The first reported percutaneous access of the kidney was performed by Dr. Willard Goodwin in 1955 during a renal arteriogram, whereby the needle was placed into the collecting system of a hydronephrotic kidney. Two decades later, in 1976, Drs. Fernström and Johansson described their removal of renal calculi through a percutaneous tract, thereby performing the first percutaneous nephrolithotomy (PCNL).¹ As PCNL gained popularity, it was realized that renal access was the most challenging portion of the case for the urologist. As of 2017, interventional radiologists gained percutaneous renal access in nearly half of PCNL cases. Interventional radiologist access for PCNL remains a challenge as Metzler and colleagues have demonstrated that interventional radiologist-gained access PCNLs were associated with a longer length of stay, and more readmission, transfusions and secondary stone procedures.²

Traditional PCNL access involves the use of fluoroscopy and different techniques are described in the literature, including monoplanar access, biplanar access, bulls-eye technique and triangulation technique.³ Given concerns of radiation exposure for the patient and staff and increasing respect for the ALARA (As Low As Reasonably Achievable) principle, the use of ultrasonography has gained popularity. Ultrasound access is further simplified with the use of renal guide attachments which allow the surgeon to visualize the needle track. In a recent review of ultrasound vs fluoroscopy Corrales and co-workers concluded there were no significant differences in success, bleeding, operative time, complications or length of stay between fluoroscopy and ultrasound-based accesses.⁴

Use of conventional techniques with fluoroscopy and/or ultrasonography can be challenging to access the desired target calyx, especially in a nondilated system. As such, endoscopic guided percutaneous renal access was developed, which resulted in decreased fluoroscopy time and needle passes. However, this technique does require the use of an assistant to hold the endoscope.⁵ While the retrograde renal access approach was initially described by Lawson et al in 1983,⁶ it was not widely adopted due to concerns of needle control. However, recent adaptations using a holmium laser fiber to facilitate laser exit of the body has rekindled interest in the topic.⁷

Additional efforts utilizing a combination of ultrasound and fluoroscopy have been described. Laser direct alignment radiation reduction technique is a combined fluoroscopy/ultrasonography technique which utilizes a laser from the image intensifier to direct the placement of a specialized needle with an enlarged hub.⁸ Other combination imaging techniques also incorporate the use of endoscopic guidance. Computerized tomography based renal access has also been described for complex cases in which conventional techniques have failed, but results in significantly greater radiation exposure.⁹

Figure 1. Immersive VR model of staghorn calculus: anterior view.

Figure 2. Immersive VR model of staghorn calculus: posterior view.

Virtual and augmented reality have been utilized to enhance renal access by improving the surgeon’s understanding of the target anatomy. Rassweiler and colleagues described their use of iPad-assisted percutaneous access.¹⁰ This requires computerized tomography performed in the prone position with additional external skin markers which are used by a computer algorithm to produce augmented-reality enhanced images displayed on the iPad^®. Further efforts were described by Parkhomenko and co-workers with the use of immersive virtual reality (VR) renal models as a preoperative planning tool for PCNL.¹¹ VR models of each case were created using the computerized tomography images, thereby allowing the surgeon to view and interact with the renal anatomy using immersive VR headsets. Figures 1 and 2 show examples of immersive VR models. Overall, in their initial experience they found that immersive VR improved the surgeon’s understanding of the renal anatomy and decreased fluoroscopy time and blood loss.¹¹

Initial efforts utilizing robotic percutaneous access to the kidney were described by Dr. Kavoussi in 1998.¹ Recent endeavors such as the automated needle targeting with x-ray described by Oo and colleagues is a computer-assisted navigation system to guide needle placement.¹² Further advancements utilizing an electromagnetic (EM) guidance system (Auris Health, Redwood City, California) hold significant promise to decrease the learning curve of percutaneous access and minimize radiation. EM guidance allows for real-time, 3-dimensional targeting by utilizing a targeting beacon that is passed through the working channel of the ureteroscope. Using this system, inexperienced surgeons were able to achieve similar success rates as experts.¹³ Currently Auris has commercialized a similar EM-based system which is being utilized in bronchoscopic clinical practice, and it is feasible that this technology could be adapted and introduced into urological practice for needle targeting in the near future, thus facilitating needle access.

The aforementioned efforts highlight the progression of PCNL access and the impact of ever evolving technologies. The ideal PCNL access method is one that has a low learning curve, and provides precise and efficient targeting with real-time feedback and guidance while minimizing or eliminating radiation exposure. An EM guidance system that allows for real-time, 3-dimensional targeting shows the greatest promise for achieving this ideal.