Thulium Laser for the Treatment of Posterior Urethral Valves in Infants

Abstract

Objective:

Thulium laser (ThL) has become popular in urology, because of its powerful action on tissue, achieving optimal ablation and hemostasis. Aim of our article was to evaluate efficacy of ThL in infants affected by posterior urethral valve (PUV) ablation.

Patients and Methods:

Clinical charts of 25 infants (age ≤12 months) who underwent PUV ablation were retrospectively reviewed. According to our protocol, all patients performed voiding cystourethrography and cystoscopy 6 to 8 months after initial treatment. Several factors, including age and weight at surgery, operative time, postoperative bleeding, catheterization period, postoperative urinary retention, retreatment for valve remnants, and stricture at follow-up, were evaluated. Preoperative, intraoperative, and postoperative data were analyzed.

Results:

Mean age at primary surgery was 4.5 months (5 days–10.5 months) and mean weight at primary surgery was 5.7 kg (2.5–10.3 kg). Mean operative time was 29.5 minutes (range 15–50 minutes). None of the patients experienced intraoperative and postoperative bleeding. In all cases, postoperative catheterization period was 1 day. Residual valves were found in 6 of 25 (24%) patients. No cases of urethral stricture were registered during follow-up (48.4 months, range: 11–95). Analyzing literature data using other techniques, complication rate of ThL PUV ablation seems lower than standard treatments (electrofulguration, cold knife) and comparable with those reported with other laser techniques.

Conclusion:

PUV ablation with ThL has proven to be feasible and safe in infants. Further studies are needed to define the real effectiveness of this laser technology in PUV ablation. Miniaturized instruments and ThL technology make early PUV treatment feasible also in low body weight newborns.

Introduction

Posterior urethral valves (PUVs) are the most common cause of congenital bladder outlet obstruction in the pediatric population and can lead to renal failure in 25% to 30% of patients.¹ The estimated incidence of PUVs is ∼1 in 5000 to 1 in 8000 male births, representing 10% of prenatally diagnosed urinary obstruction.² Several surgical options are available to treat PUVs, primary valve ablation represents the treatment of choice for this condition.^3

–6

Valve ablation has been performed over the years using different techniques and instruments. The obstructive membranes are most commonly endoscopically ablated using cold knife or electrofulguration (EF). In recent years, several studies on PUV treatment with neodymium:YAG laser and holmium:YAG laser have confirmed their efficacy and safety, and laser ablation of valves has gained wide popularity.^1,7

–12

Thulium laser (ThL) has become popular because of its powerful action on tissue, achieving optimal ablation and hemostasis in endoscopic prostate enucleation.¹³ Supported by these effective experiences in adult patients, ThL was introduced at our institution in 2014 at first for ureterocele incision and then for PUV treatment. To assess efficacy of ThL in PUV ablation, our experience has been retrospectively analyzed and compared with other techniques described in the literature.

Materials and Methods

ThL has been introduced in our clinical practice starting from 2014 as part of a research project approved by our institution on advantages and safety of new technologies in the surgical management of urinary malformation impairing urinary continence (Research/Ethical Committee Code: 201203X002862). All infants who underwent PUV ablation with ThL from January 2014 to June 2022 have been considered and their clinical charts were reviewed. Preoperatively, in all cases, informed consent on use ThL was obtained.

Inclusion criteria were antenatal and postnatal suspicion of PUV, confirmation of PUV with voiding cystourethrography (VCUG), age at valve ablation ≤12 months, body weight ≥2.500 kg, and no previous PUV treatment. Patients treated for PUV ablation using other techniques or by other surgical teams were excluded. Surgery was performed under general anesthesia, in lithotomy position. According to our protocol, antibiotic prophylaxis was administered perioperatively (a single dose of IV cefazolin, 50 mg/kg). We summarized patients' characteristics and follow-up parameters (Table 1).

Table 1.

Characteristics of Patients

Patient	Antenatal diagnosis	Weight, kg	Age, months	Operative time, minutes	Intraoperative bleeding	Postoperative bleeding	Postoperative catheterization, days	Postoperative urinary retention	Second resection	Operative time, minutes	Intraoperative bleeding	Postoperative bleeding	Postoperative catheterization, days	Postoperative urinary retention	Follow-up, months	stenosis
1	Yes	3.7	1.6	27	No	No	1	No	No						95	No
2	Yes	8	7.1	30	No	No	1	No	No						94	No
3	Yes	7	4.4	20	No	No	1	No	No						86	No
4	No	10	10.1	19	No	No	1	No	No						85	No
5	Yes	3.9	2.1	40	No	No	1	No	Yes	28	No	No	1	No	82	No
6	No	9.5	10.3	30	No	No	1	No	No						77	No
7	Yes	2.56	0.2	20	No	No	1	No	No						76	No
8	No	10.3	9.3	19	No	No	1	No	No						67	No
9	Yes	3.3	2.6	20	No	No	1	No	No						33	No
10	Yes	4.2	2.4	30	No	No	1	No	No						45	No
11	Yes	2.9	0.7	50	No	No	1	No	No						44	No
12	Yes	4.3	1.4	40	No	No	1	No	No						41	No
13	Yes	3.9	3.1	29	No	No	1	No	Yes	15	No	No	1	No	39	No
14	No	9.3	11.5	29	No	No	1	No	No						37	No
15	Yes	3.9	2.8	22	No	No	1	No	Yes	33	No	No	1	No	36	No
16	No	8	9.0	20	No	No	1	No	No						36	No
17	Yes	4.5	1.1	40	No	No	1	No	Yes	28	No	No	1	No	30	No
18	Yes	9.5	9.0	29	No	No	1	No	Yes	35	No	No	1	No	27	No
19	No	9	9.0	16	No	No	1	No	No						15	No
20	Yes	3	1.9	35	No	No	1	No	No						89	No
21	Yes	3.33	1.1	40	No	No	1	No	No						14	No
22	No	7.33	6.8	15	No	No	1	No	No						12	No
23	Yes	4.7	1.8	50	No	No	1	No	No						23	No
24	Yes	3.7	1.4	22	No	No	1	No	Yes	12	No	No	1	No	17	No
25	Yes	4.98	2.2	45	No	No	1	No	No						11	No

Surgical technique

After identification of the obstructive membranes, a transurethral guidewire (3 cm Flexible Tip PTFE Coated Urological Guidewire 0.89 mm × 150 cm) was placed in the bladder to maintain a landmark during laser ablation and to assist urethral catheter placement at the end of the procedure. ThL (Cyber 200 Watt; Quanta System) ablation was performed using a 4.7F (7° telescope) operative cystoscope in newborns and an 8F/9.8F (30° telescope) operative cystoscope in infants. The laser fiber (272 μm in newborns or 365 μm in infants) was passed through the operative channel of the cystoscope and brought in direct contact with the valves. The ThL power setting ranged from 5 to 7 watt in newborns and from 8 to 10 watt in older patients.

As recommended by the EAU Pediatric Guidelines, valve ablation was performed at 5, 7, and 12 o'clock positions.¹⁴ After valve ablation, urethral patency was evaluated intraoperatively using antegrade flow by exerting gentle pressure on the bladder with the cystoscope positioned distal to the verumontanum to exclude residual urethral obstruction; furthermore, the Credè Maneuver was performed to evaluate urinary stream at the end of the procedure.¹²

According to our protocol, a transurethral catheter was always placed at the end of the procedure. In patients with no postoperative bleeding, the catheter was removed 1 day postoperatively. When postoperative macroscopic hematuria persisted, the transurethral catheter was maintained until the bleeding resolved. During follow-up, we adopted the protocol previously established by our center¹⁵ and all patients underwent VCUG and cystoscopy at 6 to 8 months after primary treatment. When residual valves were identified, a second endoscopic ablation was performed, using the same technique as in the primary treatment. During follow-up, in case of clinical suspicion of urethral stricture (urinary tract infections, poor stream, urinary incontinence, etc.), a VCUG was repeated.

Results

From January 2014 to June 2022, 25 patients, mean age of 4.5 months (range: 5 days–11.5 months), underwent PUV ablation using ThL (Table 2). Eighteen patients were diagnosed prenatally. Mean weight at primary surgery was 5.79 kg (range: 2.56–10.3 kg); mean operative time was 29.48 minutes (range: 15–50 minutes). None of the patients experienced intraoperative and/or postoperative bleeding (macroscopic hematuria). In all cases, duration of postoperative catheterization was 1 day.

Table 2.

Summary of Preoperative, Perioperative, and Postoperative Data

Preoperative, perioperative, and postoperative data
No. of patients, n	25
Antenatal diagnosis, n	18
Weight at resection, kg, mean (range)	5.7 (2.56–10.3)
Age at resection, months, mean (range)	4.5 (5 days–10.5 months)
Operative time, minutes, mean (range)	29.5 (15–50)
Bleeding, patients
Intraoperative	0
Postoperative	0
Postoperative catheterization, days	1
Postoperative urinary retention	0
Residual valves at second look, n	6
Operative time, minutes, mean (range)	25.2 (12–35)
Bleeding, patients
Intraoperative	0
Postoperative	0
Postoperative catheterization, days	1
Postoperative urinary retention	0
Follow-up, months, mean (range)	48.4 (11–95)
Stenosis, patients	0

No episodes of urinary retention were reported after discharge. Endoscopic evidence of residual valves was found in 6 of 25 (24%) patients. Among them, two patients had normal findings at postoperative VCUG. Also after the second surgery, there were no cases of intraoperative and/or postoperative macroscopic hematuria, so the postoperative catheterization period was 1 day in all patients who underwent second look for remnant valves as well. After a mean follow-up of 48.4 months (range: 11–95 months), no cases of urethral stricture were registered and no case of external sphincter damage was reported.

Discussion

Treatment of PUV has evolved throughout the years along with greater understanding of the pathophysiology and possible consequences of this obstructive uropathy, but valve ablation remains of course the essential part in the treatment process.¹⁴ Several different modalities of endoscopic PUV ablation have been reported so far, such as cold knife incision, EF, or laser technology.^1,7,9,12 However, no standardizations or recommendations are reported regarding the best energy source and instrument to use for endoscopic PUV ablation.¹¹ EF of PUV has probably been the most common approach in the past decades.

Owing to the possible complications related to the intrinsic characteristics of this source of energy, laser technology for PUV treatment was proposed (Table 3). The first application of laser in PUV treatment dates back to 1987. Ehrlich and colleagues published an effective experience of PUV ablation through vesicostomy with neodymium:YAG laser in 6 boys.⁸ Subsequently, several promising experiences with neodymium:YAG laser or holmium:YAG laser were reported.^9

–12

Table 3.

Review of the Literature

First author	Technique	No. of patients	Age at resection	Weight at resection	Operative time	Bleeding	Postoperative catheterization, days	Urinary retention, n	Residual valves, n	Stenosis, n	Follow-up, time	Follow-up (investigation)
Babu⁷	EF	42	6.2 months (10 days–9 years)	Low weight/premature children excluded because resectoscope could not pass		1		0	1 (2.5%)	9 (21%)		VCUG 3 months postoperative ± cystoscopy
Babu⁷	Cold knife	41	3.4 months (12 days–5 years)			2		0	2 (5%)	0		VCUG 3 months postoperative ± cystoscopy
Sarhan¹	Diatermic loop	122				0	2	11		4	6.5 years (1.5–20 years)	VCUG 3 months post-operative ± cystoscopy
	Cold knife	102				2		4		1
	Bugbee	20				0		1		0
Ehrlich⁸	Nd:YAG laser	6								1
Biewald⁹	Nd:YAG laser	13	9 days (2 days–4 weeks)			0	5		1	0	2.3 months (6 months–5 y)	VCUG 4 weeks postoperative
Pagano¹⁰	Ho:YAG laser	7	<28 days		23 minutes	0	0	0	0	0	10.1 months (4–18 months)	VCUG 4 weeks postoperative
Gastaldi¹¹	Ho:YAG laser	18	12 days (1 days–5 years)		28 minutes	0	1	0	0	0	44 months (6–60 months)	VCUG 6 weeks postoperative
Mandal¹²	Bugbee	40	26 months (6–72 months)		21 minutes (15–30)		1.8		6	2	18 months (6 months–3 years)	VCUG 3–6 months postoperative ± cystoscopy
Mandal¹²	Ho:YAG laser	40	24 months (3–60 months)		15 minutes (10–20)		1		2	0		VCUG 3–6 months postoperative ± cystoscopy

EF = electrofulguration; Ho:YAG = holmium YAG laser; Nd:YAG = neodinium:YAG laser; VCUG = voiding cystourethrography.

The main advantages of this innovative techniques were a lower incidence of short- and long-time complications and a more precise ablation was obtained by using smaller instruments and a lower degree telescope angle, which permits a better observation of the urethra than the other instruments such as a resectoscope. Surprisingly, all articles have addressed the use of pulsatile wave neodymium:YAG or holmium:YAG laser for valve ablation without giving a rational for using a type of laser than another.

Since its introduction in 2005,¹⁶ continuous wave ThL has gained progressive popularity for tissue ablation, particularly for benign prostatic hyperplasia.^17,18 ThL enables more precise and efficient cutting while reducing thermal damage of the surrounding tissues,¹⁹ thanks to its wavelength of 1094 nm (similar to the water peak absorption in tissue), a four times higher absorption coefficient in water containing tissues and a smaller depth of penetrations than holmium:YAG laser (0.25 mm vs 0.4 mm).^19,20 ThL characteristics seem particularly important to reduce postoperative scars and stricture formation.

In 2016, Sheng et al. reported a higher incidence of ureteral postoperative stenosis after endoscopic ureteral fibroepithelial polyps' treatment with holmium laser than with ThL.²¹ Moreover, holmium:YAG and neodymium:YAG lasers operate exclusively in a pulse mode: this implies a slight fiber trembling during operation and a less precise action compared with ThL continuous mode.²¹ Furthermore, the continuous wave mode guarantees a more efficient hemostasis and tissues coagulation.^16,17 Another possible advantage of ThL, particularly in case of a rare disease such as PUV,¹⁵ is the hypothetical simple learning curve compared with holmium laser.

In fact, Enikeev and collagues²² have recently compared the learning curve of holmium laser vs ThL endoscopic enucleation of benign prostatic hyperplasia, reporting the need for a smaller learning curve for the latter technique (50–60 procedures for holmium laser vs 8–16 for ThL). For all these reasons, it seemed logical to us to adopt this type of laser also in newborns and infants affected by PUV, tiny membranes composed of connective tissues and scattered smooth muscle fibers that lie in proximity with delicate structures such as the external sphincter and verumontanum.²³

From January 2014 we adopted this procedure in 25 infants without complications, either in the immediate (bleeding, postoperative urinary retention) or later (stricture) postoperative period (as shown in Table 2). The absence of complication could be attributed to the aforementioned ThL characteristics. Continuous output of energy avoids the creation of pressure waves, reducing damage to adjacent tissues and allowing for greater precision when moving the fiber tip across tissue. Furthermore, the use of miniaturized instruments (4.7F cystoscope) could have contributed to the absence of complications in our study since it allows to perform less traumatic procedures also in patients with a low body weight (<3 kg).

Since none of our patients experienced postoperative bleeding, all transurethral catheters were removed in the first postoperative day, reducing morbidity and hospital stay. None of our patients experienced urinary incontinence. In the literature, damage to the sphincter and subsequent urinary incontinence have been described after electrocoagulation.^24,25 but not after EF laser or cold knife valve ablation.^1,7,12 To evaluate our surgical results, a second-look cystoscopy and VCUG were routinely performed 6 to 8 months after PUV resection: VCUG alone is reported to be less precise in diagnosing residual valves, whereas the combination of clinical, radiologic, and endoscopic evaluation seems to be the most appropriate approach.^26,27

When residual valves were present, a re-resection was performed. Need for retreatment seems to be higher in our cohort compared with data reported in the literature (Table 3), where VCUG was performed in the first weeks/months after primary ablation and a second-look cystoscopy was not routinely performed. However, in our experience, the residual valve rate obtained using ThL is comparable with that detected with EF (∼30%). Moreover, two out of six patients with residual valves had normal findings at VCUG.

Based exclusively on postoperative VCUG, only 4 of 25 (16%) patients would have undergone a second-look cystoscopy. For this reason, we believe that our most accurate postoperative control could explain the apparently higher rate of residual valves registered in our cohort than the other series included. Smeulders and colleagues reported voiding cystourethrogram alone could be imprecise (low sensitivity) in excluding residual valves after surgery and recommend a check cystoscopy in all.²⁷ As reported in their article, postoperative VCUG failed to diagnose 50% of PUV detected and consequently ablated in postoperative urethroscopy.

In their series, 16 of 30 (53%) patients underwent remnant valves ablation. Moreover, according to Haid et al., an unsuspicious posterior urethra at VCUG cannot exclude relevant PUV especially in symptomatic patients, or in case of secondary radiologic signs of bladder outlet obstruction and an endoscopic evaluation is required.²⁸

Of course, we cannot retrospectively define the clinical implications of the residual valves found in each patient: some of them, especially in case of minimal residual valves, could not have had implications on bladder and upper urinary tract, but we decided to treat all residual valves detected regardless of their entity.

Urethral stenosis caused by PUV treatment is an iatrogenic complication reported in the literature.^1,7 However, no stenosis has been registered so far in our study group. The above-mentioned characteristics of ThL could play a role in preventing deep tissue damage and cause re-epithelialization without scarring or fibrosis.²⁹ One disadvantage of ThL PUV treatment is the economic aspect, because laser technology is expensive. In our experience, the rental cost of holmium laser and ThL equipment is the same.

In our retrospective evaluation, ThL resection of PUV proved to be a feasible, safe, and effective technique in infants, because of the absence of postoperative bleeding and urethral strictures. However, the results of this study have to be further evaluated by other studies.

Our article has some limitations. First, we present the experience of a single center with a small sample; however, it is relatively small because PUV is considered a rare disease. Second, the study was performed retrospectively, comparing reports following different protocols. A prospective and preferably multicentric study is needed to better define ThL effectiveness in PUV treatment and to evaluate long-term outcomes. Comparison of ThL valve ablation with other techniques and types of lasers will be necessary to identify the “best” technique in terms of benefit and costs and the best parameters setting of the laser source.

Conclusion

In conclusion, PUV ablation using ThL has proven to be feasible and safe in infants. Further studies are needed to define the real effectiveness of this laser technology in PUV ablation. Miniaturized instruments and ThL technology make early PUV treatment feasible in the newborn with low body weight, avoiding urinary diversion. ThL can, therefore, be considered a valid option among different types of treatments for PUV management.

This study is generated within the European Reference Network for Rare Urogenital Diseases and Complex Conditions (ERN EUROGEN).

Footnotes

Authors' Contributions

V.F. contributed to writing—original draft (lead) and investigation (equal).

C.P. was in charge of data curation and writing—original draft (supporting).

F.L. was involved in investigation (equal) and formal analysis.

M.L.C. was involved in supervision (lead) and project administration.

A.V.U. was in charge of investigation (equal).

G.M. took charge of conceptualization (lead), writing—review and editing, and validation.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Abbreviations Used

References

Sarhan

, El-Ghoneimi

, Hafez

et al. Surgical complications of posterior urethral valve ablation: 20 years experience. J Pediatr Surg, 2010; 45(11):2222–2226; doi: 10.1016/j.jpedsurg.2010.07.003

Bilgutay

, Roth

, Gonzales

, et al. Posterior urethral valves: Risk factors for progression to renal failure. J Pediatr Urol, 2016; 12(3):179.e1–179.e7; doi: 10.1016/j.jpurol.2015.10.009

Walker

, Padron

. The management of posterior urethral valves by initial vesicostomy and delayed valve ablation. J Urol, 1990; 144(5):1212–1214; doi: 10.1016/S0022-5347(17)39696-9

Yohannes

, Hanna

. Current trends in the management of posterior urethral valves in the pediatric population. Urology, 2002; 60(6):947–953; doi: 10.1016/S0090-4295(02)01621-7

Smith

, Canning

, Schulman

, et al. The long-term outcome of posterior urethral valves treated with primary valve ablation and observation. J Urol, 1996; 155(5):1730–1734.

Farhat

, McLorie

, Capolicchio

, et al. Outcomes of primary valve ablation versus urinary tract diversion in patients with posterior urethral valves. Urology, 2000; 56(4):653–657; doi: 10.1016/S0090-4295(00)00784-6

Babu

, Kumar

. Early outcome following diathermy versus cold knife ablation of posterior urethral valves. J Pediatr Urol, 2013; 9(1):7–10; doi: 10.1016/j.jpurol.2012.02.014

Ehrlich

, Shanberg

, Fine

. Neodymium:Yag laser ablation of posterior urethral valves. J Urol, 1987; 138(4 Pt 2):959–962; doi: 10.1016/S0022-5347(17)43471-9

Biewald

, Schier

. Laser treatment of posterior urethral valves in neonates. Br J Urol, 1992; 69(4):425–427; doi: 10.1111/j.1464-410X.1992.tb15572.x

10.

Pagano

, van Batavia

, Casale

. Laser ablation in the management of obstructive uropathy in neonates. J Endourol, 2015; 29(5):611–614; doi: 10.1089/end.2014.0260

11.

Gastaldi

, El-Khoury

, Haddad

, et al. Preliminary experience in endoscopic section of posterior urethral valves using the Holmium:YAG laser. J Pediatr Urol, 2022; 18(3):367.e1–e367.e7; doi: 10.1016/j.jpurol.2022.03.015

12.

Mandal

, Goel

, Kumar

, et al. Use of holmium:YAG laser in posterior urethral valves: Another method of fulguration. J Pediatr Urol, 2013; 9(6):1093–1097; doi: 10.1016/j.jpurol.2013.03.015

13.

Tan

, Zhang

, Li

, et al. Transurethral vaporesection of prostate: Diode laser or thulium laser?. Lasers Med Sci, 2018; 33(4):891–897; doi: 10.1007/s10103-018-2499-4

14.

EAU Guidelines. Congenital lower urinary tract obstruction (CLUTO) In: Presented at the EAU Annual Congress Amsterdam. EAU Guidelines Office: Arnhem, The Netherlands; 2022; pp. 89–94.

15.

Pellegrino

, Capitanucci

, Forlini

, et al. Posterior urethral valves: Role of prenatal diagnosis and long-term management of bladder function; a single center point of view and review of literature. Front Pediatr, 2023; 10:1057092; doi: 10.3389/fped.2022.1057092

16.

Fried

, Murray

. High-power thulium fiber laser ablation of urinary tissues at 1.94 μm. J Endourol, 2005; 19(1):25–31; doi: 10.1089/end.2005.19.25

17.

Meng

, Peng

, Li

, et al. Comparison of enucleation between thulium laser and holmium laser for benign prostatic hyperplasia: A systematic review and meta-analysis. Asian J Surg, 2022; 45(2):689–697; doi: 10.1016/j.asjsur.2021.07.045

18.

Wani

, Sriprasad

, Bhat

, et al. Is Thulium laser enucleation of prostate an alternative to Holmium and TURP surgeries—A systematic review?. Turk J Urol, 2020; 46(6):419–426; doi: 10.5152/tud.2020.20202

19.

Bozzini

, Gastaldi

, Besana

, et al. Thulium-laser retrograde intra renal ablation of upper urinary tract transitional cell carcinoma: An ESUT Study. Minerva Urol Nephrol, 2021; 73(1):114–121; doi: 10.23736/S2724-6051.20.03689-9

20.

Rice

, Somani

. A systematic review of thulium fiber laser: Applications and advantages of laser technology in the field of urology. Res Rep Urol, 2021; 13:519–527; doi: 10.2147/RRU.S233979

21.

Sheng

, Zhang

, Qian

, et al. Treatment of ureteral fibroepithelial polyp by ureteroscopy combined with holmium laser or thulium laser: A retrospective study. Photomed Laser Surg, 2016; 34(10):456–459; doi: 10.1089/pho.2016.4133

22.

Enikeev

, Glybochko

, Rapoport

, et al. A randomized trial comparing the learning curve of 3 endoscopic enucleation techniques (HoLEP, ThuFLEP, and MEP) for BPH using mentoring approach—Initial results. Urology, 2018; 121:51–57; doi: 10.1016/j.urology.2018.06.045

23.

Krishnan

, de Souza

, Konijeti

, et al. The anatomy and embryology of posterior urethral valves. J Urol, 2006; 175(4):1214–1220; doi: 10.1016/S0022-5347(05)00642-7

24.

Nielsen

. Errors and dangers of various valve resection technics [in German]. Z Kinderchir, 1990; 45(1):40–42; doi: 10.1055/s-2008-1042547

25.

Crooks

. The protean aspects of posterior urethral valves. J Urol, 1981; 126(6):763–766; doi: 10.1016/S0022-5347(17)54739-4

26.

Oktar

, Salabas

, Acar

, et al. Residual valve and stricture after posterior urethral valve ablation: How to evaluate?. J Pediatr Urol, 2013; 9(2):184–187; doi: 10.1016/j.jpurol.2012.01.016

27.

Smeulders

, Makin

, Desai

, et al. The predictive value of a repeat micturating cystourethrogram for remnant leaflets after primary endoscopic ablation of posterior urethral valves. J Pediatr Urol, 2011; 7(2):203–208; doi: 10.1016/j.jpurol.2010.04.011

28.

Haid

, Thüminger

, Lusuardi

, et al. Is there a need for endoscopic evaluation in symptomatic boys with an unsuspicious urethra on VCUG? A consideration of secondary radiologic signs of posterior urethral valves. World J Urol, 2021; 39(1):271–279; doi: 10.1007/s00345-020-03175-2

29.

Khusid

, Khargi

, Seiden

, et al. Thulium fiber laser utilization in urological surgery: A narrative review. Investig Clin Urol, 2021; 62(2):136; doi: 10.4111/icu.20200467