The most common cause of severe obstructive uropathy in children is

Posterior Urethral ValvesThe most common cause of severe obstructive uropathy in children is posterior urethral valves, affecting 1 in 8,000 boys. The urethral valves are tissue leaflets fanning distally from the prostatic urethra to the external urinary sphincter.Valves are of unclear embryologic origin and cause varying degrees of obstruction. Ref: Nelson Textbook of Pediatrics; 20th edition; Page no: 2574