This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Surgery
[{'content': 'Most common cause of urinary retention in children includes \nSelect and explain. \nA. Posterior urethral valves, B. Urethral stenosis, C. Urethral aplasia, D. Ectopic ureteric opening', 'role': 'user'}, {'content': 'Answer: A \nExplanation: (A) Posterior urethral valves # Posterior urethral valves: These constitute an important cause of distal urinary tract obstruction in boys.> Dribbling, abnormal urinary stream, palpable bladder and recurrent UTI are the usual presenting features.> The presence of severe obstruction in the urinary tract in utero may lead to renal dysplasia.> Mild to moderate impairment of renal function may be present at birth.> The diagnosis is made on MCU, which shows dilated posterior urethra and valves at its junction with anterior urethra.', 'role': 'assistant'}]