Posterior Urethral Valves (PUV)
Summary
Posterior Urethral Valves (PUV) is the commonest cause of Lower Urinary Tract Obstruction (LUTO) in male infants. It is a congenital membrane (Type I, II, or III) obstructing the membranous urethra. The resulting back-pressure causes a spectrum of pathology: from mild hydronephrosis to severe Renal Dysplasia and Pulmonary Hypoplasia (Potter Sequence). 30% of boys progress to End Stage Renal Failure (ESRF) despite treatment. [1,2]
Clinical Pearls
The "Valve Bladder": Even after the valves are surgically ablated, the "war is not over". The bladder wall, having fought against high pressures in utero, is hypertrophied, stiff, and poorly compliant. This can lead to incontinence and ongoing high-pressure reflux damaging the kidneys in childhood.
Nadir Creatinine: The single best prognostic indicator for long-term renal function is the "Nadir Creatinine" achieved in the first year of life (after relief of obstruction).
- < 80 µmol/L: Good prognosis.
- > 100 µmol/L: High risk of future ESRF.
Urinary Ascites: Sometimes the high pressure causes a calyx in the kidney to rupture (fornix rupture). Urine leaks into the perinephric space and then the abdomen. Paradoxically, this protects renal function by "popping the valve" and relieving the lethal pressure on the renal parenchyma.
Demographics
- Incidence: 1 in 5,000-8,000 live births.
- Gender: Exclusively Male.
- Genetics: Sporadic. No specific gene identified.
Mechanism of Injury
- Obstruction: Membrane blocks urine outflow.
- Bladder: Detrusor Hypertrophy -> Trabeculation -> Diverticula -> Poor Compliance.
- Ureters: Hydro-ureter + Vesicoureteral Reflux (VUR in 50%).
- Kidneys: High pressure causes Renal Dysplasia (cysts, poor nephrogenesis).
- Lungs: Oligohydramnios -> Pulmonary Hypoplasia (Potter Sequence).
Antenatal (Severe)
Neonatal
Childhood (Mild)
- Abdomen: Palpable bladder (firm, round mass suprapubically).
- Lungs: Assess for hypoplasia (Work of breathing).
- Genitals: Inspect meatus (exclude stenosis).
Imaging
- Ultrasound: First line. Shows thick bladder wall (>3mm), hydronephrosis, keyhole sign.
- MCUG (Micturating Cystourethrogram): Gold Standard.
- Shows: Dilated posterior urethra, valve cutoff, trabeculated bladder, VUR.
- DMSA Scan: Performed later (months) to assess differential renal function and scarring.
Labs
- Creatinine: Remember neonatal creatinine reflects the mother's for the first 24-48h. A rising creatinine or failure to fall suggests renal issues.
Management Algorithm
SUSPECTED PUV
(Antenatal Scan / Dribbling)
↓
ACUTE MANAGEMENT
- Pass Urethral Catheter (Size 6/8 Fr)
(To drain bladder)
- US + Creatinine
- Antibiotics (Prophylaxis)
↓
CONFIRM DIAGNOSIS
- MCUG
↓
DEFINITIVE TREATMENT
┌─────────┴─────────┐
URETHRA OK URETHRA TOO SMALL
↓ ↓
VALVE ABLATION VESICOSTOMY
(Cystoscopy) (Suprapubic stoma
Laser/Diathermy) to drain urine)
↓ ↓
LONG TERM SURVEILLANCE
(Renal Clinic until adulthood)
Surgical Options
- Primary Valve Ablation: Cystoscope passed via penis. Valve leaflets ablated (hook or laser). Requires baby to be big enough (~2.5kg) for the scope.
- Vesicostomy: If urethra is too small, a temporary stoma (hole) is made from the bladder to the abdominal wall to allow free drainage. Ablation done later when bigger.
- Fetal Shunting: (Vesico-amniotic shunt). Rarely done. High risk of complication, but may save lungs in severe oligohydramnios.
- ESRF: 30% need transplant by adolescence.
- Bladder Dysfunction: "Valve Bladder" (Hypertonic, small capacity). May need CIC (Clean Intermittent Catheterisation) or Mitrofanoff.
- Urethral Stricture: Iatrogenic (from instrumentation).
- Infertility: Often preserved, but retrograde ejaculation possible post-surgery.
- Depends on the degree of Renal Dysplasia (incurable) and Lung Hypoplasia (lethal).
- Survival is ~95% in modern centres, but morbidity (CKD) is high.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| PUV Consensus | EAU / ESPU | Guidelines on management and follow-up. |
| BAPU | British Assoc Paed Urologists | Standards for ablation and catheterisation. |
Landmark Evidence
1. Parkhouse et al (1988)
- Classic paper describing the long-term outcomes (30% ESRF) and introducing the importance of Nadir Creatinine.
What is PUV?
It is a blockage in the water pipe (urethra) of baby boys. A small flap of skin is left over from development, acting like a dam.
Why does it affect the kidneys?
Because the urine can't get out, the pressure builds up back into the bladder (making it thick and stiff) and up the tubes to the kidneys. This back-pressure stops the kidneys growing properly.
What is the Keyhole sign?
On the ultrasound scan, the bladder looks round, and the top of the water pipe looks wide (dilated), resembling an old-fashioned keyhole. This tells us the blockage is lower down.
How do we fix it?
A surgeon passes a tiny telescope up the penis and trims away the flap of skin. This opens the dam. However, any damage already done to the kidneys cannot be reversed, so he will need kidney checks for life.
Primary Sources
- Nasir AA, et al. Posterior urethral valves. World J Pediatr. 2011.
- Hennus PML, et al. EAU Guidelines on Paediatric Urology. 2020.
- Parkhouse HF, et al. Long-term outcome of posterior urethral valves. Br J Urol. 1988.
Common Exam Questions
- Diagnosis: "Male newborn, palpable bladder, oligohydramnios?"
- Answer: PUV.
- Imaging: "Gold standard investigation?"
- Answer: MCUG.
- Sign: "Keyhole sign?"
- Answer: Dilated bladder and posterior urethra.
- Pathology: "Potter sequence cause?"
- Answer: Oligohydramnios (due to PUV or Renal Agenesis).
Viva Points
- Catheterisation: If you can't pass a urethral catheter in a baby with PUV, what do you do? Try a smaller one? No. A Suprapubic catheter is safe, but sometimes a urethral catheter catches on the valve lip. A "coude" tip or gentle manipulation helps.
- Why pulmonary hypoplasia?: Fetal breathing of amniotic fluid is required to distend the alveoli and stimulate lung growth. No fluid = No growth.
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