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Minimally Invasive Surgical Treatment for Kidney Stone Disease
Minimally Invasive Surgical Treatment for Kidney Stone Disease Dayron Rodrı´guez and Dianne E. Sacco Minimally invasive interventions for stone disease in the United States are mainly founded on 3 surgical procedures: extracorporeal shock wave lithotripsy, ureteroscopic lithotripsy, and percutaneous nephrolithotomy. With the advancement of technology, treatment has shifted toward less invasive strategies and away from open or laparoscopic surgery. The treatment chosen for a patient with stones is based on the stone and patient characteristics. Each of the minimally invasive techniques uses an imaging source, either fluoroscopy or ultrasound, to localize the stone and an energy source to fragment the stone. Extracorporeal shock wave lithotripsy uses a shock wave energy source generated outside the body to fragment the stone. In contrast, with ureteroscopy, laser energy is placed directly on the stone using a ureteroscope that visualizes the stone. Percutaneous nephrolithotomy requires dilation of a tract through the back into the renal pelvis so that instruments can be inserted directly onto the stone to fragment or pulverize it. The success of the surgical intervention relies on performing the least invasive technique with the highest success of stone removal. Q 2015 by the National Kidney Foundation, Inc. All rights reserved. Key Words: Nephrolithiasis, Ureteroscopy, Extracorporeal shock wave lithotripsy, Percutaneous nephrolithotomy
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idney stone disease is estimated to affect 1 in 11 people in the United States, and the incidence is rising.1 Individuals requiring intervention are offered mainly 1 of 3 interventions: ureteroscopic lithotripsy (URS), extracorporeal shock wave lithotripsy (ESWL), or percutaneous nephrolithotomy (PCNL). These surgical techniques have been refined over time as surgery has focused on noninvasive techniques. To appreciate the advancement of these techniques, it is important to briefly review the history of surgical intervention for stones. The first documented stone surgery was open surgery for bladder stones which dates back to the ancient Indian, Chinese, and Greek civilizations. The next main advancement was the emergence of anesthesia and aseptic techniques toward the end of the 19th century. Improvements in diagnostic capabilities for stone disease followed, prompted by the discovery of the X-ray by Roentgen in 1895. In fact, the first kidney stone was seen on an X-ray of the abdomen in 1897. Most kidney stones and ureteral stones were localized by X-ray and surgically removed by open techniques. Over time, advances in equipment, energy sources, and imaging have led to a range of options. Indeed, by the 1980s, treatment options for urinary stones included extracorporeal shock wave lithotripsy, ureteroscopy, and PCNL. Today, open surgery in the United States for renal calculi is rapidly disappearing, comprising 0.3% to 4% of all stone surgery cases.2 With the advancements of technology, minimally invasive surgery for stone disease has been refined with less morbidity and increased rates of stone clearance. From Department of Urology, Massachusetts General Hospital, Harvard Medical School, Boston, MA. Financial Disclosure: The authors declare that they have no relevant financial interests. Address correspondence to Dianne E. Sacco, BA, MS, MD, Department of Urology, Massachusetts General Hospital, 55 Fruit Street, GRB 1102, Boston, MA 02114. E-mail: [email protected] Ó 2015 by the National Kidney Foundation, Inc. All rights reserved. 1548-5595/$36.00 http://dx.doi.org/10.1053/j.ackd.2015.03.005
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EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY The first human treatment of a stone by ESWL was on February 20, 1980, by Dr Chaussy who used an HM1 lithotripter by the German aerospace firm Dornier (Lindau, Germany). In 1984, the first commercially available lithotripter (HM3) was introduced.3 The technology was derived as a spinoff from military research. The aerospace firm Dornier noted unusual patterns of metal fatigue in aircrafts and theorized that shock waves created by raindrops striking an aircraft in supersonic flight could cause metal fatigue. Lithotripters generate a “shock wave,” which is a short acoustic pulse that lasts approximately 5 microseconds. To focus the shock wave on the stone, the lithotripter uses a reflector around the tip of the electrode. The “shock” is generated at the focal point of the reflector. The shock wave produced spreads and bounces off the reflector moving in a manner so that they converge simultaneously at a second focal point, which is the point of greatest force. The stone is positioned at this second focal point for maximum stone fragmentation. Lithotripters are classified based on the energy source used to generate shock waves: piezoelectric, electrohydraulic, and electromagnetic. All share some basic characteristics: an energy source, a shock wave-focusing mechanism, a coupling medium, and a system for localizing the target. During propagation and transmission of a shock wave, energy is lost at interfaces with differing densities. Therefore, a coupling medium is necessary to minimize the dissipation of energy of a shock wave as it traverses the skin surface. The combination of several events during shock wave lithotripsy are thought to cause stone fragmentation: spallation, tear and shear forces, cavitation, quasi-static squeezing, dynamic squeezing, and stone fatigue.4 In summary, the successive shock wave pressure pulses result in direct forces that fragment the stones into smaller pieces. ESWL is the one truly noninvasive treatment for stones. The American Urological Association guidelines on the management of renal calculi support the use of ESWL for kidney stones.5 It is recommended for patients with normal anatomy who have a kidney stone that is less
Advances in Chronic Kidney Disease, Vol 22, No 4 (July), 2015: pp 266-272
Minimally Invasive Surgical Treatment for Kidney Stone Disease
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than 2 cm2. This treatment is contraindicated in patients in vivo determination of the composition of urinary who are pregnant, morbidly obese, have a kidney artery stones.17,18 This in addition to the measurement of Hounsfield units (HUs) has contributed information or abdominal aortic aneurysm, coagulopathy, skeletal malused to determine stone fragility and success with formations, urinary tract infection, or have an uncorrected ESWL. Gupta and coworkers19 found a HU value of 750 obstruction distal to the stone. to be predictive of ESWL success for kidney stones. PaThe widespread use of this technology is due to its nontients with dense calculi (.750 HU) required more treatinvasiveness nature, low morbidity, and excellent initial ment sessions and were less likely to achieve complete success rates. ESWL has revolutionized the approach to stone clearance than calculi with lower HU. Therefore, patients with kidney stones. In fact, in almost 3 decades dual-energy CT examination may contribute to not only after its introduction, ESWL has become the most the identification but also the chemical characterization commonly used urinary stone treatment for patients of urinary stones, which may impact surgical and medical with upper urinary tract stone disease.5 A number of factors affect ESWL success rates, including treatment decisions. stone size, composition, and location as well as Improvements in the lithotripter have been matched by patient characteristics.6-8 Anatomic features, including both an improvement in the patient experience and the ureteropelvic obstruction, calyceal diverticuli, and fusion success rate. With early lithotripters, patients had to be anomalies, such as horseshoe kidney, can also negatively immersed in a large water bath with degassed and deionaffect the outcome.9 Increasing stone size has been ized water for acoustic coupling. In contrast, the newer inversely correlated with stone-free rates.7 Success rates and smaller lithotripters free the patient from a water are highest (80% to 90%) with calculi in the renal pelvis tank by using a dry treatment cushion head with ultraand ureteropelvic junction.10 Stone-free rates are also sound gel or oil placed against the patient’s abdomen. As dependent on stone location in the renal pelvis: upper extracorporeal shock wave lithotripsy technology evolved, (81%), middle (70%), and lower (56%) pole calyces.11 To newer generation lithotripters provided decreased cost, evaluate the discrepancy of ESWL for lower pole stones, a better portability, and increased convenience for the medmulticenter Lower Pole ical team and patient. Study Group was orgaNewer generation lithoCLINICAL SUMMARY nized to determine the tripters also reduce the optimal treatment of lower need for anesthesia The 3 main surgical treatments used to remove kidney pole calculi in a prospective, because the power has stones are extracorporeal shock wave lithotripsy, randomized trial been reduced. With these ureteroscopy, and percutaneous nephrolithotomy. comparing ESWL and improvements, ESWL has The authors PCNL.12 become a much less intim Ureteroscopy and shock wave lithotripsy are the 2 most concluded that ESWL conidating experience for the commonly used procedures for treating stones. stitutes reasonable first-line patient. However, it The decision on which technique to use is based on patient treatment only for lower should be noted that the and stone characteristics. pole stones smaller than technical improvements 1 cm. PCNL should be the in these newer models recommended therapy for have been largely based stones larger than 1 cm. Stone composition also affects on practical concerns for the user and the patient’s convethe effectiveness of ESWL. Cystine, brushite (calcium phosnience rather than a rigorous understanding of the underphate), and calcium oxalate monohydrate stones are less lying mechanisms in ESWL. prone to fracture with shock wave lithotripsy.13-15 At this Although newer machines have proved to be more time, computed tomography (CT) is the most effective convenient, an increasing number of problems have been means for identifying the composition of in vivo stones. identified. These newer dry head lithotripters can have Along with stone-related factors, patient characteristics air bubbles in the gel applied at the treatment head. This contribute to the effectiveness of ESWL. In 1994, Ackerdiminishes the efficient transfer of shock wave energy. mann and colleagues6 first described body mass index as As a result, more shock waves may be needed for fragmenan independent predictor of ESWL failure, finding that tation, which can lead to increased trauma to the kidney regardless of the positioning and technical concerns, parenchyma and potential blood vessel damage. Furtherpatients with body mass index greater than 28 (kg/m2) more, efforts to achieve high peak pressures on the stone had a suboptimal outcome after ESWL. Furthermore, it and narrow focal zones to reduce the field of transmission has been shown that a skin-to-stone distance of greater of energy have been found to produce greater tissue than 10 cm on CT scan will decrease the efficacy of the trauma and lower success rates.5 16 Recent research efforts have focused on different techtreatment. When choosing ESWL, these factors must be considered to ensure that the correct treatment is being niques to use during ESWL that improve shock wave used to optimize stone-free success rates. efficiency maximizing stone fragmentation while simultaThe development of dual-energy multidetector CT, neously minimizing tissue trauma. One area of research which provides a low- and high-energy scanning during has been the optimization of shock wave coupling, in a single acquisition, provided the ability to differentiate which shock waves are gated to fire during the patient’s materials that have similar electron densities but varying myocardial refractory period through an electrocardiophoton absorption.17,18 This technology allows for the gram. This strategy has helped avoid shock wave delivery
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during pre-excitation (shock delivered during ventricular refractory period), which can lead to life-threatening arrhythmias. Another area of research focuses on coupling the shock with respirations, in which by controlling respiratory variation allows for better targeting of the stone. Pishchalnikov and colleagues20 found an inverse relation between the surface area of air pockets at the coupling interface and the efficiency of stone fragmentation. Cartledge and others21 evaluated various coupling media and found that ultrasound jelly is the optimum coupling agent available for use. Neucks and colleagues22 showed that treatment success favored the application of the jelly to the therapy head as a bolus, rather than spreading the gel by hand. Another important area of study is the ongoing efforts to improve the methods for shock administration. In an effort to decrease procedure times and costs, extracorporeal shock wave lithotripsy was administered at an increased number of shock waves per minute to decrease operative time. However, numerous in vitro and in vivo studies have shown that faster shock wave administration rates result in decreased efficiency of stone fragmentation. A recent literature review and meta-analysis by Semins and colleagues23 found that by slowing the rate of SWL delivery to 60 shock waves per minute, patients had greater treatment success than patients treated at 120 shock waves per minute. This data contradicted the prevailing belief at the time. The study also showed improved cost-effectiveness in patients treated at slower rates because of lower retreatment rates and the need for fewer additional procedures.24 Although the mechanism by which the slower shock wave rate increases the effectiveness of the therapy is still unclear, the clinical data do support the utilization of a slower rate to increase the efficacy of the treatment. In the early years of ESWL, it was thought that shock wave energy would pass harmlessly through the kidney. However, it is now well documented that a significant amount of kidney injury can occur during shock wave therapy. The extent of kidney injury is dose dependent, with more extensive injuries observed in the setting of increased number of shocks and power/voltage settings.20 In addition, ESWL for kidney and proximal ureteral stones has been associated with the development of hypertension and diabetes mellitus. In a study from the Mayo clinic that followed 630 patients showed that at 19 years of follow-up, hypertension was more prevalent in the ESWL group (odds ratio 1.47, P ¼ .034). This development of hypertension was related to bilateral treatment (P ¼.033).25 Furthermore, the development of diabetes mellitus was related to the number of administered shocks and treatment intensity (P ¼ .005 and .007).25 To decrease tissue damage and functional impairment of the kidney, it is recommended that treatment be limited to the lowest shock wave dosage necessary to achieve stone fragmentation. Furthermore, the kidney injury associated with ESWL may be attenuated by a priming dose of low-amplitude shock waves (100 shocks), followed by a higher power setting—a strategy known as “ramping.” The reduced renal trauma observed in pretreated porcine kidneys is presumably because of vasoconstriction of vessels.26 ESWL has been
shown in the pig model to cause a temporary decrease in the blood flow and function of the kidney for up to 3 weeks.26 During this time, kidney scans show decreased uptake (reduced blood flow) and increased transit time (decreased function). ESWL, however, does not appear to have long-term deleterious effects on kidney function.27 Other complications of ESWL include hematuria, kidney or retroperitoneal hematoma, skin petechiae and ecchymosis, ureteral stricture, and steinstrasse (stone street).13 URETEROSCOPY (URS) Historically, the use of ureteroscopy started serendipitously when in 1912 Dr. Hugh H. Young unintentionally introduced a 12F pediatric cystoscope into an immensely dilated ureter of a child who had posterior urethral valves. Dr. Young was able to visualize the renal pelvis.28 This was preceded by advancements in the development of direct and indirect light guides which improved methods for delivering better illumination.29 Later on, the development of image improvement through rodlens systems, such as the Hopkins lens system, and the development of passive deflection mechanisms for flexible ureteroscopes, allowed for better visualization of the urinary system.29 No further advances were made in ureteroscopy until fiberoptic technology was introduced.28,29 The application of fiberoptics allowed for endoscope size reduction and facilitated the development of steerable deflectable ureteroscopes. In 1981, Das30 described the first transurethral ureteroscopy with stone basketing under direct vision using rigid ureteroscopy. In 1983, Bagley and colleagues31 described use of the first flexible tip pyeloscope. In the latter half of the 1980s, several flexible deflectable ureteroscopes became available in different sizes and with different options, including some with small working channels.28 Over the last 30 years, technological advancements have resulted in smaller, actively deflectable (ability to bend up to 275 ), flexible endoscopes that are easier to maneuver into the upper urinary tract. These scopes combined with powerful and precise holmium laser lithotrites and a variety of endoscopic retrieval devices have further enhanced the successful outcome of ureteroscopy. Currently, ureteroscopy is a recommended treatment for all ureteral stones independent of size and kidney stones less than 2 cm. Ureteroscopy is also recommended for distal ureteral stones independent of size as it is associated with few complications and a high success rate.32 A Cochrane review that examined the evidence from randomized controlled trials on the outcomes of ESWL or ureteroscopy in the treatment of ureteric calculi concluded that compared with ESWL, ureteroscopic removal of ureteral stones achieves a greater stone-free state but with a higher complication rate and longer hospital stay.13 For proximal stones, ESWL has a higher stone-free rate for stones less than 1 cm while URS was more effective for stones larger than 1 cm. However, both approaches are feasible.5 For kidney stones, URS now has the same indications as ESWL as first-line treatment for renal pelvic stones less than 2 cm. It is the preferred option for lower pole stones less than 1 cm.33 Patients presenting with stone characteristics that are not amenable to ESWL (cystine,
Minimally Invasive Surgical Treatment for Kidney Stone Disease
brushite, calcium oxalate monohydrate, .750 HU, and impacted stone) are treated with URS. Moreover, patients who have failed ESWL or those presenting with contraindications to ESWL are also usually better candidates for URS. In patients with ectopic, pelvic, or transplant kidneys, URS is also an option with success rates similar to ESWL and morbidity less than that of PCNL.34 Moreover, this technique can be safely used in patients taking blood thinners. The development of equipment over time has made the procedure popular for most stones. It was the introduction of fiberoptic flexible ureteroscopes that revolutionized urologic stone practice allowing stones to be treated under direct vision with a lithotriptor. The flexible ureteroscopes do have some limitations: they have limited visibility compared with semi-rigid ureteroscopes. They also are fragile and prone to damage: fibers may burn out and fracture resulting in loss of image quality. Novel flexible digital ureteroscopes have been developed to overcome these problems.35 The tip of these digital flexible ureteroscope contains light-emitting diodes that obviate the need for an external light source, which minimizes the risk of drape fires or patient burns. These ureteroscopes are much lighter than their fiberoptic counterparts because there are no external cameras or light cables. They provide high-quality digital images with high resolution, autofocusing capabilities, and digital magnification all of which allows flexible URS to become less cumbersome with clearer images. However, these newer ureteroscopes are slightly larger in diameter, which can be a challenge when performing ureteroscopy in small diameter ureters. Along with developments in the technology of the ureteroscope, several pieces of equipment have been developed to be used through the ureteroscope as a means of enhancing the treatment of stones. The holmium:YAG laser is frequently used to fragment the stone. Laser fibers are inserted through the working channel of the ureteroscope. Under direct visualization, the stone is fragmented using the holmiun:YAG laser. Attempts are being made to develop smaller diameter fibers that will not decrease the deflection of the ureteroscope. Currently, the smallest fiber available is the 200-micron fiber that impedes the deflection of a flexible ureteroscope by up to 20 .36 Another area of focus is on maximizing fiber durability. If a laser fiber fractures inside an endoscope, it can damage the ureteroscope components and lead to costly repair. The injury to the scope can also occur when the fiber is inadvertently retracted into the scope. New technology is being developed to protect the endoscope system from the laser energy using an internal sensor.37 Aside from the developments in the energy source. There is a focus on developing ancilliary equipment. Stone retrieval baskets, used along with a ureteral access sheath, allows safe removal of stones from the renal pelvis. There are continual modifications to these devices which enhance the ease of the surgery and decrease the risks. The improvements in the technology of ureteroscopes and accessory devices have increased the success of stone treatment. A novel robotic ureteroscope system is currently being developed for performing retrograde ureterorenoscopy. Although still in its very early stages, the potential advan-
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tages of robotic flexible URS compared with conventional manual URS include an increased range of motion, instrument stability, and improved ergonomics. It is believed that the patient’s experience is improved by these newer ureteroscopes. Although, there is very little literature comparing patient satisfaction between the ureteroscopes. With the development of the ureteroscope and its subsequent modifications to increase its versatility, it has become a very useful tool in the treatment of ureteral and kidney stones. Furthermore, as recently trained urologists feel more comfortable with performing the procedure, the use of ureteroscopy for treatment of stone disease has increased over time. PERCUTANEOUS NEPHROLITHOTOMY €del (1902) were the first to Joseph Hyrtl (1882) and Max Bro establish the existence of a relatively avascular plane posterior to the midline of the kidney that could be transected for surgical stone extraction.38 Howard Kelly later found that the landmarks were reliable in only two-thirds of kidneys and advocated for pyelotomy claiming that it was a much safer operation.38 In 1955, while trying to perform a renal arteriogram, Goodwin and colleagues39 serendipitously performed the first antegrade nephrostogramand and left a tube to drain the kidney, thus placing the first modern day nephrostomy tube. Later in 1976, €m and Johansson40 were the first to describe a Fernstro technique for extracting renal calculi through a percutaneous nephrostomy under radiological control. Because of this technique, PCNL almost completely eliminated the need for open stone surgery in patients who had calculi not amenable to less-invasive therapies. The procedure went on to gain wide acceptance in the early 1980s. Percutaneous removal of stones is currently recommended for patients with staghorn calculi, kidney stones greater than 2 cm, and lower pole stones greater than 1.0 cm. It is an effective means of treating certain patients with anatomical abnormalities which would not be effectively treated by ESWL or ureteroscopy. These aberrations include ureteropelvic junction obstruction, and calyceal diverticula, urinary diversions (ie, continent urinary reservoirs, bladder augmentation and ureteral re-implants), retained stents encrusted with stones, narrow ureteral lumens secondary to external compression, as well as congenital or postsurgical anatomical variations (horseshoe kidneys, pelvic kidneys, cross-fused ectopia, and transureteroureterostomy). Contraindications to PCNL include uncorrected coagulopathy, urinary tract infections, inability to tolerate prone position especially if there is respiratory compromise (although this procedure has been described in the supine position), and pregnancy. It is imperative to adequately treat any urinary tract infection prior to the procedure. Obtaining proper access into the collecting system is critical for safe and effective treatment. It is performed through a posterior calyx usually in the upper or lower pole depending on the stone location and proximity of adjacent organs. Once the access to the collecting system is obtained and the tract from the skin to the renal pelvis dilated using radiological assistance, energy sources are used to break the stone if it cannot be removed intact.
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Intracorporeal lithotripsy is then performed by inserting a rigid lithotrite through the endoscope directly onto the stone under direct vision. Ultrasonic lithotripters are commonly used with continuous suction irrigation to evacuate stone fragments quickly and to maintain clear visibility. Stones may be removed using various baskets, forceps, and graspers. Larger stones or hard calculi, such as cystine and calcium oxalate monohydrate stones, that are less efficiently fragmented and removed with ultrasonic lithotripsy can be fragmented using pneumatic or laser devices. After the stone is removed from the collecting system, either a stent or nephrostomy tube, or both, can be placed depending on the surgeon’s preference. Patients usually stay in the hospital 1 to 2 days postoperatively, with relatively good oral pain control. The nephrostomy tube if placed and foley are usually removed before discharge. Patients return to work 1 to 2 weeks after surgery. New advances in PCNL combine ultrasonic and pneumatic lithotripter features in an effort to achieve superior fragmentation. Suction is used to evacuate stone fragments simultaneously. The first of these combination devices was the Lithoclast Ultra (Boston Scientific, Marlborough, MA). In a prospective randomized trial comparing the combination device to standard ultrasonic lithotrites, the Lithoclast Ultra lithotripter exhibited much faster stone clearance times than the conventional ultrasonic lithotripters.41 Another device is the Cyberwand (Olympus, Shinjuku, Tokyo, Japan), which is an intracorporeal lithotripter, a dual ultrasonic probe design that enables efficient stone fragmentation while still allowing the suction evacuation of small fragments. In the last decade, the standard PCNL technique has been modified in an attempt to decrease morbidity and complications. Technological advancements have led to miniaturization of instruments, access sheaths, and nephroscopes. In 1997, Jackman and colleagues42 initially described the technique of “mini-PCNL” in children, using a 13F outer diameter (11F inner diameter) ureteroscopy sheath and trocar set. Other investigators have also reported on their experience using smaller sheaths and rigid nephroscopes to treat 1- to 2-cm renal calculi.43-45 Using a smaller size percutaneous tract than standard PCNL has potential advantages of decreased bleeding and trauma to renal parenchyma. Initial studies show that patients undergoing mini-PCNL have reduced bleeding, length of hospital stay, and improved analgesia compared with standard PCNL.46 With smaller incisions, there has also been a tendency to favor tubeless PCNL rather than the traditional practice of leaving a widebore nephrostomy tube.47 To enhance pain management, there is also a trend for paravertebral blocks.48 These modifications have decreased the morbidity of PCNL. PEDIATRIC POPULATION For pediatric patients with upper tract kidney stones, ESWL is an effective and safe treatment technique. Pediatric patients compared with adults have anatomical features that facilitate stone fragmentation and passage after ESWL. This is most likely because shock waves are transmitted with only a slight loss of energy through
the small body habitus with less perirenal fat.49 In addition, the pediatric ureter is shorter, more elastic and distensible, thus permitting easier transmission of stone fragments and preventing ureteral impaction.50 Finally, other contributing factors could be the composition of stones, smaller relative stone volume, and the shorter duration of uropathology in children.49 Therefore, they require fewer shocks and lower energy for comparable stone clearance.2 Predictors of success or failure are similar to those identified in the adult literature, and newly developed nomograms are now available to provide risk estimation tailored to each specific pediatric patient.2 Currently, there is no available data that convincingly shows evidence of long-term kidney function compromise on children after ESWL. Today, ESWL is the method of choice in the treatment of most pediatric urinary stones.51 Ureteroscopy with laser lithotripsy is also an effective way to treat stones in pediatric patients with similar success rates as in the adult population. PCNL offers good clearance rates with acceptable morbidity in the pediatric population. The literature suggests that complex and staghorn calculi can be approached with this technique.52 Studies demonstrate minimal scar formation and insignificant loss of kidney function in children.53 With the miniaturization of instruments, especially, development of smaller nephroscopes and newer energy sources, the morbidity has decreased and the clearance rate has improved in pediatric patients. These devices have decreased operative time and increased stone clearance. Although the three modalities for treating stones are utilized, ESWL is the most common treatment for stones in the pediatric population. PREGNANCY Acute obstructive nephrolithiasis during pregnancy can be very risky to both mother and fetus. These patients need to be managed with special care. The AUA guidelines on imaging for ureteral stones recommend ultrasound as the initial technique of choice in pregnant patients.54 If the ultrasound is inconclusive, patients in the first trimester should undergo noncontrast MRI, whereas patients in their second or third trimester can undergo either MRI or low-dose CT.55 First-line management is usually conservative (trial of stone passage and pain management) which is generally associated with a high rate of stone passage.56 Immediate drainage is required if the urinary obstruction is associated with infection. Ureteral stent placement is a convenient method for temporizing ureteral obstruction from stone disease. Stent placement is usually done using minimal fluoroscopy or ultrasound. Ultrasound is used as a means of avoiding radiation altogether.55 Drainage of the urinary tract through placement of a nephrostomy tube is another option for relief of urinary obstruction. Placement of a nephrostomy tube can be easily done using local anesthesia with a high success rate (.90%).54 It allows for immediate decompression and avoids ureteral manipulation while minimizing anesthesia risks, even in patients during acute sepsis. In addition, the tract can remain open for postpartum access if farther treatment is required.54 If conservative management fails and there
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Minimally Invasive Surgical Treatment for Kidney Stone Disease
Table 1. Recommended Therapy for Renal and Ureteral Stones According to Location and Size Renal Stones ,1 cm Upper or Middle Pole
Upper or Middle Pole
Lower Pole
ESWL or ureteroscopy
.2 cm
1-2 cm
Noncystine, non-brushite, ,750 HU, children use ESWL, otherwise ureteroscopy
Cystine, Brushite, .750 HU, or high skin to stone distance use ureteroscopy or ESWL
Lower Pole
Upper or Middle Pole
Lower Pole
PCNL
PCNL
Ureteroscopy or PCNL
Ureteral Stones Proximal
Middle
Distal
,10 mm
.10 mm
,10 mm
.10 mm
,10 mm
.10 mm
ESWL
Ureteroscopy
ESWL or Ureteroscopy
Ureteroscopy
ESWL or Ureteroscopy
Ureteroscopy
Cystine, calcium phosphate, calcium oxalate monohydrate, .750 HU, impacted stones: ureteroscopy is preferred
For ,10-mm stones in women: ureteroscopy is preferred
For ,10-mm stones in women: ureteroscopy is preferred
Abbreviations: ESWL, extracorporeal shock wave lithotripsy; HU, Hounsfield units.
is no active infection, ureteroscopy and laser lithotripsy can be offered if clinically appropriate with an overall reported stone-free rate of 88.3%.54 Obstetric complications because of ureteroscopic intervention are rare (2% to 4%) and may include premature uterine contractions and preterm labor.54 Shockwave lithotripsy and PCNL are contraindicated during pregnancy. CONCLUSIONS Technological advances in the treatment of nephrolithiasis have led to safer and more efficient minimally invasive surgical treatments. Patient and stone characteristics are used to determine the most efficient treatment with the least risk (Table 1). ESWL is popular because of its noninvasive nature. The improvements in the technique of administering the shock waves have led to improved patient experience. The developments in fiberoptics and laser technology have been instrumental in stone treatment, making ureteroscopy safe and effective. Miniaturization of PCNL instruments, access sheaths, and nephroscopes have reduced its morbidity. Ureteroscopy is the most versatile of the 3 treatments because it can be used for most patients. As technology improves, the surgical management of nephrolithiasis should achieve improved levels of success with exceptional outcomes. REFERENCES 1. Shoag J, Tasian GE, Goldfarb DS, Eisner BH. The new epidemiology of nephrolithiasis. Adv Chronic Kidney Dis. 2015;22(4):273-278. 2. Grasso M, Goldfarb DS. Urinary Stones: Medical and Surgical Management. Chichester, West Sussex, UK: John Wiley & Sons, Inc; 2014. 3. Honey RJ, Schuler TD, Ghiculete D, Pace KT, Canadian Endourology Group. A randomized, double-blind trial to compare shock wave frequencies of 60 and 120 shocks per minute for upper ureteral stones. J Urol. 2009;182(4):1418-1423.
4. Madbouly K, El-Tiraifi AM, Seida M, El-Faqih SR, Atassi R, Talic RF. Slow versus fast shock wave lithotripsy rate for urolithiasis: a prospective randomized study. J Urol. 2005;173(1):127-130. 5. Pearle MS, Calhoun EA, Curhan GC, Urologic Diseases in America Project. Urologic diseases in America project: urolithiasis. J Urol. 2005;173(3):848-857. 6. Ackermann DK, Fuhrimann R, Pfluger D, Studer UE, Zingg EJ. Prognosis after extracorporeal shock wave lithotripsy of radiopaque renal calculi: a multivariate analysis. Eur Urol. 1994;25(2):105-109. 7. Al-Ansari A, As-Sadiq K, Al-Said S, Younis N, Jaleel OA, Shokeir AA. Prognostic factors of success of extracorporeal shock wave lithotripsy (ESWL) in the treatment of renal stones. Int J Urol. 2006;38(1):63-67. 8. Patel T, Kozakowski K, Hruby G, Gupta M. Skin to stone distance is an independent predictor of stone-free status following shockwave lithotripsy. J Endourol. 2009;23(9):1383-1385. 9. Vella M, Caramia M, Maltese M, Melloni D, Caramia G. ESWL prediction of outcome and failure prevention. Urol Int. 2007;79(suppl 1): 47-50. 10. Galvin DJ, Pearle MS. The contemporary management of renal and ureteric calculi. BJU Int. 2006;98(6):1283-1288. 11. Weld KJ, Montiglio C, Morris MS, Bush AC, Cespedes RD. Shock wave lithotripsy success for renal stones based on patient and stone computed tomography characteristics. Urology. 2007;70(6):10431046. discussion 1046–1047. 12. Albala DM, Assimos DG, Clayman RV, et al. Lower pole I: a prospective randomized trial of extracorporeal shock wave lithotripsy and percutaneous nephrostolithotomy for lower pole nephrolithiasisinitial results. J Urol. 2001;166(6):2072-2080. 13. Aboumarzouk OM, Kata SG, Keeley FX, McClinton S, Nabi G. Extracorporeal shock wave lithotripsy (ESWL) versus ureteroscopic management for ureteric calculi. Cochrane Database Syst Rev. 2012::CD006029. 14. Kim SC, Burns EK, Lingeman JE, Paterson RF, McAteer JA, Williams JC Jr. Cystine calculi: correlation of CT-visible structure, CT number, and stone morphology with fragmentation by shock wave lithotripsy. Urol Res. 2007;35(6):319-324. 15. Klee LW, Brito CG, Lingeman JE. The clinical implications of brushite calculi. J Urol. 1991;145(4):715-718.
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16. Pareek G, Hedican SP, Lee FT Jr, Nakada SY. Shock wave lithotripsy success determined by skin-to-stone distance on computed tomography. Urology. 2005;66(5):941-944. 17. Boll DT, Patil NA, Paulson EK, et al. Renal stone assessment with dual-energy multidetector CT and advanced postprocessing techniques: improved characterization of renal stone composition—pilot study. Radiology. 2009;250(3):813-820. 18. Hidas G, Eliahou R, Duvdevani M, et al. Determination of renal stone composition with dual-energy CT: in vivo analysis and comparison with x-ray diffraction. Radiology. 2010;257(2):394-401. 19. Gupta NP, Ansari MS, Kesarvani P, Kapoor A, Mukhopadhyay S. Role of computed tomography with no contrast medium enhancement in predicting the outcome of extracorporeal shock wave lithotripsy for urinary calculi. BJU Int. 2005;95(9):1285-1288. 20. Pishchalnikov YA, Neucks JS, VonDerHaar RJ, Pishchalnikova IV, Williams JC Jr, McAteer JA. Air pockets trapped during routine coupling in dry head lithotripsy can significantly decrease the delivery of shock wave energy. J Urol. 2006;176(6 Pt 1):2706-2710. 21. Cartledge JJ, Cross WR, Lloyd SN, Joyce AD. The efficacy of a range of contact media as coupling agents in extracorporeal shockwave lithotripsy. BJU Int. 2001;88(4):321-324. 22. Neucks JS, Pishchalnikov YA, Zancanaro AJ, VonDerHaar JN, Williams JC Jr, McAteer JA. Improved acoustic coupling for shock wave lithotripsy. Urol Res. 2008;36(1):61-66. 23. Semins MJ, Trock BJ, Matlaga BR. The effect of shock wave rate on the outcome of shock wave lithotripsy: a meta-analysis. J Urol. 2008;179(1):194-197. discussion 197. 24. Koo V, Beattie I, Young M. Improved cost-effectiveness and efficiency with a slower shockwave delivery rate. BJU Int. 2010;105(5): 692-696. 25. Krambeck AE, Gettman MT, Rohlinger AL, Lohse CM, Patterson DE, Segura JW. Diabetes mellitus and hypertension associated with shock wave lithotripsy of renal and proximal ureteral stones at 19 years of follow-up. J Urol. 2006;175(5):1742-1747. 26. Handa RK, Bailey MR, Paun M, et al. Pretreatment with low-energy shock waves induces renal vasoconstriction during standard shock wave lithotripsy (SWL): a treatment protocol known to reduce SWL-induced renal injury. BJU Int. 2009;103(9):1270-1274. 27. el-Assmy A, el-Nahas AR, Hekal IA, Badran M, Youssef RF, Sheir KZ. Long-term effects of extracorporeal shock wave lithotripsy on renal function: our experience with 156 patients with solitary kidney. J Urol. 2008;179(6):2229-2232. 28. Johnston WK III, Low RK, Das S. The evolution and progress of ureteroscopy. Urol Clin North Am. 2004;31(1):5-13. 29. Moran ME. History of ureteroscopy. In: Monga M, ed. Ureteroscopy: Indications, Instrumentation & Technique. New York, NY: Springer; 2013. 30. Das S. Transurethral ureteroscopy and stone manipulation under direct vision. J Urol. 1981;125(1):112-113. 31. Bagley DH, Huffman JL, Lyon ES. Combined rigid and flexible ureteropyeloscopy. J Urol. 1983;130(2):243-244. 32. Elashry OM, Elgamasy AK, Sabaa MA, et al. Ureteroscopic management of lower ureteric calculi: a 15-year single-centre experience. BJU Int. 2008;102(8):1010-1017. 33. Pearle MS, Lingeman JE, Leveillee R, et al. Prospective randomized trial comparing shock wave lithotripsy and ureteroscopy for lower pole caliceal calculi 1 cm or less. J Urol. 2008;179(suppl 5):S69-S73. 34. Ferrandino MN, Preminger GM. Ureteroscopic management of stones in anomalous kidneys. Arch Ital Urol Androl. 2008;80(1):18-20.
35. Humphreys MR, Miller NL, Williams JC Jr, Evan AP, Munch LC, Lingeman JE. A new world revealed: early experience with digital ureteroscopy. J Urol. 2008;179(3):970-975. 36. Matlaga BR, Lingeman JE. Surgical management of stones: new technology. Adv Chronic Kidney Dis. 2009;16(1):60-64. 37. Xavier K, Hruby GW, Kelly CR, Landman J, Gupta M. Clinical evaluation of efficacy of novel optically activated digital endoscope protection system against laser energy damage. Urology. 2009;73(1):37-40. 38. Patel SR, Nakada SY. The modern history and evolution of percutaneous nephrolithotomy. J Endourol. 2014;29(2):153-157. 39. Goodwin WE, Casey WC, Woolf W. Percutaneous trocar (needle) nephrostomy in hydronephrosis. J Am Med Assoc. 1955;157(11):891-894. 40. Fernstr€ om I, Johansson B. Percutaneous pyelolithotomy. A new extraction technique. Scand J Urol Nephrol. 1976;10(3):257-259. 41. Pietrow PK, Auge BK, Zhong P, Preminger GM. Clinical efficacy of a combination pneumatic and ultrasonic lithotrite. J Urol. 2003;169(4): 1247-1249. 42. Jackman SV, Docimo SG, Cadeddu JA, Bishoff JT, Kavoussi LR, Jarrett TW. The “mini-perc” technique: a less invasive alternative to percutaneous nephrolithotomy. World J Urol. 1998;16(6):371-374. 43. Schuster TK, Smaldone MC, Averch TD, Ost MC. Percutaneous nephrolithotomy in children. J Endourol. 2009;23(10):1699-1705. 44. Wah TM, Kidger L, Kennish S, Irving H, Najmaldin A. MINI PCNL in a pediatric population. Cardiovasc Intervent Radiol. 2013;36(1): 249-254. 45. Zhong W, Zhao Z, Wang L, Swami S, Zeng G. Percutaneous-based management of staghorn calculi in solitary kidney: combined mini percutaneous nephrolithotomy versus retrograde intrarenal surgery. Urol Int. 2015;94(1):70-73. 46. Mishra S, Sharma R, Garg C, Kurien A, Sabnis R, Desai M. Prospective comparative study of miniperc and standard PNL for treatment of 1 to 2 cm size renal stone. BJU Int. 2011;108(6):896-899. discussion 899–900. 47. Chang CH, Wang CJ, Huang SW. Totally tubeless percutaneous nephrolithotomy: a prospective randomized controlled study. Urol Res. 2011;39(6):459-465. 48. Ak K, Gursoy S, Duger C, et al. Thoracic paravertebral block for postoperative pain management in percutaneous nephrolithotomy patients: a randomized controlled clinical trial. Med Princ Pract. 2013;22(3):229-233. 49. Skolarikos A, Alivizatos G, de la Rosette J. Extracorporeal shock wave lithotripsy 25 years later: complications and their prevention. Eur Urol. 2006;50(5):981-990. discussion 990. 50. Gofrit ON, Pode D, Meretyk S, et al. Is the pediatric ureter as efficient as the adult ureter in transporting fragments following extracorporeal shock wave lithotripsy for renal calculi larger than 10 mm.? J Urol. 2001;166(5):1862-1864. 51. Gnessin E, Chertin L, Chertin B. Current management of paediatric urolithiasis. Pediatr Surg Int. 2012;28(7):659-665. 52. Sabnis RB, Chhabra JS, Ganpule AP, Abrol S, Desai MR. Current role of PCNL in pediatric urolithiasis. Curr Urol Rep. 2014;15(7):423. 53. Mayo ME, Krieger JN, Rudd TG. Effect of percutaneous nephrostolithotomy on renal function. J Urol. 1985;133(2):167-169. 54. Wollin DA, Aponte MM. Management of urological conditions during pregnancy. AUA Update Ser. 2014;33(13):130-139. 55. Andreoiu M, MacMahon R. Renal colic in pregnancy: lithiasis or physiological hydronephrosis? Urology. 2009;74(4):757-761. 56. Semins MJ, Matlaga BR. Kidney stones during pregnancy. Nat Rev Urol. 2014;11(3):163-168.
K
idney stone disease is estimated to affect 1 in 11 people in the United States, and the incidence is rising.1 Individuals requiring intervention are offered mainly 1 of 3 interventions: ureteroscopic lithotripsy (URS), extracorporeal shock wave lithotripsy (ESWL), or percutaneous nephrolithotomy (PCNL). These surgical techniques have been refined over time as surgery has focused on noninvasive techniques. To appreciate the advancement of these techniques, it is important to briefly review the history of surgical intervention for stones. The first documented stone surgery was open surgery for bladder stones which dates back to the ancient Indian, Chinese, and Greek civilizations. The next main advancement was the emergence of anesthesia and aseptic techniques toward the end of the 19th century. Improvements in diagnostic capabilities for stone disease followed, prompted by the discovery of the X-ray by Roentgen in 1895. In fact, the first kidney stone was seen on an X-ray of the abdomen in 1897. Most kidney stones and ureteral stones were localized by X-ray and surgically removed by open techniques. Over time, advances in equipment, energy sources, and imaging have led to a range of options. Indeed, by the 1980s, treatment options for urinary stones included extracorporeal shock wave lithotripsy, ureteroscopy, and PCNL. Today, open surgery in the United States for renal calculi is rapidly disappearing, comprising 0.3% to 4% of all stone surgery cases.2 With the advancements of technology, minimally invasive surgery for stone disease has been refined with less morbidity and increased rates of stone clearance. From Department of Urology, Massachusetts General Hospital, Harvard Medical School, Boston, MA. Financial Disclosure: The authors declare that they have no relevant financial interests. Address correspondence to Dianne E. Sacco, BA, MS, MD, Department of Urology, Massachusetts General Hospital, 55 Fruit Street, GRB 1102, Boston, MA 02114. E-mail: [email protected] Ó 2015 by the National Kidney Foundation, Inc. All rights reserved. 1548-5595/$36.00 http://dx.doi.org/10.1053/j.ackd.2015.03.005
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EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY The first human treatment of a stone by ESWL was on February 20, 1980, by Dr Chaussy who used an HM1 lithotripter by the German aerospace firm Dornier (Lindau, Germany). In 1984, the first commercially available lithotripter (HM3) was introduced.3 The technology was derived as a spinoff from military research. The aerospace firm Dornier noted unusual patterns of metal fatigue in aircrafts and theorized that shock waves created by raindrops striking an aircraft in supersonic flight could cause metal fatigue. Lithotripters generate a “shock wave,” which is a short acoustic pulse that lasts approximately 5 microseconds. To focus the shock wave on the stone, the lithotripter uses a reflector around the tip of the electrode. The “shock” is generated at the focal point of the reflector. The shock wave produced spreads and bounces off the reflector moving in a manner so that they converge simultaneously at a second focal point, which is the point of greatest force. The stone is positioned at this second focal point for maximum stone fragmentation. Lithotripters are classified based on the energy source used to generate shock waves: piezoelectric, electrohydraulic, and electromagnetic. All share some basic characteristics: an energy source, a shock wave-focusing mechanism, a coupling medium, and a system for localizing the target. During propagation and transmission of a shock wave, energy is lost at interfaces with differing densities. Therefore, a coupling medium is necessary to minimize the dissipation of energy of a shock wave as it traverses the skin surface. The combination of several events during shock wave lithotripsy are thought to cause stone fragmentation: spallation, tear and shear forces, cavitation, quasi-static squeezing, dynamic squeezing, and stone fatigue.4 In summary, the successive shock wave pressure pulses result in direct forces that fragment the stones into smaller pieces. ESWL is the one truly noninvasive treatment for stones. The American Urological Association guidelines on the management of renal calculi support the use of ESWL for kidney stones.5 It is recommended for patients with normal anatomy who have a kidney stone that is less
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than 2 cm2. This treatment is contraindicated in patients in vivo determination of the composition of urinary who are pregnant, morbidly obese, have a kidney artery stones.17,18 This in addition to the measurement of Hounsfield units (HUs) has contributed information or abdominal aortic aneurysm, coagulopathy, skeletal malused to determine stone fragility and success with formations, urinary tract infection, or have an uncorrected ESWL. Gupta and coworkers19 found a HU value of 750 obstruction distal to the stone. to be predictive of ESWL success for kidney stones. PaThe widespread use of this technology is due to its nontients with dense calculi (.750 HU) required more treatinvasiveness nature, low morbidity, and excellent initial ment sessions and were less likely to achieve complete success rates. ESWL has revolutionized the approach to stone clearance than calculi with lower HU. Therefore, patients with kidney stones. In fact, in almost 3 decades dual-energy CT examination may contribute to not only after its introduction, ESWL has become the most the identification but also the chemical characterization commonly used urinary stone treatment for patients of urinary stones, which may impact surgical and medical with upper urinary tract stone disease.5 A number of factors affect ESWL success rates, including treatment decisions. stone size, composition, and location as well as Improvements in the lithotripter have been matched by patient characteristics.6-8 Anatomic features, including both an improvement in the patient experience and the ureteropelvic obstruction, calyceal diverticuli, and fusion success rate. With early lithotripters, patients had to be anomalies, such as horseshoe kidney, can also negatively immersed in a large water bath with degassed and deionaffect the outcome.9 Increasing stone size has been ized water for acoustic coupling. In contrast, the newer inversely correlated with stone-free rates.7 Success rates and smaller lithotripters free the patient from a water are highest (80% to 90%) with calculi in the renal pelvis tank by using a dry treatment cushion head with ultraand ureteropelvic junction.10 Stone-free rates are also sound gel or oil placed against the patient’s abdomen. As dependent on stone location in the renal pelvis: upper extracorporeal shock wave lithotripsy technology evolved, (81%), middle (70%), and lower (56%) pole calyces.11 To newer generation lithotripters provided decreased cost, evaluate the discrepancy of ESWL for lower pole stones, a better portability, and increased convenience for the medmulticenter Lower Pole ical team and patient. Study Group was orgaNewer generation lithoCLINICAL SUMMARY nized to determine the tripters also reduce the optimal treatment of lower need for anesthesia The 3 main surgical treatments used to remove kidney pole calculi in a prospective, because the power has stones are extracorporeal shock wave lithotripsy, randomized trial been reduced. With these ureteroscopy, and percutaneous nephrolithotomy. comparing ESWL and improvements, ESWL has The authors PCNL.12 become a much less intim Ureteroscopy and shock wave lithotripsy are the 2 most concluded that ESWL conidating experience for the commonly used procedures for treating stones. stitutes reasonable first-line patient. However, it The decision on which technique to use is based on patient treatment only for lower should be noted that the and stone characteristics. pole stones smaller than technical improvements 1 cm. PCNL should be the in these newer models recommended therapy for have been largely based stones larger than 1 cm. Stone composition also affects on practical concerns for the user and the patient’s convethe effectiveness of ESWL. Cystine, brushite (calcium phosnience rather than a rigorous understanding of the underphate), and calcium oxalate monohydrate stones are less lying mechanisms in ESWL. prone to fracture with shock wave lithotripsy.13-15 At this Although newer machines have proved to be more time, computed tomography (CT) is the most effective convenient, an increasing number of problems have been means for identifying the composition of in vivo stones. identified. These newer dry head lithotripters can have Along with stone-related factors, patient characteristics air bubbles in the gel applied at the treatment head. This contribute to the effectiveness of ESWL. In 1994, Ackerdiminishes the efficient transfer of shock wave energy. mann and colleagues6 first described body mass index as As a result, more shock waves may be needed for fragmenan independent predictor of ESWL failure, finding that tation, which can lead to increased trauma to the kidney regardless of the positioning and technical concerns, parenchyma and potential blood vessel damage. Furtherpatients with body mass index greater than 28 (kg/m2) more, efforts to achieve high peak pressures on the stone had a suboptimal outcome after ESWL. Furthermore, it and narrow focal zones to reduce the field of transmission has been shown that a skin-to-stone distance of greater of energy have been found to produce greater tissue than 10 cm on CT scan will decrease the efficacy of the trauma and lower success rates.5 16 Recent research efforts have focused on different techtreatment. When choosing ESWL, these factors must be considered to ensure that the correct treatment is being niques to use during ESWL that improve shock wave used to optimize stone-free success rates. efficiency maximizing stone fragmentation while simultaThe development of dual-energy multidetector CT, neously minimizing tissue trauma. One area of research which provides a low- and high-energy scanning during has been the optimization of shock wave coupling, in a single acquisition, provided the ability to differentiate which shock waves are gated to fire during the patient’s materials that have similar electron densities but varying myocardial refractory period through an electrocardiophoton absorption.17,18 This technology allows for the gram. This strategy has helped avoid shock wave delivery
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during pre-excitation (shock delivered during ventricular refractory period), which can lead to life-threatening arrhythmias. Another area of research focuses on coupling the shock with respirations, in which by controlling respiratory variation allows for better targeting of the stone. Pishchalnikov and colleagues20 found an inverse relation between the surface area of air pockets at the coupling interface and the efficiency of stone fragmentation. Cartledge and others21 evaluated various coupling media and found that ultrasound jelly is the optimum coupling agent available for use. Neucks and colleagues22 showed that treatment success favored the application of the jelly to the therapy head as a bolus, rather than spreading the gel by hand. Another important area of study is the ongoing efforts to improve the methods for shock administration. In an effort to decrease procedure times and costs, extracorporeal shock wave lithotripsy was administered at an increased number of shock waves per minute to decrease operative time. However, numerous in vitro and in vivo studies have shown that faster shock wave administration rates result in decreased efficiency of stone fragmentation. A recent literature review and meta-analysis by Semins and colleagues23 found that by slowing the rate of SWL delivery to 60 shock waves per minute, patients had greater treatment success than patients treated at 120 shock waves per minute. This data contradicted the prevailing belief at the time. The study also showed improved cost-effectiveness in patients treated at slower rates because of lower retreatment rates and the need for fewer additional procedures.24 Although the mechanism by which the slower shock wave rate increases the effectiveness of the therapy is still unclear, the clinical data do support the utilization of a slower rate to increase the efficacy of the treatment. In the early years of ESWL, it was thought that shock wave energy would pass harmlessly through the kidney. However, it is now well documented that a significant amount of kidney injury can occur during shock wave therapy. The extent of kidney injury is dose dependent, with more extensive injuries observed in the setting of increased number of shocks and power/voltage settings.20 In addition, ESWL for kidney and proximal ureteral stones has been associated with the development of hypertension and diabetes mellitus. In a study from the Mayo clinic that followed 630 patients showed that at 19 years of follow-up, hypertension was more prevalent in the ESWL group (odds ratio 1.47, P ¼ .034). This development of hypertension was related to bilateral treatment (P ¼.033).25 Furthermore, the development of diabetes mellitus was related to the number of administered shocks and treatment intensity (P ¼ .005 and .007).25 To decrease tissue damage and functional impairment of the kidney, it is recommended that treatment be limited to the lowest shock wave dosage necessary to achieve stone fragmentation. Furthermore, the kidney injury associated with ESWL may be attenuated by a priming dose of low-amplitude shock waves (100 shocks), followed by a higher power setting—a strategy known as “ramping.” The reduced renal trauma observed in pretreated porcine kidneys is presumably because of vasoconstriction of vessels.26 ESWL has been
shown in the pig model to cause a temporary decrease in the blood flow and function of the kidney for up to 3 weeks.26 During this time, kidney scans show decreased uptake (reduced blood flow) and increased transit time (decreased function). ESWL, however, does not appear to have long-term deleterious effects on kidney function.27 Other complications of ESWL include hematuria, kidney or retroperitoneal hematoma, skin petechiae and ecchymosis, ureteral stricture, and steinstrasse (stone street).13 URETEROSCOPY (URS) Historically, the use of ureteroscopy started serendipitously when in 1912 Dr. Hugh H. Young unintentionally introduced a 12F pediatric cystoscope into an immensely dilated ureter of a child who had posterior urethral valves. Dr. Young was able to visualize the renal pelvis.28 This was preceded by advancements in the development of direct and indirect light guides which improved methods for delivering better illumination.29 Later on, the development of image improvement through rodlens systems, such as the Hopkins lens system, and the development of passive deflection mechanisms for flexible ureteroscopes, allowed for better visualization of the urinary system.29 No further advances were made in ureteroscopy until fiberoptic technology was introduced.28,29 The application of fiberoptics allowed for endoscope size reduction and facilitated the development of steerable deflectable ureteroscopes. In 1981, Das30 described the first transurethral ureteroscopy with stone basketing under direct vision using rigid ureteroscopy. In 1983, Bagley and colleagues31 described use of the first flexible tip pyeloscope. In the latter half of the 1980s, several flexible deflectable ureteroscopes became available in different sizes and with different options, including some with small working channels.28 Over the last 30 years, technological advancements have resulted in smaller, actively deflectable (ability to bend up to 275 ), flexible endoscopes that are easier to maneuver into the upper urinary tract. These scopes combined with powerful and precise holmium laser lithotrites and a variety of endoscopic retrieval devices have further enhanced the successful outcome of ureteroscopy. Currently, ureteroscopy is a recommended treatment for all ureteral stones independent of size and kidney stones less than 2 cm. Ureteroscopy is also recommended for distal ureteral stones independent of size as it is associated with few complications and a high success rate.32 A Cochrane review that examined the evidence from randomized controlled trials on the outcomes of ESWL or ureteroscopy in the treatment of ureteric calculi concluded that compared with ESWL, ureteroscopic removal of ureteral stones achieves a greater stone-free state but with a higher complication rate and longer hospital stay.13 For proximal stones, ESWL has a higher stone-free rate for stones less than 1 cm while URS was more effective for stones larger than 1 cm. However, both approaches are feasible.5 For kidney stones, URS now has the same indications as ESWL as first-line treatment for renal pelvic stones less than 2 cm. It is the preferred option for lower pole stones less than 1 cm.33 Patients presenting with stone characteristics that are not amenable to ESWL (cystine,
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brushite, calcium oxalate monohydrate, .750 HU, and impacted stone) are treated with URS. Moreover, patients who have failed ESWL or those presenting with contraindications to ESWL are also usually better candidates for URS. In patients with ectopic, pelvic, or transplant kidneys, URS is also an option with success rates similar to ESWL and morbidity less than that of PCNL.34 Moreover, this technique can be safely used in patients taking blood thinners. The development of equipment over time has made the procedure popular for most stones. It was the introduction of fiberoptic flexible ureteroscopes that revolutionized urologic stone practice allowing stones to be treated under direct vision with a lithotriptor. The flexible ureteroscopes do have some limitations: they have limited visibility compared with semi-rigid ureteroscopes. They also are fragile and prone to damage: fibers may burn out and fracture resulting in loss of image quality. Novel flexible digital ureteroscopes have been developed to overcome these problems.35 The tip of these digital flexible ureteroscope contains light-emitting diodes that obviate the need for an external light source, which minimizes the risk of drape fires or patient burns. These ureteroscopes are much lighter than their fiberoptic counterparts because there are no external cameras or light cables. They provide high-quality digital images with high resolution, autofocusing capabilities, and digital magnification all of which allows flexible URS to become less cumbersome with clearer images. However, these newer ureteroscopes are slightly larger in diameter, which can be a challenge when performing ureteroscopy in small diameter ureters. Along with developments in the technology of the ureteroscope, several pieces of equipment have been developed to be used through the ureteroscope as a means of enhancing the treatment of stones. The holmium:YAG laser is frequently used to fragment the stone. Laser fibers are inserted through the working channel of the ureteroscope. Under direct visualization, the stone is fragmented using the holmiun:YAG laser. Attempts are being made to develop smaller diameter fibers that will not decrease the deflection of the ureteroscope. Currently, the smallest fiber available is the 200-micron fiber that impedes the deflection of a flexible ureteroscope by up to 20 .36 Another area of focus is on maximizing fiber durability. If a laser fiber fractures inside an endoscope, it can damage the ureteroscope components and lead to costly repair. The injury to the scope can also occur when the fiber is inadvertently retracted into the scope. New technology is being developed to protect the endoscope system from the laser energy using an internal sensor.37 Aside from the developments in the energy source. There is a focus on developing ancilliary equipment. Stone retrieval baskets, used along with a ureteral access sheath, allows safe removal of stones from the renal pelvis. There are continual modifications to these devices which enhance the ease of the surgery and decrease the risks. The improvements in the technology of ureteroscopes and accessory devices have increased the success of stone treatment. A novel robotic ureteroscope system is currently being developed for performing retrograde ureterorenoscopy. Although still in its very early stages, the potential advan-
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tages of robotic flexible URS compared with conventional manual URS include an increased range of motion, instrument stability, and improved ergonomics. It is believed that the patient’s experience is improved by these newer ureteroscopes. Although, there is very little literature comparing patient satisfaction between the ureteroscopes. With the development of the ureteroscope and its subsequent modifications to increase its versatility, it has become a very useful tool in the treatment of ureteral and kidney stones. Furthermore, as recently trained urologists feel more comfortable with performing the procedure, the use of ureteroscopy for treatment of stone disease has increased over time. PERCUTANEOUS NEPHROLITHOTOMY €del (1902) were the first to Joseph Hyrtl (1882) and Max Bro establish the existence of a relatively avascular plane posterior to the midline of the kidney that could be transected for surgical stone extraction.38 Howard Kelly later found that the landmarks were reliable in only two-thirds of kidneys and advocated for pyelotomy claiming that it was a much safer operation.38 In 1955, while trying to perform a renal arteriogram, Goodwin and colleagues39 serendipitously performed the first antegrade nephrostogramand and left a tube to drain the kidney, thus placing the first modern day nephrostomy tube. Later in 1976, €m and Johansson40 were the first to describe a Fernstro technique for extracting renal calculi through a percutaneous nephrostomy under radiological control. Because of this technique, PCNL almost completely eliminated the need for open stone surgery in patients who had calculi not amenable to less-invasive therapies. The procedure went on to gain wide acceptance in the early 1980s. Percutaneous removal of stones is currently recommended for patients with staghorn calculi, kidney stones greater than 2 cm, and lower pole stones greater than 1.0 cm. It is an effective means of treating certain patients with anatomical abnormalities which would not be effectively treated by ESWL or ureteroscopy. These aberrations include ureteropelvic junction obstruction, and calyceal diverticula, urinary diversions (ie, continent urinary reservoirs, bladder augmentation and ureteral re-implants), retained stents encrusted with stones, narrow ureteral lumens secondary to external compression, as well as congenital or postsurgical anatomical variations (horseshoe kidneys, pelvic kidneys, cross-fused ectopia, and transureteroureterostomy). Contraindications to PCNL include uncorrected coagulopathy, urinary tract infections, inability to tolerate prone position especially if there is respiratory compromise (although this procedure has been described in the supine position), and pregnancy. It is imperative to adequately treat any urinary tract infection prior to the procedure. Obtaining proper access into the collecting system is critical for safe and effective treatment. It is performed through a posterior calyx usually in the upper or lower pole depending on the stone location and proximity of adjacent organs. Once the access to the collecting system is obtained and the tract from the skin to the renal pelvis dilated using radiological assistance, energy sources are used to break the stone if it cannot be removed intact.
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Intracorporeal lithotripsy is then performed by inserting a rigid lithotrite through the endoscope directly onto the stone under direct vision. Ultrasonic lithotripters are commonly used with continuous suction irrigation to evacuate stone fragments quickly and to maintain clear visibility. Stones may be removed using various baskets, forceps, and graspers. Larger stones or hard calculi, such as cystine and calcium oxalate monohydrate stones, that are less efficiently fragmented and removed with ultrasonic lithotripsy can be fragmented using pneumatic or laser devices. After the stone is removed from the collecting system, either a stent or nephrostomy tube, or both, can be placed depending on the surgeon’s preference. Patients usually stay in the hospital 1 to 2 days postoperatively, with relatively good oral pain control. The nephrostomy tube if placed and foley are usually removed before discharge. Patients return to work 1 to 2 weeks after surgery. New advances in PCNL combine ultrasonic and pneumatic lithotripter features in an effort to achieve superior fragmentation. Suction is used to evacuate stone fragments simultaneously. The first of these combination devices was the Lithoclast Ultra (Boston Scientific, Marlborough, MA). In a prospective randomized trial comparing the combination device to standard ultrasonic lithotrites, the Lithoclast Ultra lithotripter exhibited much faster stone clearance times than the conventional ultrasonic lithotripters.41 Another device is the Cyberwand (Olympus, Shinjuku, Tokyo, Japan), which is an intracorporeal lithotripter, a dual ultrasonic probe design that enables efficient stone fragmentation while still allowing the suction evacuation of small fragments. In the last decade, the standard PCNL technique has been modified in an attempt to decrease morbidity and complications. Technological advancements have led to miniaturization of instruments, access sheaths, and nephroscopes. In 1997, Jackman and colleagues42 initially described the technique of “mini-PCNL” in children, using a 13F outer diameter (11F inner diameter) ureteroscopy sheath and trocar set. Other investigators have also reported on their experience using smaller sheaths and rigid nephroscopes to treat 1- to 2-cm renal calculi.43-45 Using a smaller size percutaneous tract than standard PCNL has potential advantages of decreased bleeding and trauma to renal parenchyma. Initial studies show that patients undergoing mini-PCNL have reduced bleeding, length of hospital stay, and improved analgesia compared with standard PCNL.46 With smaller incisions, there has also been a tendency to favor tubeless PCNL rather than the traditional practice of leaving a widebore nephrostomy tube.47 To enhance pain management, there is also a trend for paravertebral blocks.48 These modifications have decreased the morbidity of PCNL. PEDIATRIC POPULATION For pediatric patients with upper tract kidney stones, ESWL is an effective and safe treatment technique. Pediatric patients compared with adults have anatomical features that facilitate stone fragmentation and passage after ESWL. This is most likely because shock waves are transmitted with only a slight loss of energy through
the small body habitus with less perirenal fat.49 In addition, the pediatric ureter is shorter, more elastic and distensible, thus permitting easier transmission of stone fragments and preventing ureteral impaction.50 Finally, other contributing factors could be the composition of stones, smaller relative stone volume, and the shorter duration of uropathology in children.49 Therefore, they require fewer shocks and lower energy for comparable stone clearance.2 Predictors of success or failure are similar to those identified in the adult literature, and newly developed nomograms are now available to provide risk estimation tailored to each specific pediatric patient.2 Currently, there is no available data that convincingly shows evidence of long-term kidney function compromise on children after ESWL. Today, ESWL is the method of choice in the treatment of most pediatric urinary stones.51 Ureteroscopy with laser lithotripsy is also an effective way to treat stones in pediatric patients with similar success rates as in the adult population. PCNL offers good clearance rates with acceptable morbidity in the pediatric population. The literature suggests that complex and staghorn calculi can be approached with this technique.52 Studies demonstrate minimal scar formation and insignificant loss of kidney function in children.53 With the miniaturization of instruments, especially, development of smaller nephroscopes and newer energy sources, the morbidity has decreased and the clearance rate has improved in pediatric patients. These devices have decreased operative time and increased stone clearance. Although the three modalities for treating stones are utilized, ESWL is the most common treatment for stones in the pediatric population. PREGNANCY Acute obstructive nephrolithiasis during pregnancy can be very risky to both mother and fetus. These patients need to be managed with special care. The AUA guidelines on imaging for ureteral stones recommend ultrasound as the initial technique of choice in pregnant patients.54 If the ultrasound is inconclusive, patients in the first trimester should undergo noncontrast MRI, whereas patients in their second or third trimester can undergo either MRI or low-dose CT.55 First-line management is usually conservative (trial of stone passage and pain management) which is generally associated with a high rate of stone passage.56 Immediate drainage is required if the urinary obstruction is associated with infection. Ureteral stent placement is a convenient method for temporizing ureteral obstruction from stone disease. Stent placement is usually done using minimal fluoroscopy or ultrasound. Ultrasound is used as a means of avoiding radiation altogether.55 Drainage of the urinary tract through placement of a nephrostomy tube is another option for relief of urinary obstruction. Placement of a nephrostomy tube can be easily done using local anesthesia with a high success rate (.90%).54 It allows for immediate decompression and avoids ureteral manipulation while minimizing anesthesia risks, even in patients during acute sepsis. In addition, the tract can remain open for postpartum access if farther treatment is required.54 If conservative management fails and there
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Table 1. Recommended Therapy for Renal and Ureteral Stones According to Location and Size Renal Stones ,1 cm Upper or Middle Pole
Upper or Middle Pole
Lower Pole
ESWL or ureteroscopy
.2 cm
1-2 cm
Noncystine, non-brushite, ,750 HU, children use ESWL, otherwise ureteroscopy
Cystine, Brushite, .750 HU, or high skin to stone distance use ureteroscopy or ESWL
Lower Pole
Upper or Middle Pole
Lower Pole
PCNL
PCNL
Ureteroscopy or PCNL
Ureteral Stones Proximal
Middle
Distal
,10 mm
.10 mm
,10 mm
.10 mm
,10 mm
.10 mm
ESWL
Ureteroscopy
ESWL or Ureteroscopy
Ureteroscopy
ESWL or Ureteroscopy
Ureteroscopy
Cystine, calcium phosphate, calcium oxalate monohydrate, .750 HU, impacted stones: ureteroscopy is preferred
For ,10-mm stones in women: ureteroscopy is preferred
For ,10-mm stones in women: ureteroscopy is preferred
Abbreviations: ESWL, extracorporeal shock wave lithotripsy; HU, Hounsfield units.
is no active infection, ureteroscopy and laser lithotripsy can be offered if clinically appropriate with an overall reported stone-free rate of 88.3%.54 Obstetric complications because of ureteroscopic intervention are rare (2% to 4%) and may include premature uterine contractions and preterm labor.54 Shockwave lithotripsy and PCNL are contraindicated during pregnancy. CONCLUSIONS Technological advances in the treatment of nephrolithiasis have led to safer and more efficient minimally invasive surgical treatments. Patient and stone characteristics are used to determine the most efficient treatment with the least risk (Table 1). ESWL is popular because of its noninvasive nature. The improvements in the technique of administering the shock waves have led to improved patient experience. The developments in fiberoptics and laser technology have been instrumental in stone treatment, making ureteroscopy safe and effective. Miniaturization of PCNL instruments, access sheaths, and nephroscopes have reduced its morbidity. Ureteroscopy is the most versatile of the 3 treatments because it can be used for most patients. As technology improves, the surgical management of nephrolithiasis should achieve improved levels of success with exceptional outcomes. REFERENCES 1. Shoag J, Tasian GE, Goldfarb DS, Eisner BH. The new epidemiology of nephrolithiasis. Adv Chronic Kidney Dis. 2015;22(4):273-278. 2. Grasso M, Goldfarb DS. Urinary Stones: Medical and Surgical Management. Chichester, West Sussex, UK: John Wiley & Sons, Inc; 2014. 3. Honey RJ, Schuler TD, Ghiculete D, Pace KT, Canadian Endourology Group. A randomized, double-blind trial to compare shock wave frequencies of 60 and 120 shocks per minute for upper ureteral stones. J Urol. 2009;182(4):1418-1423.
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