Is Non-Papillary Puncture in Ultrasound-Guided Standard-Access Percutaneous Nephrolithotomy Safe and Feasible for Complex Renal Stones?

Abstract

Purpose:

To investigate the safety and feasibility of non-papillary puncture in total ultrasound (US)-guided standard size access percutaneous nephrolithotomy (PCNL) for patients with complex renal stones.

Patients and Methods:

We retrospectively reviewed the charts of complex renal stones (Guy’s scoring system 3–4) patients who had undergone standard size access PCNL in our department from January 2019 to October 2023 (n = 422). Renal abnormalities, history of PCNL and pyelolithotomy/nephrolithotomy, and multiple tracts PCNL were excluded. Two hundred A total of 218 eligible patients were finally enrolled. These patients were allocated to two groups according to puncture site: papillary (Group 1, n = 182) and non-papillary (Group 2, n = 36). All procedures were guided by total US. Single standard access (22–24 F) was achieved in all patients. Relevant patient characteristics, operative variables, and postoperative data were collected and analyzed, with a focus on the stone-free rate (SFR) and bleeding complications.

Results:

Successful percutaneous renal puncture was achieved in all patients. Patients’ basic characteristics (gender, age, body mass index, stone size, surgical side) were similar between the two groups. The SFRs in the papillary puncture group were significantly higher than the non-papillary puncture group (81.3% vs 69.4%, p = 0.03). Hemoglobin loss in Group 2 is much more significant than in Group 1 (18.4 ± 5.4 g/L vs 10.4 ± 4.7 g/L, p = 0.02). Overall non-severe complication (Clavien-Dindo Grade 1–2) rates were significantly lower in Group 1 (p = 0.02, 0.03). The operative duration, transfusion rate, severe complication rate, and renal function changes show no significant difference between the two groups.

Conclusion:

US-guided PCNL through a standard-access tract is necessary for renal papilla puncture. Non-papillary puncture increases bleeding volume and reduces SFR, and should be avoided in complex stones whenever possible.

Keywords

percutaneous nephrolithotomy kidney renal papillary stone ultrasound

Introduction

Large kidney stones are widely managed by percutaneous nephrolithotomy (PCNL).¹ This procedure requires a percutaneous access to the collecting system, which is gained by puncturing the target with an open tip needle, guided by fluoroscopy or ultrasound (US). For a long time, puncture through the renal papilla has been regarded as the best approach, mainly based on anatomical factors, the least distribution of blood vessels in the caliceal fornix, and therefore the lowest risk of damage to the vessels after the establishment of the tract.² Sampaio et al. also reported that puncture through the non-papillary route has a higher risk of interlobar or segmental artery injury than caliceal fornix puncture.³ In recent years, Liatsikos et al. have reported many cases of non-papillary puncture under X-ray guidance, and the results suggested that this method is safe and feasible,^4,5 which seems to subvert our traditional understanding and concept. Different from X-ray guidance, US-guided PCNL is a prominent feature of China, has been popular for more than 20 years, and is now increasingly spreading to the world.⁶ On US images, the visibility of the caliceal fornix varies according to the degree of hydronephrosis. In patients with moderate hydronephrosis, it is relatively easy to identify the renal papilla and caliceal fornix after training.⁷ For anomalous kidneys, irregular collecting systems, nonrenal papillary puncture may occur. Furthermore, the technical nuances and clinical outcomes of US-guided non-papillary PCNL remain understudied. In the present study, we retrospectively reviewed our single-center experience with a large cohort with the aim of evaluating the safety and feasibility of nonrenal papillary puncture in US-guided standard size access PCNL with complex renal stones.

Patients and Methods

Study design and population

We retrospectively reviewed the consecutive patients (n = 422) who underwent PCNL from January 2019 to October 2023 in our single institution, which is also the urinary calculi research center of North China. The informed consent was exempted by the Institutional Review Board of the local ethics committee for its retrospective nature. The following inclusive criteria were applied: complex renal stones (Guy’s scoring system 3–4), urolithiasis in patients with normal renal anatomy, patients treated with standard (22–24 F) PCNL, and procedure fulfilled through only one tract. The exclusion criteria included patients with renal abnormalities (horseshoe kidney, multiple cyst kidney, duplicated kidney, medullary sponge kidney), history of PCNL and pyelolithotomy/nephrolithotomy, and multiple tracts PCNL.

The definition of non-papillary puncture, distinct from radiographically guided approaches, is determined by endoscopic visualization. After tract establishment, if a split renal papilla is observed, the access is classified as transpapillary (papillary access). Conversely, if only renal parenchyma or exclusively perirenal fat is visualized along the tract without identifiable papillary structures, the access is defined as non-papillary (including direct pelvic access and non-papillary caliceal puncture) (Fig. 1).

FIG. 1.

(A) Papillary puncture, signs of papillary splitting can be observed. (B) Infundibulum puncture, renal sinus fat along the tract, with no renal papilla visible, infundibulum is positioned anterior to the access tract. (C) Direct puncture into the renal pelvis through renal sinus.

In total, 218 cases were included in the study. Patients’ data were collected from our institutional prospective database for registration of PCNL cases.

Surgical technique

All procedures were performed under general anesthesia. First, the patient was placed in the lithotomy position, and a 5F ureteral catheter was inserted retrograde into the affected ureter up to the renal pelvis. The distal end of the catheter was connected to a saline bag suspended at a height of 100 cm, secured to the urinary catheter, and continuously infused to distend the renal pelvis for optimal puncture visualization. The patient was then placed in the prone position (or lateral decubitus position if prone was intolerable). A 3.5 MHz convex US probe was used to scan the kidney, and the optimal target calix was selected according to the “three 30-degree triangulation” described in our previous study.⁸ When puncturing the lower calix, we will move the US probe downward, making the previously mentioned “triangulation” smaller, which will increase the probability of puncturing through the renal papilla. A 17.5-gauge puncture needle (Urotech, Germany) was employed for the puncture. Upon successful access, a J-tipped guidewire was advanced into the target calix, with its position confirmed in real-time via US. Subsequently, a 24F or 22F tract was established using an Alken coaxial metal dilator (Richard Wolf, Germany) or a high-pressure balloon dilation catheter (X Force® N30, Bard, USA). After tract establishment, an 18F nephroscope was used in all cases to verify tract positioning. The LithoClast® US/pneumatic lithotripsy system (Switzerland) was utilized for stone fragmentation and clearance. The surgeon determined procedural progression (conclusion of surgery or creation of additional tracts) based on intraoperative findings. At the end of the procedure, US was used to confirm the presence of residual stones. a 14F nephrostomy tube was placed in each tract, and a 6F Double-J stent was indwelled for 2–4 weeks. The nephrostomy tube was removed 3–5 days postoperatively.

The size of the calculi is determined by measuring the maximum diameter of the calculi. For multiple calculi, the sum of the maximum diameters is calculated. Operative time refers to the time from puncture to access exit. Stone-free status was evaluated after surgery with a non-contrast computed tomography (CT) scan 1 month after the procedure. Stone-free data were classified into three grades: Grade A (no stones on CT scan) absolute stone free, Grade B (Grade A stones plus ≤2 mm fragments) relative stone free, and Grade C (Grade A and B stones plus C 2.1–4 mm fragments) fragments relative stone free. Estimated blood loss was evaluated by hemoglobin drop 24 hours postoperatively. Estimated glomerular filtration rate (eGFR) was used to evaluate the renal function. The modified Clavien-Dindo classification system was used to grade the perioperative complications.

Statistical analysis

Continuous data are shown as the mean ± standard deviation and were compared between the study groups by one-way analysis of variance. Categorical data are shown as the number and/or percentage and were analyzed using the χ² test or Fisher’s exact test. All statistical analyses were performed using SPSS version 20.0 (IBM Corp., Armonk, NY, USA). A p-value <0.05 was considered statistically significant.

Results

A total of 218 patients with complex renal stones underwent US-guided standard-access PCNL, including 182 papillary punctures (Group 1) and 36 non-papillary punctures (Group 2). There were no significant differences in baseline parameters (age, sex ratio, body mass index, surgical side) between the two groups of patients. In selecting access, both groups were basically consistent, with the middle calix group being the most targeted renal calix, followed by the upper and lower calix groups. Papillary puncture demonstrated superior stone clearance, with an overall SFR (Grade C: ≤4 mm residual fragments) of 81.3% compared with 69.4% in non-papillary puncture (p = 0.03). Absolute stone-free rates (SFRs) (Grade A) were comparable between groups (19.8% vs 13.9%, p = 0.15). Operative time (51.6 ± 18.7 vs 59.2 ± 17.6 minutes, p = 0.19) showed no statistical differences. Non-papillary puncture was associated with significantly greater hemoglobin loss (18.4 ± 5.4 g/L vs 10.4 ± 4.7 g/L, p = 0.02). However, transfusion rates (2.2% vs 2.8%, p = 0.19) did not differ significantly. Overall non-severe complication (Clavien-Dindo Grade 1–2) rates were significantly lower in Group 1 (p = 0.02, 0.03). No significant differences were observed in severe complication rate, location of residual stones, renal function (pre- and postoperative eGFR), or stone composition between groups (p > 0.05). Table 1 summarizes and compares the patient demographics and characteristics for the two groups.

Table 1.

Cohort Patient Characteristics

Variables	Group 1 (n = 182)	Group 2 (n = 36)	p-Value
Age (years), mean ± SD	47.6 ± 14.2	48.3 ± 11.2	0.88
Sex ratio (female/male)	95/87	20/16	0.24
BMI (kg/m²), mean ± SD	24.9 ± 7.9	26.9 ± 8.7	0.75
Surgical side (right/left)	93/89	19/17	0.89
Patient position
Prone	181	36	0.22
Lateral	1	/
Target calix, n (%)			0.59
Upper pole	48 (26.4)	10 (27.8)
Middle pole	106 (58.2)	20 (55.6)
Lower pole	28 (15.4)	6 (16.7)
Stone size (cm), mean ± SD	4.3 ± 1.6	4.5 ± 1.7	0.15
Access site, n (%)			/
Papillary	182	/
Non-papillary	/	36
Infundibulum puncture		28 (77.8)
Renal sinus puncture		8 (22.2)
Operative time(min), mean ± SD	51.6 ± 18.7	59.2 ± 17.6	0.19
SFR, n (%)
Grade A	36 (19.8)	5 (13.9)	0.15
Grade B	89 (48.9)	17 (47.2)	0.68
Grade C	148 (81.3)	25 (69.4)	0.03
Residual stone calix, n (%)			0.60
Upper	7 (20.6)	3 (27.3)
Middle	10 (29.4)	3 (27.3)
Lower	17 (50)	5 (45.5)
Mean decline in hemoglobin level, g/L, mean ± SD	10.4 ± 4.7	18.4 ± 5.4	0.02
Blood transfusion rate, n (%)	4 (2.2)	1 (2.8)	0.09
Preoperative eGFR, mL/min/1.73 m², mean (SD)	73.7 ± 27.6	75.8 ± 37.2	0.41
Postoperative eGFR, mL/min/1.73 m², mean (SD)	66.8 ± 32.4	64.4 ± 29.7	0.58
Complications, n (%)
Grade 1			0.02
Transient fever	52 (28.6)	18 (50)
Pain/Vomit	22 (12.1)	8 (22.2)
Transient bleeding	25 (13.7)	6 (16.7)
Grade 2			0.03
Fever	5 (2.7)	4 (11.1)
Blood transfusion	24 (13.2)	9 (25)
DVT	19 (10.4)	8 (22.2)
Grade 3			0.13
Subcapsular renal drainage	4 (2.2)	1 (2.8)
Embolization	1 (0.5)	/
Cystoscopy	3 (1.6)	1 (2.8)
Grade 4	1	/
	1	1
	1	/
	/	/
Stone composition, n (%)			0.25
COM/COD	129 (70.9)	23 (63.9)
Brushite	12 (6.6)	3 (8.3)
Uric acid	7 (3.8)	2 (5.6)
Struvite	28 (15.4)	7 (19.4)
Others	6 (3.3)	1 (2.8)

BMI = body mass index; COM/COD = calcium oxalate monohydrate/calcium oxalate dihydrate; DVT = deep vein thrombosis; eGFR = estimated glomerular filtration rate; SD = standard deviation; SFR = stone-free rate.

Discussion

PCNL remains the gold standard for managing large and complex renal stones, with puncture site selection being a critical determinant of procedural success and safety. Historically, papillary puncture through the caliceal fornix has been favored due to its anatomical advantages. The caliceal fornix, located at the tip of the renal papilla, is a relatively avascular zone compared with the renal parenchyma or pelvis, minimizing the risk of vascular injury during tract establishment. This anatomical rationale was first validated by Sampaio et al.³ in cadaveric studies, which demonstrated that only 7.1%–8.3% of papillary tracts (fornix) injured intrarenal arteries, whereas 38.4%–68.2% of non-papillary tracts (infundibulum) traversed major vessels. Regardless of renal region, puncture through a caliceal fornix was safe, and a non-papillary tract should be avoided due to the high risk of intrarenal vessel lesions. Subsequent in vitro animal studies (porcine) by Hao et al.⁹ found papillary puncture group yielded minimal bleeding (1.59 ± 1.01 mL/min) compared with the infundibular puncture group (p < 0.001), renal column puncture group (p = 0.001), and minor caliceal neck puncture group (p = 0.011), further confirmed that papillary puncture resulted in significantly less parenchymal injury and blood loss compared with non-papillary approaches. These findings are consistent with the anatomical rationale that papillary puncture minimizes trauma to the renal vasculature. This anatomical distinction underpins the reduced bleeding risk associated with papillary access, as evidenced by our findings: papillary puncture resulted in significantly lower hemoglobin loss (10.4 ± 4.7 g/L vs 18.4 ± 5.4 g/L, p = 0.02).

In contrast, non-papillary puncture—defined as access through the renal parenchyma, infundibulum, or direct pelvic puncture—has been considered a secondary option, reserved for cases where anatomical constraints (e.g., severe hydronephrosis, caliceal distortion) preclude papillary targeting. It remains contentious due to conflicting safety reports across imaging modalities. Proponents of non-papillary puncture cite fluoroscopy-based studies reporting comparable outcomes to papillary access. Liatsikos et al.⁸ analyzed non-papillary PCNL cases through the randomized controlled trial study, noting a similar hemoglobin drop (p = 0.916) and transfusion rate (p = 1.0) did not differ among papillary cohorts. In the following years, their team also successively discovered through research that these two puncture methods yielded similar outcomes in the treatment of patients with staghorn calculi, upper ureteral stones, and abnormal kidney stones. Similarly, Tahra A et al.¹⁰ found no significant difference in mean hematocrit decreases (p = 0.56), transfusion rate (p = 0.43), and overall complication rate (p = 0.89) between non-papillary and papillary groups. These studies attributed the safety of non-papillary access to “oblique triangulation” techniques under fluoroscopy, which purportedly avoid vascular hotspots. These conflicting findings have sparked debates regarding the universal applicability of papillary puncture as the gold standard. However, such conclusions are limited by selection bias: most excluded staghorn stones (Guy’s 4), which approximately accounted for half of our cohort.

The use of US guidance in PCNL has gained significant attention due to its advantages, including real-time visualization, absence of radiation exposure, and suitability for obese patients. The precision of US-guided papillary puncture further enhances its safety profile. Unlike fluoroscopy, which visualizes contrast-filled cavities, US delineates the echogenic renal pyramids and hypoechoic caliceal fornices in real time.¹¹ In our cohort, this precision translated to superior SFR (81.3% vs 69.4%, p = 0.03). The “three 30-degree triangulation” technique—aligning the skin entry point, target calix, and stone position—optimized tract trajectory, minimizing parenchymal injury and maximizing endoscopic maneuverability.¹² US’s high-resolution imaging reveals the inherent vascular hazards of non-papillary access. Doppler US and contrast-enhanced US techniques aid in identifying interlobar arteries and even arcuate arteries, providing valuable assistance in reducing arterial vascular injury along the puncture tract.¹³ However, whether the application of Doppler technology ultimately prevents severe hemorrhage has not been fully established.

To our knowledge, this is the first comparative study of US-guided PCNL using non-papillary vs papillary puncture approaches in the human body. We determined whether the access was papillary by direct visualization of the tract location, which proved more reliable than relying solely on US imaging. Because the visualization information provided by US imaging technology is primarily constrained by the limited cross-sectional imaging plane at the transducer’s central region. Although needle insertion can be maintained within the imaging plane during percutaneous puncture procedures, the asymmetrical mechanical interactions at the beveled tip of geometrically angled needles induce nonlinear bending deformations in soft tissues, which demonstrate dependency on tissue-needle relative stiffness and bevel angle parameters.¹⁴ This biomechanical phenomenon engenders two critical technical challenges: First, the inherent low signal-to-noise ratio of US imaging restricts clear delineation of tissue boundaries. Second, the coupling effect between the weak acoustic reflectivity of interventional needles and their dynamic deformation characteristics poses significant precision challenges for medical image-based real-time needle tracking systems. These challenges become particularly pronounced when addressing complex deformation fields arising from tissue heterogeneity, where the interaction between heterogeneous tissue properties and needle deformation dynamics substantially compromises tracking accuracy. Therefore, the ultrasonographic imaging representation of needle positioning may not consistently correspond to its true anatomical configuration in clinical practice. In our study, the significantly higher SFR in the papillary puncture group aligns with classical anatomical principles. The renal papilla provides direct access to the caliceal infundibulum, enabling efficient stone fragmentation and clearance by minimizing angular deviations during nephroscopy. In contrast, non-papillary punctures—whether through parenchyma or perirenal fat—often result in oblique or suboptimal trajectories, limiting visualization and maneuverability of lithotripsy devices. This finding corroborates earlier studies emphasizing the importance of “straight-line access” for maximizing SFRs in PCNL. In this study, there was no significant difference in the number of accesses between the two groups, which may be related to the greater intraoperative bleeding in the non-papillary group, resulting in difficulties in proceeding with the surgery smoothly. Regarding postoperative complications, there were no significant differences between the two groups in terms of transfusion rates, selected renal artery embolism, or overall complication rates. However, whether there are differences in long-term complications between the two groups remains to be further followed up.

There were some limitations to our study. First, potential selection bias, particularly in group allocation (non-papillary puncture was often necessitated by anatomical challenges) due to the study’s retrospective nature, prospective studies are needed to validate causality. Second, the non-papillary group (n = 36) was smaller than the papillary cohort (n = 182), which may reduce statistical power for rare outcomes (e.g., selected embolization). Third, our study only reflects the results of US-guided standard PCNL in non-papillary renal puncture and may not represent the conclusions of studies under X-ray and mini-perc studies. Therefore, further systematic validation of the safety of non-papillary puncture is still needed. Fourth, this study exclusively enrolled patients with normal collecting system anatomy. Since non-papillary puncture is more frequently employed in cases with anomalous kidney, our findings cannot reflect real outcomes in this specific patient population. Last but not least, discrepancies in outcomes may exist between the two subgroups undergoing non-papillary puncture; however, direct comparison was precluded by limited case numbers, potentially influencing the interpretation of results.

Conclusion

Our study found that in complex renal calculi, the optimal access site for US-guided standard-track PCNL should be via papillary puncture. Compared with non-papillary access, this approach significantly improves the SFR and reduces perioperative blood loss. However, no significant difference in overall complications was observed between the two groups, which may require further validation through larger-scale studies.

Authors’ Contributions

B.X.: Article writing. Y.C., S.L., X.Z., Y.X., H.H., and Z.L.: Data analysis. Y.L. and W.B.: Article editing. J.L.: Project development.

Footnotes

Author Disclosure Statement

The authors declare that they have no conflicts of interest.

Funding Information

Beijing Hospitals Authority Clinical Medicine Development of Special Funding Support (No. ZLRK202520).

Abbreviations

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