Lasers in Surgery and Medicine 12:490-493(1992)
Treatment of Distal Ureteral Tumors Using Endoscopic Argon Photoirradiation Douglas E. Johnson, MD Department of Urology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030
This is the first report on the use of endoscopic argon photoirradiation to treat patients with low-gradeureteral tumors involving the distal ureter. Using a rigid ureteropyeloscope, a 300 p or 600 p quartz fiber, and 5 watts (W) of power in a continuous-wave mode, the lesions were ablated without complication. Patients remain free of ureteral recurrence after 5, 7, and 22 months. We conclude that the shallow (1 mm) depth of penetration and the ability to use the fiber in either a contact or noncontact mode provide the surgeon a large margin of safety and low risk of ureteral perforation. 0 1992 Wiley-Liss, Inc. Key words: endourology, transitional cell carcinoma, ureteroscopy
INTRODUCTION
The variable natural history and malignant expression of ureteral tumors occurring among patient populations of different geographic areas have caused investigators, over a three-quarter century period, to urge conservative surgery in treating primary ureteral carcinoma. Since the first attempt to conserve the kidney by Albarran [ l ] in 1903, a variety of conservative techniques have been employed, including electrocauterization or local excision through a ureterotomy, transurethral resection (TURP) and fulguration through the ureter for intramural and distal ureteral tumors, and resection of the involved ureter and re-establishment of urinary drainage by performing either a ureteroureterostomy, transurethral ureterostomy, or ureteroneocystostomy [263. The introduction of transurethral ureteropyeloscopy by Perez-Castro Ellendt and Martinez-Pineiro in 1980 [71 and the continued refinements in instruments, which permitted endoscopic treatment of ureteral tumors in selected patients, led Hofstetter and colleagues [8,9] t o rep o r t the first successful treatment of ureteral tumorS using the Neodymium:YAG (Nd:YAG) laser* Other investigators rePorted similar successful results and today, laser photoirradiation using the Nd:YAG for treatment 0 1992 Wiley-Liss, Inc.
of ureteral tumors has gained acceptance in our therapeutic armamentarium. Use of argon lasers operating in the visible green portion of the electromagnetic spectrum (488-514 nm) for treatment of urothelial tumors has lagged behind that of both the Nd:YAG (1064 nm) and the KTP (532 nm) lasers. However, Smith and Dixon [141 reported as early as 1984 the successful use of the argon laser to treat 11 patients with superficial transitional cell bladder tumors, and we have also satisfactorily treated 14 patients with superficial low-grade papillary bladder tumors with no in-field recurrence noted [GI. These findings, combined with the shallow depth of tissue penetration (1.0 mm) and ease of delivery using either a 300 p or 600 p fiber, led us to use similar techniques for treating patients with ureteral carcinomas. We report here on the first use of the argon laser to treat patients with distal superficial transitional cell carcinomas of the distal ureter.
Accepted for publication May 12, 1992. Address reprint requests to Dr. Douglas E. Johnson, Department of Urology, Box 110, University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard. Houston. TX 77030.
Distal Ureteral Tumor Treatment PATIENTS AND METHODS
Three male patients (ages 58, 61, and 69) with superficial low-grade, noninvasive tumors arising in the distal ureter were treated with argon laser photoirradiation between September 1989 and February 1991 in the Department of Urology at the University of Texas M.D. Anderson Cancer center in Houston. These patients had undergone prior TURP for multiple superficial (stage 0)papillary, low-grade (I or 11) transitional cell carcinomas (TCC) of the bladder, and in each case, tumors projecting from a ureteral orifice were identified and the ureteral orifice was resected using electrocautery. Two patients had received intravesical bacillus Calmette-Guerin (BCG) prior to ureteroscopy and argon photoirradiation. Rigid ureteropyeloscopy was performed in all patients under general anesthesia and after insertion of a 0.035 guide wire and ureteral dilatation. In the first patient two lesions measuring - 3 and 5 mm in diameter were located just inside the recently resected ureteral orifice and 3 cm farther up the ureter. The two remaining patients had tumors involving the intramural ureters. The lesions were photoablated under direct vision using the Model 20 HGM Endocoagulator (HGM Medical Laser System, Salt Lake City, UT). Continuous-wave argon laser energy was delivered through either a 300 p. or a 600 w quartz fiber in a contact mode with a power set at 5 W. At the completion of therapy in 2 patients, a double J ureteral stent was passed over the guide wire and left in place for 6 weeks, at which time it was removed endoscopically under local anesthesia. In the patient in whom a ureteral stent was not placed at the time of surgery, percutaneous nephrostomy was performed on an emergency basis 4 hours after surgery because of severe lower abdominal pain; there was no evidence of urinary extravasation. The etiology for his pain remained obscure. The following morning the percutaneous nephrostomy was converted to an indwelling ureteral stent. All 3 patients had the ureteral stents removed on an outpatient basis 6 weeks later. RESULTS
All 3 patients remained free of disease at 5, 7, and 22 months. However, the first patient developed ureteral meatal stenosis with superficial tumor (Grade II/Stage 0)involving the meatus at 18 months and required TURP using electrocau-
491
tery. Four months later he remains free of ureteral tumors. The second and third patients developed recurrent superficial bladder recurrence at sites distant from their affected ureters at 5 and 7 months, which has required electrocautery resection and fulguration; however, they have not developed evidence of ureteral recurrence. In all patients, urinary cytology remains negative for malignant cells. Patients in whom the ureteral stents were placed immediately following laser photoirradiation were discharged from the hospital within 24 and 48 hours: The patient requiring a delayed ureteral stent was discharged from the hospital on the 5th postoperative day. DISCUSSION
Our favorable results in this small series of patients attest to the safety and success that can be achieved by managing patients who have small, low-grade, and low-stage distal ureteral tumors endoscopically using laser photoirradiation. Although heretofore patients have been treated using the Nd:YAG laser, the argon laser is especially suitable for endoscopic management of upper urinary tract urothelial cancers. Precise alignment of the laser fiber tip, frequently difficult to achieve endoscopically when using the Nd: YAG, is not as critical with the argon because the argon lasr fiber tip can be conveniently used in either the contact or noncontact mode. The shallowness of argon laser tissue penetration (1mm) and its adequacy for ablating small ureteral tumors afford a large margin of safety and carry a low chance of ureteral perforation. Although none of our patients had evidence of ureteral perforation, our second patient required a delayed percutaneous nephrostomy and insertion of a ureteral stent because of severe lower abdominal pain and the concern of possible urinary extravasation. However, at the time of nephrostomy insertion, radiographic studies failed to provide evidence of perforation. Sommer et al. [16] demonstrated highly disturbed ureteral function immediately after laser coagulation and recommended that the ureter be stented for a period of 2-3 weeks. From their investigations they concluded that changes in peristalsis after laser coagulation, such as a rise in basal pressure and frequent waves with small-pressure amplitudes in the ureter above the lased area, are similar to urodynamic findings in other conditions of partial obstruction. Most likely our patient experienced a
492
Johnson
ureteral obstruction secondary t o a disturbance of the stimulus conduction system in this area. In retrospect, at the time of operation we should have left an indwelling stent in place. Recent advances in instrumentation have provided urologists today with “miniscopes,” which obviate the need for routine ureteral dilatation as was performed in our cases. Eliminating ureteral dilatation prior to insertion of the ureteroscope reduces the risk for local trauma and subsequent stricture formation. These smaller instruments readily accept laser fibers, giving laser therapy an additional advantage over electrocautery, which requires the use of larger ureteroscopes. Although Huffman and associates [171 should be credited for demonstrating the feasibility of treating patients with superficial tumors of the lower ureter by ureteroscopic resection and fulguration, laser photoirradiation would appear to offer greater advantages. Blute and associates [lll noted local recurrence within the ureter in 2 of 11 patients (18%) treated with ureteroscopic Nd:YAG laser (9, 23 months), but in each instance patients responded to repeat endoscopic laser fulguration. Schilling et al. [lo] reported successfully treating 19 patients with ureteral tumors and during follow-up noted one laser-induced stricture and one recurrence in the ureter. Although one patient had a recurrence in the area of a stenotic ureteral orifice, no tumor was identified within the ureter. The ureteral stenosis and tumor responded to repeat transurethral electroresection. Schmeller and Pensel 112) noted that in 8 patients treated with laser and electroresection, 3 patients developed a ureteral stricture; it was their conclusion that the higher incidence of ureteral stricture was related to the electroresection. They offered supportive evidence by finding only one ureteral stricture in 8 patients treated with laser alone, and in that instance, the ureter had been lased circumferentially with a high dose. All of our patients had undergone prior electroresection of the ureteral orifices at the time of-or immediately prior to-laser photoirradiation. Consequently, the development of a ureteral meatal stenosis in one of our patients was not unexpected. Although experience has shown that patients with low-grade, low-stage ureteral tumors can be treated satisfactorily with laser photoirradiation with little attendant morbidity, these patients are at high risk for subsequent development of bladder carcinomas. Each of our 3 patients required electroresection for recurrent
bladder cancer and Blute et al. [ll]reported a 31% bladder failure rate. Therefore, these patients need to be monitored carefully with periodic cystoscopy,urinary cytology, and appropriate upper tract radiologic and endoscopic studies. Although too few patients have been treated endoscopically using laser photoirradiation and followed for a sufficient period of time to formulate precise recommendations regarding methods and timing for surveillance of the affected upper urinary tract, ureteroscopy should be an integral part of the follow-up. It is our practice to include ureteroscopy as part of the endoscopic examination of these patients 3-4 months postoperatively and thereafter at periodic intervals depending upon the cystoscopic and urinary cytologic findings. REFERENCES 1. Petkovic SD. A plea for conservative operation for ureteral tumors. J Urol 1972; 107:220-223. 2. Cook EN, Counseller VS. Primary epithelioma of ureter. JAMA 1941; 116~122-127. 3. Vest SA. Conservative surgery in certain benign tumors of the ureter. J Urol 1945; 53:97-121. 4. Popesco C. Resection de l’uretere ileo-pelvien pour tumeur papillaire. Restauration de la voie excretice par abaissment renal et elevation vesicale. J Urol Nephrol (Paris) 1967; 73:269-272. 5. Grossman HB. The late recurrence of grade I transitional cell carcinoma of the ureter after conservative therapy. J Urol 1978; 120:251-252. 6. Johnson DE, Babaian FLJ.Conservative surgical management for noninvasive distal ureteral carcinoma. Urology 1979; 13:365-367. 7. Perez-Castro EE, Martinez-Pineiro JA. Transurethral ureteroscopy: A current urological procedure. Arch Exp Urol 1980; 33:445-460. 8. Hofstetter A, Bowering R, Keiditsch E. Zerstorung von uretertumoren mit dem Nd-YAG-laser. Fortschr Med 1983; 101~625-628. 9. Hofstetter AG, Keiditsch E: Lasers for renal pelvis and ureteral tumors. Laser 1985; 1:75-77. 10. Schilling A, Bowering R, Keiditsch E. Use of the Nd:YAG laser in the treatment of ureteral tumors and ureteral condylomata acuminata. Eur Urol 1986; 12:30-33. 11. Blute ML, Segura JW, Patterson DE, Benson RC Jr, Zincke H. Impact of endourology on diagnosis and management of upper urinary tact urothelial cancer. J Urol 1989; 14111298-1301. 12. Schmeller NT, Pensel J. Ureteral tumors. In: Smith J A Jr, Stein BS, Benson RC Jr, eds. “Lasers in Urologic Surgery,’’ Chicago: Year Book Medical Publishers, 1989, pp 81-91. 13. Schmeller NT, Pensel J. Ureteral tumors. In: Smith J A Jr, Stein BS, Bensen RC J r , eds. “Lasers in Urologic Surgery.” Chicago: Year Book Medical Publishers (personal communication: Schilling A, Friesen A, et al.) 1989, p 90. 14. Smith JA J r , Dixon JA. Argon laser phototherapy of su-
Distal Ureteral Tumor Treatment perficial transitional cell carcinoma of the bladder. J Urol 1984; 131~655-656. 15. Levinson AK, Johnson DE. The argon laser in urology. Presented at 69th Annual Meeting South Central Section of the American Urological Association, October 14, 1990. Santa Fe, NM. 16. Sommer K, Pensel J, Lieck P, Baretton G, Schuller J.
493
Healing of the ureter after Nd:YAG laser coagulation: Morphologic and physiological aspects. Journal of Endourology 1989; 3:439-445. 17. Huffman JL, Bagley DH, Lyon ES, Morse MJ, Herr HW, Whitmore WJ Jr. Endoscopic diagnosis and treatment of upper-tract urothelial tumors: A preliminary report. Cancer 1985; 55:1422-1428.
Treatment of Distal Ureteral Tumors Using Endoscopic Argon Photoirradiation Douglas E. Johnson, MD Department of Urology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030
This is the first report on the use of endoscopic argon photoirradiation to treat patients with low-gradeureteral tumors involving the distal ureter. Using a rigid ureteropyeloscope, a 300 p or 600 p quartz fiber, and 5 watts (W) of power in a continuous-wave mode, the lesions were ablated without complication. Patients remain free of ureteral recurrence after 5, 7, and 22 months. We conclude that the shallow (1 mm) depth of penetration and the ability to use the fiber in either a contact or noncontact mode provide the surgeon a large margin of safety and low risk of ureteral perforation. 0 1992 Wiley-Liss, Inc. Key words: endourology, transitional cell carcinoma, ureteroscopy
INTRODUCTION
The variable natural history and malignant expression of ureteral tumors occurring among patient populations of different geographic areas have caused investigators, over a three-quarter century period, to urge conservative surgery in treating primary ureteral carcinoma. Since the first attempt to conserve the kidney by Albarran [ l ] in 1903, a variety of conservative techniques have been employed, including electrocauterization or local excision through a ureterotomy, transurethral resection (TURP) and fulguration through the ureter for intramural and distal ureteral tumors, and resection of the involved ureter and re-establishment of urinary drainage by performing either a ureteroureterostomy, transurethral ureterostomy, or ureteroneocystostomy [263. The introduction of transurethral ureteropyeloscopy by Perez-Castro Ellendt and Martinez-Pineiro in 1980 [71 and the continued refinements in instruments, which permitted endoscopic treatment of ureteral tumors in selected patients, led Hofstetter and colleagues [8,9] t o rep o r t the first successful treatment of ureteral tumorS using the Neodymium:YAG (Nd:YAG) laser* Other investigators rePorted similar successful results and today, laser photoirradiation using the Nd:YAG for treatment 0 1992 Wiley-Liss, Inc.
of ureteral tumors has gained acceptance in our therapeutic armamentarium. Use of argon lasers operating in the visible green portion of the electromagnetic spectrum (488-514 nm) for treatment of urothelial tumors has lagged behind that of both the Nd:YAG (1064 nm) and the KTP (532 nm) lasers. However, Smith and Dixon [141 reported as early as 1984 the successful use of the argon laser to treat 11 patients with superficial transitional cell bladder tumors, and we have also satisfactorily treated 14 patients with superficial low-grade papillary bladder tumors with no in-field recurrence noted [GI. These findings, combined with the shallow depth of tissue penetration (1.0 mm) and ease of delivery using either a 300 p or 600 p fiber, led us to use similar techniques for treating patients with ureteral carcinomas. We report here on the first use of the argon laser to treat patients with distal superficial transitional cell carcinomas of the distal ureter.
Accepted for publication May 12, 1992. Address reprint requests to Dr. Douglas E. Johnson, Department of Urology, Box 110, University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard. Houston. TX 77030.
Distal Ureteral Tumor Treatment PATIENTS AND METHODS
Three male patients (ages 58, 61, and 69) with superficial low-grade, noninvasive tumors arising in the distal ureter were treated with argon laser photoirradiation between September 1989 and February 1991 in the Department of Urology at the University of Texas M.D. Anderson Cancer center in Houston. These patients had undergone prior TURP for multiple superficial (stage 0)papillary, low-grade (I or 11) transitional cell carcinomas (TCC) of the bladder, and in each case, tumors projecting from a ureteral orifice were identified and the ureteral orifice was resected using electrocautery. Two patients had received intravesical bacillus Calmette-Guerin (BCG) prior to ureteroscopy and argon photoirradiation. Rigid ureteropyeloscopy was performed in all patients under general anesthesia and after insertion of a 0.035 guide wire and ureteral dilatation. In the first patient two lesions measuring - 3 and 5 mm in diameter were located just inside the recently resected ureteral orifice and 3 cm farther up the ureter. The two remaining patients had tumors involving the intramural ureters. The lesions were photoablated under direct vision using the Model 20 HGM Endocoagulator (HGM Medical Laser System, Salt Lake City, UT). Continuous-wave argon laser energy was delivered through either a 300 p. or a 600 w quartz fiber in a contact mode with a power set at 5 W. At the completion of therapy in 2 patients, a double J ureteral stent was passed over the guide wire and left in place for 6 weeks, at which time it was removed endoscopically under local anesthesia. In the patient in whom a ureteral stent was not placed at the time of surgery, percutaneous nephrostomy was performed on an emergency basis 4 hours after surgery because of severe lower abdominal pain; there was no evidence of urinary extravasation. The etiology for his pain remained obscure. The following morning the percutaneous nephrostomy was converted to an indwelling ureteral stent. All 3 patients had the ureteral stents removed on an outpatient basis 6 weeks later. RESULTS
All 3 patients remained free of disease at 5, 7, and 22 months. However, the first patient developed ureteral meatal stenosis with superficial tumor (Grade II/Stage 0)involving the meatus at 18 months and required TURP using electrocau-
491
tery. Four months later he remains free of ureteral tumors. The second and third patients developed recurrent superficial bladder recurrence at sites distant from their affected ureters at 5 and 7 months, which has required electrocautery resection and fulguration; however, they have not developed evidence of ureteral recurrence. In all patients, urinary cytology remains negative for malignant cells. Patients in whom the ureteral stents were placed immediately following laser photoirradiation were discharged from the hospital within 24 and 48 hours: The patient requiring a delayed ureteral stent was discharged from the hospital on the 5th postoperative day. DISCUSSION
Our favorable results in this small series of patients attest to the safety and success that can be achieved by managing patients who have small, low-grade, and low-stage distal ureteral tumors endoscopically using laser photoirradiation. Although heretofore patients have been treated using the Nd:YAG laser, the argon laser is especially suitable for endoscopic management of upper urinary tract urothelial cancers. Precise alignment of the laser fiber tip, frequently difficult to achieve endoscopically when using the Nd: YAG, is not as critical with the argon because the argon lasr fiber tip can be conveniently used in either the contact or noncontact mode. The shallowness of argon laser tissue penetration (1mm) and its adequacy for ablating small ureteral tumors afford a large margin of safety and carry a low chance of ureteral perforation. Although none of our patients had evidence of ureteral perforation, our second patient required a delayed percutaneous nephrostomy and insertion of a ureteral stent because of severe lower abdominal pain and the concern of possible urinary extravasation. However, at the time of nephrostomy insertion, radiographic studies failed to provide evidence of perforation. Sommer et al. [16] demonstrated highly disturbed ureteral function immediately after laser coagulation and recommended that the ureter be stented for a period of 2-3 weeks. From their investigations they concluded that changes in peristalsis after laser coagulation, such as a rise in basal pressure and frequent waves with small-pressure amplitudes in the ureter above the lased area, are similar to urodynamic findings in other conditions of partial obstruction. Most likely our patient experienced a
492
Johnson
ureteral obstruction secondary t o a disturbance of the stimulus conduction system in this area. In retrospect, at the time of operation we should have left an indwelling stent in place. Recent advances in instrumentation have provided urologists today with “miniscopes,” which obviate the need for routine ureteral dilatation as was performed in our cases. Eliminating ureteral dilatation prior to insertion of the ureteroscope reduces the risk for local trauma and subsequent stricture formation. These smaller instruments readily accept laser fibers, giving laser therapy an additional advantage over electrocautery, which requires the use of larger ureteroscopes. Although Huffman and associates [171 should be credited for demonstrating the feasibility of treating patients with superficial tumors of the lower ureter by ureteroscopic resection and fulguration, laser photoirradiation would appear to offer greater advantages. Blute and associates [lll noted local recurrence within the ureter in 2 of 11 patients (18%) treated with ureteroscopic Nd:YAG laser (9, 23 months), but in each instance patients responded to repeat endoscopic laser fulguration. Schilling et al. [lo] reported successfully treating 19 patients with ureteral tumors and during follow-up noted one laser-induced stricture and one recurrence in the ureter. Although one patient had a recurrence in the area of a stenotic ureteral orifice, no tumor was identified within the ureter. The ureteral stenosis and tumor responded to repeat transurethral electroresection. Schmeller and Pensel 112) noted that in 8 patients treated with laser and electroresection, 3 patients developed a ureteral stricture; it was their conclusion that the higher incidence of ureteral stricture was related to the electroresection. They offered supportive evidence by finding only one ureteral stricture in 8 patients treated with laser alone, and in that instance, the ureter had been lased circumferentially with a high dose. All of our patients had undergone prior electroresection of the ureteral orifices at the time of-or immediately prior to-laser photoirradiation. Consequently, the development of a ureteral meatal stenosis in one of our patients was not unexpected. Although experience has shown that patients with low-grade, low-stage ureteral tumors can be treated satisfactorily with laser photoirradiation with little attendant morbidity, these patients are at high risk for subsequent development of bladder carcinomas. Each of our 3 patients required electroresection for recurrent
bladder cancer and Blute et al. [ll]reported a 31% bladder failure rate. Therefore, these patients need to be monitored carefully with periodic cystoscopy,urinary cytology, and appropriate upper tract radiologic and endoscopic studies. Although too few patients have been treated endoscopically using laser photoirradiation and followed for a sufficient period of time to formulate precise recommendations regarding methods and timing for surveillance of the affected upper urinary tract, ureteroscopy should be an integral part of the follow-up. It is our practice to include ureteroscopy as part of the endoscopic examination of these patients 3-4 months postoperatively and thereafter at periodic intervals depending upon the cystoscopic and urinary cytologic findings. REFERENCES 1. Petkovic SD. A plea for conservative operation for ureteral tumors. J Urol 1972; 107:220-223. 2. Cook EN, Counseller VS. Primary epithelioma of ureter. JAMA 1941; 116~122-127. 3. Vest SA. Conservative surgery in certain benign tumors of the ureter. J Urol 1945; 53:97-121. 4. Popesco C. Resection de l’uretere ileo-pelvien pour tumeur papillaire. Restauration de la voie excretice par abaissment renal et elevation vesicale. J Urol Nephrol (Paris) 1967; 73:269-272. 5. Grossman HB. The late recurrence of grade I transitional cell carcinoma of the ureter after conservative therapy. J Urol 1978; 120:251-252. 6. Johnson DE, Babaian FLJ.Conservative surgical management for noninvasive distal ureteral carcinoma. Urology 1979; 13:365-367. 7. Perez-Castro EE, Martinez-Pineiro JA. Transurethral ureteroscopy: A current urological procedure. Arch Exp Urol 1980; 33:445-460. 8. Hofstetter A, Bowering R, Keiditsch E. Zerstorung von uretertumoren mit dem Nd-YAG-laser. Fortschr Med 1983; 101~625-628. 9. Hofstetter AG, Keiditsch E: Lasers for renal pelvis and ureteral tumors. Laser 1985; 1:75-77. 10. Schilling A, Bowering R, Keiditsch E. Use of the Nd:YAG laser in the treatment of ureteral tumors and ureteral condylomata acuminata. Eur Urol 1986; 12:30-33. 11. Blute ML, Segura JW, Patterson DE, Benson RC Jr, Zincke H. Impact of endourology on diagnosis and management of upper urinary tact urothelial cancer. J Urol 1989; 14111298-1301. 12. Schmeller NT, Pensel J. Ureteral tumors. In: Smith J A Jr, Stein BS, Benson RC Jr, eds. “Lasers in Urologic Surgery,’’ Chicago: Year Book Medical Publishers, 1989, pp 81-91. 13. Schmeller NT, Pensel J. Ureteral tumors. In: Smith J A Jr, Stein BS, Bensen RC J r , eds. “Lasers in Urologic Surgery.” Chicago: Year Book Medical Publishers (personal communication: Schilling A, Friesen A, et al.) 1989, p 90. 14. Smith JA J r , Dixon JA. Argon laser phototherapy of su-
Distal Ureteral Tumor Treatment perficial transitional cell carcinoma of the bladder. J Urol 1984; 131~655-656. 15. Levinson AK, Johnson DE. The argon laser in urology. Presented at 69th Annual Meeting South Central Section of the American Urological Association, October 14, 1990. Santa Fe, NM. 16. Sommer K, Pensel J, Lieck P, Baretton G, Schuller J.
493
Healing of the ureter after Nd:YAG laser coagulation: Morphologic and physiological aspects. Journal of Endourology 1989; 3:439-445. 17. Huffman JL, Bagley DH, Lyon ES, Morse MJ, Herr HW, Whitmore WJ Jr. Endoscopic diagnosis and treatment of upper-tract urothelial tumors: A preliminary report. Cancer 1985; 55:1422-1428.
