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Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
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What does Hirschsprung's disease involve? SELECT ONE.
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The correct answer is  In Hirschsprung's disease, there is an absence of myenteric plexus in the upper anal segment (i.e., the most distal portion of the cloaca). In 15%, the myenteric plexus involves only the upper anus; in 70%, the rectum is also involved; and in 15%, part of the colon is also involved. The abnormal segment is contracted; whereas, the dilated bowel is proximal to the diseased segment.