INTRODUCTION — Posterior urethral valves (PUV) are obstructing membranous folds within the lumen of the posterior urethra (figure 1). PUV is the most common etiology of urinary tract obstruction in the newborn male, occurring in 1 in 5000 to 8000 pregnancies . PUV are also the most common cause of chronic kidney disease (CKD) due to urinary tract obstruction in children .
The management of PUV will be reviewed here. The clinical presentation and diagnosis of PUV are discussed separately. (See "Clinical presentation and diagnosis of posterior urethral valves".)
PRENATAL INTERVENTION — With prenatal detection of PUV and technological advances in surgical equipment, the management of PUV has evolved to include prenatal surgical intervention. However, this remains investigational, and the vast majority of affected infants should be treated soon after birth.
The first case of prenatal surgery to relieve obstructive uropathy was performed in 1981 [3,4]. Surgical intervention, primarily vesicoamniotic shunt placement, was based upon the rationale that restoring amniotic fluid to normal levels by shunting fetal urine from the obstructed urinary system to the amniotic space would prevent lung hypoplasia and, thus, improve neonatal survival. In addition, relief of the obstruction would also reduce back pressure and reduce injury to the developing nephron, thus improving long-term renal function postnatally. (See "Clinical presentation and diagnosis of posterior urethral valves", section on 'Renal and urologic consequences' and "Fetal hydronephrosis: Etiology and prenatal management", section on 'Prenatal management'.)
However, over the past three decades since the introduction of fetal intervention for obstructive uropathy, data on outcome of fetal surgery for PUV suggest that it is associated with a risk of fetal and maternal morbidity without proven benefit for long-term renal outcome.
This was illustrated in a case series from 1988 to 1991 of 40 fetuses cared for at one of the most active tertiary centers for fetal intervention . Criteria for fetal intervention included normal karyotype, favorable fetal urinary electrolytes with beta-microglobulin levels predictive of normal renal function, and a detailed prenatal renal ultrasound that did not show evidence of renal cystic disease . Of the 40 eligible fetuses, 36 underwent surgical intervention, including 14 with PUV at a mean gestational age of 22.5 weeks. In the 14 patients with PUV, procedures included placement of a vesicoamniotic shunt in nine cases, ablation of PUV in two cases, and fetal bladder marsupialization (ie, bladder was surgically opened and secured to the abdominal wall) in two cases, plus creation of a ureterostomy in one case. The following findings were noted in the 14 PUV cases:
●Five deaths occurred in infants who were born prematurely and had respiratory failure.
●One pregnancy was terminated because of evidence of shunt failure and findings indicative of poor lung and renal development and function.
●Eight patients were alive at a mean follow-up of 11.6 years. Five patients had chronic kidney disease (CKD) demonstrated by an elevated serum creatinine, of whom two had undergone renal transplantation, and another patient was awaiting organ donation.
Similar results were seen in a case series from a single fetal treatment center of 20 fetuses with lower urinary tract obstruction, including seven with posterior urethral valves . The mean gestational age was 34.6 weeks with a mean birth weight of 2.57 kg. There were two neonatal deaths due to pulmonary hypoplasia. Among the survivors, six developed end-stage renal disease (ESRD) requiring either dialysis or renal transplantation, and four had minor renal insufficiency at a mean age of 5.83 years.
In a multicenter retrospective report of 50 fetal cystoscopies performed from 2004 to 2013, laser fulguration of PUV was performed in 30fetuses . Four pregnancies were terminated, and 24 live-born infants were delivered at a mean gestational age (GA) of 35 weeks. Seven infants died in the neonatal period. All infants who survived the neonatal period were alive at one year of age, including 13 with normal renal function; and at two years of life, there were 15 survivors, including 11 with normal renal function. Two patients were receiving dialysis within two years of life.
These results demonstrated a significant mortality and morbidity rate of prenatal intervention for PUV. Ongoing efforts to develop new technology and increased training and experience of the surgeon hopefully will result in improved mortality and morbidity outcome. But until that time, fetal surgery for PUV should be considered only for fetuses who have a high risk of in utero or neonatal death due to midtrimester severe oligohydramnios, and who have both a normal karyotype and evidence of good renal function based upon fetal urinary evaluation. Fetal urine evaluation is performed by urine sampling from the bladder by catheter placement under ultrasound guidance on more than one occasion. The urine from the initial drainage is discarded and a urine sample obtained after bladder refilling is sent for analysis. A favorable urine sample indicating good renal function has a urine sodium of less than 100 mmol/L, chloride less than 90 mmol/L, osmolality less than 210 mOsm/L, and a beta-2 microglobulin less than 6 mg/L [8,9]. If fetal surgery is being considered, it should only be performed in fetal treatment centers with considerable experience and expertise due to the risks to the mother and fetus.
POSTNATAL MANAGEMENT — In patients without fetal intervention, once the diagnosis of PUV is suspected or diagnosed, initial postnatal management includes stabilization of the patient and drainage of the urinary tract.
●Medical management includes correction of electrolyte abnormalities, particularly hyperkalemia, and intervention to treat respiratory distress and urosepsis. In addition, renal function is monitored before, during temporary bladder drainage, and after PUV ablation. (See "Fluid and electrolyte therapy in newborns" and "Chronic kidney disease in children: Overview of management".)
●Temporary drainage of the urinary tract − Drainage of the bladder should be done once the patient is stabilized. In most instances, temporary drainage is performed by placement of a catheter in the bladder. In some centers, primary ablation is used without initial drainage .
In general, we use a soft feeding tube rather than a Foley catheter with a balloon to drain the bladder. The feeding tube has a larger internal diameter, allowing for better drainage, and the inflated balloon of the Foley catheter may occlude the ureteral orifices. We typically use an 8 French or greater feeding tube depending upon the size of the urethral meatus. Ultrasonography can be used to document the correct placement of the catheter into the bladder. It is common for any type of urethral catheters to coil in the dilated posterior urethra. If urethral catheter drainage cannot be established, then emergent consultation with a pediatric urologist is necessary for cystoscopic evaluation.
Once drainage is established, the patient may have large urinary water and solute losses because of tubular dysfunction, resulting in an inability to concentrate the urine or normally absorb solutes (eg, sodium and potassium) . In addition, some patients with PUV due to urinary obstruction may have type IV renal tubular acidosis. As a result, careful monitoring of serum electrolyte including serum bicarbonate, and fluid status is required with timely replacement of fluid and electrolytes as needed.
Cystoscopy — Cystoscopy confirms the diagnosis with direct visualization of the PUV. In addition to advances in surgical technique and instruments, primary ablation during cystoscopy is the preferred initial surgical treatment of PUV because it is a less invasive procedure that may preserve bladder function, and it decreases the need for subsequent surgical intervention [4,10,12]. The timing of this procedure is dependent on the overall health status of the neonate and issues with general anesthesia. The ability to perform this procedure is determined by whether the size of the male urethra can accommodate the neonatal cystoscope.
For preterm infants, cystoscopy is challenging. For these infants, a small catheter (5 or 8 French feeding tube) is temporarily placed into the bladder through the urethra for urinary drainage. An observational study of 126 neonatal males reported that progressive urethral catheter dilation improved the rate of successful primary ablation to 97 percent compared with the 82 percent that was cited in the literature . However, we have found that placement of a temporary feeding tube is sufficient until the urethra is large enough to accommodate the cystoscope.
Although primary ablation is not generally performed in premature infants, in one small case series of 17 low birth weight infants (median birth weight 2100 g, range 1760 to 2690 g), a Fogarty catheter under direct visual guidance of a neonatal cystoscope was used to disrupt PUV . In 14 of the surviving infants (three died of causes unrelated to the procedure), voiding cystourethrography demonstrated effective ablation and adequate bladder drainage. The advantage of this technique is that it avoided long-term catheterization and the need for vesicostomy. However, the use of this technique has been very limited, and it should only be performed by an experienced pediatric urologist for the rare premature infant with obstructive uropathy due to PUV.
Valve ablation relieves the urethral obstruction in most patients [10,15-17]. With relief of bladder pressure in those patients with vesicoureteral reflux (VUR), resolution of VUR will occur in one-third of the patients after ablation.
Vesicostomy — If primary valve ablation cannot be done, generally for technical reasons, vesicostomy is the next preferred procedure as it allows good drainage of the urinary tract, which relieves back pressure, and is a reversible procedure. It also allows for the normal cyclical filling and emptying of the bladder at low vesical pressure. Vesicostomy is performed in very preterm infants in whom safe visualization or ablation of the valves is not possible.
Higher diversions — Higher diversions with cutaneous ureterostomies and pyelostomies are rarely indicated and do not improve outcomes compared with vesicostomy. They commit a patient to subsequent major upper tract reconstruction. In addition, higher diversions disrupt the filling and emptying of the bladder, which may further impact bladder function .
POST-PROCEDURE MANAGEMENT — After a successful procedure that relieves or bypasses the intervention, management includes detecting and treating bladder dysfunction, monitoring renal function, and, if necessary, managing the consequences of chronic kidney disease (CKD).
Bladder function — Bladder function should be evaluated by imaging and urodynamic studies. The use of clean intermittent catheterization (CIC) and anticholinergic medications lowers bladder pressures in patients with severe bladder dysfunction (ie, low capacity, poorly compliant bladders with high filling pressure). It may reduce the rate of vesicoureteral reflux, if present, post-ablation. (See "Clinical presentation and diagnosis of posterior urethral valves", section on 'Bladder dysfunction' and "Evaluation and diagnosis of bladder dysfunction in children".)
After PUV ablation, persistent hydronephrosis and/or hydroureteronephrosis may reflect abnormal bladder function. In these patients, urodynamic studies are indicated with therapy (ie, CIC and/or anticholinergic therapy) directed towards improved bladder compliance and complete emptying . The use of nocturnal bladder emptying with indwelling Foley catheter may be helpful in those patients who have persistent hydroureteronephrosis. A series of 18 boys who had successful ablation of valves showed marked improvement in hydroureteronephrosis when nighttime drainage was implemented .
In one series of 119 patients with PUV who were almost all treated with initial early bladder drainage and cystoscopy with primary ablation, one-third of patients had severe bladder dysfunction and required clean intermittent catheterization (CIC) . In another study, although 27 of 65 patients had symptoms of bladder dysfunction, continence was achieved in 42 of 55 toilet-trained children, and only 3 required CIC . In both reports, pharmacologic treatment using anticholinergic and alpha-blocker medications was used in children depending upon the results of urodynamic testing. In a small case series of 18 patients with high voiding pressures and/or small bladder capacity, early administration of oxybutynin (anticholinergic agent) after PUV ablation was associated with improved bladder function on urodynamic testing prior to toilet training .
Renal function — Because there is a high risk of CKD in these patients, ongoing monitoring of the renal function of these patients is important. In patients with CKD, management is directed at caring for the associated complications of CKD and is discussed separately. (See "Chronic kidney disease in children: Overview of management" and 'Outcome' below.)
Patients with CKD may have a urinary concentrating defect resulting in excessive urinary losses. This may overwhelm the carrying capacity of the urinary tract, resulting in an enlarged and poorly functioning bladder and persistent hydronephrosis. In these patients, nighttime catheter drainage to completely decompress the urinary tract may be an effective intervention .
Survival — Ten-year survival is over 90 percent for patients diagnosed within the first year of life. In a retrospective review from the Pediatric Health Information System (PHIS) database of 685 patients (5 percent) with PUV diagnosed and treated by one year of life between 1992 and 2006, 34 children (5 percent) died: over half during their first hospitalization, primarily due to pulmonary hypoplasia . In this cohort, the probability of ten-year survival was 94 percent.
Renal function — Despite prenatal diagnosis and early intervention, a significant number of patients with PUV will develop end-stage kidney disease (ESKD) [23-28].
●In the largest multicenter case series of 274 patients who began treatment within the first 90 days of life and were born between 1995 and 2015, 42 (15 percent) progressed to renal replacement therapy (RRT, dialysis or renal transplantation) during the follow-up period (median 6.3 years). Multivariate analysis demonstrated that the only independent risk factor was the serum nadir creatinine level in the first year of life (SnCr1) . In this cohort, the risk of RRT increased as the SnCr1 increased. After stratifying by the SNCr1, the estimated risk of progressing to RRT by 10 years of age was 0, 2, 27, and 100 percent for an SNC1 of <0.4, an SNC1 of 0.4 to 0.69, an SNC1 of 0.7 to 0.99, and an SNC1 of ≥1.0 mg/dL, respectively.
●From the previously discussed PHIS study, dialysis catheters were placed in 59 of the 685 patients (9 percent) with PUV . Kidney transplantation was performed in 36 patients (7 percent) at a median age of three years. The diagnosis of kidney dysplasia was associated with both an increased risk of dialysis and kidney transplantation.
Although it has been speculated that patients who present later in life might have milder disease, it remains unclear whether or not a later presentation is associated with a better outcome [29-32].
In a large case series of 315 patients from two centers treated between 1990 and 2010, patients who were prenatally diagnosed (median age of valve ablation one month, range one day to three months) compared with those diagnosed postnatally (median age of valve ablation three years, range 1 month to 15 years) were less likely to have developed chronic kidney disease (CKD) at the end of a median follow-up of 5.5 years (19 versus 40 percent) . Mean serum creatinine values for the two groups were similar at diagnosis but were lower for the prenatally diagnosed group at the end of follow-up (0.96 versus 1.75 mg/dL). In contrast, results from two other smaller case series suggest that patients who present before one year of life were more likely to have poorer renal outcome [33,34].
These results demonstrate that a significant number of patients with PUV will have renal impairment, and some will progress to ESRD and require renal replacement therapy. Persistently elevated serum creatinine after relief of the obstruction is a risk factor for ESRD [15,29,35]. As discussed above, the impact of the age at presentation on the risk of renal impairment remains uncertain.
Ongoing monitoring of renal function is important in this group of patients in order to anticipate associated CKD medical conditions that may require intervention, and to provide counseling to patients at risk for ESRD and their caregivers regarding options for renal replacement therapy. (See "Chronic kidney disease in children: Overview of management".)
Nadir creatine is not only predictive of progression to ESRD but also can correlate with overall bladder function. A case series of 73 boys followed for at least five years, the nadir creatinine increased with the risk of progressive bladder dysfunction at five years of age .
Renal transplantation — Renal transplant survival for patients with PUV is the same as the overall pediatric allograft survival for all children undergoing transplantation based on case series that compared outcome of boys with PUV and children with other underlying primary causes of ESRD [37,38]. This was best illustrated by a study from a single tertiary center of 418 children who underwent renal transplantation at a mean age of 5.6 years . There was no difference in the rate of allograft failure between the 59 boys with PUV and 359 children with other primary causes of ESRD at eight-year follow-up. (See "Kidney transplantation in children: Outcomes".)
Lower urinary tract function — Patients after PUV ablation are at risk for bladder dysfunction and may require clean intermittent catheterization [24,28] and have delays in achieving daytime and nighttime urinary continence.
A case series of 76 patients with PUV reported delays for achieving both daytime (mean age 5.5±3.3 versus 2.3±0.5 years) and nighttime urinary continence (mean age 5.4±3.0 versus 2.9±1.2 years) compared with reference population .
Lower urinary tract (LUT) symptoms are commonly seen in adult patients with PUV [28,40]. In one study, adult patients (median age 38.5 years) with PUV were more likely than age and sex-matched controls to have one or more moderate to severe LUT symptom (32.4 versus 15.8 percent) . Symptoms included mild hesitancy, weak stream, incomplete emptying, staining, and urgency and stress incontinence.
SUMMARY AND RECOMMENDATIONS
●Definition – Posterior urethral valves (PUV) are obstructing membranous folds within the lumen of the posterior urethra that are the most common cause of congenital urinary obstruction (figure 1).
●Indications for prenatal surgery – We suggest that fetal surgery should only be considered in select patients with a high risk of perinatal mortality because of the morbidity associated with fetal intervention and the lack of evidence that intervention reduces the risk of chronic kidney disease (CKD) (Grade 2C). In addition, fetal surgery should be performed in centers with expertise in these procedures. (See 'Prenatal intervention' above.)
●Postnatal management – The postnatal management of PUV includes stabilization of the patient and drainage of the urinary tract. Medical management includes correction of electrolyte abnormalities, and treatment for possible complications such as respiratory distress and infection. (See 'Postnatal management' above.)
●Valve ablation – With advancements in surgical technique and instruments, primary ablation during cystoscopy has become the preferred surgical procedure to relieve the obstruction. It can be performed in most neonates with PUV, including some premature infants. If primary valve ablation cannot be done, vesicostomy is the next preferred procedure. (See 'Cystoscopy' above.)
●Possible urologic complications – Although all patients with PUV are at risk for developing CKD, patients with a persistently elevated creatinine after relief of their urinary obstruction (eg, PUV ablation) are at increased risk for end-stage renal disease. In addition, a significant number of patients will have persistent bladder dysfunction, vesicoureteral reflux, and/or hydronephrosis, which in some cases may require clean intermittent catheterization and anticholinergic medications. (See "Clinical presentation and diagnosis of posterior urethral valves", section on 'Renal and urologic consequences' and 'Post-procedure management' above.)
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