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Neodymium:Yag Laser Ablation of Posterior Urethral Valves
0022-534 7/87 /1381-0959$02.00/0
THE
Vol. 138, October
JOURNAL OF UROLOGY
Copyright© 1987 by The Williams & Wilkins Co.
Printed in U.S.A.
Surgical Techniques NEODYMIUM:YAG LASER ABLATION OF POSTERIOR URETHRAL VALVES RICHARD M. EHRLICH, ALLAN SHANBERG
AND
RICHARD N. FINE
From the Department of Surgery, Division of Urology and Division of Pediatric Nephrology, UCLA Medical Center, Los Angeles and Reider Laser Center, Memorial Medical Center of Long Beach, University of California, Irvine, California
ABSTRACT
We report successful neodymium:YAG laser ablation of posterior urethral valves in 6 boys. No strictures or incontinence resulted. (J. Ural., part 2, 138: 959-962, 1987)
The neodymium:YAG laser has found wide applicability in the treatment of numerous urological disorders. We describe the use of this modality to ablate posterior urethral valves in children. MATERIALS AND METHODS
From June 1985 to September 1986, 6 boys with posterior urethral valves underwent neodymium:YAG laser photoirradiation and ablation of urethral valves via cutaneous vesicostomy. Of the 6 boys 3 were diagnosed as having bilateral hydroureteronephrosis as determined by prenatal ultrasonography, as well as posterior urethral valves that were identified at term by voiding cystourethrography. Two patients presented with marked azotemia from severe bilateral renal dysplasia. Severe vesicoureteral reflux was present bilaterally in 2 patients and unilaterally in 1. In the latter patient the kidney with reflux was nonfunctional. Cutaneous vesicostomy1 was performed in all patients shortly after the diagnosis of posterior urethral valves was established and after stabilization of metabolic parameters. Average patient age at which laser ablation of the valves was performed was 11 months (range 7 to 20 months). Treatment was performed with the noncontact endo-Lase neodymium:YAG laser* with power settings of 20 watts, with an average of 900 joules in 5 patients. The SLT lasert contact probe had a power setting of 12 watts and 850 joules in 1 patient. All treatments were performed with the patient under general anesthesia, using the Olympus flexible nephroscope+ via the cutaneous vesicostomy in 5 patients, with the flexible laser fiber passed through the side channel of the nephroscope. Under direct vision laser photoirradiation was delivered to each valve leaflet at the 5 and 7 o'clock positions (fig. 1). In 1 patient laser photoirradiation was delivered suprapubically via a rigid pediatric cystoscope. In no instance was a cystoscope passed transurethrally in a retrograde manner. Initially, a No. 8 feeding tube was passed per urethram and grasped through the vesicostomy. A flexible metal catheter guide wire then was Supported in part by the University Urological Research Foundation, UCLA School of Medicine. * Endo-Lase, 1729 21st St., N. W., Washington, D. C. 20009. t Surgical Laser Technologies, 1 Great Valley Parkway, Malven, Pennsylvania 19355. :j: Olympus, 4 Nevada Dr., Lake Success, New York 11042.
passed through the lumen of the feeding tube, which was removed leaving the guide wire within the urethra to aid in identifying from above the valve leaflets (fig. 1, B). Type I urethral valves were present in all 6 patients. After laser photoirradiation the No. 8 feeding tube was replaced over the guide wire, which then was removed. The feeding tube was left in place for 24 to 48 hours, at which time voiding cystourethrography was repeated. If the antegrade urethrogram demonstrated successful ablation of the valves the vesicostomy was closed. In 2 instances bilateral ureteral tapering and reimplantation were done at the same time and in 1 patient a nephroureterectomy also was performed simultaneously. RESULTS
Neodymium:YAG laser ablation of the posterior urethral valves was successful in all 6 patients (figs. 2 and 3). In 1 boy postoperative antegrade urethrography showed moderate diminution in the width of the posterior urethra but there was a suggestion of persistent valve leaflets. This finding prompted repeat laser photoirradiation of the remaining leaflets 2 weeks later, which was successful. It is uncertain whether the remaining cusps would have been obstructive functionally but we thought that it was necessary to repeat the photoirradiation before the vesicostomy was closed. There have been no strictures nor demonstrable incontinence. Followup ranges from 4 to 15 months (mean 12 months). All patients void to completion. Vesicoureteral reflux has been corrected in both boys with bilateral reflux. In 1 child persistent grade II unilateral vesicoureteral reflux is being managed con servatively with antibacterial therapy. One child has undergone successful live donor renal transplantation and another awaits transplantation. The latter 2 patients underwent repeat voiding cystourethrograms in anticipation of transplantation, both of which were normal and showed no late stricture formation. DISCUSSION
The technique of valve ablation has become more precise since early reports suggested splitting the symphysis pubis with resection under direct vision. Valve rupture from prolonged catheter drainage as well as passage of an insulated hook or Fogarty catheter without direct vision but under fluoroscopic 959
960
EHRLICH, SHANBERG AND FINE
Fm. 1. A, view from bladder neck shows valve leaflets occluding urethra distal to prominent verumontanum. Small slit is seen between valves. B, valve leaflets stretched by metal guide wire. C, right valve leaflet turned white by neodymium:YAG laser irradiation. D, both valve leaflets whitened after laser irradiation. Secondary slough occurs thereafter.
control has been advocatE:Jd, 2• 3 as has perinea! urethrostomy with endoscopic diathermy coagulation via an auriscope. 4 Currently, the most popular method as advocated by Hendren5 and Crooks,6 is to use electrocoagulation via an infant cystoscope with a wire stylet passed through a 3F ureteral catheter. This method produces less thermal injury to deep tissues than use of the pediatric resectoscope.5 In several recent reports antegrade techniques have been recommended via either an established suprapubic vesicostomy
or percutaneous suprapubic cystotomy, particularly in premature or underweight term infants. 7- 9 We similarly adopted this suprapubic technique and in several prior instances we used a flexible fiberoptic nephroscope,10 which proved to be safe technically and obviated retrograde instrumentation. Multiple reports attest to a significant complication rate associated with primary valve ablation by conventional retrograde techniques. Urethral stricture remains the most significant complication, with a reported incidence ranging from 8 to
NEODYMIUM:YAG LASER ABLATION OF POSTERIOR URETHRAL VALVES
961
The laser physics and precise tissue destruction capability of neodymium make it an ideal modality for photoirradiation of posterior urethral valves. In theory this modality offers an improvement over electrocoagulation with its potential for deep urethral injury. 5 Indeed, our 6 successful cases of laser photoirradiation of posterior urethral valves in this pilot study, which has caused no stricture or incontinence, encourage us to continue to use the technique. Moreover, we are impressed that the suprapubic visualization of posterior urethral valves is superior to that afforded from below. It has the decided advantage of precise location of valve leaflets and it is less likely to injure the proximate sphincteric mechanism. We do not suggest that all posterior urethral valves be destroyed by neodymium: YAG laser irradiation but, in an everexpanding search for refinement in surgical technique, we believe that this is a precise, controlled alternative to electrocoagulation and it offers significant theoretical advantages.
REFERENCES
1. Duckett, J. W., Jr.: Current management of posterior urethral
FIG. 2. Preoperative (A) and postoperative (B) urethrograms in boy
25 per cent. 5 • 6 • 11 • 12 Sphincter damage and subsequent incontinence also are major complications. 13 Technological advances in pediatric instrumentation and optics that improve visualization with small cystoscopes designed for the neonatal urethra eventually may mitigate some of these problems. Nonetheless, many neonatal urethras will not accommodate even the smallest instrument comfortably and dilation of the infant urethra must be avoided. 14 Accordingly, Myers and Walker advocated cutaneous vesicostomy in neonates and infants to allow for appropriate upper tract decompression and prevention of urethral strictures, 11 a view to which we subscribe. Moreover, added impetus for the suprapubic approach was given by Krueger and associates, who suggested improved renal function and subsequent enhanced growth potential in azotemic infants younger than 30 days old compared to those treated only with primary valve ablation. 15 The primary effects of the neodymium: YAG laser are thermal coagulation of tissue with negligible vaporization and immediate tissue removal. 16 After secondary tissue slough, subsequent re-epithelialization without scarring or fibrosis results. 17 The neodymium:YAG laser has proved to be excellent for endoscopic application, particularly for ablation of urothelial tumors, by affording a well defined depth of tissue penetration with circumscribed tissue necrosis, 18 which is controlled precisely, constant and reproducible, as opposed to electrocoagulation, which is less homogeneous. 19 Histological studies have verified that the thermal injury resulting from neodymium: Y AG laser photoirradiation may heal with more elastic properties and less fibrous contraction than an electrocautery burn. 16' 2° Controlled pulsing by a shutter mechanism allows for millisecond interruption of laser energy, thus, allowing for precise photoirradiation and causing less damage to surrounding tissues. 20 Sapphire ceramic tips (contact probes) provide for a more intense effect in a smaller zone of tissue owing to reduced forward scatter of energy. 21 The tip comes into direct contact with the tissue.
valves. Urol. Clin. N. Amer., 1: 471, 1974. 2. Williams, D. I., Whitaker, R.H., Barratt, T. M. and Keeton, J.E.: Urethral valves. Brit. J. Urol., 45: 200, 1973. 3. Whitaker, R. H. and Sherwood, T.: An improved hook for destroying posterior urethral valves. J. Urol., 135: 531, 1986. 4. Johnston, J. H. and Kulatilake, A. E.: Posterior urethral valves: results and sequelae. In: Problems in Paediatric Urology. Edited by J. H. Johnston and R. J. Scholtmeijer. Amsterdam: Excerpta Medica, chapt. VIII, p. 161, 1972. 5. Hendren, W. H.: Complications of urethral valve surgery. In: Complications of Urologic Surgery. Edited by R. B. Smith and D. G. Skinner. Philadelphia: W. B. Saunders Co., chapt. 16, p. 307, 1976. 6. Crooks, K. K.: Urethral strictures following transurethral resection of posterior urethral valves. J. Urol., 127: 1153, 1982. 7. Zaontz, M. R. and Gibbons, M. D.: An antegrade technique for ablation of posterior urethral valves. J. Urol., 132: 982, 1984. 8. Zaontz, M. R. and Firlit, C. F.: Percutaneous antegrade ablation of posterior urethral valves in premature or underweight term neonates: an alternative to primary vesicostomy. J. Urol., 134: 139, 1985. 9. Zaontz, M. R. and Firlit, C. F.: Percutaneous antegrade ablation of posterior urethral valves in infants with small caliber urethras: an alternative to urinary diversion. J. Urol., 136: 247, 1986. 10. Lewis, R. M. and McCullough, D. L.: Use of the flexible fiberoptic nephroscope in the preoperative evaluation and delayed repair of traumatic urethral strictures. J. Urol., 133: 1036, 1985. 11. Myers, D. A. and Walker, R. D., III: Prevention of urethral strictures in the management of posterior urethral valves. J. Urol., 126: 655, 1981. 12. Churchill, B. M., Krueger, R. P., Fleisher, M. H. and Hardy, B. E.: Complications of posterior urethral valve surgery and their prevention. Urol. Clin. N. Amer., 10: 519, 1983. 13. Crooks, K. K.: The protean aspects of posterior urethral valves. J. Urol., 126: 763, 1981. 14. King, L. R.: Posterior urethra. In: Clinical Pediatric Urology, 2nd ed. Edited by P. P. Kelalis, L. R. King and A. B. Belman. Philadelphia: W. B. Saunders Co., vol. 1, chapt. 16, p. 547, 1985. 15. Krueger, R. P., Hardy, B. E. and Churchill, B. M.: Growth in boys with posterior urethral valves. Primary valve resection vs. upper tract diversion. Urol. Clin. N. Amer., 7: 265, 1980. 16. Hofstetter, A. and Frank, F.: Laser use in urology. In: Surgical Application of Lasers. Edited by J. A. Dixon. Chicago: Year Book Medical Publishers, chapt. 8, p. 150, 1983. 17. Smith, J. A., Jr. and Dixon, J. A.: Neodymium:YAG laser treatment of benign urethral strictures. J. Urol., 131: 1081, 1984. 18. Staehler, G., Chaussy, C., Jocham, D. and Schmiedt, E.: The use of neodymium-YAG lasers in urology: indications, technique and critical assessment. J. Urol., 134: 1155, 1985.
962
EHRLICH, SHANBERG AND FINE
Fm. 3. Preoperative (left) and postoperative (right) urethrograms in 3 boys 19. Keiditsch, E., Hofstetter, A., Rothenberger, K., Maiwald, H., Stern, J., Pense!, J. and Frank, F.: Comparative morphological investigations of the effects of the neodymium-YAG laser and electrocoagulation in experimental animal research. In: Gynecological Laser Surgery. Edited by J. H. Bellina. New York: Plenum Press, sect. 7, p. 327, 1981.
20. Fuller, T. A.: Fundamentals of lasers in surgery and medicine. In: Surgical Application of Lasers. Edited by J. A. Dixon. Chicago: Year Book Medical Publishers, chapt. 2, p. 11, 1983. 21. Von Eschenbach, A. C.: The neodymium-yttrium aluminum garnet (Nd:YAG) laser in urology. Urol. Clin. N. Amer., 13: 381, 1986.
THE
Vol. 138, October
JOURNAL OF UROLOGY
Copyright© 1987 by The Williams & Wilkins Co.
Printed in U.S.A.
Surgical Techniques NEODYMIUM:YAG LASER ABLATION OF POSTERIOR URETHRAL VALVES RICHARD M. EHRLICH, ALLAN SHANBERG
AND
RICHARD N. FINE
From the Department of Surgery, Division of Urology and Division of Pediatric Nephrology, UCLA Medical Center, Los Angeles and Reider Laser Center, Memorial Medical Center of Long Beach, University of California, Irvine, California
ABSTRACT
We report successful neodymium:YAG laser ablation of posterior urethral valves in 6 boys. No strictures or incontinence resulted. (J. Ural., part 2, 138: 959-962, 1987)
The neodymium:YAG laser has found wide applicability in the treatment of numerous urological disorders. We describe the use of this modality to ablate posterior urethral valves in children. MATERIALS AND METHODS
From June 1985 to September 1986, 6 boys with posterior urethral valves underwent neodymium:YAG laser photoirradiation and ablation of urethral valves via cutaneous vesicostomy. Of the 6 boys 3 were diagnosed as having bilateral hydroureteronephrosis as determined by prenatal ultrasonography, as well as posterior urethral valves that were identified at term by voiding cystourethrography. Two patients presented with marked azotemia from severe bilateral renal dysplasia. Severe vesicoureteral reflux was present bilaterally in 2 patients and unilaterally in 1. In the latter patient the kidney with reflux was nonfunctional. Cutaneous vesicostomy1 was performed in all patients shortly after the diagnosis of posterior urethral valves was established and after stabilization of metabolic parameters. Average patient age at which laser ablation of the valves was performed was 11 months (range 7 to 20 months). Treatment was performed with the noncontact endo-Lase neodymium:YAG laser* with power settings of 20 watts, with an average of 900 joules in 5 patients. The SLT lasert contact probe had a power setting of 12 watts and 850 joules in 1 patient. All treatments were performed with the patient under general anesthesia, using the Olympus flexible nephroscope+ via the cutaneous vesicostomy in 5 patients, with the flexible laser fiber passed through the side channel of the nephroscope. Under direct vision laser photoirradiation was delivered to each valve leaflet at the 5 and 7 o'clock positions (fig. 1). In 1 patient laser photoirradiation was delivered suprapubically via a rigid pediatric cystoscope. In no instance was a cystoscope passed transurethrally in a retrograde manner. Initially, a No. 8 feeding tube was passed per urethram and grasped through the vesicostomy. A flexible metal catheter guide wire then was Supported in part by the University Urological Research Foundation, UCLA School of Medicine. * Endo-Lase, 1729 21st St., N. W., Washington, D. C. 20009. t Surgical Laser Technologies, 1 Great Valley Parkway, Malven, Pennsylvania 19355. :j: Olympus, 4 Nevada Dr., Lake Success, New York 11042.
passed through the lumen of the feeding tube, which was removed leaving the guide wire within the urethra to aid in identifying from above the valve leaflets (fig. 1, B). Type I urethral valves were present in all 6 patients. After laser photoirradiation the No. 8 feeding tube was replaced over the guide wire, which then was removed. The feeding tube was left in place for 24 to 48 hours, at which time voiding cystourethrography was repeated. If the antegrade urethrogram demonstrated successful ablation of the valves the vesicostomy was closed. In 2 instances bilateral ureteral tapering and reimplantation were done at the same time and in 1 patient a nephroureterectomy also was performed simultaneously. RESULTS
Neodymium:YAG laser ablation of the posterior urethral valves was successful in all 6 patients (figs. 2 and 3). In 1 boy postoperative antegrade urethrography showed moderate diminution in the width of the posterior urethra but there was a suggestion of persistent valve leaflets. This finding prompted repeat laser photoirradiation of the remaining leaflets 2 weeks later, which was successful. It is uncertain whether the remaining cusps would have been obstructive functionally but we thought that it was necessary to repeat the photoirradiation before the vesicostomy was closed. There have been no strictures nor demonstrable incontinence. Followup ranges from 4 to 15 months (mean 12 months). All patients void to completion. Vesicoureteral reflux has been corrected in both boys with bilateral reflux. In 1 child persistent grade II unilateral vesicoureteral reflux is being managed con servatively with antibacterial therapy. One child has undergone successful live donor renal transplantation and another awaits transplantation. The latter 2 patients underwent repeat voiding cystourethrograms in anticipation of transplantation, both of which were normal and showed no late stricture formation. DISCUSSION
The technique of valve ablation has become more precise since early reports suggested splitting the symphysis pubis with resection under direct vision. Valve rupture from prolonged catheter drainage as well as passage of an insulated hook or Fogarty catheter without direct vision but under fluoroscopic 959
960
EHRLICH, SHANBERG AND FINE
Fm. 1. A, view from bladder neck shows valve leaflets occluding urethra distal to prominent verumontanum. Small slit is seen between valves. B, valve leaflets stretched by metal guide wire. C, right valve leaflet turned white by neodymium:YAG laser irradiation. D, both valve leaflets whitened after laser irradiation. Secondary slough occurs thereafter.
control has been advocatE:Jd, 2• 3 as has perinea! urethrostomy with endoscopic diathermy coagulation via an auriscope. 4 Currently, the most popular method as advocated by Hendren5 and Crooks,6 is to use electrocoagulation via an infant cystoscope with a wire stylet passed through a 3F ureteral catheter. This method produces less thermal injury to deep tissues than use of the pediatric resectoscope.5 In several recent reports antegrade techniques have been recommended via either an established suprapubic vesicostomy
or percutaneous suprapubic cystotomy, particularly in premature or underweight term infants. 7- 9 We similarly adopted this suprapubic technique and in several prior instances we used a flexible fiberoptic nephroscope,10 which proved to be safe technically and obviated retrograde instrumentation. Multiple reports attest to a significant complication rate associated with primary valve ablation by conventional retrograde techniques. Urethral stricture remains the most significant complication, with a reported incidence ranging from 8 to
NEODYMIUM:YAG LASER ABLATION OF POSTERIOR URETHRAL VALVES
961
The laser physics and precise tissue destruction capability of neodymium make it an ideal modality for photoirradiation of posterior urethral valves. In theory this modality offers an improvement over electrocoagulation with its potential for deep urethral injury. 5 Indeed, our 6 successful cases of laser photoirradiation of posterior urethral valves in this pilot study, which has caused no stricture or incontinence, encourage us to continue to use the technique. Moreover, we are impressed that the suprapubic visualization of posterior urethral valves is superior to that afforded from below. It has the decided advantage of precise location of valve leaflets and it is less likely to injure the proximate sphincteric mechanism. We do not suggest that all posterior urethral valves be destroyed by neodymium: YAG laser irradiation but, in an everexpanding search for refinement in surgical technique, we believe that this is a precise, controlled alternative to electrocoagulation and it offers significant theoretical advantages.
REFERENCES
1. Duckett, J. W., Jr.: Current management of posterior urethral
FIG. 2. Preoperative (A) and postoperative (B) urethrograms in boy
25 per cent. 5 • 6 • 11 • 12 Sphincter damage and subsequent incontinence also are major complications. 13 Technological advances in pediatric instrumentation and optics that improve visualization with small cystoscopes designed for the neonatal urethra eventually may mitigate some of these problems. Nonetheless, many neonatal urethras will not accommodate even the smallest instrument comfortably and dilation of the infant urethra must be avoided. 14 Accordingly, Myers and Walker advocated cutaneous vesicostomy in neonates and infants to allow for appropriate upper tract decompression and prevention of urethral strictures, 11 a view to which we subscribe. Moreover, added impetus for the suprapubic approach was given by Krueger and associates, who suggested improved renal function and subsequent enhanced growth potential in azotemic infants younger than 30 days old compared to those treated only with primary valve ablation. 15 The primary effects of the neodymium: YAG laser are thermal coagulation of tissue with negligible vaporization and immediate tissue removal. 16 After secondary tissue slough, subsequent re-epithelialization without scarring or fibrosis results. 17 The neodymium:YAG laser has proved to be excellent for endoscopic application, particularly for ablation of urothelial tumors, by affording a well defined depth of tissue penetration with circumscribed tissue necrosis, 18 which is controlled precisely, constant and reproducible, as opposed to electrocoagulation, which is less homogeneous. 19 Histological studies have verified that the thermal injury resulting from neodymium: Y AG laser photoirradiation may heal with more elastic properties and less fibrous contraction than an electrocautery burn. 16' 2° Controlled pulsing by a shutter mechanism allows for millisecond interruption of laser energy, thus, allowing for precise photoirradiation and causing less damage to surrounding tissues. 20 Sapphire ceramic tips (contact probes) provide for a more intense effect in a smaller zone of tissue owing to reduced forward scatter of energy. 21 The tip comes into direct contact with the tissue.
valves. Urol. Clin. N. Amer., 1: 471, 1974. 2. Williams, D. I., Whitaker, R.H., Barratt, T. M. and Keeton, J.E.: Urethral valves. Brit. J. Urol., 45: 200, 1973. 3. Whitaker, R. H. and Sherwood, T.: An improved hook for destroying posterior urethral valves. J. Urol., 135: 531, 1986. 4. Johnston, J. H. and Kulatilake, A. E.: Posterior urethral valves: results and sequelae. In: Problems in Paediatric Urology. Edited by J. H. Johnston and R. J. Scholtmeijer. Amsterdam: Excerpta Medica, chapt. VIII, p. 161, 1972. 5. Hendren, W. H.: Complications of urethral valve surgery. In: Complications of Urologic Surgery. Edited by R. B. Smith and D. G. Skinner. Philadelphia: W. B. Saunders Co., chapt. 16, p. 307, 1976. 6. Crooks, K. K.: Urethral strictures following transurethral resection of posterior urethral valves. J. Urol., 127: 1153, 1982. 7. Zaontz, M. R. and Gibbons, M. D.: An antegrade technique for ablation of posterior urethral valves. J. Urol., 132: 982, 1984. 8. Zaontz, M. R. and Firlit, C. F.: Percutaneous antegrade ablation of posterior urethral valves in premature or underweight term neonates: an alternative to primary vesicostomy. J. Urol., 134: 139, 1985. 9. Zaontz, M. R. and Firlit, C. F.: Percutaneous antegrade ablation of posterior urethral valves in infants with small caliber urethras: an alternative to urinary diversion. J. Urol., 136: 247, 1986. 10. Lewis, R. M. and McCullough, D. L.: Use of the flexible fiberoptic nephroscope in the preoperative evaluation and delayed repair of traumatic urethral strictures. J. Urol., 133: 1036, 1985. 11. Myers, D. A. and Walker, R. D., III: Prevention of urethral strictures in the management of posterior urethral valves. J. Urol., 126: 655, 1981. 12. Churchill, B. M., Krueger, R. P., Fleisher, M. H. and Hardy, B. E.: Complications of posterior urethral valve surgery and their prevention. Urol. Clin. N. Amer., 10: 519, 1983. 13. Crooks, K. K.: The protean aspects of posterior urethral valves. J. Urol., 126: 763, 1981. 14. King, L. R.: Posterior urethra. In: Clinical Pediatric Urology, 2nd ed. Edited by P. P. Kelalis, L. R. King and A. B. Belman. Philadelphia: W. B. Saunders Co., vol. 1, chapt. 16, p. 547, 1985. 15. Krueger, R. P., Hardy, B. E. and Churchill, B. M.: Growth in boys with posterior urethral valves. Primary valve resection vs. upper tract diversion. Urol. Clin. N. Amer., 7: 265, 1980. 16. Hofstetter, A. and Frank, F.: Laser use in urology. In: Surgical Application of Lasers. Edited by J. A. Dixon. Chicago: Year Book Medical Publishers, chapt. 8, p. 150, 1983. 17. Smith, J. A., Jr. and Dixon, J. A.: Neodymium:YAG laser treatment of benign urethral strictures. J. Urol., 131: 1081, 1984. 18. Staehler, G., Chaussy, C., Jocham, D. and Schmiedt, E.: The use of neodymium-YAG lasers in urology: indications, technique and critical assessment. J. Urol., 134: 1155, 1985.
962
EHRLICH, SHANBERG AND FINE
Fm. 3. Preoperative (left) and postoperative (right) urethrograms in 3 boys 19. Keiditsch, E., Hofstetter, A., Rothenberger, K., Maiwald, H., Stern, J., Pense!, J. and Frank, F.: Comparative morphological investigations of the effects of the neodymium-YAG laser and electrocoagulation in experimental animal research. In: Gynecological Laser Surgery. Edited by J. H. Bellina. New York: Plenum Press, sect. 7, p. 327, 1981.
20. Fuller, T. A.: Fundamentals of lasers in surgery and medicine. In: Surgical Application of Lasers. Edited by J. A. Dixon. Chicago: Year Book Medical Publishers, chapt. 2, p. 11, 1983. 21. Von Eschenbach, A. C.: The neodymium-yttrium aluminum garnet (Nd:YAG) laser in urology. Urol. Clin. N. Amer., 13: 381, 1986.