This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology and Rheumatology, Subject name: Medicine
[{'content': 'A very tall, slender 16-year-old boy is referred for evaluation of an abnormal CXR. He reports no pulmonary or cardiac symptoms, and feels well. On physical examination, he has long fingers, pectus excavatum, and a high arched palate. Which of the following is most likely to be seen on his CXR? \nSelect and explain. \nA. dextrocardia, B. aortic dilatation, C. pneumothorax, D. apical interstitial fibrosis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In Marfan syndrome, inheritance is autosomal dominant, and the aortic lesion is a cystic medial necrosis with loss of elastic tissue, resulting in aneurysm formation. Pneumothorax can occur but is not as characteristic. Mitral valve prolapse can also be part of the syndrome. Dislocation of the lens is the most apparent eye abnormality. Severe chest deformities and long limbs are characteristic. High, arched palate; high pedal arches; and pes planus are common.', 'role': 'assistant'}]