Posterior Urethral Valves (PUV)

Introduction And Epidemiology

Posterior urethral valves (PUV) are the most common cause of severe lower urinary tract obstruction in male infants.
The estimated incidence is between 1 in 4000 to 8000 live births.
They are characterized by the formation of obstructing, sail-like membrane folds.
These folds fan distally from the verumontanum to the prostatic urethra.
This anatomy produces a slit-like opening that severely impedes antegrade urine flow.

The exact embryologic origin remains incompletely understood.
Proposed mechanisms include the
- Hypertrophy of urethral mucosal folds.
- Incomplete canalization or persistence of the urogenital membrane
- Abnormal development of the Wolffian or Müllerian ducts
Familial cases demonstrate autosomal dominant inheritance.
These familial cases are linked to rare variants in the BNC2 gene, which encodes basonuclin 2.

Type 1 constitutes 90 to 95 percent of cases.
It is composed of a ridge continuous from the verumontanum.
This ridge divides into two fork-like leaflets attaching to the anterior urethra.
Type 2 is no longer considered a true form of PUV.
It is now recognized as a dissection artifact.

The obstruction causes severe upstream anatomical and functional changes.
The prostatic urethra dilates proximal to the obstruction.
The bladder muscle undergoes massive hypertrophy and trabeculation.
Elevated intravesical pressures are transmitted to the upper urinary tract.
Vesicoureteral reflux (VUR) is present in up to 50 percent of patients due to distortion of the ureterovesical junction.
Chronic high-pressure obstruction during critical phases of fetal nephrogenesis results in renal dysplasia.
This leads to oligohydramnios and subsequent pulmonary hypoplasia.

Nature occasionally provides pressure-relief valves to preserve renal function in at least one kidney.
VURD Syndrome involves Valves, Unilateral Reflux, and Dysplasia.
In VURD, massive unilateral reflux destroys one kidney but protects the contralateral kidney.
Urinary ascites occurs due to rupture of the renal fornices.
This rupture allows urine to extravasate into the peritoneal cavity, decompressing the upper tracts.
Large, distensible bladder diverticula can also serve as a pop-off mechanism.

Most antenatal cases are suspected on a routine second-trimester ultrasound.
Fetuses manifest with bilateral hydroureteronephrosis, a distended thick-walled bladder, and oligohydramnios.
Neonatal male infants typically present with a palpably distended bladder.
This is often described as a walnut-sized mass above the pubic symphysis.
Infants display a weak, dribbling urinary stream.

Diagnostic Modality	Key Findings And Clinical Utility
Prenatal Ultrasonography	Reveals the classic keyhole sign, which is a dilated bladder with a dilated proximal urethra. A thickened bladder is a better predictor of PUV than the keyhole sign.
Postnatal Ultrasonography	Assesses hydroureteronephrosis severity and bladder wall thickening. Detects echogenic renal parenchyma, suggesting cystic dysplasia.
Voiding Cystourethrography (VCUG)	The definitive gold standard for diagnosing PUV. Demonstrates a dilated, elongated prostatic urethra and hypertrophied bladder neck. Reveals a transverse linear filling defect representing the valve leaflets.
Renal Scintigraphy (DMSA/MAG3)	Utilized to assess split or differential renal function. Evaluates drainage characteristics and the extent of cortical scarring post-obstruction relief.
Fetal Urine Analysis	Evaluated prior to considering in-utero intervention. Urinary sodium or chloride greater than 100 mmol/L suggests irreversible tubular damage.

The immediate postnatal priority is bladder decompression.
A small 5 or 8 French polyethylene feeding tube or a catheter without a balloon is inserted.
Foley catheters with balloons are strictly contraindicated.
The balloon can trigger severe bladder spasms and cause secondary ureterovesical junction obstruction.
Prompt correction of fluid, electrolyte imbalances, and metabolic acidosis is mandatory.

Once the patient is hemodynamically stable, primary transurethral endoscopic ablation of the valve leaflets is the treatment of choice.
A check cystoscopy or a VCUG is performed to confirm the procedure's effectiveness.
Cutaneous vesicostomy is performed as temporary diversion in small premature infants.
Vesicostomy ensures low-pressure urinary drainage when the urethra cannot accommodate a cystoscope.
High urinary diversion is considered if progressive dilatation of the upper tract persists despite adequate bladder drainage.

Ten-year survival is more than 90 percent for those diagnosed in the first year of life.
Up to 30 percent of children surviving the neonatal period eventually progress to end-stage kidney disease (ESKD).
High baseline creatinine in the first year and associated renal dysplasia are risk factors for ESKD progression.
Lower renal parenchymal area in the first six months indicates a higher risk for progressing to chronic kidney disease.

Patients frequently suffer from long-term neuropathic-like bladder dysfunction post-ablation.
This condition is called valve bladder syndrome.
It is characterized by poor compliance, detrusor overactivity, and polyuria.
This syndrome requires lifelong management with urodynamic monitoring and anticholinergics.