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: Radiology
[{'content': '. If the right cardiac silhouette is obliterated, it means the pathology involves: \nSelect and explain. \nA. Right middle lobe, B. Right lower lobe, C. Right atrium of hea, D. Right ventricle of hea', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Right middle lobe An intra-thoracic radio-opacity, if in anatomic contact with a border of hea, aoa or diaphragm, will obscure that border. This is known as silhouette sign. An intra-thoracic lesion not anatomically contiguous with a border or a normal structure will not obliterate that border. When examining the lung fields of a normal CXR, the silhouettes of the hea borders, the ascending and descending aoa, the aoic knob and the hemidiaphragms should be clear. Obliteration of any of these silhouettes by a radio-opacity can be caused by infection in the lung, blood, pus, etc. All of these silhouettes, or structures, are in contact with a specific poion of the lung. Therefore, by determining exactly which structure is obliterated, you can determine where the lung pathology is located. Silhouette/Structure Contact with lung Upper right hea horderlascending aoa Anterior segment of RUL Right hea border RML (medial) Upper left hea border Anterior a sement of LUL ,,, Left hea border Lingula (anterior) Aoic knob Apicoposterior segment of LUL Hemidiaphragms Basal seg.of lower lobes', 'role': 'assistant'}]