SWL consists of transmission of high-energy shock waves, created by an energy source, such as electrohydraulic, electromagnetic, and others, through the patient. The shockwave can be focused on the stone in question using an acoustic lens and transmitted through water or a membrane in contact with the patient. When these shock waves approach the calculus and thus pass through two different acoustic mediums, energy is released, resulting in fragmentation of the calculus due to a disruption in the internal structure of the stone. This can be achieved with the aid of fluoroscopy or ultrasound guidance as a means to target the exact location of the calculus, and thus focus the acoustic waves precisely on the calculus. SWL is non-invasive, can be delivered with or without general anesthesia, and can be done on an outpatient basis. Success rates vary when compared to alternative modalities, however, in a comparison study between SWL, URS, and PCNL, single treatment rates were significantly better in patients who underwent PCNL and URS when compared to SWL [1]. SWL was shown to necessitate repeated treatments in order to match the efficacies of PCNL and URS [1, 2].

SWL has reduced effectiveness in patients who are more obese, as well as patients with hard stones and stones which are large or involve complex anatomy. Impacted ureteral and/or lower pole stones can prove more difficult to clear and may benefit from pre-SWL manipulation to an upper or mid-polar location; ureteral stent placement may also be performed during this setting to facilitate passage of stone fragments. Post-procedural positioning exercises may also improve clearance. In rare circumstances, SWL is shown to have potential consequences including significant hemorrhage from the kidney, spleen, and liver. Its relationship to diabetes mellitus and hypertension is less certain and has been a subject of contention [2, 3]. Nonetheless, due to its non-invasive nature and minimal anesthesia requirements, SWL is often administered as a first line of treatment for stones less than 2 cm.

Advances in fiber optics and digital imaging as well as improvements with ancillary equipment have led to significant progress in the endoscopic management of ureteral and renal stones. Ureteroscopy (URS) consists of retrograde passage of an endoscope per urethra and upward through to the affected ureter and kidney allowing access to the calculus as well as delivery of instruments such as guidewires, balloon dilators, laser fibers, and baskets. This is relatively non-invasive but does warrant spinal or general anesthesia. A meta-analysis reviewing seven large randomized controlled trials including 1,205 patients demonstrated that ureteroscopic management of ureteral and renal stones, when compared to SWL, achieved a higher stone-free rate after treatment and lower need for retreatment [4]. As such, URS is considered treatment of choice for most ureteral and renal calculi. However, URS is associated with a higher procedure-related complication rate and longer hospital stays. Rigid ureteroscopes are reserved for more distal ureteral stones whereas flexible ureteroscopes, with their ability to deflect up to 300° in some models, can reach the extremes of renal poles as well as negotiate otherwise difficult to access anatomic variants of renal calices. As the deflection capabilities can be reduced significantly once the working channel is utilized, it may help to move the calculus to a more accessible calyx.

Improved endoscopic equipment has also facilitated this procedure greatly with improved stone-free rates. Ureteral stents when placed prior to ureteroscopic treatment for urinary lithiasis were shown to be associated with higher stone-free rates [5]. Ureteral access sheaths allow repetitive passage of ureteroscopes to and from the renal pelvis while minimizing trauma to the urothelium. Ureteral access sheaths also allow continuous flow of irrigation fluid thereby improving visualization and facilitating a low-pressure system. While flexible electrohydraulic lithotripters are available for both rigid and flexible ureteroscopes, laser lithotripsy remains the preferred method of choice for lithotripsy in most first-world centers; the most efficient laser system being the Ho:YAG system, due to its rapid absorption in water and minimal tissue penetration. There exists an increasing array of basketing and grasping instruments available to the surgeon. While graspers allow for easier release of the stone if removal becomes difficult, extraction usually takes longer than when using baskets. With regard to guidewires, it is recommended to leave a safety wire in place, as in the case of ureteral injury access may be lost otherwise. Ureteral stent placement over the wire will also obviate the need for a percutaneous nephrostomy tube to be placed for urinary drainage.

PCNL involves direct passage of an endoscope percutaneously into the kidney. Access is achieved under fluoroscopic or ultrasonic guidance or combined endoscopic/radiographic imaging techniques. With the patient in either a prone or supine position, the kidney is located using anatomical markings as a rough guide; a posterior approach below the 12th rib is preferred to avoid the pleura as well as the intercostal vessels and nerve. Access via a posterior calyx is preferred rather than the renal pelvis so as to avoid the posterior branches of the renal artery which runs along the renal pelvis. A percutaneous puncture is done with a needle followed by injection of contrast to reveal the intrarenal anatomy. This can be done as an outpatient procedure in an angiography suite or during the same setting of the PCNL. Cystoscopy and placement of a ureteral catheter with retrograde injection of contrast can dramatically aid in localizing and accessing the kidney prior to placement of the percutaneous needle.

Once access has been obtained, and a guide wire can be advanced in an antegrade fashion to maintain access as well as to allow passage of dilators in order to expand the tract; sequential dilators or a balloon dilator can be used. Speculation regarding the safety, efficacy, and long-term sequelae of either method has been put forth, but no large long-term studies have proven either method to be superior. Once access and dilation is achieved, with a working sheath in place, a rigid or flexible nephroscope can be passed along with a variety of lithotripters: laser, pneumatic, ultrasonic, or a combined pneumatic/ultrasonic lithotripter. Calculi can then be removed in fairly large sizes as the access sheaths can be as large as 30 Fr. Antegrade access to the ureter can be achieved depending on ureteral diameter.

Bleeding can obstruct visibility and often requires termination of the procedure with placement of a nephrostomy tube and a return to the operating room at a later date. Anatomical limitations can also make it difficult or impossible to access calyces with a narrow infundibulum or with entrances at acute angles to the tract. In these cases, a second and sometimes third access tract is required to obtain complete stone clearance. A combined retrograde approach is also an option. Critical to successful PCNL is optimal positioning of the nephrostomy tract for complete stone removal and thus if a radiologist is placing the nephrostomy tube prior to the PCNL, good communication between the urologist and the radiologist is paramount.