INTRODUCTION
Posterior urethral valves (PUV) represent the most common aetiology of congenital urethral obstruc- tion in boys and the most common urologic cause for end-stage renal disease in children.
Historically, four types of posterior urethral valves have been described. However, only types I and III are generally acknowledged as obstructing valvular lesions. Type I valves are the most common, and oc- cur in 95% of cases. They typically arise from the posterior and inferior edge of the verumontanum, and radiate distally toward the membranous urethra, where they insert and fuse anteriorly near the proxi- mal margin of the membranous urethra. Type II valves are not considered obstructive lesions and usually represent hypertrophy of the superficial trigonal muscle in response to distal urethral ob- struction. Type III valves occur in 5% of cases, and usually consist of an obstructing circumferential membrane that sits distal to the verumontanum at the level of the membranous urethra. These may form long folds that prolapse distally and lead to a windsock appearance. Type IV valves are usually seen in prune belly syndrome, where there is a kink- ing of the flabby, poorly supported prostate.
Voiding cystourethrogram (VCUG) is a gold stan- dard for confirmation of the diagnosis of PUV. On VCUG, a distended bladder with prostatic urethral
dilation is usually seen with a linear filling defect coursing from the verumontanum to the membra- nous urethra, which represents the obstructing valve.
Other radiographic features may also be present, such as massive unilateral vesicoureteral reflux, large bladder diverticuli, and urinary ascites, all of which appear to be associated with improved prognosis, as these findings indicate the presence of a “pop-off valve” mechanism (Rittenberg et al. 1988). These are thought to reduce intraluminal pressures, thereby al- lowing the fetal renal parenchyma to develop more normally.
In the past, many infants with PUV presented with dehydration, severe electrolyte abnormalities, uro- sepsis, and renal insufficiency. In these situations, a small feeding tube should be placed transurethrally to allow for adequate vesical drainage during the in- itiation of parental antibiotics and rehydration. In placing the tube, one must avoid coiling in the pros- tatic urethra due to the elevated bladder neck and di- lated prostatic urethra. Currently, however, the ma- jority of patients are diagnosed by prenatal ultra- sound, avoiding the severe illness previously asso- ciated with this anomaly.With the introduction of in- fant-size cystoscopes and miniature electrocautery, endoscopic ablation of the valves has become the treatment of choice for neonates with PUV.
Chester J. Koh, David A. Diamond
Figure 50.1, 50.2
Endoscopic valve ablation involves three essential steps: the assessment of the urethral calibre, the de- lineation of the anatomy, and the ablation of the valve tissue.
Most newborn urethras will comfortably accom- modate a 7.5F or 8F endoscope. For older infants and children, a 9F or 10F instrument can be used. The cal- ibre of the urethral meatus and the fossa navicularis tend to be the limiting anatomic factors in passing an instrument. To determine the maximum capacity of the urethra, pediatric Campbell’s sounds should be passed into the anterior urethra only. Calibration of the anterior urethra should occur to one size larger than the instrument to be used, with care taken to avoid overdilation of the urethra.
The anatomy can most easily be determined by passing the endoscope under direct vision into the bladder, then carefully withdrawing the scope. The bladder neck may be quite high, which will require positioning of the endoscope almost vertically to en- ter the bladder. Then, with the irrigation flowing, the endoscope is gradually withdrawn. In the case of a
type I valve, a prominent lip will appear posteriorly just distal to the bladder neck. Then one can visualize prominent urethral folds radiating upward from the verumontanum. The sail-like folds of the type I valve then emanate distally and laterally from the lower portion of the verumontanum and join anteriorly at the 12 o’clock position. The folds can most clearly be seen at the 5 and 7 o’clock positions, and one can see the external sphincter just distal to the valve leaflets.
To best visualize the valves, the bladder should be full, and the end of the cystoscope should be placed at the level of the external sphincter. The lower ab- dominal wall should then be pressed from above in a Crede fashion with the drainage channel open on the cystoscope to create a urinary flow. This should fill the valve leaflets, which usually snap into an ob- structing position.
In the case of the type III valve, which appears like a narrow obstructing diaphragm in the posterior urethra, the passage of the endoscope through the aperture in this diaphragm will often disrupt this type of valve.
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Figure 50.3
The optimal anatomic location for valve ablation is still the subject of debate. The 12 o’clock position has been referred to as the most critical area to ablate, as this is where the anteriorly fused membrane lies.
Others have argued that fulguration at the 5 and 7 o’clock positions is optimal since the leaflets are best visualized and most safely fulgurated at these posi- tions. Our preference is to ablate the valve leaflets at 5 and 7 o’clock positions, although we acknowledge that ablation of the valves at one location alone may disrupt the ring-like obstruction and be curative.
The 9F infant resectoscope allows one to safely ab- late the valve under direct vision. Once the bladder and urethra have been inspected with the cystoscope, the resectoscope sheath can be introduced after gen- tle urethral calibration. The sheath of the resecto- scope should be passed into the anterior urethra on- ly with the use of the obturator, then the working ele- ment can be placed to direct the instrument into the
bladder under vision. The visibility with the resecto- scope is usually slightly inferior to that with the cys- toscope because of the reduced flow of irrigation, so one should re-establish landmarks at this point.
With the use of the zero degree lens, the leaflets can best be visualized at the 5 and 7 o’clock positions.
Once the valves are in view, the resectoscope loop can then be used to hook the leaflets and draw them into the resectoscope sheath (Fig. 3). Applying a pure cutting current at 20–30 W will lead to ablation of the valve tissue. In addition, the instrument can be rotat- ed 180º to visualize and ablate the obstructing valve tissue at the 12 o’clock position. One advantage of the resectoscope is its ability to distinguish insignificant leaflets, which do not produce enough resistance to be hooked by the loop. If the fossa navicularis can not accommodate the resectoscope sheath comfortably, one may use the 7.5F cystoscope and the 3F Bugbee electrode.
Figure 50.1 Figure 50.2
Figure 50.3
Figure 50.4
Ablation with the Bugbee electrode is performed by engaging the medial edge of the leaflet with the elec- trode and then gently pushing toward the bladder and applying the current. The cautery settings should be at 25 W on pure cut.
Ablation at the 5 and 7 o’clock positions should render the valve incompetent. The remnant leaflets should flutter with the expressed urine. Repeat fulgu- ration may be necessary if residual obstructive tissue is noted.
For smaller infants, an alternative means of valve ablation may be necessary with the use of a 3F ureter- ic catheter and a wire stylet. The urethras of these children may only allow this smaller catheter to be passed through or alongside the 7.5F infant cysto- scope while permitting the flow of irrigant during the procedure for adequate visualization. The wire stylet is cut distally to protude from the end of the catheter, and the proximal end is clamped to the cautery elec- trode. The catheter itself acts as the insulator to the wire. The catheter is usually advanced through the
cystoscope to the level of the valve before the wire is advanced. Then the wire should be advanced 2 to 3 mm out of the catheter and pushed just into the valve leaflet. Fulguration can occur in a similar fash- ion as with the larger Bugbee electrode; however, sev- eral short bursts of current may be necessary to ef- fectively ablate the valves. Care should be taken to avoid overzealous fulguration, as this complication can lead to injury to the prostatic urethra and exter- nal sphincter.
Following valve ablation, an indwelling catheter is left in place for 24 h, although this may not be always necessary.
In select cases, alternative techniques may be use- ful. In developing countries without miniature equipment, or in premature infants in whom safe ab- lation is limited by urethral calibre, ablation with a Fogarty balloon catheter may be advantageous. In similar settings, the Whitaker insulated hook pro- vides another alternative approach.
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Figure 50.4
CONCLUSION
As the ability to prenatally diagnose PUV has devel- oped over time, so has the temptation of in utero intervention to relieve urinary obstruction secon- dary to valves. However, the long-term benefits of in utero intervention are currently unclear, and they must be weighed against the significant risks to the mother and fetus. Currently, the most compelling scenario for proceeding with prenatal intervention is when a male fetus with signs of infravesical obstruc- tion is initially noted to have normal amounts of am- niotic fluid, but subsequently has oligohydramnios, while having evidence of good renal function based on serial urine electrolyte aspirations.
Transurethral ablation usually leads to relief of ure- thral obstruction and often resolution of reflux via a minimally invasive approach that entails minimal risk. The benefits of ablation include decompression of the urinary tract and the tendency toward maxi- mum recoverability of overall renal function during a period of substantial renal growth. In addition, transurethral ablation is also believed to allow the
bladder to fill and empty on a regular cycle, which is thought to lead to more normal voiding patterns and to decreased collagen deposition and perhaps a re- duction in the risk of bladder non-compliance.
Certain prognostic factors have been reported in the literature. At age 12 months, a nadir creatinine of 0.8 mg/dl or less is associated with normal long-term renal function and improved prognosis. On the other hand, the presence of daytime urinary incontinence after age 5 years is associated with abnormal long- term renal function.
Yet, even with successful fulguration of valves, bladder dysfunction, which has also been described as the valve bladder syndrome, is always a distinct possibility. In general, management of the valve blad- der consists of anticholinergic medications to reduce uninhibited detrusor contractions, clean intermit- tent catheterization to ensure adequate bladder emp- tying, or bladder augmentation to improve bladder compliance and bladder volume.
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SELECTED BIBLIOGRAPHY
Diamond DA, Ransley PG (1987) Fogarty balloon catheter ab- lation of neonatal posterior urethral valves. J Urol 137 : 1209–1211
Glassberg KI (1985) Current issues regarding posterior ure- thral valves. Urol Clin North Am 12 : 175–185
Parkhouse HF, Barratt TM et al (1988) Long-term outcome of boys with posterior urethral valves. Br J Urol 62 : 59–62
Rittenberg MH, Hulbert WC et al (1988) Protective factors in posterior urethral valves. J Urol 140 : 993–996
Warshaw BL, Hymes LC et al (1985) Prognostic features in in- fants with obstructive uropathy due to posterior urethral valves. J Urol 133 : 240–243
Whitaker RH, Sherwood T (1986) An improved hook for de- stroying posterior urethral valves. J Urol 135 : 531–532
