Posterior urethral valves (PUVs), first described by Hugh Hampton Young and coworkers in 1919,  cause bladder obstruction in males that can manifest along a spectrum of severity, ranging from disease incompatible with postnatal life to conditions that have such minimal impact that they may not manifest until later in life.
Treatment of PUVs remains a clinical challenge, requiring long-term management from early infancy into adulthood in order to avoid progressive bladder dysfunction and deterioration of both upper and lower urinary tracts.
During the early stages of embryogenesis, the most caudal end of the wolffian duct is absorbed into the primitive cloaca at the site of the future verumontanum in the posterior urethra. In healthy males, the remnants of this process are the posterior urethral folds, called plicae colliculi. Histologic studies suggest that PUVs are formed at approximately 4 weeks' gestation, as the wolffian duct fuses with the developing cloaca.
Congenital obstructing posterior urethral membrane (COPUM) was first proposed by Dewan and Goh and was later supported by histologic studies by Baskin.  This concept proposes that instead of a true valve, a persistent oblique membrane is ruptured by initial catheter placement and, secondary to rupture, forms a valvelike configuration.
The morbidity of PUVs is not merely limited to transient urethral obstruction. The congenital obstruction of the urinary tract at a critical time in organogenesis may profoundly affect lifelong kidney, ureteral, and bladder function. In a dynamic process, bladder dysfunction may cause ongoing and progressive renal deterioration. Renal insufficiency is caused by PUVs in approximately 10-15% of children undergoing renal transplantation, and approximately one third of patients born with PUVs progress to end-stage renal disease (ESRD).
Moreover, as a result of the obstructive process, increased collagen deposition and muscle hypertrophy can significantly thicken the bladder wall. Hypertrophy and hyperplasia of the detrusor muscle and increases in connective tissue limit bladder compliance during filling. Bladder emptying then occurs at high intravesical pressures, which, in turn, can be transmitted to the ureters and up into the renal collecting system. Ultimately, patients with PUV may be susceptible to incontinence, infection, and progressive renal damage.
As patients with PUV age, bladder decompensation may develop, resulting in detrusor failure and increased bladder capacity. Many boys with PUV will develop larger-than-expected bladder volumes by age 11 years, possibly as a consequence of overproduction of urine caused by tubular dysfunction and an inability to concentrate urine (nephrogenic diabetes insipidus).
Bladder function may change at puberty, resulting in high-pressure, chronic retention and necessitating the need for lifelong bladder management.  Symptoms of bladder dysfunction may persist into adulthood in up to one third of patients and include urinary incontinence in up to 15% of adults with a history of PUV. 
Young's original description divided PUVs into three types, as follows  :
Type I - Valves representing folds extending inferiorly from the verumontanum to the membranous urethra (~95% of PUVs)
Type II - Bicuspid valves as leaflets radiating from the verumontanum proximally to the bladder neck
Type III - Valves as concentric diaphragms within the prostatic urethra, either above or below the verumontanum (~5% of PUVs)
Most pediatric urologists now regard the existence of type II PUVs as doubtful.
A PUV is a congenital obstruction caused by a malformation of the posterior urethra. The significance of this obstruction depends on the secondary effects on the bladder, ureters, and kidneys.
A type I PUV is believed to result from abnormal insertion and absorption of the most distal aspects of the wolffian ducts during bladder development. In the healthy male, the remnants of these ducts are observed as the plicae colliculi. Type III PUVs are observed as a membrane in the posterior urethra believed to originate from incomplete canalization between the anterior and the posterior urethra.
In the United States, PUV is the most common cause of lower urinary tract obstruction in male neonates; the reported incidence ranges from 1 per 8000 to 1 per 25,000 live births.
PUVs are usually diagnosed before birth or at birth when a boy is evaluated for antenatal hydronephrosis. Before the era of antenatal ultrasonography, PUVs were discovered during evaluation of urinary tract infection (UTI), voiding dysfunction, or renal failure. Although rare, adult presentation of PUVs has been described in case reports, with symptoms ranging from obstructive voiding symptoms to postejaculatory dysuria. In the preultrasonography era, a late presentation of PUV was considered a good prognostic indicator suggestive of a lesser degree of obstruction.
PUVs occur exclusively in males. The homolog to the male verumontanum from which the valves originate is the female hymen.
Over the past 30 years, the prognosis of children with PUV has steadily improved. In the past, most children were found to have PUV only after presenting with urosepsis or progressive renal insufficiency. Older series demonstrated mortality figures approaching 50% by late adolescence. Today, most individuals with PUV are discovered when antenatal ultrasonography reveals hydronephrosis. Prompt resolution of bladder obstruction, aggressive treatment of bladder dysfunction, and improved surgical techniques have lowered the neonatal mortality to less than 3%.
PUVs are the cause of renal insufficiency in approximately 10-15% of children undergoing renal transplant, and approximately one third of patients born with PUV progress to ESRD in their lifetimes. Early initial presentation, pneumothorax, bilateral vesicoureteral reflux (VUR), and recurrent UTIs after valve ablation are all associated with risk for progression to ESRD.  As the child grows, renal metabolic demand increases proportionately. Failure of creatinine to nadir below 0.8 mg/dL in the first year of life is an indication of limited renal reserve. These patients are at risk for progression to ESRD with somatic growth, such as occurs at puberty.
Improved dialysis and transplantation techniques have significantly improved not only mortality but also quality of life for these children . Additionally, medical and surgical management can achieve urinary continence in nearly all patients.
An interesting group of patients are those with vesicoureteral reflux dysplasia (VURD) syndrome. In these patients, one kidney is hydronephrotic, nonfunctioning, and has high-grade VUR. The high-grade VUR is thought to act as a pop-off valve, leading to reduced overall bladder pressures and preservation of contralateral renal function.
In the past, these patients were thought to have a better outcome as a result of preserved renal function in one kidney at the sacrifice of the other. Subsequent work by Narasimhan et al suggested that although short-term serum creatinine levels may be favorable, these patients may suffer long-term adverse renal function with hypertension, proteinuria, and renal failure.  In the long run, VURD syndrome may not have the favorable outcome it was once thought to have.
PUV is a lifelong condition that requires continued medical management. Because of this, both the physician and family must understand the potential long-term complication of renal deterioration if bladder function is not adequately treated.
Patients and families need realistic expectations regarding continence. Although continence is achievable in nearly all patients, it often depends on adherence to a timed voiding schedule and intermittent catheterization.
Patients and families must also realize that medications, such as anticholinergics and suppressive antibiotics, are for controlling the symptoms of PUV and are not curative.
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