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
[{'content': 'A most common cause of urinary obstruction in a male infant is – \nSelect and explain. \nA. Anterior urethral valves, B. Posterior urethral valves, C. Stone, D. Stricture', 'role': 'user'}, {'content': 'Answer: B \nExplanation: "The most common cause of severe obstructive uropathy in children is posterior urethral valves".___\xa0Nelson\nPosterior urethral valves\n\nThese are symmetrical folds of urothelium extending distally from prostatic urethra to external urinary sphincter.\nIt most commonly lies just distal to the verumontanum or at the verumontanum.\nIt occurs only in males.\nIt behaves as flap valves so, although urine does not flow normally a urethral catheter can be passed without difficulty.\nSometimes, the valves are incomplete and the patient remains without symptoms until adolescence or adulthood.\nApproximately 30% of patients experience end-stage renal disease\nVesicoureteral reflux occurs in 50% of patients.\nDiagnosis is made by\n\n\nVoiding cystourethrogram\nEndoscopy\n\n\nBoth of these investigations clearly depict the site of obstruction.\nThe diagnosis can be established prenatally by ultrasound.', 'role': 'assistant'}]