(1)
Pediatric Surgery, AlSadik Hospital, Qatif, Saudi Arabia
19.1 Introduction
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).
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
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
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
19.2 Embryology
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 uro-genital sinus, preventing normal migration of these ducts and their anterior fusion.
PUVs may represent an abnormality of the cloacal membrane.
Early classification of PUV was done by Hugh Hampton Young in 1919, who described three types of PUVs, I–III based on post-mortem dissection studies.
Subsequently, Dewan et al. suggested a more uniform and similar appearance to the obstructing posterior urethral membrane.
Their endoscopic appraisal revealed the membrane to attach posteriorly, just distal to the verumontanum. The membrane extended anteriorly and obliquely beyond the external sphincter with a variable sized aperture located within it, at the level of the verumontanum.
They described the membrane as congenital obstructing posterior urethral membrane (COPUM).
Congenital obstructing posterior urethral membrane (COPUM) was first proposed by Dewan and Goh and was later supported by histological 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 valve like configuration.
19.3 Pathophysiology
Posterior urethral valve is known to be associated with significant morbidity which 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 as follows:
Outflow obstruction leads to increased collagen deposition and muscle hypertrophy of the urinary bladder which can significantly thicken the bladder wall.
Hypertrophy and hyperplasia of the detrusor muscle of the urinary bladder and increases in connective tissue limit bladder compliance during filling.
As a result of this, bladder emptying occurs at high intravesical pressures.
This high intravesical pressure, in turn, can be transmitted to the ureters and up into the renal collecting system and kidneys.
The end result of this is increased susceptibility to incontinence, infection, and progressive renal damage.
The 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).
PUVs lead to mechanical obstruction which affect normal bladder emptying and this will lead to:
High intraluminal pressure
Increases voiding pressures
Maldevelopment of the kidneys, ureters and urinary bladder
Renal maldevelopment:
Renal parenchymal dysplasia is common and may be related to maldevelopment of the metanephric blastema
Renal tubular function may be affected by high pressures that result in poor urinary concentrating ability
Diuresis secondary to high urinary production
This high urinary production will lead to ureteral and bladder dysfunction
Renal deterioration may also occur due to hyperfiltration injury that causes:
Glomerulosclerosis
Chronic pyelonephritis associated with vesicoureteral reflux
Urinary stasis
Incomplete bladder emptying
These will also cause further insult to the developing kidneys.
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.
19.4 Classification
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
In 1919, H. H. Young was the first to classify posterior urethral valves into three types as follows:
Type I:
This is the most common type.
This type of obstruction 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.
This type is believed to be due to anterior fusing of the plicae colliculi, mucosal fins extending from the bottom of the verumontanum distally along the prostatic and membranous urethra.
Type II:
This is the least common variant.
It is characterized by vertical or longitudinal folds between the verumontanum and proximal prostatic urethra and bladder neck.
Type III:
This is the second common variant.
It is due to a disc of tissue distal to verumontanum.
These valves are observed as a membrane in the posterior urethra
These are believed to originate from incomplete canalization between the anterior and posterior urethra.
It is also theorized to be a developmental anomaly of congenital urogenital remnants in the bulbar urethra.
It has been suggested that obstructions in the posterior urethra are more appropriately termed congenital obstructions of the posterior urethral membrane (COPUMs).
The congenital urothelial remnants of type III posterior urethral valves have been eponymously referred to as Cobb’s collar or Moorman’s ring.
19.5 Clinical Features
PUV is the most common cause of lower urinary tract obstruction in male neonates.
The reported incidence is 1 per 8,000–1 per 25,000 live births.
PUVs are the cause of renal insufficiency in approximately 10–15 % of children undergoing renal transplant.
Approximately one third of patients born with PUV progress to end stage renal disease (ESRD).
PUVs are usually diagnosed before birth or at birth when a boy is evaluated for antenatal hydronephrosis.
Before the era of prenatal ultrasonography, PUVs were discovered during evaluation of urinary tract infection (UTI), voiding dysfunction, or renal failure.
In the pre-antenatal ultrasonography era, a late presentation of PUV was considered a good prognostic indicator suggestive of a lesser degree of obstruction.
Prenatal diagnosis
The widespread use of antenatal ultrasonography has made it possible to diagnose more cases of posterior urethral valves antenatally.
Currently, the diagnosis of PUV is usually made early at birth when a boy is evaluated for antenatally diagnosed hydronephrosis.
It was estimated that 10 % of boys diagnosed with prenatal hydronephrosis had PUVs.
Patients who are not diagnosed by antenatal ultrasound may present shortly after birth with distended bladder and difficulty to pass urine.
Despite widespread use of antenatal ultrasonography, some patients with PUVs do present later in life.
Delayed presentation
PUVs manifest as a spectrum of disease severity.
The delayed clinical presentation of PUVs include:
Urinary tract infection
Diurnal enuresis in boys older than 5 years
Secondary diurnal enuresis
Voiding pain or dysfunction
An abnormal urinary stream
PUVs are sometimes discovered during evaluation of abdominal mass or renal failure.
Hydronephrosis or proteinuria found on examination for unrelated conditions may be the first sign of PUVs.
Neonates born with severe posterior urethral valve may present with severe pulmonary distress secondary to pulmonary hypoplasia due to oligohydramnios. Physical findings can include the followings:
Poor fetal breathing movements
Small chest cavity
Abdominal mass (ascites)
Potter facies
Limb deformities (skin dimpling)
Indentation of the knees and elbows due to compression within the uterus
In older children, physical findings can include:
Poor growth
Hypertension
Lethargy
A large lower abdominal mass representing a markedly distended urinary bladder
A smaller number of patients with PUV will present late and their clinical presentation include:
Diurnal enuresis
Dribbling or poor urine stream
Urinary tract infection
Hematuria
19.6 Investigations and Diagnosis
With routine use of obstetric ultrasonography the prenatal diagnosis of posterior urethral valve is becoming increasingly common.
The antenatal ultrasound demonstrates significant hydronephrosis with possible renal cortical thinning. The kidney is larger than expected for the patient’s gestational age. The hydronephrosis may be bilateral and both kidneys may be affected.
As a result of the routine use of antenatal ultrasound, the number of cases of PUV diagnosed prenatally has increased.
Currently, approximately 50–75 % of boys with PUV will be suspected on prenatal ultrasound.
The prenatal ultrasound findings suggestive of PUV include:
A thick walled bladder
The ‘keyhole’ sign with a dilated bladder and posterior urethra
Unilateral or bilateral hydroureteronephrosis
Echo bright kidneys
Oligohydramnios
Postnatally, the patient must be stabilized prior to any investigation.
Complete blood count
Serum electrolytes, BUN and creatinine.
To be accurate and to avoid maternal placental effect, these should be checked at least 24 h after birth.
The newborn is unable to concentrate urine because of renal immaturity at birth.
This defect is exacerbated by renal dysplasia such as that found with posterior urethral valves and if the renal dysplasia is significant, the serum creatinine fails to reach a normal level during the first year of life.
Serum creatinine levels >0.8 mg/dL during the first year of life have been demonstrated to be associated with poor long-term renal function.
This is considered a negative prognostic indicator.
Plain abdominal radiographs do not add to the actual diagnosis of posterior urethral valves but may show the ground-glass appearance seen in those with urinary ascites.
Chest radiographs may be useful in the evaluation of pulmonary hypoplasia.
Renal and bladder ultrasonography
Postnatal renal ultrasonography is the initial investigation to be done in those with suspected posterior urethral valve.
This is important as an initial noninvasive and devoid of radiation investigation.
Ultrasonography is helpful but not diagnostic (Figs. 19.2, 19.3, and 19.4).
Figs. 19.2, 19.3, and 19.4
Abdominal ultrasound showing an atrophic dysplastic kidney seen in a patient with posterior urethral valve and vesicoureteric reflux
Features suggestive of posterior urethral valves are:
Unilateral or bilateral hydronephrosis
Enlarged kidneys with thinning of the renal cortex
In those with renal dysplasia, the renal parenchyma is typically hyperechogenic with visible small cysts (<10 mm), but in the most mildly affected cases, renal ultrasonographic findings may be normal.
A thickened bladder wall with trabeculations, and bladder diverticula
The bladder may be of large or small volume, but it is invariably thick-walled.
A dilated posterior urethra
Echogenic lines that are the actual valve leaflets might be seen.
The combination of the dilated, thick-walled bladder and dilated posterior urethra has been described as having a keyhole appearance.
Urinary ascites or perinephric collections due to urinomas may also be seen, most commonly soon after birth, and are caused by rupture of the urinary tract, typically at the level of the calyces.
Voiding cystourethrogram (VCUG) (Figs. 19.5, 19.6, 19.7, 19.8, 19.9, 19.10, and 19.11):
Figs. 19.5 and 19.6
A micturating cystourethrogram showing posterior urethral valve. Note the dilated posterior urethra. Note also the dilated thickened urinary bladder. Note also the absence of vesicoureteric reflux
Fig. 19.7
A micturating cystourethrogram showing posterior urethral valve. Note the dilated posterior urethra and the small anterior urethra. Note also the dilated thickened urinary bladder
Fig. 19.8
A micturating cystourethrogram showing posterior urethral valve. Note the dilated posterior urethra and the small anterior urethra. Note also the dilated thickened urinary bladder and severe unilateral vesicoureteric reflux
Fig. 19.9
A micturating cystourethrogram showing posterior urethral valve. Note the dilated posterior urethra and the dilated thickened urinary bladder. Note also the absence of vesicoureteric refluxRelated posts:
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