POSTERIOR URETHRAL VALVES

POSTERIOR URETHRAL VALVES

P A R T V INFRAVESICAL URINE FLOW IMPAIRMENTS CHAPTER 33 POSTERIOR URETHRAL VALVES Clare E. Close and Michael E. Mitchell The fetal bladder cy...

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P A R T

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INFRAVESICAL URINE FLOW IMPAIRMENTS CHAPTER

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POSTERIOR URETHRAL VALVES Clare E. Close and Michael E. Mitchell

The fetal bladder cyclically fills and empties from early in development. This action provides stretch forces on the components of the developing bladder wall to produce a compliant organ that can store urine at low pressures and empty effectively. With fetal bladder outlet obstruction by posterior urethral valves (PUV), the developing bladder must carry out pressure work to empty. Normal cycling does not occur, and the bladder wall becomes thickened and noncompliant. As a result, high intravesical pressures develop and are transmitted to the upper tracts, resulting in ureteral dilation, urinary stasis, and parenchymal compression. The elevated upper tract pressures further damage renal parenchyma that may be primarily abnormal. In addition to the insult to the bladder and upper tracts, the elevated voiding pressures cause distention of the prostatic urethra and distortion of the bladder neck and developing external urinary sphincter. So devastating is this constellation of abnormalities that those fetuses with the highest grades of obstruction often do not survive in utero. Historically, severe PUV that remained undetected after birth resulted in urinary sepsis and even death in infancy. Over the last half-century, a variety of surgical interventions, together with improvements in medical management of infant sepsis, have allowed many infants to survive, only to face the continued problems of progressive renal failure and inadequate bladder function. Today, most infants with PUV are diagnosed in utero, allowing ablation of the urethral obstruction in the first days of life. Although underlying primary renal dysplasia cannot be altered by postnatal intervention, bladder function can often be preserved, thereby avoiding the cascading decline in renal function associated with persistent high bladder pressures. In order to maximize the long-term health of children with valves, it is essential to understand the management issues from the time of antenatal diagnosis through infancy, potty training, and adolescence. Appropriate diagnosis, treatment, and follow-up can result in improved long-term outcomes for the population with this difficult problem.

ANATOMY OF POSTERIOR URETHRAL  OBSTRUCTION In 1919, Hugh Hampton Young and his associates published their historic description of PUV. This classification is still widely accepted, although the description was based on a small

number of cases and included adult patients who had previously been instrumented. The most common type of obstruction according to the Young classification is type I valves, which lie as fins of mucosal tissue that radiate from the urethral crest of the distal verumontanum and sweep across the urethral lumen to fuse anteriorly.1 Young type III valves are obstructing diaphragms that lie in a transverse plane to the urethral lumen and originate distal to the verumontanum, near the bulbomembranous junction. The openings in the type III diaphragm valve vary in size and location. Type II valves, rarely mentioned in the literature, are mucosal folds that radiate from the proximal aspect of the verumontanum and extend cephalad to the bladder neck.1 Among the original 21 valve cases described by Young and colleagues in 19191 and Young and McKay in 1929,2 there were only 2 type II valves. Later, type II valves were described in patients with voiding abnormalities, but their association with abnormal urethral or bladder function is not documented. Both Pieretti3 and Hendren4 found patients with simultaneous type II and type I or III valves, perhaps suggesting that the type II lesion results from a more distal obstruction. The Young classification of valves has been challenged by several urologists, who have argued that prior instrumentation, inadequate direct endoscopic visualization, and distortion of the anatomy at postmortem examination tended to make the Young classification incorrect. Indeed, only 8 of Young and associates’ 21 patients were examined endoscopically. Few can argue that modern videoendoscopic techniques allow a more rigorous assessment of urethral anatomy. Postmortem and endoscopic data suggest a diaphragmatic configuration in all valves that is iatrogenically altered by urethral instrumentation.5-7 Robertson and Hayes6 unroofed the anterior urethral wall in 17 formalin-fixed postmortem specimens and found an obstructing diaphragm with a posterior opening, rather than two valve leaflets, in all cases. In a prospective endoscopic study, Dewan5 evaluated infants with suspected urethral obstruction prior to any other urethral instrumentation. On cystourethroscopy, he found that the obstructing lesions were urethral membranes with a posterior opening. On passage of the cystoscope, the membrane split into two leaflets, as had previously been described by Parkkulainen.7 Using endoscopic videorecording, Dewan5 performed a retrospective study of obstructive urethral anatomy. By comparing Young and associates’ descriptions with his modern observations, Dewan5 concluded that lesions described as either type I or type III valves were actually membranes extending from 437

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the distal end of the verumontanum with a pinhole opening in the posterior aspect of the diaphragm. In an attempt to provide a simple yet anatomically correct nomenclature for these lesions, Dewan and coworkers8 advocated replacing the complex Young classification with the unifying terminology congenital obstructing posterior urethral membranes (COPUM). The exact etiology of PUV or membranes has never been established. The prostatic urethra develops from the urogenital sinus by the 8th week of gestational life. The mesonephric ducts and paramesonephric ducts are both absorbed in this region of the vesicourethral canal. The mesonephric ducts develop into the ductus deferens, with the openings (ejaculatory ducts) lying lateral to the verumontanum. The distal paramesonephric ducts form part of the prostatic utricle, a small diverticulum on the verumontanum. The colliculus seminalis or verumontanum forms on the dorsal floor of the prostatic urethra as a result of the elevation of the urethral wall by the expanding ejaculatory ducts and utricle. The ends of the wolffian ducts form the normal urethral crest as they migrate cranially from an anterolateral position in the internal cloaca to a posterior position at the verumontanum.9 Stephens and associates10 hypothesized that the wolffian duct orifices in valve patients are initially misplaced and integrate abnormally into the urethral wall to form the obstructing lesion.

URETHRAL VALVES AS A SPECTRUM DISEASE There is clear clinical evidence that congenital urethral obstruction creates a spectrum disease. The timing and degree of the obstruction and the associated anatomy of the upper tracts are responsible for the range of abnormalities found in valve patients. Anatomic postmortem investigations support the clinical observation that the degree of urethral obstruction is variable, with the anteroposterior dimension of the urethral lumen at the level of the valves measuring from 3 mm to greater than 1 cm.10 In 1971, Hendren4 reported the incidence of secondary anatomic problems in 182 boys with PUV. Significant upper tract changes requiring operation because of infection or scarring occurred in 15% of the patients, with another 15% demonstrating severe hydronephrosis, megaureter, and renal insufficiency. The boys with high-grade urethral obstruction presented early in life with urinary sepsis, renal insufficiency, and pulmonary hypoplasia. Milder obstructive disease was diagnosed in older children who presented with incontinence and urinary tract infections. Controversy still surrounds the classification of patients with apparent PUV and minimal or no upper tract changes. Hendren4 reported normal upper tracts with or without associated low-grade vesicoureteral reflux (VUR) or paraureteral diverticula in 70% of the patients. Some believe that this end of the spectrum represents normal urethral variation or the functional obstruction of voiding dyssynergia. In support of Hendren’s observations, Pieretti3 reported mild valves in 41% of 87 boys he treated for PUV. These patients had no upper tract dilation, VUR, or paraureteral diverticula. Diurnal or nocturnal enuresis, urinary tract infection, and urinary frequency were the most common symptoms reported. The resolution of symptoms in 34 of the 36 boys after valve ablation seems to validate the significance of these minor lesions. Mild cases of PUV have also been described in boys who did not demonstrate the expected radiographic changes in the posterior urethra and bladder on voiding cystourethrography.11 These patients demonstrated abnormal urodynamic findings suggestive of obstructive damage to the bladder, including high filling and voiding pressures and detrusor

instability. The researchers found minor valve leaflets on cystoscopy and reported improvement in symptoms after valve ablation.11 The contribution of bladder retraining alone in this population has not yet been addressed, leaving intact the argument that these minor urethral lesions exist with functional rather than anatomic obstruction.

CHANGING TREATMENT PHILOSOPHIES OF POSTERIOR URETHRAL VALVES Although Young is remembered for his valve nomenclature, he should also be recognized for his surgical management of valves. After decades of controversy regarding the management of valve patients, Young and McKay’s2 1929 recommendation for primary valve ablation is now recognized as the appropriate initial treatment in almost all cases. Young and McKay advocated bladder drainage via a urethral catheter after valve ablation to allow decompression of the distended urinary tract. The duration of bladder drainage was determined by improvement in renal function. In spite of this early recommendation for primary ablation of valves, treatment by suprapubic catheter drainage became popular. Not surprisingly, the persistent indwelling catheter led to persistent urinary tract infection and poor patient survival.12 Furthermore, there was concern that total decompression of the bladder could result in a functional ureteral obstruction from compression by the thickened wall of the congenitally obstructed bladder. In 1963, Johnson13 advocated high urinary tract diversion by temporary cutaneous ureterostomy to decrease the risk of infection in patients with stasis of the dilated upper tracts and poor renal reserve. He argued that ureterostomies provided drainage without tubes and that temporary upper tract diversion could restore bladder function. A decade later, however, there was evidence in the literature that urinary diversion in valve patients is detrimental to the bladder. Unlike normal bladders or bladders with acquired obstruction, congenitally obstructed bladders develop severe, irreversible hypertonicity when defunctionalized. Lome and coworkers14 studied the bladders of children undergoing upper tract diversion by ureterostomy. All patients showed normal bladder capacity before the diversion. After diversion, all but one patient with valves showed reduced bladder capacity with poor bladder distention and compliance. Tanagho15 likewise demonstrated permanent contraction of the bladder in valve patients defunctionalized from 10 to 48 months of age. Two infant patients who were undiverted after 2 and 3 months had return of normal bladder capacity, although bladder compliance and subsequent function were not reported. In 1970, Hendren16 also argued against upper tract diversion, reporting that upper tract emptying was often not effective with diversion by ureterostomy and that the popular treatment could result in continued infection and poor patient outcome. He thought that primary valve ablation alone was appropriate for mild cases of obstruction but believed that the massive upper tract dilation and bladder neck hypertrophy associated with severe obstruction necessitated concurrent reconstruction of the megaureter and bladder neck. With or without upper tract reconstruction, Hendren’s early definitive valve treatment allowed the bladder to normally fill and empty in the newborn period. This concept, however, was overshadowed by the continued focus on renal function and the belief that upper tract diversion preserves or even improves renal function. In 1990, high diversion was again heralded as the best primary treatment for newborns with

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PUV who do not demonstrate a nadir creatinine level of 0.8 mg/dL within 5 days after bladder drainage by urethral catheter.17 Supravesical urinary diversion was advocated because of concern for persistent obstruction of the ureterovesical junction after relief of urethral obstruction. Arguing against this practice, Tietjen and associates18 used the Whitaker test to demonstrate fixed ureterovesical junction obstruction in only 4% of renal units in valve patients who had undergone proximal urinary diversion for newborn renal insufficiency. Furthermore, 85% of the patients demonstrated renal dysplasia by biopsy, and 42% of patients had progressed to end-stage renal failure at a mean follow-up of 9 years. During the 1990s, there was new focus on the true nature of renal insufficiency in patients with PUV. In a review of a large group of these patients, Smith and colleagues19 found no evidence that urinary diversion delayed the onset of end-stage renal failure. A multicenter study of 178 infants treated for PUV during the first year of life likewise found no long-term renal benefit with proximal urinary diversion.20 When comparing patients with newborn nadir creatinine levels greater than 1.2 mg/dL treated by early valve ablation alone versus upper tract diversion, Close and coworkers21 found that progression to end-stage failure occurred with either treatment if renal insufficiency was present after creatinine stabilization at birth. Three of six children in each treatment group required dialysis before age 3 years. Therefore, if there is no hope of reversing the primary renal dysplasia and in utero damage already suffered by these kidneys, diversion can be avoided and treatment can focus instead on the preservation of bladder function.

RENAL PATHOLOGY AND URETHRAL VALVES Renal insufficiency associated with congenital urethral ob­stru­ction may result from either primary renal dysplasia or progressive renal deterioration after birth. Experimental models and clinical cases demonstrate the pathogenesis of renal dysplasia associated with urethral obstruction. Severe obstruction in utero has been theorized to transmit damaging back-­pressure to the upper tracts, thereby causing deformation of the developing nephrons. Animal data suggest that early obstruction may result in severe upper tract changes. Fetal lamb studies showed that early second-trimester ureteral obstruction resulted in renal dysplasia similar to that seen with severe PUV.22 Similarly, Beck’s23 experimental work in fetal sheep demonstrated dysplasia occurring with early obstruction, whereas later in utero obstruction resulted only in hydronephrosis. Henneberry and Stephens24 supported a competing hypothesis known as the “bud theory” of renal dysplasia. They suggested that aberrant caudal budding of the ureter from the mesonephric duct causes aberrant induction of the renal mesenchyme. In support of this theory, they examined 34 renal units from autopsies of valve patients, with 14 of the 19 patients being younger than 6 months of age. They found a significant positive correlation between lateral trigone placement of the ureteral orifice and the gross renal morphologic changes of hydronephrosis and parenchymal thinning. Histologic evaluation demonstrated lower mean glomerular counts and the most severe degree of dysplasia in renal units with the most lateral ureteral placement. Nevertheless, four renal units with grossly dilated and tortuous ureters demonstrated normal parenchymal development. This finding suggests that the obstruction in these cases may have occurred later in gestation and provides evidence that backpressure and VUR alone are not responsible for dysplasia. The

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­ bservation of poor function in the refluxing unit of patients o with PUV seems to be very common, more so than in patients who have high-grade reflux without urethral obstruction. This may indicate overlapping pathologies, namely that in utero pressure work combined with primary dysmorphism results in dysplasia and poor function. There are limited clinical histopathologic data in the literature demonstrating the renal damage associated with urethral obstruction. A series of renal biopsies from valve patients with renal insufficiency and reflux demonstrated histologic changes of obstruction in 60%, dysplasia in 25%, interstitial fibrosis in 25%, and infectious change in 15%.25 The authors contended that the relatively low incidence of primary dysplasia in their series provided support to the practice of supravesical urinary diversion. However, the patients studied were not newborns, so these findings may reflect secondary or postdevelopmental influences. In contrast, Tietjen and associates18 reported renal dysplasia in 85% of renal units from babies treated by proximal diversion for renal insufficiency at birth. Daikha-Dahmane and coworkers26 analyzed kidney lesions from fetuses demonstrating bilateral urinary tract obstruction and surviving 14 to 37 weeks’ gestation. All fetuses older than 20 weeks’ gestation showed renal dysplasia with blastema cells, interstitial fibrosis, and an arrest of nephrogenesis. These findings support the irreversibility of obstructive changes occurring early in gestation.

PRESSURE POP-OFF MECHANISMS IN URETHRAL  OBSTRUCTION Hoover and Duckett27 introduced the concept of pressure popoffs in the obstructed urinary tract in 1982. They noted preserved contralateral renal function in patients with unilateral reflux into a nonfunctioning kidney. This phenomenon, known as the valves, unilateral reflux, and renal dysplasia (VURD) syndrome, suggests that mechanisms that relieve bladder pressure may have a protective effect on renal function. In addition to VUR, other less common pop-off mechanisms include large bladder diverticula, bladder rupture with urinary ascites, and renal urinary extravasation with urinoma formation. There is growing evidence that decompressive mechanisms may also affect bladder development. If the bladder is protected from pressure work during development, can its morphology and function be preserved? Chen and associates28 presented unusual documentation of three different pop-off mechanisms in a surviving infant with severe PUV. In their patient, oligohydramnios, bladder dome perforation, and ascites were diagnosed at 26 weeks’ gestation. At 37 weeks’ gestation, bilateral urinomas developed. Postnatal evaluation revealed bilateral VUR and a small, dystrophic bladder, but there was no long-term follow-up of bladder function. Kaefer and colleagues29 reported favorable bladder outcomes in 87% of valve patients with pop-off mechanisms. Rather than the typical thick-walled, trabeculated bladder, patients with upper tract pop-off mechanisms may demonstrate a smoothwalled bladder on voiding cystourethrography (VCUG).

PRENATAL DIAGNOSIS OF URETHRAL  OBSTRUCTION In the developed countries where obstetric sonography is routinely performed, most fetuses with urinary tract dilation are detected prenatally. The sensitivity for detection of obstructive uropathy by prenatal ultrasonography in multiple series was between 90% and 100%. Although in some cases the

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a­ bnormalities causing obstruction are lethal, most babies can be monitored with sequential ultrasound studies and undergo prompt workup and management after delivery. In many communities, obstetricians and perinatologists refer expec­ t­ant mothers to a pediatric urologist for prenatal consultation if significant obstructive uropathy is suspected. The consultant must be familiar with the urologic details of prenatal ultrasonography and should understand the limitations of the examination in predicting postnatal diagnosis and outcome. Prenatal ultrasonography should specifically address renal pelvic anteroposterior diameter, amniotic fluid volume, renal echogenicity, renal cortex thickness, bladder distention, bladder wall thickness, presence of urethral dilation, and evidence of urachal patency. Fetal genitourinary tract screening by ultrasound is possible at 20 weeks’ gestation, at which time the kidney is of adequate size for evaluation. A renal pelvic diameter between 4 and 10 mm in the second trimester is considered to represent mild dilation and does not persist postnatally in 97% of cases. A diameter exceeding 10 mm, or the presence of dilated calyces with a pelvic diameter of less than 10 mm, suggests significant pathology and warrants postnatal follow-up.30,31 The fetal renal parenchyma should be evaluated for thickness and echogenicity. Renal cortical echogenicity equal to that of the adjacent liver can occur in infants less than 4 months of age with normal kidneys. Echogenicity brighter than liver or spleen denotes underlying renal pathology, although the finding is nonspecific and occurs in glomerular, interstitial, tubular, and vascular renal disease.32 Cortical cysts in a brightly echogenic kidney are an unmistakable indication of primary renal dysplasia. Cortical atrophy can be seen in association with hydronephrosis and is defined as fetal renal cortex less than 2 mm in thickness.30 The fetal bladder is more difficult to assess by ultrasonography. By definition, the bladder wall is considered thickened if it is visible when the bladder is full. The diagnostic reliability of wall thickness is questionable, because the bladder is not always full at the time of the examination. Additionally, wall thickening may not occur until later in gestation and therefore will not be seen on early sonograms. Amniotic fluid volume is a key feature of the fetal ultrasound study. Oligohydramnios is a decrease in the normal amniotic fluid volume that results in restricted fetal movement or fetal compression.33 It is often a subjective measurement, graded as mild, moderate, or severe. Although there are many nonurologic causes of oligohydramnios, when it is found in association with increased renal echogenicity and persistent bladder distention, the cause is often PUV.34 However, most large prenatal ultrasound series show oligohydramnios in fewer than half of the patients in whom PUV is suspected. If hydroureteronephrosis and persistent bladder dilation are found together, the diagnosis of PUV is suspected, although similar findings may be found in patients with prune-belly syndrome, primary megaureter, or VUR (Fig. 33-1). Because the long-term outcomes for these diagnoses differ significantly, there has been an effort to identify characteristics of the obstetric sonogram that differentiate posterior urethral obstruction from other conditions. Of fetuses monitored for persistent megacystis and hydronephrosis suggestive for valves, 42% to 48% had confirmed posterior urethral obstruction at postnatal diagnosis.31,35 The findings of increased renal echogenicity and oligohydramnios in addition to hydronephrosis and bladder dilation greatly increase the predictive value of prenatal ultrasonography. Kaefer and coworkers34 reported PUV in 100% of eight male fetuses demonstrating this constellation of findings.

Figure 33-1  Antenatal ultrasound demonstrates bilateral hydrone-

phrosis and dilated bladder. These findings suggest posterior urethral valves. Postnatal evaluation in this infant revealed high-grade vesicoureteral reflux but no evidence of valves.

POSTNATAL DIAGNOSIS OF URETHRAL  OBSTRUCTION All newborn males with a history of significant prenatal hydronephrosis should be evaluated for possible urethral obstruction. Because volume depletion is common in the first 48 hours of life, ultrasound studies obtained during this period can be falsely negative and should be repeated at 1 week of age. The more severe cases of obstruction typically show hydroureteronephrosis, even with relative volume depletion (Fig. 33-2). A common misconception among some pediatricians is that normal voiding guarantees a normal urethra. Although some infants with obstruction have palpable bladder distention or delayed voiding, others have a normal physical examination and regularly wet diapers. A VCUG should be considered before discharge from the nursery if any significant degree of renal collecting system dilation is present on prenatal ultrasonography. In the infant without prenatal renal imaging, severe urethral obstruction can manifest as abdominal distention from a large full bladder, massive hydroureteronephrosis, or urinary ascites. Patent urachus and retroperitoneal urinoma are other findings that raise the suspicion of bladder outlet obstruction. Newborns with bladder outlet obstruction also present with respiratory distress secondary to pulmonary hypoplasia, severe abdominal distention, or pneumothorax. Other infants with PUV may have a delayed diagnosis made after workup for urinary tract infection, sepsis, acute renal failure, or failure to thrive in the first months of life. The VCUG remains the “gold standard” for postnatal diagnosis of PUV. Typically, the study is accomplished through retrograde bladder filling via a feeding tube or Foley catheter. A 5F (1.65-mm) feeding tube is preferable to a balloon catheter, which may obscure the diagnosis of nonvalve abnormalities (e.g., ureterocele). Alternatively, some institutions place a 5F suprapubic tube for antegrade bladder filling. The VCUG is best performed by a radiologist versed in pediatric evaluation. The newborn bladder requires cyclic filling during the study to adequately distend the bladder and urethra. Inadequate filling or poor voiding may result in failure to

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demonstrate VUR or prostatic urethral dilation. The VCUG should be ­personally reviewed by the urologist, particularly if no obstruction is reported. An oblique view of the urethra in the voiding phase is required to rule out the diagnosis of PUV (Fig. 33-3). On this image, the prostatic urethra is typically elongated and dilated, resulting in elevation of the bladder neck. On the cystogram, the bladder may appear smoothwalled or trabeculated. If there is high-grade reflux, the bladder may not fully distend. Transperitoneal ultrasonography is reported to be an alternative diagnostic tool that can demonstrate the urethral changes seen with PUV and possibly the obstructive lesion. The limitations of this method include the infrequent voiding in infants and the difficulty of coordinating the study with a sufficient void to demonstrate the anatomic changes.36

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Figure 33-2  Postnatal ultrasonograms in a newborn with posterior urethral valves. Right (A) and left (B) kidneys demonstrate gross ­hydronephrosis with parenchymal thinning on the left. C, Transverse image of the thick-walled bladder and bilateral hydroureter.

The ultimate improvement in renal function and upper tract dilation can be evaluated only after complete decompression of the bladder. If attempts to catheterize the bladder fail, the catheter should be placed under fluoroscopy. Rarely, a very premature infant with urethral obstruction requires bladder drainage through a suprapubic catheter placed with ultrasonographic guidance. Creatinine measurements during the first days of life reflect the maternal levels and are not indicative of the infant’s renal function. Serial creatinine measurements taken 7 to 10 days after bladder drainage establish the newborn preoperative nadir in full-term infants. After this initial period of stabilization, most infants can safely undergo primary ablation of valves.

Endoscopic Valve Ablation in the Newborn TREATMENT OF POSTERIOR URETHRAL VALVES  IN THE NEWBORN The initial treatment in a newborn diagnosed with PUV should begin with bladder drainage by urethral catheter, antibiotic administration, and correction of fluid and electrolyte abnormalities. A 6F (1.98-mm) catheter can typically be placed per urethra, with a coudé-tipped catheter or a catheter with a malleable guide facilitating bladder intubation over the elevated bladder neck. Ultrasonography can be used to verify that the catheter is in the bladder and not coiled in the dilated prostatic urethra. Such misplacement is common and often goes unrecognized because the catheter does drain intermittently.

New pediatric endoscopic equipment has drastically changed the surgical approach to valve treatment. Many newborns were treated with vesicostomy in the past only because of the relatively large resectoscopes available. The 8.5F (2.8-mm) resectoscope with a 5-degree lens and cold knife hook working element can be employed in infants as small as 2000 g.37 Although some surgeons continue to prefer to incise the valves with a Bugbee ball–tipped electrode, the minimal bleeding encountered after cold knife incision of even the fleshiest valves does not require electrocoagulation. Videoendoscopy and cold knife incision allow safe, effective ablation of obstructing urethral lesions without risk of thermal injury to the external sphincter.

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Figure 33-3  A, Inadequate newborn

voiding cystourethrogram (VCUG).There is poor distention on the urethra and no oblique image. This was misread as a normal urethra. B, VCUG of a newborn with posterior urethral valves (arrow). This is the same patient as A, but a repeat VCUG was done with adequate bladder cycling. Urethra is well dilated with voiding, revealing elongation of the prostatic urethra and bladder neck hypertrophy in the oblique image.

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A Bugbee electrode passed through the working channel of a 5F cystourethroscope is a useful technique in very small infants whose urethras cannot accommodate the larger instruments. Potassium-titanyl-phosphate (KTP) laser valve ­ablation has been reported to be safe in newborn infants, with no urethral stricture formation at 3 years’ follow-up; incontinence was not addressed in this study.38 Because the KTP laser penetrates up to 2 mm and has some forward scatter, its use in the newborn urethra is not without risk. On preliminary urethrocystoscopy, it is important to define the infant urethral anatomy for safe, effective treatment of the obstruction. Distortion of the normal urethral anatomy may occur secondary to obstruction and can cause confusion in distinguishing the obstructive lesion from the normal contours of the posterior urethra. The concept of the external sphincter as a short band of circumferential striated muscle distal to the verumontanum is widely held. However, postmortem dissections in term infants demonstrate the urethral sphincter extending the entire length of the prepenile urethra.39 The muscle is horseshoe-shaped at the bladder neck and extends down over the lateral surfaces of the prostatic urethra. The proximal extent of the sphincter can be quite prominent, causing confusion even to the experienced surgeon. Although uninterrupted from the bladder to the perineal membrane, the distal end of the sphincter as it surrounds the membranous urethra is twice as thick as the proximal end. The configuration of the sphincter changes after the newborn period, with further modifications at puberty and adulthood secondary to the muscle’s association with the prostate, bulbourethral glands, and ejaculatory ducts. The verumontanum is the critical landmark to identify before valve incision. An endoscopic evaluation of congenital urethral lesions in 44 boys indicated that all obstructing lesions of the posterior urethra were attached to the caudal end of the verumontanum, extending obliquely from the back of the posterior urethra and ending distally on the anterior urethral wall.5 The prominent distal aspect of the external urinary sphincter appears very separate from the distal end of the verumontanum and should not be confused with a valve lesion. Such a finding is common in boys with functional bladder outlet obstruction only. Once

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the structures are clearly identified, the valve tissue can safely be incised at the 5-, 7-, and 12-o’clock positions. An indwelling catheter is typically left in place at the end of the procedure for immediate postoperative fluid management.

Management after Valve Ablation A common concern of pediatricians managing the patient with PUV is the persistence of severe hydroureteronephrosis after valve ablation. Frequently, this is interpreted as evidence of ureterovesical junction obstruction, and, when it is combined with elevated creatinine levels, it leads to supravesical diversion in some institutions. Chronic dilation of the collecting system and ureters from in utero obstruction or reflux does not resolve immediately but is usually not evidence of continued high intrarenal pressure. Tietjen and associates18 used the Whitaker test to demonstrate fixed ureterovesical junction obstruction in only 4% of renal units in valve patients who had undergone proximal urinary diversion for newborn renal insufficiency. Furthermore, primary renal dysplasia was identified by biopsy in 85% of these patients. The fact that more than 40% of these patients progressed to end-stage renal failure with proximal diversion supports the belief that renal insufficiency demonstrated after newborn creatinine level stabilization is caused by underlying primary renal dysplasia and is not the result of continued obstruction. Vigilant follow-up is essential in the neonatal period after hospital discharge. Persistent hydroureteronephrosis is common but should be closely monitored. Urodynamic evaluation can confirm that resting bladder pressures are in a safe range (<30 cm H2O) and are not the cause of persistent hydronephrosis. Ultrasonography is also used to evaluate the renal parenchymal echogenicity and to demonstrate the presence of corticomedullary junctions. Hulbert and colleagues40 found that distinct corticomedullary differentiation in infants with PUV imaged before 6 months of age reliably predicted serum creatinine levels lower than 0.8 mg/dL at follow-up 1 to 4 years later. Although the obstructive effects on the prostatic urethra and bladder neck do not resolve immediately, a postoperative

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Figure 33-4  Newborn ultrasonogram in a male infant with severe renal and bladder abnormalities associated with posterior urethral valves. A, Left multicystic dysplastic kidney with massive right hydroureter in midline. B, Right dysplastic kidney.

VCUG should confirm complete valve ablation. In cases of severe preoperative urethral distortion, some surgeons prefer to perform repeat cystourethroscopy to rule out and treat possible residual valve tissue. A nuclear medicine renal scan is best obtained after 4 weeks of life to establish a baseline for differential renal function and to identify nonfunctioning renal units. Cooperative management by pediatric urology and nephrology staff facilitates the medical management in these infants. Acidosis and salt-wasting nephropathy are common and necessitate frequent monitoring of serum electrolytes. Infants suffering the most severe degrees of obstruction typically do not survive in utero because of elective termination or fetal demise. If these infants do survive, the degree of renal dysplasia and bladder damage can be so severe that management must be tailored to allow their survival, with acceptance that both renal and bladder function are often unsalvageable.

Case Report An infant boy was born at term with minimal maternal prenatal care and no prenatal ultrasonography. Bilateral pneumothoraces led to abdominal imaging and renal ultrasonography demonstrating bilateral cystic, dysplastic kidneys (Fig. 33-4). The VCUG demonstrated massive right VUR, ­ several large bladder diverticula, and a small bladder (Fig. 33-5). The gross dilation of the prostatic urethra was so severe that it was initially mistaken for the bladder. The serum creatinine level fell from 4.1 to 3.9 mg/dL after catheter drainage. Cystourethroscopy confirmed large fleshy valves, which were incised. The bladder was unusually small, and the right ureteral orifice was obscured within a large diverticulum. At 6 weeks of life, a furosemide (Lasix) renogram was obtained that demonstrated no function in the left kidney and poor drainage from the right refluxing kidney. Ultrasonography continued to demonstrate poor right renal parenchyma, right hydroureteronephrosis, and a left cystic kidney without visualization of the left ureter. In the first 4 months of life, the infant developed recurrent episodes of urosepsis despite prophylactic antibiotic therapy. A right end-cutaneous ureterostomy was performed, at which time a narrowed ureteral segment proximal to the right paraureteral diverticulum was

Figure 33-5  Newborn voiding cystourethrogram in a patient with

severe urethral obstruction (same infant as in Fig. 33-4). Note the small bladder (b) with multiple diverticula (d) and high-grade right vesicoureteral reflux into the grossly dilated right ureter. p, prostatic urethra; u, right refluxing, obstructed ureter.

found. After diversion, the infant had no further episodes of infection. The patient required dialysis beginning at 8 months of age. The diverted bladder capacity at 2 years of age was 5 mL, and a sigmoid conduit was created before renal ­transplantation. This case demonstrates the extreme example of both renal and bladder impairment associated with PUV. Fortunately, most infants have reasonable preservation of bladder and kidney function and do well with careful management.

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Reflux grade

(R) Pre-op (L)

5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0

1

2

3

4

(R) Post-op (L)

6 7 8 9 10 11 Patients Figure 33-6  Spontaneous resolution of vesicoureteral reflux 1 year after valve ablation alone. Results from 19 refluxing units in 11 patients are depicted. Persistence of reflux is associated with a nonfunctioning renal unit in 2 patients and upper tract duplication in 1 patient. Post-op, 1 year postoperative; Pre-op, before valve ablation; L, left; R, right.

Table 33-1    Anatomic Changes and Clinical

­ onsequences in the Valve Bladder C ­Syndrome

Organ

Pathology

Clinical Results

Kidneys

Dysplasia, c­ oncentrating defect

High urine volume

Ureters

Dilated, poor ­peristalsis

Large “dead space” Poor emptying Possible obstruction after reimplantation

Bladder

Poor compliance, ­relatively small ­volume, reduced sensation to high pressure

High bladder pressure most of time Progressive renal damage Progressive bladder ­damage

Urethra

Voiding dysfunction

Difficulty with bladder emptying Magnified bladder ­pressure effect

5

VESICOURETERAL REFLUX RESOLUTION AFTER PRIMARY VALVE ABLATION VUR occurs in up to 75% of infants diagnosed with PUV in the first year of life.21,41 Traditionally, routine management of these patients has included ureteral reimplantation, often done at the same time as contralateral nephroureterectomy of nonfunctioning renal units. There is long-standing evidence that reimplantation is not necessary in most valve patients, and conservative management alone is safe and effective.41 In a series of infants treated by primary valve ablation alone, Close and coworkers21 found improvement in reflux grade in 18 of 19 refluxing renal units after 1 year (Fig. 33-6). Complete resolution of reflux occurred within 2 years after valve ablation in 12 (86%) of 14 patients. Reflux into nonfunctioning kidneys typically does not resolve.27 Nephroureterectomy has been performed in the past to improve voiding dynamics in these patients, although ureteral preservation for possible ureterocystoplasty is appropriate in some cases.42-44

BLADDER FUNCTION IN VALVE PATIENTS There is wide acceptance of the concept that maximizing the long-term outcome in PUV patients centers on maintaining bladder function. Older patients with a missed diagnosis of severe PUV and valve patients with a history of urinary diversion were described by Mitchell in 198645 as illustrative cases of the “valve bladder syndrome.” For many, recognition of this syndrome has changed the approach to management of PUV in infants. Boys with a valve bladder demonstrate the long-term effect of persistent renal obstruction from high bladder pressures after relief of urethral obstruction. Pathologic changes in the entire urinary tract combine to further compromise renal function (Table 33-1). Progressive hydroureteronephrosis, polydipsia, polyuria, urinary frequency, and enuresis with renal insufficiency are hallmarks of the syndrome. Renal tubular dysfunction results in a severe urine concentrating defect with polyuria and polydipsia. Urine production in these children can range from 3 to 6 L/day. In patients with VUR and grossly dilated upper tracts, ureteral peristalsis is poor, and large urine volumes result in incomplete emptying of the collecting

system, ureters, and bladder. The thick-walled valve bladder is poorly compliant and functionally lacks normal sensation. These patients learn to tolerate high intravesical pressures and are able to hold large urine volumes at these pressures without pain. With gross distention, the thick wall of the bladder causes increased resistance to urine flow through the ureterovesical junction. Urine holding thus results in increased upper tract dilation and pressure and, ultimately, causes progressive renal damage. There is an increasing focus on the role of the bladder in the long-term outcome of patients with PUV. Urodynamic patterns described in older valve patients include bladder hyperreflexia, hypertonia (noncompliance), and myogenic failure.46 Although these changes are attributed to bladder outlet obstruction, the contribution of primary treatment to dysfunction cannot be ascertained from such reports. Many of the studies of bladder and ureteral function in valve patients are complicated by the inclusion of different primary treatment modalities and treatment ages in the same study group. Studies have now been published that focus on the functional outcome in newborns undergoing primary ablation alone for the treatment of congenital urethral obstruction. Holmdahl and associates47 demonstrated normal bladder compliance by 1 year of age in all infants undergoing primary valve ablation at a mean age of less than 2 months. They did not find the three dysfunctional patterns described by Peters and colleagues46 in older boys. In a retrospective evaluation of 23 newborn infants treated by valve ablation in the first weeks and followed up from 1 to 9 years, Close and coworkers21 found good bladder function as well as resolution of upper tract abnormalities. VCUG performed 1 year after valve ­ resection showed resolution of trabeculation in more than 85% of patients (Fig. 33-7).Additionally, when compared with infants treated by urinary diversion, those boys undergoing early valve ablation had significantly better bladder compliance and potty-training results. The mean bladder compliance was 17.2 mL/cm H2O in those infants treated by early primary incision, compared with 5.8 mL/cm H2O in boys treated by diversion. Ninety-two percent of the boys undergoing early ablation were potty trained by 4 years of age, whereas only 17% of the diverted boys were dry by age 4. Low bladder compliance and high bladder pressures led to bladder augmentation in 3 (38%) of the 8 diverted

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33:  Posterior Urethral Valves

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Figure 33-7  A, Voiding cystourethrogram (VCUG) of a newborn infant with posterior urethral valves. Note bladder wall trabeculation and

diverticula. B, VCUG of the same patient 1 year after newborn valve ablation demonstrates a healed bladder with a smooth wall and normal capacity.

patients. Only 1 (4%) of 23 patients undergoing primary ablation required bladder augmentation, and that patient had severe urethral obstruction that was undetected until 4 months of age.

URETHRAL VALVES AND RENAL TRANSPLANTATION Chronic renal failure necessitates renal transplantation in a significant number of boys with PUV. With appropriate management, many patients with moderate renal insufficiency at birth reach adolescence before requiring transplantation. Modern studies have addressed the possible detrimental effects of the valve bladder on renal graft survival. Reinberg and colleagues48 demonstrated significantly ­poorer 5-year graft survival for patients undergoing transplantation for valve-related renal failure than was found in those patients with nonobstructive etiologies. Similarly, Dewan and associates49 reported that valve bladder led to allograft failure in 12% of valve patients receiving a renal transplant. Other authors50,51 have demonstrated good allograft survival but elevated creatinine levels occurring over long-term follow-up in transplanted valve patients.

A large study with 10-year follow-up after renal transplantation demonstrated no difference in graft survival and creatinine levels when comparing children with PUV and children with nonobstructive causes of renal failure.52 These data may reflect the improvement in urologic management of valve bladder. The conclusion that the valve bladder will not negatively affect renal allografts is not supported by a ­ long-term follow-up evaluation addressing bladder function and outcomes of renal transplantation. Salomon and coworkers53 reviewed the voiding history of 44 valve patients who were monitored for a mean of 9 years after renal transplantation. They found an elevation of serum creatinine after 5 years of follow-up in boys with symptoms of bladder dysfunction including incontinence, urinary urgency, frequency, and difficulty emptying. Because of the relentless effects of the bladder on the upper tracts, the preservation of bladder function must be of primary consideration in all patients with PUV as management decisions are made.

REFERENCES For complete list of references log onto www.expertconsult.com