The surgical treatment of urolithiasis has undergone a marked evolution over the past 30 years Surgical treatments have evolved from maximally invasive open stone surgery to minimally invasive techniques including ureteroscopy (URS), extracorporeal shock wave lithotripsy (ESWL), and percutaneous nephrolithotomy (PCNL).
As technology in fiber optics, miniaturization, and imaging has evolved alongside improvements in lithotripsy (laser, ultrasonic, and hydraulic), rendering patients stone free with minimal morbidity has become the standard of care. All are outpatient procedures except PCNL.
In acute clinical situations, intervention is indicated in those patients presenting with urosepsis, renal failure, bilateral obstruction, or intractable pain. In most cases, a stent composed of a flexible polymer is placed from the kidney to the bladder within the lumen of the ureter, using cystoscopy and fluoroscopy, to bypass the obstruction. Manipulation of stones in the setting of infection is contraindicated, as high-pressure irrigation and lithotripsy will induce bacteremia and urosepsis. Therefore, infected stones are left in place and treated electively after stenting. In cases where acute intervention is indicated and infection has been excluded, URS can be performed.
In non-acute clinical situations, the treatment modality is based on stone size, location, number, density, body habitus, and patient preference. Treatment goals are rendering the patient stone free with the minimum amount of morbidity.
ESWL delivers a shock wave through the skin and surrounding tissues to focus on the stone and subsequently fragment it. The shock wave is delivered with image guidance, either fluoroscopy or ultrasound, though most use fluoroscopic guidance, presenting a challenge for stones that are radiolucent.
Classic ESWL generators use electrohydraulic energy to pulverize the stone These machines offer the greatest efficacy but least amount of control of both pulse focus and energy delivery. More modern lithotripters use electromagnetic generators that emit cone-shaped shock waves that concentrate on the stone but spread onto a greater surface area of the skin, causing less pain. Both of these generators require general anesthesia, due to the pain with increasing shockwave energy.
General anesthesia also allows for timed breathing, limiting excursion of the kidney during shock wave delivery that decreases damage to surrounding tissue and maximizes energy focused on stones. Other modern low-intensity lithotripters, such as piezoelectric lithotripters, developed for their tolerance in awake patients, have had limited efficacy.
Complications of ESWL include perinephric hematomas, with an incidence of 0.6% with electrohydraulic generators and 3%-12% with electromagnetic generators.1,2 Surrounding tissue damage may also occur, but is generally self-limited.
A classic complication of ESWL is known as steinstrasse (German for “stone street”) impaction of small stone fragments in the ureter created during lithotripsy causing obstruction. This can occur with any type of lithotripsy, but is most common with ESWL as the stone fragments are not removed.
URS can be used for both ureteral and kidney stones. The ureter is accessed via a small-caliber endoscope. Distal stones can be visualized and treated with semirigid ureteroscopes, whereas stones above the distal third of the ureter are usually treated using a flexible ureteroscope. When using a flexible ureteroscope, a ureteral access sheath is usually placed so that the scope can be removed and replaced easily during treatment.
Ureteroscopes have small working ports that allow for a single small Holmium laser fiber up to 200 microns for pulverization or a small wire basket used to remove stone fragments. URS complication rates are low and include ureteral stricture, ureteral perforation, ureteral avulsion, and ureteral intussusception. After URS, a ureteral stent is generally left in place for varying amounts of time to avoid post procedural edema causing obstruction.
PCNL is reserved for larger and more complex kidney stone burdens and has almost completely replaced open stone surgery in this indication. Access to the collecting system is obtained either by interventional radiology prior to surgery or by the urologist intraoperatively with fluoroscopic guidance through a percutaneous tract directed through the flank.
This tract is then dilated and a sheath is placed to allow direct access to the collecting system with a nephroscope. The large caliber of this access sheath allows for powerful ultrasonic and hydraulic lithotripters and tools to grasp and remove large stone fragments. While still minimally invasive, this procedure does incur greater risks than ESWL and URS, including hemorrhage and renal pelvis perforation. Multiple tracts are placed for complex collecting system anatomy.
Should a postoperative scan reveal residual stone burden, the same tract can be used for a second look PCNL. Use of open stone surgery, including anatrophic nephrolithotomy, is now only reserved for patients in whom PCNL has failed or rendered impossible because of patient anatomy.
Stones located in the kidney that are larger than 2 cm (cumulative stone burden) and staghorn calculi should be treated with PCNL. Lower pole kidney stones have low stone-free rates with ESWL and URS, regardless of size because fragments do not easily pass down the ureter. With URS, small stones can be moved from the lower kidney to the upper kidney, making URS the choice for small lower pole stones.
Stones smaller than 1cm not located in the lower pole can usually be treated effectively with ESWL. Stones 1-2 cm that are not in the lower pole, less than 1000 Hounsfield units (HFU) on computed tomography scans, and with a short skin to stone distance (less than 10 cm) also can be effectively treated with ESWL. Harder 1-2 cm stones (greater than 1000 HFU) can be treated with URS/laser lithotripsy.
Stones in the ureter are generally treated with URS. ESWL can be used for stones at the most upper portions of the ureter. PCNL for ureteral stones is reserved for very large stones at the ureteropelvic junction or proximal ureter. While ESWL is often the treatment modality preferred by patients as it is the least invasive, ureteral stone free rates are higher with ureteroscopic lithotripsy, especially as stone density and size increases. For this reason ureteroscopy is considered the gold standard for ureteral stones.
Dr. Conti is a urology resident and Dr. Chung is Assistant Professor of Urology, Director of Robotic and Minimally Invasive Urologic Surgery, Stanford University School of Medicine.
- Dhar NB, Thornton J, Karafa MT, Streem SB. A multivariate analysis of risk factors associated with subcapsular hematoma formation following electromagnetic shock wave lithotripsy. J Urol2004;172 (6 Pt 1):2271-2274.
- Chaussy C, Schmiedt E. Extracorporeal shock wave lithotripsy (ESWL) for kidney stones. An alternative to surgery? Urol. Radiol 1984;6:80-87.