With the incidence and prevalence of urinary stone disease on the rise,¹ percutaneous nephrolithotomy (PCNL) remains an important surgical treatment for the efficient extraction of large renal calculi. Per AUA and European Association of Urology guidelines, PCNL should be first-line therapy offered for a total renal stone burden > 20 mm. Compared to standard PCNL (24F-30F sheath size), recent advances in laser technology allowing for stone dusting combined with intrarenal vacuum suction devices have raised the question of whether laser lithotripsy with either ureteroscopy/retrograde intrarenal surgery (RIRS), mini-PCNL (14F-22F), or even ultra–mini-PCNL should replace standard PCNL and be considered the new treatment of choice. In our opinion, there continues to be a role for standard PCNL.

The discussion of replacing standard PCNL with mini-PCNL or RIRS centers around the following points: (1) stone-free rates, (2) infectious risk, (3) kidney trauma/transfusion rates, and (4) operative efficiency and length of stay. This update serves not only to address what the current evidence reflects, but also to share our belief that mini-PCNL should not be the only form of PCNL in a urologist’s armamentarium. Standard PCNL remains an appropriate option for medium (1-2 cm) and large stone burdens (>2 cm).

Stone-Free Rates

Historical studies have demonstrated that standard PCNL has a higher stone-free rate among size- and complexity-matched stones in comparison to RIRS.² When comparing standard to mini-PCNL, studies have shown no difference in stone-free rates.^3,4 To date, no study that we are aware of has prospectively compared stone-free rates using either vacuum-assisted RIRS or vacuum-assisted mini-PCNL to standard PCNL for large stone burdens. Certainly, this is an area of clinical practice that deserves prospective trials.

Infectious Risk

While the contribution of intrastone bacteria and bacterial endotoxins to postoperative infection continues to be studied,⁵ many attribute the risk of infection following kidney stone surgery to be related to increased intrarenal pressure with subsequent pyelovenous backflow.⁶ Historically, PCNL has been shown to have renal pressures < 30 mm Hg,⁷ and a recent study comparing intrapelvic pressures during standard PCNL, mini-PCNL, and flexible ureteroscopy in a kidney model redemonstrated that standard PCNL had the lowest intrarenal pressure compared to RIRS and mini-PCNL.⁸

Kidney Trauma/Transfusion Rates

Any discussion on kidney trauma and PCNL needs to mention the most important step in achieving a successful PCNL: obtaining percutaneous renal access. Supine or prone split-leg allow for simultaneous visualization of this percutaneous access with a ureteroscope whenever possible (Figure), ie, endoscopic combined intrarenal surgery. Additionally, ultrasound-guided access has emerged as an alternative to fluoroscopy allowing for visualization of surrounding organs and in experienced hands a more accurate puncture location. Both endoscopic combined intrarenal surgery and ultrasound guidance are evolutions that have made for safer standard PCNL compared to historic reports.

Figure. Endoscopic confirmation of an ultrasound-guided renal access with visualization of the percutaneous needle entering the calyx.

Where standard PCNL differs from mini-PCNL is in the dilation of the tract and the subsequent increase in renal parenchyma affected by the larger-diameter balloon and renal sheath. Decreasing a 30F tract to a 20F tract decreases the volume of renal parenchyma dilated by 56% (volume = π × radius of sheath² × length of tract). Mini-PCNL is undoubtedly less traumatic to the renal parenchyma and has been shown to be associated with fewer blood transfusions, however the transfusion rate is already low for standard PCNL in experienced hands.^3,4 In addition, long term, a larger diameter of the access tract does not appear to be associated with a significantly greater loss of renal parenchyma.⁹

Operative Efficiency and Length of Stay

A recent systematic review comparing 7 randomized controlled trials of mini-PCNL vs standard PCNL (both 30F and 24F) found that standard PCNL had significantly shorter operative times with similar stone-free rates.⁴ Most likely, this is related to the efficiency of an effective lithotrite in fragmenting and suctioning out the large volume of stone. What we have found is that the use of Bernoulli’s principle/Venturi effect technique, one that is familiar for those who perform mini-PCNL without active vacuum suction, can be quite effective for small-/medium-sized fragments. However, standard PCNL allows for the extraction of the largest-sized fragments, representing the ultimate in efficiency. A 1-cm stone can literally be removed in seconds.

Meanwhile, for length of stay following PCNL, ambulatory standard PCNL has gradually grown more popular with multiple studies demonstrating this to be safe.¹⁰ For many endourologists, ambulatory standard PCNL is the new standard in performing PCNL.

New Technologies

With encouraging new technologies emerging, how urologists incorporate and study these technologies moving forward will help determine how these new devices find a home in this ever-changing field. For example, steerable ureteral access sheaths with suction and vacuum-assisted mini-PCNL sheaths are beginning to change the landscape of stone treatment. While standard PCNL remains a viable option now for many renal stones, this update may look different with the development and improvement of these technologies.

Summary

Large stone burdens (>2 cm) are still best managed with standard PCNL and many endourologists prefer to perform PCNL for medium stone burdens (stone sizes between 1 and 2 cm), for which PCNL is also an option per guidelines. The reasons for this are simple: in the hands of experienced endourologists there are low intrarenal pressure, efficient removal of stones, and low complication rates. We believe that selecting which technique is most appropriate for a patient’s stone burden should be based on the most efficient and safe removal of the maximum amount of stone for each case. Done right, standard PCNL is an option for medium to large stone sizes and offers the greatest efficiency.