This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
Most common cause of urinary obstruction in a male infant is - 
Select and explain. 
A. Anterior urethral valves, B. Posterior urethral valves, C. Stone, D. Stricture
B: Posterior urethral valves
Answer: B: Posterior urethral valves 
Explanation: Ans. is 'b' i.e., Posterior urethral valve "The most common cause of severe obstructive uropathy in children is posterior urethral valves"._ Nelson Posterior urethral valves These are symmetrical folds of urothelium extending distally from prostatic urethra to external urinary sphincter. It most commonly lies just distal to the verumontanum or at the verumontanum. It occurs only in males. It behaves as flap valves so, although urine does not flow normally a urethral catheter can be passed without difficulty. Sometimes, the valves are incomplete and the patient remains without symptoms until adolescence or adulthood. Approximately 30% of patients experience end stage renal disease o Vesicoureteral reflux occurs in 50% of patients. o Diagnosis is made by a) Voiding cystourethrogram b) Endoscopy Both of these investigations clearly depict the site of obstruction. The diagnosis can be established prenatally by ultrasound.