A newborn male infant presents with a palpably distended bladder, weak dribbling urine stream and bilateral flank masses. Ultrasound shows bilateral hydronephrosis and a dilated posterior urethra. Which single investigation will confirm the diagnosis?

• A Retrograde urethrography
• B Diuretic renography
• C Urethrocystoscopy under anaesthesia
• D Micturating cystourethrogram ✓

Explanation

The clinical picture is classic for posterior urethral valves, the commonest cause of lower urinary tract obstruction in male infants. A micturating cystourethrogram demonstrates the dilated posterior urethra above the valves, giving the characteristic spinetop appearance, along with a trabeculated bladder and often high-grade vesicoureteric reflux. Retrograde urethrography may fail to show the valves because a catheter passing retrogradely holds them open. Cystoscopy confirms but does not document the dynamic voiding picture, and renography assesses function, not anatomy.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.