Posterior Urethral Valve

19.1Introduction

•Posterior urethral valve (PUV) disorder is an obstructive developmental anomaly of the male urethra.

•It is characterized by a congenital membrane obstructing the posterior male urethra.

•As a result of urinary obstruction, there is a backward pressure and reverse urinary flow which can affect the urethra, bladder, ureters, and kidneys (Fig. 19.1).

•Hugh Hampton Young published the first description of posterior urethral valves (PUVs) in 1919.

•PUVs occur exclusively in males. The homolog to the male verumontanum from which the valves originate is the female hymen.

•It is considered the most common cause of bladder outlet obstruction in male newborns.

•The incidence of posterior urethra is 1 in 5,000–8,000 live male newborns.

•The valve is believed to result from abnormal embryologic development of the fetal posterior urethra.

•PUV mechanically obstruct normal bladder emptying and increases voiding pressures.

•The disorder varies in degree of obstruction from mild to severe incompatible with postnatal life.

•Severe posterior urethral valves are known to be associated with renal and respiratory failure from lung underdevelopment as result of low amniotic fluid volumes.

•An increasing number of cases are diagnosed antenatally.

•Patients with PUVs have a higher incidence of cryptorchidism when compared to normal patients.

•Other known associated anomalies include VATER or VACTERL and rarely ano-rectal malformation.

•Prenatal intervention in those with PUV does not appear to confer a benefit in the long-term outcome of renal function.

•Primary valve ablation is the recommended treatment of choice with diversion being reserved for specific individual cases.

•The most life-threatening problem in the newborn period is the potential pulmonary hypoplasia related to in utero oligohydramnios and renal dysfunction. These patients may present with pneumothoraces at birth which will complicate their pulmonary management.

•Newborns are also susceptible to urosepsis as a result of urinary stasis.

•The presentation of PUV is variable depending on the degree of obstruction and the spectrum of renal dysfunction and subsequent functional outcomes also vary widely.

•A significant number of boys with PUV will develop chronic kidney disease and end stage renal failure.

•This is attributed to its consequences, including:

–Renal dysplasia

–Upper urinary tract dilatation

Fig. 19.1 A voiding cystourethrogram showing posterior urethral valve. Note the dilated posterior urethra with the valve, the associated bladder diverticulum and right side vesicoureteric reflux

VESICOURETERIC

REFLUX

ANTERIOR

URETHRA

URINARY

BLADDER

BLADDER

DIVERTICULUM

POSERIOR URETHRA WITH VALVE

–Vesico-ureteric reflux

–Urinary tract infection

–Bladder dysfunction

•PUV accounts for 25–30 % of pediatric renal transplantations.

•The VURD (valves unilateral reflux dysplasia) syndrome:

–This was described by Hoover and Duckett.

–It results in very poor or non-function of the kidney on the refluxing side with a relative sparing of renal function on the contralateral, non-refluxing side.

–The authors also postulated that this mechanism of ‘pop-off’ results in long-term normal renal function, as the contralateral kidney is spared and normal.

–This hypothesis was subsequently challenged by Cuckow et al. who showed with serum creatinine and GFR measurements that renal function was impaired in cases with VURD, implying that the protection offered by the ‘pop-off’ mechanism was not complete

19.2Embryology

•Embryologically, 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.

•The embryological abnormality giving rise to posterior urethral valves is not well known.

•It has been suggested that posterior urethral valves result from fusion of the plicae colliculi (posterior urethral folds) between the entrances of the seminal vesicles at the veromontanum, and extend to the membranous urethra.

•PUVs are formed at approximately 4 weeks’ gestation, as the Wolffian duct fuses with the developing cloaca.

•There are several theories explaining the embryological origin of PUVs:

–PUVs may represent an anomalous insertion of the mesonephric duct into the

•Hydronephrosis is common in these patients for several reasons:

–Bladder dysfunction with high back pressures on the ureter.

–An abnormally deficient musculature of the ureter due to chronic distention from high pressure or high urine flow.

–High urinary flow due to the lack of urinary concentrating ability of the nephron can dilate the kidneys and ureters.

–Abnormalities of the vesicoureteral junction, such as reflux or, rarely, ureterovesical obstruction.

•Vesicoureteral reflux is present in one half of male patients with a posterior urethral valve for the following reasons:

–Secondary to increased intravesical pressure which overcomes the competence of the ureterovesical junction.

–Secondary to abnormal ureteral orifice position resulting from abnormal ureteral bud development during embryogenesis.

•Bladder dysfunction in patients with PUV is secondary to:

–Alterations in collagen deposition.

–Alteration in the development of detrusor smooth muscle cells.

–Poor compliance or uninhibited contraction of the detrusor muscle and eventual myogenic failure.

–In mild cases, incontinence may be present.

–In severe cases, ongoing deterioration of renal function occurs.

–Bladder dysfunction often improves over time after definitive treatment of the obstruction.

–Persistence of bladder dysfunction increases the risk of:

•Urinary tract infection

•Persistent hydronephrosis

•Vesicoureteral reflux

•Incontinence

–All of these diminish renal function further.

•Several protective mechanisms may develop in boys with a posterior urethral valve; these may lower intraluminal pressures and allow at least one renal unit to develop more

normally. These protective mechanisms include:

–Massive unilateral vesicoureteral reflux.

–This is usually associated with an ipsilateral dysplastic kidney, known as vesicoureteral reflux and dysplasia syndrome.

–Development of bladder diverticula.

–Rupture of renal calyces and development of urinary ascites.

•As patients with PUV age, bladder decompensation may develop, resulting in detrusor failure and increased bladder capacity.

•Many boys with PUV as they grow older will develop larger-than-expected bladder volumes possibly due to 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.

19.4Classification

•A PUV is a congenital obstruction caused by an embryological malformation of the posterior urethra.

•Posterior urethral valves are usually fusion of the plicae colliculi between the entrances of the seminal vesicles at the veromontanum, and extend to the membranous urethra.

•The verumontanum, or mountain ridge, is a distinctive landmark in the prostatic urethra and it is important in the classification of posterior valves.

•This malformation will result in urethral obstruction.

•The significance of this obstruction depends on the secondary effects on:

–The urinary bladder

–The ureters

–The kidneys