# Posterior Urethral Valves

> Posterior urethral valves for NEET-PG Paediatrics: antenatal and postnatal clues, keyhole sign on MCU, valve ablation and long-term renal outcome in boys.

- Canonical URL: https://prepelephant.com/topics/neet-pg/paediatrics/posterior-urethral-valves
- Exam / course: NEET-PG · Subject: Paediatrics
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Campbell-Walsh-Wein Urology; Nelson Textbook of Pediatrics
- How to cite: "Posterior Urethral Valves", PrepElephant, https://prepelephant.com/topics/neet-pg/paediatrics/posterior-urethral-valves

## Direct answer

Posterior urethral valves are congenital membranes in the male posterior urethra that obstruct bladder outflow and are the commonest cause of lower urinary tract obstruction in boys. Presentation ranges from antenatal hydronephrosis and oligohydramnios to a poor urinary stream and urosepsis in infancy. Diagnosis rests on the keyhole sign on micturating cystourethrogram, and long-term renal outcome depends largely on the renal dysplasia present at diagnosis.

## What you must remember

- **Anatomy:** classic type I valves are obstructive folds arising from the verumontanum and extending distally in the posterior urethra.
- **Antenatal clues:** bilateral hydronephrosis, a distended thick-walled bladder and oligohydramnios on prenatal ultrasound.
- **Postnatal presentation:** poor stream, palpable bladder, urinary infection, failure to thrive, or renal failure in severe cases.
- **Keyhole sign:** a dilated posterior urethra on MCU, with bladder trabeculation and often vesicoureteric reflux.
- **Pulmonary hypoplasia:** severe oligohydramnios causes Potter sequence and lung hypoplasia, a major cause of neonatal death.
- **Initial management:** urinary drainage by catheter or vesicostomy in unstable infants, followed by cystoscopic valve ablation.
- **Renal prognosis:** determined by dysplasia at diagnosis; serum creatinine and renal size are key markers, and a substantial proportion progress to chronic kidney disease.
- **Long-term follow-up:** blood pressure, urinalysis, creatinine and bladder function, because bladder dysfunction and reflux persist.

## A pathway from antenatal clue to renal follow-up

A male infant has bilateral hydronephrosis and a thick-walled bladder on the anomaly scan, and the mother has low liquor volume. The sequence below turns a suspicion into definitive treatment and long-term monitoring.

1. **Suspect in boys.** Bilateral hydronephrosis with bladder dilatation or oligohydramnios points to valves.
2. **Stabilise urine flow.** Catheterise, treat any urosepsis, and check electrolytes and creatinine.
3. **Image the tract.** Renal and bladder ultrasound, then MCU to look for the keyhole sign and reflux.
4. **Divert if needed.** Vesicostomy for severe obstruction, sepsis or deteriorating renal function in infancy.
5. **Ablate the valves.** Cystoscopic valve ablation is the definitive step, usually in early infancy.
6. **Monitor long term.** Creatinine, blood pressure, urinalysis, growth and bladder function are reviewed for years.

## Where the exam tries to catch you

Valve questions reward recognising the male infant with a dilated posterior urethra.

- **Trap:** labelling the picture as isolated vesicoureteric reflux. **Correct:** in a boy with a dilated posterior urethra, think valves first, since reflux is often secondary to them.
- **Trap:** taking a normal neonatal creatinine as proof of normal kidneys. **Correct:** creatinine may be normal early, and dysplasia shows up later as progressive decline.
- **Trap:** delaying drainage in a septic infant while planning definitive surgery. **Correct:** urinary drainage is the urgent step, and valve ablation follows once the infant is stable.
- **Trap:** attributing the lung problem to primary lung disease. **Correct:** it results from oligohydramnios caused by urinary obstruction, which produces Potter sequence.

## Frequently asked questions

### What is the keyhole sign in posterior urethral valves?

The keyhole sign is a dilated posterior urethra seen on micturating cystourethrogram in a male infant with posterior urethral valves. It appears as a rounded, dilated posterior urethral segment with a narrow distal urethra, and it is the classic imaging finding.

### Which antenatal findings suggest posterior urethral valves?

Bilateral hydronephrosis, a distended bladder with a thick wall, and oligohydramnios on antenatal ultrasound suggest posterior urethral valves. Hydronephrosis with a distended bladder in a male fetus should prompt a careful search for valves.

### What is the definitive treatment for posterior urethral valves?

Cystoscopic ablation of the valves is the definitive treatment for posterior urethral valves. It is usually performed in early infancy, after urinary drainage has been established and the infant is stable enough for the procedure.

### What determines long-term renal outcome in posterior urethral valves?

The degree of renal dysplasia present at diagnosis determines long-term renal outcome in posterior urethral valves. Creatinine at presentation, renal size, and the presence of bladder dysfunction or reflux are also important markers for later progression.

### Why is oligohydramnios important in posterior urethral valves?

Oligohydramnios is important because it results from fetal urinary obstruction and can cause Potter sequence and pulmonary hypoplasia. Severe oligohydramnios in a male fetus with valves carries a poor neonatal prognosis, mainly from lung hypoplasia.