A 2-day-old term male newborn presents with a distended abdomen, poor urinary stream, and respiratory distress. Palpation reveals a ballotable mass in the lower abdomen extending to the umbilicus. Ultrasound shows bilateral hydronephrosis, a thick-walled distended bladder, and a dilated posterior urethra. What is the most likely diagnosis?

• A Bilateral vesicoureteral reflux (grade V)
• B Posterior urethral valves ✓
• C Bilateral ureteropelvic junction obstruction
• D Neurogenic bladder

Explanation

Posterior urethral valves are the most common cause of lower urinary tract obstruction in male newborns. The triad of a poor stream, distended bladder, and bilateral hydronephrosis with a dilated posterior urethra (keyhole sign on ultrasound) is pathognomonic. Respiratory distress occurs due to diaphragmatic compression from the distended bladder and ascites. Bilateral VUR would not cause urethral dilatation or bladder outlet obstruction.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.