A Safe and Effective Two-Step Tract Dilation Technique in Totally Ultrasound-Guided Percutaneous Nephrolithotomy

Background To evaluate Methods From Oct 2018 to Mar 2020, we prospectively and consecutively enrolled 18 patients with 19 kidney units with urolithiasis. The nephrostomy tract was established by the following four steps: 1) ultrasound-guided renal puncture, 2) first-stage serial dilation to 16 Fr with Amplatz dilators, 3) check and adjustment of the partially dilated tract with a ureteroscope, 4) second-stage dilation with a 24-Fr balloon dilator. Herein we present a radiation-free 2-step tract dilation technique, which is characterized by ureteroscopic check of the partially dilated tract in between the first dilation with serial fascial dilators and the second dilation with balloon. Our data suggest that it is a safe and effective method.


Abstract Background
To evaluate the safety and the efficacy of a radiation-free 2-step tract dilation technique in totally ultrasound-guided percutaneous nephrolithotomy (PCNL).

Methods
From Oct 2018 to Mar 2020, we prospectively and consecutively enrolled 18 patients with 19 kidney units with urolithiasis. The nephrostomy tract was established by the following four steps: 1) ultrasound-guided renal puncture, 2) first-stage serial dilation to 16 Fr with Amplatz dilators, 3) check and adjustment of the partially dilated tract with a ureteroscope, 4) second-stage dilation with a 24-Fr balloon dilator.

Conclusions
Herein we present a radiation-free 2-step tract dilation technique, which is characterized by ureteroscopic check of the partially dilated tract in between the first dilation with serial fascial dilators and the second dilation with balloon.
Our data suggest that it is a safe and effective method.

Keywords
Percutaneous Nephrolithotomy · Ultrasound · Urolithiasis · Fascial Dilator · Balloon Dilator 4 Background Percutaneous nephrolithotomy (PCNL) has remained the treatment of choice for large and complex kidney stones, since it was first introduced in 1970s(1). The step of establishing an access to the collecting system, including renal puncture and the subsequent tract dilation, is the crucial part of this surgery and significantly affects the outcome. Traditionally, fluoroscopy has been used to establish the nephrostomy tract in PCNL and to date it remains the most common image modality to guide PCNL (2). It facilitates the tract establishment by providing a clear mapping of the whole collecting system. Besides, almost all kinds of tract dilators, such as Amplatz, balloon, and Alken telescopic metal dilators, are designed to be visible under fluoroscopy, which ensures a successful access to the collecting system. Despite these advantages, there has been a persistent concern about the patients' and the operators' exposure to the ionizing radiation with fluoroscopic guidance(3).
Ultrasound-guided PCNL has gained a growing popularity in the past few years. It has the merit of reducing or even totally avoiding radiation exposure.
Other advantages include visualization of the surrounding organs, prevention of vascular injury by Doppler imaging, no need of wearing lead apron, and so on(4). However, while it is usually not difficult to perform renal puncture under ultrasound, the subsequent tract dilation solely by ultrasound is considered challenging and sometimes impossible (5). This is because that almost all kinds of dilators are less echogenic and barely visible under ultrasound (6). In the literature, many so-called "ultrasound-guided" PCNLs actually refer to ultrasound-guided renal puncture followed by fluoroscopy-guided tract dilation (7)(8)(9). While some authors solely use ultrasound to monitor the advancement of Amplatz, telescopic metal, or balloon dilators (10,11), these generally require an advanced ultrasound technique and are considered limited to experienced hands (12).
To overcome the above challenging tract dilation during totally ultrasound-guided PCNL, we utilized a radiation-free nephrostomy tract establishment technique in the past few years. The dilation was carried out in a 2-step manner, and in between the tract was checked by a quick look with a ureteroscope. As it did not require an advanced technique to monitor the dilators' advancement under ultrasound, this method should be much easier for surgeons with any level of ultrasound expertise. The objective of the current study was to evaluate the safety and the efficacy of this radiation-free 2-step tract dilation technique in totally ultrasound-guided PCNL.

Patient selection
From Oct 2018 to Mar 2020, we consecutively enrolled 18 subjects with 19 renal units with urolithiasis. A total 19 operations were included in the study. All the operations were performed by a single surgeon (CHH).

Results
The characteristics of the study subjects are shown on Table 1 (Table 2).
Postoperatively, pyuria was noted in eight (42.1%) operations: the majority was asymptomatic and only three (15.8%) developed fever. Pleural injury occurred in two (10.5%) operations, in both supracostal puncture was made to gain access to the upper calyx. One was asymptomatic and was conservatively treated, while the other was symptomatic and was successfully treated with pigtail drainage. Stone-free status was achieved in 15 (78.9%) operations at 3 months after operation. Three (15.8%) underwent an ancillary procedure of extracorporeal shockwave lithotripsy or ureteroscopy.

9
In the current study, we described a technique of radiation-free tract establishment in totally ultrasound-guided PCNL. relatively sharp, which tend to successfully penetrate the kidney parenchyma and enter the collecting system. This largely prevented the status of short dilation. This was supported by those studies of mini-PCNL (13,14), in which the failure rate of serial dilation up to 18 Fr was generally less than 5%. On the contrary, the tips of large-sized Amplatz dilators are relatively blunt and tend to push the kidney away before they enter the collecting system, which causes a status of short dilation (15,16). Second, all the small-sized (8-Fr to 16-Fr) Amplatz dilators were advanced at a fixed depth as measured earlier.
This avoided the injury to the opposite pelvic membrane in the collecting system. With the above two mechanisms, we could confidently dilate the tract until a diameter of 16 Fr was reached without monitoring by either fluoroscopy or ultrasound. Third, after the tract was initially dilated, we checked the entrance of the 16-Fr tract with a ureteroscope. In our experience, the 16-Fr sheath had been perfectly placed in the collecting system at this step in the majority. Although short dilation did occur in a few cases, it was not difficult to fix by the following procedure: following the guidewire, the ureteroscope was advanced into the collecting system; then the 16-Fr sheath was gently advanced over the shaft of the ureteroscope. The appropriately positioned 16-Fr sheath almost ensured the success of the final dilation with a balloon.
In one study with 138 subjects, totally ultrasound-guided balloon dilation was achieved in 131 (94.9%), and the remaining 7 (5.1%) cases required a switch to fluoroscopy (17). In another study with 207 cases undergoing ultrasoundguided balloon dilation, the success rate of tract dilation on the first attempt was 88.4% (11). Short dilation was considered to be the main cause of failure with balloon dilation (15,16). Obesity was reported to predict failure of ultrasound-guided balloon dilation, as it was reported that the success rate was 76.9% in normal weight and 79.0% in overweight, but it was only 45.7% in obese subjects (6). In another study, the presence of staghorn stones, previous ipsilateral open nephrolithotomy, and low pole access independently predicted a failure of tract establishment with balloon, while the presence of hydronephrosis of the target calyx increased the likelihood of success (11). In general, to monitor these dilators under ultrasound is an advanced technique and is limited to experts and is specially technically challenging in cases without hydronephrosis (16). Different from the above techniques by using ultrasound to monitor the process of dilation, our method was characterized by checking the initial small-sized dilation with a ureteroscope. This was considered as a 2-step were comparable to the those of the above studies (5,11,20). Our study generally confirmed that the safety and the efficacy of the 2-step technique 12 were at least not inferior to those of fluoroscopy-guided or ultrasound-guided tract dilation, while it maintained the merits of no radiation and lower ultrasound expertise required.
The major limitation of the current study was a small case number.
However, we believed that the results were still robust enough to support the feasibility of this technique. First, among the 19 consecutive operations, there was only one failure, which was due to an unintentional withdraw of the guidewire. This should not be considered as a failure of the technique itself.
Second, the time of tract establishment was consistent and short, suggesting that this technique was easy to perform and was highly reproducible. Third, the overall complication rates, regarding the blood loss, transfusion rate, and fever were generally low and were comparable to those in the literature. There was a relatively higher rate of pleural injury, which was because that upper calyx was the primary target of puncture (supracostal) in the majority of the cases.

Conclusions
Herein we present a radiation-free tract dilation method. It is a 2-step technique: in between the first dilation with serial fascial dilators and the second dilation with balloon, the partially dilated tract is checked and adjusted with ureteroscope. Our data suggest that it is a safe and effective method.