A neonatal boy presents with poor urinary stream and a palpable suprapubic mass. Voiding cystourethrogram shows a dilated posterior urethra with an abrupt transition to a normal calibre anterior urethra, plus a trabeculated bladder and bilateral vesicoureteric reflux. What is the most likely diagnosis?

• A Anterior urethral valve
• B Posterior urethral valve ✓
• C Urethral stricture
• D Prune belly syndrome

Explanation

Posterior urethral valves are the commonest cause of lower urinary tract obstruction in male infants. The VCUG shows dilatation of the posterior urethra down to the level of the valve with an abrupt caliber change at the membranous urethra, often described as a keyhole appearance, together with a thick walled trabeculated bladder and high grade reflux. Anterior urethral valves are far rarer and cause dilatation distal to the lesion, while prune belly syndrome shows a lax abdominal wall without an obstructing membrane.

Reference: Grainger and Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.