This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Embryology and abdominal wall layer, Subject name: Anatomy
[{'content': 'A 4-day-old baby boy has not defecated since coming home from the hospital even though feeding has been normal without any excessive vomiting. Rectal examination reveals a normal anus, anal canal and rectum. However, a large fecal mass is found in the colon and a large release of flatus and feces followsthe rectal examination. Which of the following conditions would be suspected? \nSelect and explain. \nA. Imperforate anus, B. Anal agenesis, C. Anorectal agenesis, D. Colonic aganglionosis', 'role': 'user'}, {'content': 'Answer: D \nExplanation: This baby boy suffers from colonic aganglionosis, or Hirschsprung disease, which results in the retention of fecal material, causing the normal colon to enlarge. The retention of fecal material results from a lack of peristalsis in the narrow segment of colon distal to the enlarged colon. A biopsy of the narrow segment of colon would reveal the absence of parasympathetic ganglion cells in the myenteric plexus caused by failure of neural crest migration.', 'role': 'assistant'}]