34 (82.9)	0.08^b
Grade I	13 (25)	4 (9.8)
Grade II	1 (1.9)	3 (7.3)
Grade III	1 (1.9)	0 (0)

	Mean ± SD	Mean ± SD
Stone Density (HU)	962 ± 312	1040 ± 346	0.34^a
Stone Size (mm)	12.2 ± 1.7	12.9 ± 1.8
	(min. = 9.7 max. = 14.9)	(min. = 9.8 max. = 14.9)	0.07^a
Operative Time (min.)	59.8 ± 11.2	120.1 ± 13.5	<0.001 ^a
Fluoroscopy Time (min.)	1.58 ± 0.97	4.85 ± 1.63	<0.001 ^a
Preop. Creatinine (mg/dL)	0.94 ± 0.31	0.89 ± 0.43	0.61^a
Preop. HCT (%)	40.6 ± 5.6	40.7 ± 4.8	0.87^a
Hospital Stay in days	1.2 ± 0.4	2.7 ± 0.8	<0.001 ^a

Student’s t-test.

Chi square test.

fURS = flexible ureteroscopic laser lithotripsy; mini-PCNL = mini-percutaneous nephrolithotomy; SD = standard deviation; HU = hounsfield units; BMI = body mass index; HCT = hematocrit.

Note: The P values in bold represent the significant parameters.

The stone-free rates according to the grade and stone location are presented in Table 2. The overall stone-free rate was 77.4%. When the stone-free rates were examined according to the calix groups, Group 2 was significantly more effective in terms of stone-free rates in the lower calix (52% vs 84%, p = 0.03). When we evaluated the emergency readmission cases in fURS group, there were a total of 8 (15.4%) patients (4 patients had renal colic, 3 patients had fever, and 1 patient had urinary retention). In contrast, 4 (9.8%) patients (2 patients had hematuria, 1 patient had fever, and 1 patient had renal colic) in mini-PCNL group were readmitted to the emergency department. The overall stone-free and emergency readmission rates were similar between the groups (p = 0.53, p = 0.42, respectively). Although postoperative creatinine levels decreased significantly in both groups (p = 0.001), no significant difference was observed between the groups (p = 0.61, p = 0.84, respectively). In contrast, there was no significant decrease in the hematocrit (HCT) level in Group 1 (p = 0.53), HCT decreased significantly in Group 2, and the postoperative HCT difference was significantly higher in Group 2 (p = 0.001 and p = 0.04, respectively).

Table 2.

The Peri-/Post-Operative Complications and Outcomes of Flexible Ureteroscopic Laser Lithotripsy and Mini-Percutaneous Nephrolithotomy

	fURS (Group 1) (n = 52)	Mini-PCNL (Group 2) (n = 41)	p-value
	Mean ± SD	Mean ± SD	p-value
Postoperative Creatinine (mg/dL)	0.90 ± 0.29	0.92 ± 0.39	0.84^a
Postoperative HCT (%)	38.5 ± 5.5	36.3 ± 4.8	0.04 ^a

	n (%)	n (%)
Perioperative Complications	8 (15.3)	7 (17.1)	0.44^c
	Access Failure (n = 4)	Hemorrhage (n = 4)
	Mucosal Laceration (n = 4)	Rupture of calix (n = 2) Puncture Failure (n = 1)
Emergency Readmission	8 (15.4)	4 (9.8)	0.42^c
Overall Stone-Free Rate	39 (75)	33 (80.5)	0.53^b
Stone-Free Rate According to Calix
Lower	12 (52)	16 (84)	0.03 ^d
Middle	15 (88)	9 (75)	0.35^c
Upper	12 (100)	8 (80)	0.10^c
Postoperative Additional Treatment Requirement	4 (7.6)	1 (2.4)	0.26^c
Clavien–Dindo Score
0	48 (92.3)	34 (82.9)	0.09^c
1	4 (7.7)	3 (7.3)
	Fever (n = 3)	Hematuria (n = 2)
	Urinary retention (n = 1)	Fever (n = 1)
2	0 (0)	4 (9.8)
		Blood transfusion (n = 4)

Student’s t-test.

Paired t-test.

Chi Square test.

Z test.

fURS = flexible ureteroscopic laser lithotripsy; mini-PCNL = mini-percutaneous nephrolithotomy; SD = standard deviation; HCT = hematocrit.

Note: The P values in bold represent the significant parameters.

Upon analysis of perioperative complications, 8 (15.3%) patients in fURS and 7 (17.1%) patients in mini-PCNL group had complications (p = 0.44). Among these perioperative complications in fURS group, the procedure was halted in 4 (7.7%) patients because of unsuccessful UAS placement, and 4 (7.7%) patients had urothelial mucosal lacerations. When we evaluated perioperative complications in mini-PCNL group, four (9.8%) patients had bleeding that complicated the operation, two (4.9%) patients had rupture of the pelvicaliceal system, and one (2.4%) patient had failed kidney puncture. In these cases, a retrograde Double-J stent was inserted into the stone-containing kidney to conclude the intervention. Blood transfusion was applied only to patients with perioperative hemorrhage with slow flow perioperatively and continued in the recovery room. The modified Clavien–Dindo score system was used to evaluate postoperative complications. In fURS group, there were 4 (7.7%) patients with a Clavien score of 1 (3 patients had fever and 1 patient had urinary retention). In mini-PCNL group, there were 3 (7.3%) patients with a Clavien score of 1 (2 patients had gross hematuria and 1 patient had fever), and there were 4 (9.8%) patients who required blood transfusion with a Clavien score of 2. There were no patients with Clavien grade 3 or 4 in either group. The perioperative and postoperative complications and outcomes are presented in Table 2.

Discussion

The incidence of urolithiasis is increasing because of environmental and dietary factors.⁷ Although a certain percentage of renal calculi may not require any treatment (but a close follow-up) if they are small and/or asymptomatic, stones causing pain, obstruction, and infection require removal in most cases as they affect the patient’s quality of life during this period. Regarding the management of these stones, rational decision-making based on stone and patient-related factors should be made to identify the best option for stone removal. Among the stone-related factors evaluated thus far, the location of the stone in the renal collection system is an important parameter affecting both the decision and outcomes of the dedicated treatment alternative.⁸

Compared with the management of stones in normal locations, the management of stones in these cases is more difficult because of factors, including the abnormal anatomy and aberrant vascular structure of the kidney, the intestinal structures surrounding the kidney, and the kinked ureter with a high insertion into the renal pelvis. Although open procedure was the only option during the pre-endourologic era, minimal or noninvasive techniques have replaced this approach based on the remarkable advantages of instrument technology. Related to this issue, as the only noninvasive option, although SWL has been applied for these stones in a safe and practical manner, the reported rates of a completely stone-free status are highly limited.⁹

Concerning the minimally invasive management of such calculi, European Association of Urology guidelines do not provide clear recommendations for anterior caliceal stones.¹⁰ SWL, fURS, and PCNL are the available options for stone removal in such cases.¹¹ An evaluation of the literature on this aspect and accumulated experience indicate that (although limited) both fURS and PCNL can be applied to remove calculi located in anteriorly located calices.¹² However, it has been well demonstrated that because of the challenging location of these calices compared with the posterior ones (based on the anatomy-related application of these procedures in routine practice), reaching the stones, either retrograde or percutaneous, could be difficult, necessitating a certain level of experience.

Among the commonly applied options in the management of caliceal stones, the PCNL procedure has undergone extensive evolution, owing to evident advancements in instrument technology and newly introduced miniaturized techniques.¹³ The invasiveness of the procedure decreased to a certain extent with the application of the Mini/Mini-ultra methods, and the success rates continued to be acceptable. Currently, PCNL is the preferred treatment modality for renal calculi >20 mm.¹⁰ In contrast, the application of flexible ureteroscopic laser disintegration of kidney stones has increased tremendously due to the clinical introduction of the holmium-YAG laser for stone disintegration and significant advancements in instrumentation and fiberoptic technology. The effective use of newly designed access sheets has brought this modality into a distinct position for the safe and effective management of such stones, particularly stones in the lower caliceal position. Currently, the available guidelines recommend this modality as a valuable treatment choice for renal stones sizing 10–20 mm.^10,14
–16

Although stone size and composition were not found to affect the final outcomes of this particular modality, similar to all other available management options, the complexity of the pelvicaliceal system has been identified as a critical factor because of its impact on the success of all available treatment modalities for stones.^6,8 In contrast, this concept (the critical impact of caliceal anatomy) was also added to the agenda of endourologists based on the available clinical guidelines. Anterior caliceal stones represent a challenge to endourologists in selecting the best management modality with higher success rates and, of course, the least morbidity. Related to this issue, highly limited information can be derived from the published literature focusing on the proper management of the anterior caliceal.¹⁷ El-Shazly stated that PCNL is a feasible modality for treating large anterior caliceal stones (>15 mm) with a high stone clearance rate and that RIRS is a good alternative to PCNL, with the advantages of less radiation exposure and less bleeding.¹² Our study, with its relatively larger number of cases, sheds light on the rational management of stones smaller than 15 mm.

Mini-PCNL has superior stone-free rates, whereas fURS is associated with fewer complications and bleeding.^18,19 We also observed that stone-free rates were better with mini-PCNL, especially for lower pole stones. Although innovations have been developed in fURS, this procedure may not be sufficient for extracting and clearing lower pole stones in all patients.²⁰ However, we observed that both mini-PCNL and fURS had similar stone-free rates in middle and upper pole anterior calix stones. In contrast, in addition to fewer complications and less bleeding, fURS had a shorter fluoroscopy, operation time, and hospital stay, which are valuable advantages over mini-PCNL. When we consider all of these findings together, we think that fURS and mini-PCNL are alternatives to each other, depending on surgical experience and equipment availability.

Our study has some limitations. First, the retrospective nature of the methodology could lead to certain limitations. In addition, the patient population was relatively low because patients with isolated anterior caliceal stones, which were selective locations with many exclusion criteria, were also examined. In addition, the anatomical structures of all patients might not be exactly the same, but similar anterior calix positioning of the stones and the application of the same procedure by a single surgeon are the advantages of this study. Another limitation might be that in mini-PCNL, we evaluated the anterior and posterior access together. In our clinical approach, we preferred to try posterior calix puncture first, but we used anterior calix access in patients in whom the stone could not be reached with posterior calix puncture. We believe that it would be more accurate to compare patients with fURS with both posterior and anterior access in mini-PCNL procedures. In addition, another treatment alternative for the patients in our study could have been SWL. We offered SWL to some patients, especially those who could not tolerate the operation. However, our main purpose in this study was to compare fURS and mini-PCNL.

Conclusions

Surgical intervention for anterior calix stones should be evaluated differently in addition to stone size and the pole in which the stone is located. Mini-PCNL has much better stone-free rates especially in lower pole stones; in contrast, less radiation exposure, shorter hospital stay, and fewer postoperative complications are the prominent advantages of fURS. The decision on which intervention to perform in anterior calix stones would be made on a patient-by-patient basis, depending on surgical experience and equipment availability, and it should not be forgotten that the two interventions could be alternatives to each other.

Footnotes

Authors’ Contributions

Conceptualization: F.Y.S. and K.S.; Methodology: F.Y.S., M.A., and K.S.; Writing: F.Y.S., M.A., and K.S.; Editing: F.Y.S., M.A., A.S.D., A.A., and H.Y.; Statistics: F.Y.S., E.E., and E.B.Ş.; and Supervision: E.V.K. and K.S.

Ethics Committee Approval

Ethics committee approval was received for this study from the Ethics Committee of the Health Science University, Umraniye Training and Research Hospital (IRB Number: 374 Date: 17.10.2024).

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Author Disclosure Statement

The authors declare no conflicts of interest.

Funding Information

The authors declare that this study received no financial support.

Abbreviations Used

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