Ultrasound-guided renal access for percutaneous nephrolithotomy (PCNL) is a safe, effective, and low-cost procedure commonly performed worldwide, but a technique underutilized by urologists in the United States. The purpose of this article is to familiarize the practicing urologist with methods for ultrasound guidance for percutaneous renal access. We discuss two alternative techniques for gaining renal access for PCNL under ultrasound guidance. We also describe a novel technique of using the puncture needle to reposition residual stone fragments to avoid additional tract dilation. With appropriate training, ultrasound-guided renal access for PCNL can lead to reduced radiation exposure, accurate renal access, and excellent stone-free success rates and clinical outcomes.

Introduction

To assess the effect of a hands-on ultrasound training session to teach urologic trainees ultrasound-guided percutaneous needle placement.

Materials and methods

University of California, San Francisco (UCSF) urology residentes completed a time trial, placing a needle into a phantom model target under ultrasound guidance. Participants were randomized into three educational exposure groups: Group 1's time trial occurred prior to any teaching intervention, group 2's after experiencing a hands-on training module, and group 3's after exposure to both the training module and one-on-one attending feedback. Needle placement speed and accuracy as well as trainees' perceived confidence in utilizing ultrasound were measured.

Results

The study cohort consisted of 15 resident trainees. Seven were randomized to group 1, three to group 2, and five to group 3. All residents reported minimal prior ultrasound experience. Their confidence in using ultrasound improved significantly after completing the training module with the most significant improvement seen among junior residents. Time to needle placement was fastest after receiving attending feedback (46.6sec in group 3 vs. 82.7sec in groups 1 and 2, p<0.01). Accuracy also improved with attending feedback, though the number of repositioning attempts did not differ significantly between groups.

Conclusions

A hands-on training module and use of an abdominal phantom trainer increased resident confidence and skill in their use of ultrasound to guide percutaneous needle positioning. Attending feedback is critical for improving accuracy in needle guidance toward a target. Ultrasound-guided needle positioning is a teachable skill and can be applicable to multiple urologic procedures.

Introduction: Ultrasound guidance is a unique alternative to fluoroscopy for percutaneous renal access. Besides being free of ionizing radiation exposure to the patient and intraoperative personnel, it offers several advantages including easier identification of the posterior renal calix and surrounding visceral structures. In this video, we demonstrate how ultrasound can be used to guide percutaneous nephrolithotomy (PCNL) in a step-by-step manner. Materials and Methods: From March to June 2016, 16 consecutive patients of age 18 and more with kidney or proximal ureteral stones underwent completely X-ray-free ultrasound-guided PCNL. No patients were excluded during the study period. Under general anesthesia, we place an externalized ureteral catheter through a flexible cystoscope with the patient in a frog-leg position. Retrograde saline injection is used to distend the collecting system only when needed. Then the patient is placed in a prone position. An ultrasound machine with a 3.5-MHz convex abdominal probe (Hitachi Aloka Medical America) is used to guide all steps of PCNL. For renal access, a longitudinal approach for needle insertion is usually chosen.1 An 18-gauge Echotip needle (Cook Medical) is slowly advanced through the skin either in front of or behind the probe. On the ultrasound screen, the entire needle should be fully seen from skin to kidney and into the targeted calix. Entry into the collecting system is confirmed with either aspiration of urine or efflux of urine through the puncture needle. Then, the needle stylet is removed and a J-tip coaxial guidewire (Bard Medical) is inserted into the renal pelvis or down the proximal ureter under ultrasound monitoring. Gently moving the wire back and forth will help identify the location of the wire tip relative to the collecting system. Subsequently, the needle is withdrawn, a 1-cm skin incision is made surrounding the wire, and a 10F fascial dilator and a safety wire introducer are then passed over the wire. Although the wire appears with a bright echogenic signal, the dilator and the safety wire introducer are not echogenic. Their advancement over the wire can be observed ultrasonographically as they obscure the echogenic appearance of the wire. A second wire is subsequently advanced into the collecting system through the safety wire introducer. A high-pressure balloon dilator (BARD X-Force, Bard Medical) is then advanced into the collecting system over one of the wires. Because the deflated balloon tip can be difficult to identify on the ultrasound screen, the wire should be moved back and forth while passing the balloon and the operative surgeon should look for a change in the wire contour to judge where the balloon tip is relative to the wire. The placement of the tip of this balloon dilator is crucial, as ideally, it should be just within the collecting system of the target calix.2 A working tract is then dilated and the access sheath is carefully advanced until the back end of the balloon is seen. Then the balloon is withdrawn, an offset rigid nephroscope is inserted, and the stone is treated. Results: The mean age of patients was 48.8 ± 19.9 years. Forty-four percent of patients were male with a mean body mass index of 29.9 ± 7.9 kg/m2 and a mean stone size of 33.7 ± 15.0 mm. All procedures were effectively performed with ultrasound guidance with a mean operative time of 101.3 ± 32.2 minutes. Patients and intraoperative personnel were not exposed to any ionizing radiation during the surgery. No patients experienced any significant immediate postoperative complication. All patients were stone free (no visible stone fragments) based on intraoperative visual inspection using a flexible nephroscope and a renal ultrasound and KUB at 30 days after surgery, and no secondary procedures were required. Conclusions: Ultrasound guidance for renal access and tract dilation in prone PCNL is feasible and efficient. Although some situations such as obese patients or nondilated collecting system may present a challenge, the benefits of adopting this technique-namely eliminating ionizing radiation exposure and live imaging of anatomy surrounding the collecting system-provide value during PCNL. Acknowledgments: This study was supported by the NIH R21-DK-109433 (TC) and the NIH NIDDK K12-DK-07-006: Multidisciplinary K12 Urologic Research Career Development Program (TC). No competing financial interests exist. Runtime of video: 5 mins 12 secs.

Objectives

To define the learning curve associated with adopting ultrasound guidance for prone percutaneous nephrolithotomy (PCNL) for the experienced surgeon.

Methods

A prospective cohort study of consecutive patients undergoing PCNL with ultrasound guidance for renal tract access and dilation was performed. Clinical data reviewed included success in gaining renal access with ultrasound guidance, total fluoroscopic screening time, and radiation exposure dose. PCNL cases performed with fluoroscopic guidance matched for stone size served as control cases.

Results

One hundred consecutive ultrasound-guided procedures performed by a single experienced endourologist were divided into five experience groups. Significant improvement in renal access success rate with ultrasound was seen after 20 cases (p < 0.05). Total fluoroscopic screening time, radiation exposure dose, and operative time were also statistically significantly improved over the study period. When compared with fluoroscopy-guided PCNL, significant decreases in total fluoroscopic screening time (33.4 ± 35.3 seconds vs 157.5 ± 84.9 seconds, p < 0.05) and radiation exposure (7.0 ± 8.7 mGy vs 47.8 ± 45.9 mGy, p < 0.05) were seen. No differences in complication rates were found.

Conclusions

Ultrasound-guided renal access for PCNL can be performed effectively after 20 cases. Transition to the use of ultrasound will quickly reduce radiation exposure for patients and intraoperative personnel.

Background

Interracial disparities in nephrolithiasis prevalence have been reported, but the interplay between genetics and the environment for urinary stone disease risk factors is poorly understood. To examine how environment may alter genetic predisposition for stone formation, we established the International Chinese Consortium on Nephrolithiasis (ICCON) as a multi-institutional collaboration to examine patterns of nephrolithiasis presentation between Chinese patients living in different countries.

Methods

Chinese patients undergoing percutaneous nephrolithotomy (PCNL) at six participating institutions in China and North America over 4 years were reviewed retrospectively. Patient demographics and clinical data were compared between Chinese patients living in China and North America.

Results

A total of 806 patients were included, encompassing 721 Chinese patients living in China and 85 living in North America. Nephrolithiasis patients living in China were more likely to be male (67% vs. 56%, P=0.02), present at a younger age (48.6±15.0 vs. 55.0±13.0 years, P<0.01), and have a lower BMI (24.6±4.0 vs. 25.9±5.7, P=0.04) but were less likely to form struvite stones (5.5% vs. 14.1%, P<0.01). No cystine stone patients were seen in North American Chinese patients, whereas 1.8% of nephrolithiasis patients living in China presented with cystine stones. Similar rates of calcium-based and uric acid calculi as well as urinary pH were seen among both groups.

Conclusions

Significant differences exist between Chinese nephrolithiasis patients living in China compared to those living in North America, highlighting the importance of environmental factors in addition to genetics in modulating risk for urinary stone disease.