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RETROGRADE URETEROPYELOSCOPY FOR LOWER POLE CALICEAL CALCULI
0022-5347/99/1626-1904/0 THE JOURNAL OF UROLOGY® Copyright © 1999 by AMERICAN UROLOGICAL ASSOCIATION, INC.®
Vol. 162, 1904 –1908, December 1999 Printed in U.S.A.
RETROGRADE URETEROPYELOSCOPY FOR LOWER POLE CALICEAL CALCULI MICHAEL GRASSO
AND
MICHAEL FICAZZOLA
From the Department of Urology, The New York University School of Medicine, New York, New York
ABSTRACT
Purpose: Contemporary treatment of lower pole renal calculi includes extracorporeal shock wave lithotripsy, percutaneous nephrostolithotomy and retrograde ureteropyeloscopy. Success rates for shock wave lithotripsy are reduced in this setting, especially for stones greater than 1 cm. and/or in patients with anatomical variants. Percutaneous treatment, although effective, subjects the patient to increased morbidity. We studied the safety and efficacy of retrograde ureteroscopic treatment of lower pole intrarenal calculi. Materials and Methods: We evaluated 90 stone burdens localized to the lower pole and treated with a small diameter, actively deflectable, flexible ureteropyeloscope and a 200 m. holmium laser fiber. Stone burdens were classified as group 1—10 or less, group 2—11 to 20 and group 3— greater than 20 mm. in largest diameter. Patients with calculi less than 2.5 cm. were treated as outpatients unless concurrent medical conditions required hospitalization. Larger stones and partial staghorn calculi (group 3) frequently required 2-stage endoscopic procedures with retrograde intrarenal irrigation for 36 hours to clear debris. An acceptable immediate surgical outcome was defined as complete fragmentation reducing the stone burden to dust and 2 mm. or less fragments. Success was defined as clear imaging (that is stone-free) on renal sonography with minimum 3-month followup. Extreme anatomical variants, including a long infundibulum, acute infundibulopelvic angle and a dilated collecting system, were noted and correlated with surgical failures. Results: Endoscopic access and complete stone fragmentation were achieved in 94, 95 and 45% of groups 1, 2 and 3, respectively. After a second treatment the success rate increased to 82% in group 3, with an overall rate of 91%. Of the 19 surgical failures 8 were secondary to inability to access the lower pole and 11 were secondary to inability to render the patient stone-free. In 2 of the 19 cases infundibular strictures hindered ureteroscopic access. In addition, of the anatomical variants a long lower pole infundibulum was the most statistically significant predictor of failure. Mean operative time ranged from 38 minutes for small to 126 for the largest calculi. There were no major complications. Overall stone-free rates with minimum 3-month followup were 82, 71 and 65% in groups 1, 2 and 3, respectively, and 88, 77 and 81%, respectively, in patients with an acceptable initial surgical outcome (that is excluding those with access failures from analysis). Conclusions: Retrograde ureteropyeloscopy is a safe and effective surgical treatment for lower pole intrarenal calculi. KEY WORDS: kidney calculi; endoscopy; lithotripsy, laser
Treatment of upper urinary tract calculi includes shock waves to fragment stones into more easily passable pieces, or endoscopic inspection with extraction or fragmentation under direct vision. The indication for using either modality has been refined and broadened based on new technology and instrumentation. Shock wave lithotriptors have evolved and require less anesthesia for treatment. Second and third generation devices decrease the energy delivered and the size of the focal or treatment zone, with a corresponding decline in success rates compared to the original HM3* lithotriptor. The indications for shock wave lithotripsy have been refined such that a stone burden in excess of 2 cm. within the intrarenal collecting system is now considered to be treated best with endoscopic techniques.1 In addition, other anatomical variants and co-morbidities can preclude successful shock wave lithotripsy.2 Endoscopic therapy, and in particular ureteroscopic lithotripsy, was initially used only for ureteral calculi, with success rates superior to shock wave lithotripsy but using an obviously more invasive surgical treatment. With these trends the indications for retrograde ureteroAccepted for publication June 18, 1999. * Dornier Medical Systems, Inc., Marietta, Georgia.
scopic techniques have been broadened to include intrarenal stones.3, 4 Lower pole intrarenal calculi are the least likely to clear with shock wave lithotripsy.5 Specifically, in an extensive experience prospectively reviewed the success rate with shock wave lithotripsy of lower pole intrarenal calculi was particularly poor when stones exceeded 1 cm. in diameter.6 In the other treatment arm of that study percutaneous nephrostolithotomy had a superior success rate in clearing stone burdens, but it is one of the most invasive treatments, with a small but significant rate of major complications. We reviewed our experience treating stones in the lower pole with retrograde ureteropyeloscopic techniques and specifically examined whether variables of intrarenal anatomy, including a long infundibulum, acute infundibulopelvic angle and a dilated collecting system, impacted success.
MATERIALS AND METHODS
Patients and accrual criteria. During a 5-year period patients with intrarenal calculi were accrued for retrograde 1904
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RETROGRADE URETEROPYELOSCOPY FOR CALICEAL CALCULI
endoscopic therapy. A total of 79 patients and 90 lower pole, dependent caliceal stone burdens were evaluated. Stone burdens were classified as group 1—10 mm. or less, group 2—11 to 20 mm. and group 3— greater than 20 mm. Of the patients 6 had bilateral lower pole calculi and 3 had complex lower pole collecting systems with large stone burdens treated in a bifid lower pole. The 54 men and 25 women ranged from 10 to 82 years old and many had undergone prior treatment with shock wave lithotripsy or other more invasive therapies, including open surgery, before referral. Prior failed treatment with another modality or endoscopic therapy elsewhere did not preclude entry into the study. There were no restriction criteria as far as patient age, sex or history of co-morbid medical conditions which may preclude more invasive treatments, including percutaneous puncture (for example bleeding diathesis, chronic obstructive pulmonary disease, azotemia, renal ectopia and so forth). In all patients the intrarenal collecting system anatomy was diagrammatically constructed perioperatively based on contrast imaging. In addition, stone size and specific location, associated anatomical abnormalities including infundibular strictures, and a history of urinary tract infections and infectious stones were obtained. From this prospectively developed database we reviewed our experience with lower pole intrarenal calculi. Major variables were evaluated in regard to intrarenal anatomy. Specifically, the infundibulopelvic angle was defined, which refers to the angle obtained when a line is drawn along the long axis of the ureter and that of the lower pole infundibulum. Angles were considered acute if less than 45 degrees. The lower pole infundibulum was considered long if in excess of 3 cm. Finally, dilatation of the intrarenal collecting system was evaluated on retrograde contrast imaging, with grade IV or greater hydronephrosis considered a potential negative parameter. Instrumentation and technique. All patients underwent standard rigid cystoscopy and a guide wire was placed into the upper urinary tract under fluoroscopic guidance. A 10F dual lumen catheter was used to dilate the intramural ureter and to obtain a retrograde ureteropyelogram by applying radiopaque contrast material into the second port. Through the second port an additional guide wire was also inserted, and represents the working guide wire over which the flexible ureteroscope was passed into the upper urinary tract in a monorail fashion. The working guide wire is 0.035 inch in diameter, composed of nickel titanium and lubriciously coated or had a shrink-wrapped polytetrafluoroethylene outer sheathing. If the flexible ureteroscope did not pass easily through the intramural ureter, a 12F graduated Nottingham dilator was used over 1 of the 2 guide wires. If the endoscope still did not pass, a 12F 4 cm. dilating balloon was used. Finally, if the flexible endoscope still would not pass through the intramural ureter, direct semirigid endoscopy was performed to evaluate the intramural segment and dilate under direct vision. An actively deflectable, flexible ureteroscope was used in all cases. These instruments were 7.5F or smaller at the tip, had 2-way active tip deflection and secondary deflection, which refers to a weakness in the durometer of the endoscope proximal to the actively deflecting segment. This secondary deflecting segment allows the endoscope to buckle while being maximally deflected at the tip and allows tip placement into the most dependent lower pole calix. All flexible endoscopes maintained a 3.6F working channel. Sterile saline irrigant was applied through the endoscope working channel with a piston driven syringe system to maintain a clear field of view. Endoscopic lithotripsy was used exclusively with holmium laser energy using a 200 m. laser fiber. Energies varied depending on stone composition with an average energy of 1.0
J. Frequency of pulsation varied from 5 to 20 Hz. depending on whether a solid stone was treated or small fragments were pulverized, with the end result being fragments 2 mm. or less in diameter and fine dust. A polytetrafluoroethylene sheathed 2.5F wire prong grasper through the working channel of the flexible ureteroscope was commonly used to move stone fragments from the lower pole to a more cephalad position. When the endoscope could not be precisely placed onto the entire lower pole stone burden because of the decreased deflectability when using the laser fiber, large fragments were created and moved with the more flexible grasper. Placing the patient in a deep Trendelenburg position also facilitated fragment migration to the upper pole where stones were more readily pulverized to finer fragments and dust. Second look endoscopy was performed in the majority of lower pole calculi in excess of 2.5 cm. In our experience with treating large, branching calculi in a retrograde fashion frequently after the first sitting the entire collecting system is lined by fine dust and debris which can obscure a large, hidden crescent of stone.7 In these cases retrograde catheters were placed and the intrarenal collecting system was irrigated postoperatively. Inflow was through a 5F Cobra catheter with its tip positioned in the most dependent lower pole. A larger open ended catheter (6F or greater) with its tip positioned in the upper pole was used for outflow. The most commonly used irrigant was sterile saline with 80 mg./l. gentamicin at 100 cc per hour. If the stone burden was composed of uric acid or cystine, an alkalizing irrigant was used. Tromethamine solution was used for cystine and sodium bicarbonate based irrigant was used for uric acid stones. For endoscopic lithotripsy regional (that is epidural or spinal) or general anesthesia was used based on patient preference and the specific choice of the anesthesiologist. Patients with stone burdens less than 2.5 cm. were treated as outpatients and discharged home with an internal ureteral stent in place that was removed 3 to 10 days postoperatively. Before second look endoscopy for large stone burdens patients underwent 36 hours of intrarenal irrigation. They were discharged home shortly after the second stage with an internal stent in place that was removed the same time postoperatively as for those patients with smaller stone burdens. All patients received prophylactic parenteral cephalosporin based antibiotics and postoperatively received a 5-day course of quinolone based oral antibiotics with adjustments for comorbid medical conditions. All patients were followed with serial radiographs and renal sonography approximately 4 weeks postoperatively to rule out silent obstruction and hydronephrosis, and to quantify the residual stone burden. Depending on the initial postoperative imaging, additional interval imaging was obtained. An acceptable immediate surgical outcome was defined as complete fragmentation of the stone burden to fine dust and 2 mm. or less fragments. However, success was defined as clear imaging (that is stone-free) on subsequent renal sonography. Statistical analysis was based on calculation of odds ratios and the 95% confidence interval was determined by Woolf’s method. RESULTS
A total of 101 procedures were performed on 79 patients. Stone burdens and operative time are presented in table 1.
TABLE 1. Stone burden and corresponding operative times Group No. (mean mm. stone diameter)
No. Stones
Mean Mins. Operative Time 6 SD (range)
1 (10 or less) 2 (11–20) 3 (greater than 20)
47 21 22
38 6 18 (20–72) 59 6 12 (40–73) 126 6 56 (40–190)
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RETROGRADE URETEROPYELOSCOPY FOR CALICEAL CALCULI
Intramural ureteral dilation with a 12F balloon or graduated dilator was required for access of 7 stone burdens (8%). However, 24% of patients presented with a ureteral stent preoperatively. An acceptable surgical outcome was based on endoscopic access and complete stone fragmentation (table 2). Complete fragmentation at a single sitting, including stone burdens of all sizes, was performed in 82% of cases. Complete fragmentation was noted in 94% of group 1 (stones 10 mm. or less) and achieved with single surgery in 45% of group 3 (stones greater than 20 mm.). A second sitting was planned preoperatively for group 3 and intrarenal irrigation was done for up to 36 hours between sittings. Including the 2-stage cases the fragmentation rate for these exceptionally large stone burdens increased to 82%, improving the overall treatment rate to 91%. Endoscopic access to a lower pole infundibulum and treatment of dependent calculi required secondary deflection as an endoscopic maneuver in 76% of stone burdens. Failure of endoscopic access was noted in 8 stone burdens (9%), including 2 of 3 patients with lower pole infundibular strictures. A long lower pole infundibulum, acute infundibulopelvic angle, significantly dilated collecting system and infundibular stricture disease were evaluated in regard to successful endoscopic lithotripsy (table 3). Of the stone burdens 35 were not associated with any of these variants and all but 1 were treated successfully. A long lower pole infundibulum and an infundibular stricture were statistically significant as negative parameters for success of retrograde endoscopic therapy of lower pole caliceal calculi. Stone composition included all major types. Calcium oxalate calculi were noted in 45 cases and the majority of these stones were primarily composed of the monohydrate variety. Stone burden was cystine in 9 patients (11%), calcium phosphate in 10, uric acid in 14 and sodium urate in 1. The holmium laser was able to fragment stones of all of these compositions and, thus, failures were secondary to inability of endoscopic access or failure to clear debris. Success was based on clear postoperative imaging (that is stone-free) with minimum 3-month followup. Followup data were available for 70 stone burdens with an overall stonefree rate of 76% (table 4). As stone burdens increased, the ultimate stone-free rates decreased from 82% for the smallest stones to 65% for calculi in excess of 20 mm. The overall success rate increased to 84% of patients with successful endoscopic access to the stone burden. If the 8 patients with failed access are excluded from analysis, the rate of complete clearance of debris and fragments after an acceptable immediate surgical outcome was 88%, 77 and 81% for groups 1, 2 and 3, respectively. Complications were classified as intraoperative, postoperative or long-term sequelae of the procedure. There were no major intraoperative complications. Minor postoperative complications included renal colic secondary to the internal stent in 6 cases (8%) and colic while passing debris in 1 which required stent replacement after removal. In addition, 3 patients (4%) presented with symptomatic urinary tract infec-
TABLE 2. Endoscopic access and rate of complete fragmentation of stone burden to fine dust and 2 mm. or less fragments Group No. Group 1 Group 2 Group 3: After 1 sitting After 2 sittings Totals
No. Endoscopic Access 1 Complete Fragmentation/ Total No. (%) 44/47 (94) 20/21 (95) 10/22 (45) 18/22 (82) 82/90 (91)
No. Intraop. Surgical Failures/ Total No. (%) 3/47 (6) 1/21 (5) 4/22 (18)
8/90 (9)
TABLE 3. Prevalence of collecting system variants and predictive values for surgical failure Collecting System Variants Long lower pole infundibulum (greater than 3 cm.) Acute infundibulopelvic angle Dilated collecting system Infundibular stricture * Statistically significant.
No. No. Failures Prevalence With Variants (%) (%)
Odds Ratio (CI)
21 (23)
8 (38)
7.9 (5.1 6 12.2)*
29 (32)
5 (17)
1.3 (0.9 6 2.1)
23 (26) 3 (3)
4 (17) 2 (67)
1.3 (0.8 6 2.1) 13.8 (10.9 6 17.4)*
tions that required longer courses of antibiotic therapy. There were no major postoperative complications, including ureteral strictures. DISCUSSION
Shock wave lithotripsy represents first line therapy for most moderate size intrarenal calculi. Since the evolution of the shock wave lithotriptor to second and third generation devices with lower power and smaller focal zones, the overall success rate of this procedure has decreased.5, 6 Concurrently innovations in endoscopes and endoscopic lithotrites now allow not only the entire intrarenal collecting system to be accessed in a retrograde fashion, but also treatment of complex stone burdens previously reserved for primary percutaneous puncture and nephrostolithotomy. The holmium laser represents a significant improvement from prior technology in that stone burdens of all compositions and sizes can be fragmented into fine dust and small debris with a range of energy applied through flexible, optical quartz fibers.7, 8 Improvement in endoscope design and, specifically, the addition of the small diameter, actively deflectable, flexible ureteropyeloscope facilitated complete upper urinary tract access to every infundibulum and calix in up to 94% of cases.9 The combination of the flexible ureteroscope and the 200 m. holmium laser fiber allows treatment of intrarenal calculi within the lower pole caliceal system. Historically, ureteropyeloscopy for intrarenal calculi has been based on electrohydraulic lithotripsy probes or laser lithotripsy.9 –11 In 1996 Elashry et al reported a success rate of 92% when intrarenal calculi were treated with a flexible ureteroscope and 1.9F electrohydraulic lithotripsy probe.11 In a contemporary series a similar modest cohort of patients treated with the holmium laser had an 88.5% success rate with a single session of endoscopic lithotripsy.7 In 1998, 2 large series were published of intrarenal calculi treated with retrograde ureteropyeloscopy. Fabrizio et al presented 100 patients who underwent retrograde endoscopy with the holmium laser or electrohydraulic lithotripsy probe, and reported an immediate postoperative success rate of 89%.12 There were few complications and no long-term sequelae of treatment. In a similar series Grasso and Chalik reported on 99 patients with intrarenal calculi, including large, branching staghorn stone burdens, treated in a retrograde fashion.13 An 80% success rate after a single session was reported and when the largest of these stone burdens was treated with a staged procedure the overall success rate increased to 90%. Larger stone burdens, in particular branching staghorn calculi, have been the subject of a clinical guidelines panel summary.1 In 1994 the panel established that the majority of these stone burdens are best treated in a percutaneous fashion rather than by shock wave lithotripsy monotherapy. A recently published series of 48 stone burdens in excess of 2 cm. in largest diameter, including branching staghorn calculi treated with retrograde ureteroscopy, underscores the usefulness of the holmium laser in debulking and clearing com-
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RETROGRADE URETEROPYELOSCOPY FOR CALICEAL CALCULI TABLE 4. Stone-free rates and residual debris on renal sonography with minimum 3-month followup No. Cases/Total No. (%) Group No. Stone-Free 1 2 3* Totals * Includes 1 and 2 surgical
36/44 (82) 10/14 (72) 13/20 (65) 59/78 (76) sittings.
Small Lower Pole Debris (4 mm. or less)
Greater Vol. Debris (5 mm. or greater)
Failure Endoscopic Access
3/44 (7) 2/14 (14) 1/20 (6) 6/78 (8)
2/44 (5) 1/14 (7) 2/20 (13) 5/78 (6)
3/44 (6) 1/14 (7) 4/20 (20) 8/78 (10)
plex stone burdens in a minimally invasive fashion.14 The combination of the flexible ureteroscope and small holmium laser fibers allowed treatment of the largest stone burdens as well as calculi of all compositions, and only a small subset of patients had postoperative complications, including pyelonephritis (1), prostatic bleeding on anticoagulant therapy (1) and cerebral vascular incident 24 hours after endoscopic lithotripsy (1). The Lower Pole Stone Study Group attempted to define in a prospective randomized fashion the success rates of shock wave lithotripsy and percutaneous nephrostolithotomy for dependent lower pole intrarenal calculi.6 The premise was that the dependent nature of the lower pole would preclude successful therapy with shock wave lithotripsy. Fragments would most likely remain in the lower pole as opposed to passing up into the renal pelvis and down the ureter. To date 128 patients have been accrued and success rates in both treatment arms have been stratified based on stone size. The success rate for calculi less than 1 cm. was 63% with shock wave lithotripsy compared to 100% completely cleared with percutaneous nephrostolithotomy. The success rates were 23% for larger stones less than 2 cm. and a dismal 14% for stone burdens in excess of 2 cm. with shockwave lithotripsy compared to a better than 86% rate of clearance with percutaneous nephrostolithotomy for both groups. Retrograde ureteropyeloscopy represents a significantly less invasive treatment than percutaneous nephrostolithotomy for dependent lower pole caliceal calculi. Although not a double armed randomized trial, all patients referred for retrograde intrarenal lithotripsy in our series were accrued and treated. There was no preoperative exclusion criterion. Our success (that is stone-free) rate for treating calculi 1 cm. or less was 82%. Our failures were subdivided into failure of endoscopic access (8 cases) and persistent lower pole fragments. In the 8 cases failure of access was secondary to severe anatomical variants, including infundibular stenosis. In the remaining majority endoscopic access and complete fragmentation were successful, with clearance ranging from 88% for calculi 10 mm. in diameter to 81% for stone burdens in excess of 2 cm. Elbahnasy et al studied intrarenal anatomical variants and their impact on extracorporeal shock wave lithotripsy of lower pole caliceal calculi.15 An acute infundibulopelvic angle or long lower pole infundibulum was a negative parameter for success. In this same study 13 patients were treated ureteroscopically with a 62% success rate. The authors suggested that these intrarenal anatomical variants which inhibited extracorporeal treatment had a smaller role in the overall success rate of retrograde endoscopic lithotripsy. To determine preoperatively which patients would be treated best ureteroscopically versus a primary percutaneous approach, we also examined variables of intrarenal anatomy and their impact on success of retrograde endoscopic therapy. We defined a subgroup of patients with long lower pole infundibulum (greater than 3 cm.) which alone had a 38% predictive value of failure. An acute infundibulopelvic angle and dilated collecting system were less prohibitive in regard to endoscopic access to the stone burden, and were compli-
cating factors in a smaller subpopulation. Finally, infundibular strictures can preclude endoscopic access into the calix and if defined preoperatively should alert the surgeon to possible percutaneous intervention as noted in 2 of 3 patients in our series. CONCLUSIONS
Lower pole caliceal calculi present a clinical challenge. From the data presented by Lingeman and the Lower Pole Stone Study Group the stone-free rate with extracorporeal shock wave lithotripsy in this setting is low when the stone burden is in excess of 1 cm.6 Percutaneous nephrostolithotomy represents a definitive but extremely invasive alternative compared to retrograde endoscopy for managing intrarenal calculi. In our large series of lower pole calculi the majority were successfully treated ureteroscopically with the holmium laser with minimal morbidity. Variants in intrarenal anatomy, specifically a long lower pole infundibulum, may preclude successful treatment when using the defined retrograde technique. If a long lower pole infundibulum is noted on preoperative imaging, the patient should be counseled that the success rate in general with ureteropyeloscopy is decreased and percutaneous nephrostolithotomy may be required. Philip Alcabes assisted with the statistical analysis. REFERENCES
1. Segura, J. W., Preminger, G. M., Assimos, D. G., Dretler, S. P., Kahn, R. I., Lingeman, J. E., Macaluso, J. N., Jr. and McCullough, D. L.: Nephrolithiasis Clinical Guidelines Panel summary report on the management of staghorn calculi. J. Urol., 151: 1648, 1994. 2. Grasso, M., Loisides, P., Beaghler, M. and Bagley, D.: The case for primary endoscopic management of upper urinary tract calculi: I. A critical review of 121 extracorporeal shock wave lithotripsy failures. Urology, 45: 363, 1995. 3. Fuchs, A. M. and Fuchs, G. J.: Retrograde intrarenal surgery for calculous disease: new minimally invasive treatment approach. J. Endourol., 4: 337, 1990. 4. Denstedt, J. D. and Clayman, R. V.: Electrohydraulic lithotripsy of renal and ureteral calculi. J. Urol., 143: 13, 1990. 5. Lingeman, J. E., Siegel, Y. I., Steele, B., Nyhuis, A. W. and Woods, J. R.: Management of lower pole nephrolithiasis: a critical analysis. J. Urol., 151: 663, 1994. 6. Lingeman, J. E.: Prospective randomized trial of extracorporeal shock wave lithotripsy and percutaneous nephrostolithotomy for lower pole nephrolithiasis: initial long-term follow up. J. Urol., part 2, 157: 43, abstract 159, 1997. 7. Grasso, M.: Experience with the holmium laser as an endoscopic lithotrite. Urology, 48: 199, 1996. 8. Matsuoka, K., Iida, S., Nakanami, M., Koga, H., Shimada, A., Mihara, T. and Noda, S.: Holmium:yttrium-aluminum-garnet laser for endoscopic lithotripsy. Urology, 45: 947, 1995. 9. Grasso, M. and Bagley, D.: Small diameter, actively deflectable, flexible ureteropyeloscopy. J. Urol., 160: 1648, 1998. 10. Bagley, D. H., Huffman, J. L. and Lyon, E. S.: Flexible ureteropyeloscopy: diagnosis and treatment in the upper urinary tract. J Urol., 138: 280, 1987. 11. Elashry, O. M., DiMeglio, R. B., Nakada, S. Y., McDougall, E. M.
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and Clayman, R. V.: Intracorporeal electrohydraulic lithotripsy of ureteral and renal calculi using small caliber (1.9F) electrohydraulic lithotripsy probes. J. Urol., 156: 1581, 1996. 12. Fabrizio, M. D., Behari, A. and Bagley, D. H.: Ureteroscopic management of intrarenal calculi. J. Urol., 159: 1139, 1998. 13. Grasso, M. and Chalik, Y.: Principles and applications of laser lithotripsy: experience with the holmium laser lithotrite. J. Clin. Laser Med. Surg., 16: 3, 1998.
14. Grasso, M., Conlin, M. and Bagley, D.: Retrograde ureteropyeloscopic treatment of 2 cm. or greater upper urinary tract and minor staghorn calculi. J. Urol., 160: 346, 1998. 15. Elbahnasy, A. M., Shalhav, A. L., Hoenig, D. M., Elashry, O. M., Smith, D. S., McDougall, E. M. and Clayman, R. V.: Lower caliceal stone clearance after shock wave lithotripsy or ureteroscopy: the impact of lower pole radiographic anatomy. J. Urol., 159: 676, 1998.
Vol. 162, 1904 –1908, December 1999 Printed in U.S.A.
RETROGRADE URETEROPYELOSCOPY FOR LOWER POLE CALICEAL CALCULI MICHAEL GRASSO
AND
MICHAEL FICAZZOLA
From the Department of Urology, The New York University School of Medicine, New York, New York
ABSTRACT
Purpose: Contemporary treatment of lower pole renal calculi includes extracorporeal shock wave lithotripsy, percutaneous nephrostolithotomy and retrograde ureteropyeloscopy. Success rates for shock wave lithotripsy are reduced in this setting, especially for stones greater than 1 cm. and/or in patients with anatomical variants. Percutaneous treatment, although effective, subjects the patient to increased morbidity. We studied the safety and efficacy of retrograde ureteroscopic treatment of lower pole intrarenal calculi. Materials and Methods: We evaluated 90 stone burdens localized to the lower pole and treated with a small diameter, actively deflectable, flexible ureteropyeloscope and a 200 m. holmium laser fiber. Stone burdens were classified as group 1—10 or less, group 2—11 to 20 and group 3— greater than 20 mm. in largest diameter. Patients with calculi less than 2.5 cm. were treated as outpatients unless concurrent medical conditions required hospitalization. Larger stones and partial staghorn calculi (group 3) frequently required 2-stage endoscopic procedures with retrograde intrarenal irrigation for 36 hours to clear debris. An acceptable immediate surgical outcome was defined as complete fragmentation reducing the stone burden to dust and 2 mm. or less fragments. Success was defined as clear imaging (that is stone-free) on renal sonography with minimum 3-month followup. Extreme anatomical variants, including a long infundibulum, acute infundibulopelvic angle and a dilated collecting system, were noted and correlated with surgical failures. Results: Endoscopic access and complete stone fragmentation were achieved in 94, 95 and 45% of groups 1, 2 and 3, respectively. After a second treatment the success rate increased to 82% in group 3, with an overall rate of 91%. Of the 19 surgical failures 8 were secondary to inability to access the lower pole and 11 were secondary to inability to render the patient stone-free. In 2 of the 19 cases infundibular strictures hindered ureteroscopic access. In addition, of the anatomical variants a long lower pole infundibulum was the most statistically significant predictor of failure. Mean operative time ranged from 38 minutes for small to 126 for the largest calculi. There were no major complications. Overall stone-free rates with minimum 3-month followup were 82, 71 and 65% in groups 1, 2 and 3, respectively, and 88, 77 and 81%, respectively, in patients with an acceptable initial surgical outcome (that is excluding those with access failures from analysis). Conclusions: Retrograde ureteropyeloscopy is a safe and effective surgical treatment for lower pole intrarenal calculi. KEY WORDS: kidney calculi; endoscopy; lithotripsy, laser
Treatment of upper urinary tract calculi includes shock waves to fragment stones into more easily passable pieces, or endoscopic inspection with extraction or fragmentation under direct vision. The indication for using either modality has been refined and broadened based on new technology and instrumentation. Shock wave lithotriptors have evolved and require less anesthesia for treatment. Second and third generation devices decrease the energy delivered and the size of the focal or treatment zone, with a corresponding decline in success rates compared to the original HM3* lithotriptor. The indications for shock wave lithotripsy have been refined such that a stone burden in excess of 2 cm. within the intrarenal collecting system is now considered to be treated best with endoscopic techniques.1 In addition, other anatomical variants and co-morbidities can preclude successful shock wave lithotripsy.2 Endoscopic therapy, and in particular ureteroscopic lithotripsy, was initially used only for ureteral calculi, with success rates superior to shock wave lithotripsy but using an obviously more invasive surgical treatment. With these trends the indications for retrograde ureteroAccepted for publication June 18, 1999. * Dornier Medical Systems, Inc., Marietta, Georgia.
scopic techniques have been broadened to include intrarenal stones.3, 4 Lower pole intrarenal calculi are the least likely to clear with shock wave lithotripsy.5 Specifically, in an extensive experience prospectively reviewed the success rate with shock wave lithotripsy of lower pole intrarenal calculi was particularly poor when stones exceeded 1 cm. in diameter.6 In the other treatment arm of that study percutaneous nephrostolithotomy had a superior success rate in clearing stone burdens, but it is one of the most invasive treatments, with a small but significant rate of major complications. We reviewed our experience treating stones in the lower pole with retrograde ureteropyeloscopic techniques and specifically examined whether variables of intrarenal anatomy, including a long infundibulum, acute infundibulopelvic angle and a dilated collecting system, impacted success.
MATERIALS AND METHODS
Patients and accrual criteria. During a 5-year period patients with intrarenal calculi were accrued for retrograde 1904
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RETROGRADE URETEROPYELOSCOPY FOR CALICEAL CALCULI
endoscopic therapy. A total of 79 patients and 90 lower pole, dependent caliceal stone burdens were evaluated. Stone burdens were classified as group 1—10 mm. or less, group 2—11 to 20 mm. and group 3— greater than 20 mm. Of the patients 6 had bilateral lower pole calculi and 3 had complex lower pole collecting systems with large stone burdens treated in a bifid lower pole. The 54 men and 25 women ranged from 10 to 82 years old and many had undergone prior treatment with shock wave lithotripsy or other more invasive therapies, including open surgery, before referral. Prior failed treatment with another modality or endoscopic therapy elsewhere did not preclude entry into the study. There were no restriction criteria as far as patient age, sex or history of co-morbid medical conditions which may preclude more invasive treatments, including percutaneous puncture (for example bleeding diathesis, chronic obstructive pulmonary disease, azotemia, renal ectopia and so forth). In all patients the intrarenal collecting system anatomy was diagrammatically constructed perioperatively based on contrast imaging. In addition, stone size and specific location, associated anatomical abnormalities including infundibular strictures, and a history of urinary tract infections and infectious stones were obtained. From this prospectively developed database we reviewed our experience with lower pole intrarenal calculi. Major variables were evaluated in regard to intrarenal anatomy. Specifically, the infundibulopelvic angle was defined, which refers to the angle obtained when a line is drawn along the long axis of the ureter and that of the lower pole infundibulum. Angles were considered acute if less than 45 degrees. The lower pole infundibulum was considered long if in excess of 3 cm. Finally, dilatation of the intrarenal collecting system was evaluated on retrograde contrast imaging, with grade IV or greater hydronephrosis considered a potential negative parameter. Instrumentation and technique. All patients underwent standard rigid cystoscopy and a guide wire was placed into the upper urinary tract under fluoroscopic guidance. A 10F dual lumen catheter was used to dilate the intramural ureter and to obtain a retrograde ureteropyelogram by applying radiopaque contrast material into the second port. Through the second port an additional guide wire was also inserted, and represents the working guide wire over which the flexible ureteroscope was passed into the upper urinary tract in a monorail fashion. The working guide wire is 0.035 inch in diameter, composed of nickel titanium and lubriciously coated or had a shrink-wrapped polytetrafluoroethylene outer sheathing. If the flexible ureteroscope did not pass easily through the intramural ureter, a 12F graduated Nottingham dilator was used over 1 of the 2 guide wires. If the endoscope still did not pass, a 12F 4 cm. dilating balloon was used. Finally, if the flexible endoscope still would not pass through the intramural ureter, direct semirigid endoscopy was performed to evaluate the intramural segment and dilate under direct vision. An actively deflectable, flexible ureteroscope was used in all cases. These instruments were 7.5F or smaller at the tip, had 2-way active tip deflection and secondary deflection, which refers to a weakness in the durometer of the endoscope proximal to the actively deflecting segment. This secondary deflecting segment allows the endoscope to buckle while being maximally deflected at the tip and allows tip placement into the most dependent lower pole calix. All flexible endoscopes maintained a 3.6F working channel. Sterile saline irrigant was applied through the endoscope working channel with a piston driven syringe system to maintain a clear field of view. Endoscopic lithotripsy was used exclusively with holmium laser energy using a 200 m. laser fiber. Energies varied depending on stone composition with an average energy of 1.0
J. Frequency of pulsation varied from 5 to 20 Hz. depending on whether a solid stone was treated or small fragments were pulverized, with the end result being fragments 2 mm. or less in diameter and fine dust. A polytetrafluoroethylene sheathed 2.5F wire prong grasper through the working channel of the flexible ureteroscope was commonly used to move stone fragments from the lower pole to a more cephalad position. When the endoscope could not be precisely placed onto the entire lower pole stone burden because of the decreased deflectability when using the laser fiber, large fragments were created and moved with the more flexible grasper. Placing the patient in a deep Trendelenburg position also facilitated fragment migration to the upper pole where stones were more readily pulverized to finer fragments and dust. Second look endoscopy was performed in the majority of lower pole calculi in excess of 2.5 cm. In our experience with treating large, branching calculi in a retrograde fashion frequently after the first sitting the entire collecting system is lined by fine dust and debris which can obscure a large, hidden crescent of stone.7 In these cases retrograde catheters were placed and the intrarenal collecting system was irrigated postoperatively. Inflow was through a 5F Cobra catheter with its tip positioned in the most dependent lower pole. A larger open ended catheter (6F or greater) with its tip positioned in the upper pole was used for outflow. The most commonly used irrigant was sterile saline with 80 mg./l. gentamicin at 100 cc per hour. If the stone burden was composed of uric acid or cystine, an alkalizing irrigant was used. Tromethamine solution was used for cystine and sodium bicarbonate based irrigant was used for uric acid stones. For endoscopic lithotripsy regional (that is epidural or spinal) or general anesthesia was used based on patient preference and the specific choice of the anesthesiologist. Patients with stone burdens less than 2.5 cm. were treated as outpatients and discharged home with an internal ureteral stent in place that was removed 3 to 10 days postoperatively. Before second look endoscopy for large stone burdens patients underwent 36 hours of intrarenal irrigation. They were discharged home shortly after the second stage with an internal stent in place that was removed the same time postoperatively as for those patients with smaller stone burdens. All patients received prophylactic parenteral cephalosporin based antibiotics and postoperatively received a 5-day course of quinolone based oral antibiotics with adjustments for comorbid medical conditions. All patients were followed with serial radiographs and renal sonography approximately 4 weeks postoperatively to rule out silent obstruction and hydronephrosis, and to quantify the residual stone burden. Depending on the initial postoperative imaging, additional interval imaging was obtained. An acceptable immediate surgical outcome was defined as complete fragmentation of the stone burden to fine dust and 2 mm. or less fragments. However, success was defined as clear imaging (that is stone-free) on subsequent renal sonography. Statistical analysis was based on calculation of odds ratios and the 95% confidence interval was determined by Woolf’s method. RESULTS
A total of 101 procedures were performed on 79 patients. Stone burdens and operative time are presented in table 1.
TABLE 1. Stone burden and corresponding operative times Group No. (mean mm. stone diameter)
No. Stones
Mean Mins. Operative Time 6 SD (range)
1 (10 or less) 2 (11–20) 3 (greater than 20)
47 21 22
38 6 18 (20–72) 59 6 12 (40–73) 126 6 56 (40–190)
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RETROGRADE URETEROPYELOSCOPY FOR CALICEAL CALCULI
Intramural ureteral dilation with a 12F balloon or graduated dilator was required for access of 7 stone burdens (8%). However, 24% of patients presented with a ureteral stent preoperatively. An acceptable surgical outcome was based on endoscopic access and complete stone fragmentation (table 2). Complete fragmentation at a single sitting, including stone burdens of all sizes, was performed in 82% of cases. Complete fragmentation was noted in 94% of group 1 (stones 10 mm. or less) and achieved with single surgery in 45% of group 3 (stones greater than 20 mm.). A second sitting was planned preoperatively for group 3 and intrarenal irrigation was done for up to 36 hours between sittings. Including the 2-stage cases the fragmentation rate for these exceptionally large stone burdens increased to 82%, improving the overall treatment rate to 91%. Endoscopic access to a lower pole infundibulum and treatment of dependent calculi required secondary deflection as an endoscopic maneuver in 76% of stone burdens. Failure of endoscopic access was noted in 8 stone burdens (9%), including 2 of 3 patients with lower pole infundibular strictures. A long lower pole infundibulum, acute infundibulopelvic angle, significantly dilated collecting system and infundibular stricture disease were evaluated in regard to successful endoscopic lithotripsy (table 3). Of the stone burdens 35 were not associated with any of these variants and all but 1 were treated successfully. A long lower pole infundibulum and an infundibular stricture were statistically significant as negative parameters for success of retrograde endoscopic therapy of lower pole caliceal calculi. Stone composition included all major types. Calcium oxalate calculi were noted in 45 cases and the majority of these stones were primarily composed of the monohydrate variety. Stone burden was cystine in 9 patients (11%), calcium phosphate in 10, uric acid in 14 and sodium urate in 1. The holmium laser was able to fragment stones of all of these compositions and, thus, failures were secondary to inability of endoscopic access or failure to clear debris. Success was based on clear postoperative imaging (that is stone-free) with minimum 3-month followup. Followup data were available for 70 stone burdens with an overall stonefree rate of 76% (table 4). As stone burdens increased, the ultimate stone-free rates decreased from 82% for the smallest stones to 65% for calculi in excess of 20 mm. The overall success rate increased to 84% of patients with successful endoscopic access to the stone burden. If the 8 patients with failed access are excluded from analysis, the rate of complete clearance of debris and fragments after an acceptable immediate surgical outcome was 88%, 77 and 81% for groups 1, 2 and 3, respectively. Complications were classified as intraoperative, postoperative or long-term sequelae of the procedure. There were no major intraoperative complications. Minor postoperative complications included renal colic secondary to the internal stent in 6 cases (8%) and colic while passing debris in 1 which required stent replacement after removal. In addition, 3 patients (4%) presented with symptomatic urinary tract infec-
TABLE 2. Endoscopic access and rate of complete fragmentation of stone burden to fine dust and 2 mm. or less fragments Group No. Group 1 Group 2 Group 3: After 1 sitting After 2 sittings Totals
No. Endoscopic Access 1 Complete Fragmentation/ Total No. (%) 44/47 (94) 20/21 (95) 10/22 (45) 18/22 (82) 82/90 (91)
No. Intraop. Surgical Failures/ Total No. (%) 3/47 (6) 1/21 (5) 4/22 (18)
8/90 (9)
TABLE 3. Prevalence of collecting system variants and predictive values for surgical failure Collecting System Variants Long lower pole infundibulum (greater than 3 cm.) Acute infundibulopelvic angle Dilated collecting system Infundibular stricture * Statistically significant.
No. No. Failures Prevalence With Variants (%) (%)
Odds Ratio (CI)
21 (23)
8 (38)
7.9 (5.1 6 12.2)*
29 (32)
5 (17)
1.3 (0.9 6 2.1)
23 (26) 3 (3)
4 (17) 2 (67)
1.3 (0.8 6 2.1) 13.8 (10.9 6 17.4)*
tions that required longer courses of antibiotic therapy. There were no major postoperative complications, including ureteral strictures. DISCUSSION
Shock wave lithotripsy represents first line therapy for most moderate size intrarenal calculi. Since the evolution of the shock wave lithotriptor to second and third generation devices with lower power and smaller focal zones, the overall success rate of this procedure has decreased.5, 6 Concurrently innovations in endoscopes and endoscopic lithotrites now allow not only the entire intrarenal collecting system to be accessed in a retrograde fashion, but also treatment of complex stone burdens previously reserved for primary percutaneous puncture and nephrostolithotomy. The holmium laser represents a significant improvement from prior technology in that stone burdens of all compositions and sizes can be fragmented into fine dust and small debris with a range of energy applied through flexible, optical quartz fibers.7, 8 Improvement in endoscope design and, specifically, the addition of the small diameter, actively deflectable, flexible ureteropyeloscope facilitated complete upper urinary tract access to every infundibulum and calix in up to 94% of cases.9 The combination of the flexible ureteroscope and the 200 m. holmium laser fiber allows treatment of intrarenal calculi within the lower pole caliceal system. Historically, ureteropyeloscopy for intrarenal calculi has been based on electrohydraulic lithotripsy probes or laser lithotripsy.9 –11 In 1996 Elashry et al reported a success rate of 92% when intrarenal calculi were treated with a flexible ureteroscope and 1.9F electrohydraulic lithotripsy probe.11 In a contemporary series a similar modest cohort of patients treated with the holmium laser had an 88.5% success rate with a single session of endoscopic lithotripsy.7 In 1998, 2 large series were published of intrarenal calculi treated with retrograde ureteropyeloscopy. Fabrizio et al presented 100 patients who underwent retrograde endoscopy with the holmium laser or electrohydraulic lithotripsy probe, and reported an immediate postoperative success rate of 89%.12 There were few complications and no long-term sequelae of treatment. In a similar series Grasso and Chalik reported on 99 patients with intrarenal calculi, including large, branching staghorn stone burdens, treated in a retrograde fashion.13 An 80% success rate after a single session was reported and when the largest of these stone burdens was treated with a staged procedure the overall success rate increased to 90%. Larger stone burdens, in particular branching staghorn calculi, have been the subject of a clinical guidelines panel summary.1 In 1994 the panel established that the majority of these stone burdens are best treated in a percutaneous fashion rather than by shock wave lithotripsy monotherapy. A recently published series of 48 stone burdens in excess of 2 cm. in largest diameter, including branching staghorn calculi treated with retrograde ureteroscopy, underscores the usefulness of the holmium laser in debulking and clearing com-
1907
RETROGRADE URETEROPYELOSCOPY FOR CALICEAL CALCULI TABLE 4. Stone-free rates and residual debris on renal sonography with minimum 3-month followup No. Cases/Total No. (%) Group No. Stone-Free 1 2 3* Totals * Includes 1 and 2 surgical
36/44 (82) 10/14 (72) 13/20 (65) 59/78 (76) sittings.
Small Lower Pole Debris (4 mm. or less)
Greater Vol. Debris (5 mm. or greater)
Failure Endoscopic Access
3/44 (7) 2/14 (14) 1/20 (6) 6/78 (8)
2/44 (5) 1/14 (7) 2/20 (13) 5/78 (6)
3/44 (6) 1/14 (7) 4/20 (20) 8/78 (10)
plex stone burdens in a minimally invasive fashion.14 The combination of the flexible ureteroscope and small holmium laser fibers allowed treatment of the largest stone burdens as well as calculi of all compositions, and only a small subset of patients had postoperative complications, including pyelonephritis (1), prostatic bleeding on anticoagulant therapy (1) and cerebral vascular incident 24 hours after endoscopic lithotripsy (1). The Lower Pole Stone Study Group attempted to define in a prospective randomized fashion the success rates of shock wave lithotripsy and percutaneous nephrostolithotomy for dependent lower pole intrarenal calculi.6 The premise was that the dependent nature of the lower pole would preclude successful therapy with shock wave lithotripsy. Fragments would most likely remain in the lower pole as opposed to passing up into the renal pelvis and down the ureter. To date 128 patients have been accrued and success rates in both treatment arms have been stratified based on stone size. The success rate for calculi less than 1 cm. was 63% with shock wave lithotripsy compared to 100% completely cleared with percutaneous nephrostolithotomy. The success rates were 23% for larger stones less than 2 cm. and a dismal 14% for stone burdens in excess of 2 cm. with shockwave lithotripsy compared to a better than 86% rate of clearance with percutaneous nephrostolithotomy for both groups. Retrograde ureteropyeloscopy represents a significantly less invasive treatment than percutaneous nephrostolithotomy for dependent lower pole caliceal calculi. Although not a double armed randomized trial, all patients referred for retrograde intrarenal lithotripsy in our series were accrued and treated. There was no preoperative exclusion criterion. Our success (that is stone-free) rate for treating calculi 1 cm. or less was 82%. Our failures were subdivided into failure of endoscopic access (8 cases) and persistent lower pole fragments. In the 8 cases failure of access was secondary to severe anatomical variants, including infundibular stenosis. In the remaining majority endoscopic access and complete fragmentation were successful, with clearance ranging from 88% for calculi 10 mm. in diameter to 81% for stone burdens in excess of 2 cm. Elbahnasy et al studied intrarenal anatomical variants and their impact on extracorporeal shock wave lithotripsy of lower pole caliceal calculi.15 An acute infundibulopelvic angle or long lower pole infundibulum was a negative parameter for success. In this same study 13 patients were treated ureteroscopically with a 62% success rate. The authors suggested that these intrarenal anatomical variants which inhibited extracorporeal treatment had a smaller role in the overall success rate of retrograde endoscopic lithotripsy. To determine preoperatively which patients would be treated best ureteroscopically versus a primary percutaneous approach, we also examined variables of intrarenal anatomy and their impact on success of retrograde endoscopic therapy. We defined a subgroup of patients with long lower pole infundibulum (greater than 3 cm.) which alone had a 38% predictive value of failure. An acute infundibulopelvic angle and dilated collecting system were less prohibitive in regard to endoscopic access to the stone burden, and were compli-
cating factors in a smaller subpopulation. Finally, infundibular strictures can preclude endoscopic access into the calix and if defined preoperatively should alert the surgeon to possible percutaneous intervention as noted in 2 of 3 patients in our series. CONCLUSIONS
Lower pole caliceal calculi present a clinical challenge. From the data presented by Lingeman and the Lower Pole Stone Study Group the stone-free rate with extracorporeal shock wave lithotripsy in this setting is low when the stone burden is in excess of 1 cm.6 Percutaneous nephrostolithotomy represents a definitive but extremely invasive alternative compared to retrograde endoscopy for managing intrarenal calculi. In our large series of lower pole calculi the majority were successfully treated ureteroscopically with the holmium laser with minimal morbidity. Variants in intrarenal anatomy, specifically a long lower pole infundibulum, may preclude successful treatment when using the defined retrograde technique. If a long lower pole infundibulum is noted on preoperative imaging, the patient should be counseled that the success rate in general with ureteropyeloscopy is decreased and percutaneous nephrostolithotomy may be required. Philip Alcabes assisted with the statistical analysis. REFERENCES
1. Segura, J. W., Preminger, G. M., Assimos, D. G., Dretler, S. P., Kahn, R. I., Lingeman, J. E., Macaluso, J. N., Jr. and McCullough, D. L.: Nephrolithiasis Clinical Guidelines Panel summary report on the management of staghorn calculi. J. Urol., 151: 1648, 1994. 2. Grasso, M., Loisides, P., Beaghler, M. and Bagley, D.: The case for primary endoscopic management of upper urinary tract calculi: I. A critical review of 121 extracorporeal shock wave lithotripsy failures. Urology, 45: 363, 1995. 3. Fuchs, A. M. and Fuchs, G. J.: Retrograde intrarenal surgery for calculous disease: new minimally invasive treatment approach. J. Endourol., 4: 337, 1990. 4. Denstedt, J. D. and Clayman, R. V.: Electrohydraulic lithotripsy of renal and ureteral calculi. J. Urol., 143: 13, 1990. 5. Lingeman, J. E., Siegel, Y. I., Steele, B., Nyhuis, A. W. and Woods, J. R.: Management of lower pole nephrolithiasis: a critical analysis. J. Urol., 151: 663, 1994. 6. Lingeman, J. E.: Prospective randomized trial of extracorporeal shock wave lithotripsy and percutaneous nephrostolithotomy for lower pole nephrolithiasis: initial long-term follow up. J. Urol., part 2, 157: 43, abstract 159, 1997. 7. Grasso, M.: Experience with the holmium laser as an endoscopic lithotrite. Urology, 48: 199, 1996. 8. Matsuoka, K., Iida, S., Nakanami, M., Koga, H., Shimada, A., Mihara, T. and Noda, S.: Holmium:yttrium-aluminum-garnet laser for endoscopic lithotripsy. Urology, 45: 947, 1995. 9. Grasso, M. and Bagley, D.: Small diameter, actively deflectable, flexible ureteropyeloscopy. J. Urol., 160: 1648, 1998. 10. Bagley, D. H., Huffman, J. L. and Lyon, E. S.: Flexible ureteropyeloscopy: diagnosis and treatment in the upper urinary tract. J Urol., 138: 280, 1987. 11. Elashry, O. M., DiMeglio, R. B., Nakada, S. Y., McDougall, E. M.
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and Clayman, R. V.: Intracorporeal electrohydraulic lithotripsy of ureteral and renal calculi using small caliber (1.9F) electrohydraulic lithotripsy probes. J. Urol., 156: 1581, 1996. 12. Fabrizio, M. D., Behari, A. and Bagley, D. H.: Ureteroscopic management of intrarenal calculi. J. Urol., 159: 1139, 1998. 13. Grasso, M. and Chalik, Y.: Principles and applications of laser lithotripsy: experience with the holmium laser lithotrite. J. Clin. Laser Med. Surg., 16: 3, 1998.
14. Grasso, M., Conlin, M. and Bagley, D.: Retrograde ureteropyeloscopic treatment of 2 cm. or greater upper urinary tract and minor staghorn calculi. J. Urol., 160: 346, 1998. 15. Elbahnasy, A. M., Shalhav, A. L., Hoenig, D. M., Elashry, O. M., Smith, D. S., McDougall, E. M. and Clayman, R. V.: Lower caliceal stone clearance after shock wave lithotripsy or ureteroscopy: the impact of lower pole radiographic anatomy. J. Urol., 159: 676, 1998.