A newborn boy has a palpably distended bladder, a weak urinary stream, and bilateral flank masses. Ultrasound shows bilateral hydronephrosis and a thick-walled bladder. Which investigation will confirm the diagnosis?
- A Renal scintigraphy with DMSA
- B Retrograde urethrogram showing a bulbar stricture
- C Micturating cystourethrogram showing dilatation of the posterior urethra ✓
- D Urodynamics demonstrating detrusor underactivity
Correct answer: C. Micturating cystourethrogram showing dilatation of the posterior urethra
Explanation
Posterior urethral valves, the commonest cause of bladder outlet obstruction in male infants, are diagnosed on micturating cystourethrogram, classically showing a dilated posterior urethra with a sharp transition at the valve site, plus trabeculated bladder and vesicoureteric reflux. C retrograde urethrogram evaluates anterior strictures and trauma, not valves. DMSA assesses renal scarring but cannot show the obstructing membrane.
Reference: Campbell-Walsh Urology, 12th ed.
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