Introduction

Complex renal stones, including staghorn stones, are large and branched stones that occupy all or part of the renal pelvis and calyces [1, 2]. Furthermore, they can be asymptomatic and induce urinary tract infections, urinary tract obstruction, hematuria, and decreased kidney function [2, 3]. If left untreated or conservatively treated, complex renal stones can lead to an increased risk of renal failure and mortality [2–5]. Therefore, complex renal stones require aggressive treatment [2–5].

Many surgical and non-surgical treatment options have been introduced to remove complex renal stones, including percutaneous nephrolithotomy (PCNL), shock wave lithotripsy (SWL), PCNL and SWL combinations, and open surgery [1, 2]. PCNL is the first-choice treatment for large and complex renal stones [1, 4, 6, 7], but percutaneous nephrostomy (PCN), a well-established renal access technique, must precede PCNL [8]. PCN is relatively safe and easy for a dilated renal collecting system [9]. However, few reports have described PCN for complex renal stones [10, 11]. Moreover, those few reports emphasized the difficulty of PCN for complex renal stones, reporting a technical success rate of 82 to 85% compared with 96 to 100% for a dilated renal system [10, 11].

Ultrasound imaging is a well-established renal pathology evaluation method [12].

Specifically, ultrasound imaging reliably and efficiently detects larger renal stones exhibiting posterior acoustic shadowing [12]. Therefore, percutaneous renal access behind a stone allows efficient renal entry under ultrasound guidance [13].

Therefore, to clarify the efficacy and safety of PCN with complex renal stones, we compared the technical success rate and complications associated with two rental entry approaches: renal entry behind the stone and renal calyx dilation.

Materials and methods

The PCN placement technique

All PCN procedures were performed by one of three experienced interventional radiologists with 4–16 years of clinical experience. A percutaneous approach through the posterior calyx in the lower or middle pole was preferred in all cases to prevent vascular injury [13]. All PCN procedures were performed under ultrasound and fluoroscopic guidance.

Renal access was performed under ultrasound guidance using a 21G Chiba needle (Cook Medical Inc., Bloomington, IN, USA) to puncture the renal collecting system. The procedures after Chiba needle insertion were performed under fluoroscopic guidance. For dilated renal calyces with hydronephrosis, renal access was the same as PCN for a dilated renal collecting system, and the Chiba needle targeted the dilated renal calyces (Fig 1) [17]. However, if the renal calyces were replaced with complex stones with little hydronephrosis, the Chiba needle targeted the center of the renal pyramid behind the stone.

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Fig 1. Renal access for dilated renal calyx with hydronephrosis under ultrasound guidance.

(A) A grayscale ultrasonography image showed a dilated middle and superior renal calyces and replaced inferior renal calyx with renal stone in the right kidney. (B) A 21-G Chiba needle (arrowhead) was advanced to the center of the renal pyramid at middle pole. (C)The Chiba needle (arrowhead) was introduced into the dilated renal calyx. (D) Finally an 8.5Fr drainage catheter was successfully inserted after renal access via dilated renal calyx.

https://doi.org/10.1371/journal.pone.0278485.g001

All PCNs were performed with the patient in the prone position. First, ultrasound scanning was performed using a 7.5 MHz transducer to obtain a signal through the kidney. Once the initial puncture site was selected, it was cleaned and draped. Then, local anesthesia with 2% lidocaine was injected at the puncture site. When renal calyces were observed on ultrasound, a 21-G Chiba needle was advanced to the dilated renal calyx (i.e., the rental entry via renal calyx dilation group). If complex renal stones with little hydronephrosis replaced renal calyces (Fig 2B), then a 21-G Chiba needle was introduced into the periphery of the complex renal stone through the center line of the renal pyramid (i.e., the renal entry behind the stone group; Fig 2C and 2D). The urine from hydronephrosis was drained after the inner stylet was removed. If the Chiba needle did not induce a release of urine due to complex stones with little hydronephrosis, a few milliliters of contrast medium was injected to ensure proper positioning of the needle tip and opacify the targeted renal calyx under fluoroscopic guidance (Fig 2E). Once the position of the needle was ensured, a 0.018-inch guidewire was introduced through the needle with rotating movement to minimize resistance at the tip as the wire advanced to accommodate the complex renal stone (Fig 2F). Next, the needle was exchanged with a 5Fr introducer sheath (A&A Medical Device Company, Seongnam, Korea), followed by a 0.035-inch hydrophilic guide wire (Terumo Corporation, Tokyo, Japan) into the renal pelvis or proximal ureter. Once the guidewire was in position, an 8Fr dilator (Cook Medical Inc.) was inserted for tract dilatation (Fig 2G). After tract dilation, an 8.5Fr pigtail catheter (Cook Medical Inc.) was introduced over the guidewire (Fig 2H). All procedures were completed by confirming that the PCN catheter tip was in the renal pelvis near the proximal ureter on the final radiograph. A successful PCN was defined as satisfactory placement of a PCN catheter in the renal pelvis with successful opacification of the renal collecting system on antegrade pyelography.

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Fig 2. A representative case of a 61-year-old man with a right, partial staghorn stone.

(A) A kidney, ureter, and bladder imaging exam identified a right, partial staghorn stone. (B) A grayscale ultrasonography image showed a staghorn stone in the right kidney with marked posterior acoustic shadowing. (C) A 21-G Chiba needle (arrowhead) was introduced into the periphery of the complex stone through the center line of the renal pyramid. (D) A radiograph image showed that the 21-G Chiba needle was introduced behind the stone. (E) A few millilters of contrast medium was injected, then the renal calyx was opacified by contrast medium (arrowhead). (F) A 0.018-inch guide wire (arrow) was introduced with rotating movements to minimize resistance at the tip as the wire advanced. (G) A 0.035-inch hydrophilic guidewire was introduced, and track dilatation was performed under fluoroscopic guidance. (H) An 8.5-Fr pigtail catheter was placed after sequential tract dilatation.

https://doi.org/10.1371/journal.pone.0278485.g002

Results

Overall, 39 patients underwent PCN via puncture behind the stone, and 31 underwent PCN via puncture of the dilated renal calyx. Table 1 presents the baseline demographics. Overall, the technical success rate was 100%. During the follow-up period (mean, 12 days; range 1–58 days), 40 patients (40 PCNs) underwent PCNL, and 14 patients (14 PCNs) underwent other surgeries for stone removal, including ureterolithotomy or extracorporeal shockwave lithotripsy. Furthermore, 15 patients (16 PCNs) underwent only conservative treatment because of older age and accompanying malignancies. One patient died four days after PCN due to old age, pneumonia, and acidosis progression.

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Table 1. Patient demographics.

https://doi.org/10.1371/journal.pone.0278485.t001

Table 2 presents the complication rates per group. The overall complication rate was 20.0% (14/70). Furthermore, the complication rate was 15.4% (6/39) for the group with renal access behind the stone; none had major complications, and 6 patients had minor complications. However, 6 patients (6 PCNs) had transient gross hematuria. The complication rate was 25.8% (8/31) for the dilated renal calyx group; 1 patient had major bleeding complications that required transfusion. After the procedure, the patient’s hemoglobin level decreased from 9.6 g/dL to 6.9 g/dL. Therefore, one unit of red blood cells was transfused. The hemoglobin level recovered to 8.4 g/dL, and the patient stabilized. Furthermore, 7 patients had transient gross hematuria. Overall, there was no mortality, and all transient gross hematuria resolved within 72 hours. Finally, the complication rates did not differ between the two percutaneous access techniques (p = 0.279).

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Table 2. PCN complications based on the renal approach technique.

https://doi.org/10.1371/journal.pone.0278485.t002

Discussion

PCNL is the preferred option for complex renal stones or stones resistant to SWL or ureteroscopy [1, 4, 6, 7, 18]. Proper access to the renal collecting system plays a crucial role in the procedure’s success [18]. However, little attention has been paid to percutaneous renal access. Thus, we compared two percutaneous renal access techniques: entry behind the stone and entry via a dilated renal calyx, which, to our knowledge, has not been done before.

In this study, the percutaneous nephrostomy technical success rate for complex renal stones under ultrasound and fluoroscopic guidance was 100%, higher than the 82 to 85% technical success rate previously reported [11]. Furthermore, our success rate was higher than the 80% minimum threshold set by the SIR for PCN with complex stone disease and staghorn calculi [11]. This study used a simultaneous ultrasound and fluoroscopic guidance approach for percutaneous access. Traditionally, the puncture during PCNL is performed under fluoroscopic guidance [19, 20], but there are disadvantages to this approach, including radiation exposure and possible iatrogenic visceral injury to the colon, liver, spleen, and pleura [19–23]. Ultrasound-guided percutaneous access is an alternative method associated with less radiation exposure and possible injury to nearby organs [20]. However, a few studies reported difficulties in ultrasound-guided (USG) PCNL with a non-dilated collecting system [24, 25], concluding that USG PCNL is safe for patients with a single stone at the renal pelvis in moderately to markedly dilated renal calyces [25]. When renal access occurs via the underlying stone, the renal approach targets the dilated renal calyx. However, if the renal calyx is filled with a stone instead of urine, the calyceal USG findings differ. For example, we identified a hyperechoic stricture (stone) accompanied by posterior shadowing and a hypoechoic stricture filled with urine (hydronephrosis).

During the procedure, it is best to aim for the center of the renal pyramid behind the stone because the Chiba needle passing through a hyperechoic stone is almost invisible by USG imaging. Furthermore, the renal pyramid center projects onto a minor calyx [26]. Therefore, a puncture through the renal pyramid midline goes through the axis of the corresponding minor calyx obscured by the complex renal stone.

Table 2 details the reported complications. There were no major complications in the group that underwent renal access behind the stone. However, one patient experienced a major complication (3.2%) in the group that underwent access by dilated renal calyx, which was acceptable considering that the SIR recommends a major complication rate of less than 4% [11]. Moreover, transient gross hematuria resolved within 72 hours in all cases, which was considered a clinically minor complication since the hematuria improved with conservative treatment regardless of the technique. The minor complication rates were 15.4% for the behind-the-stone approach and 25.8% for the dilated renal calyx approach, higher than the 15% upper margin for minor complications recommended by the Royal College of Radiologists [27]. However, the rates correspond with the reported 5.3 to 28% incidence rate during general PCN procedures [28–32]. Finally, septic shock, vascular injuries requiring embolization, individual threshold complications resulting in an unexpected transfer to the intensive care unit, or emergency surgery related to the PCN procedure did not occur.

This study has several limitations. First, this study retrospectively reviewed the clinical and imaging findings. Therefore, data from some clinical charts and notes were limited and could not be included. Second, PCN placement was performed by three interventional radiologists with differing degrees of experience in PCN procedures for complex renal stones, although they had sufficient clinical experience. Third, data on radiation exposure during PCN were not fully obtained. Thus, we were limited to analyzing radiation exposure during each PCN procedure.

Conclusion

PCN for complex renal stones has a high technical success rate and an acceptable complication rate regardless of the specific technique. Renal entry behind the stone is as safe and feasible as the dilated renal calyx approach.

Supporting information