This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Imaging of Alveolar Lung Disease, Subject name: Radiology
[{'content': 'Air bronchogram on chest Xray denotes - \nSelect and explain. \nA. Intrapulmonary lesion, B. Extrapulmonary lesion, C. Intrathoracic lesion, D. Extrathoracic lesion', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Intrapulmonary lesionAir bronchogramo Normally, air in the bronchi through normal lung parenchyma is not visible as the wall of the bronchi are very thin and they are surrounded by air in the alveoli. Howerver, if the surrounding alevoli are opacified (e.g., in consolidation), air in bronchi become visible as linear branching structure. Because air in bronchi is visualized it is called air bronchogram. Air bronchogram indicates intrapulmonary pathology. It excludes any pleural or mediastinal pathology . Air bronchogram can be caused by : -Common causes : - Consolidation (m.c. cause), Pulmonary edema, Hyaline membrane disease.Less common causes : - Sarcoidosis, lymphoma, alveolar proteinosis, ARDS, Alveolar cell carcinoma. Normal person w ith phase of long exposure.", 'role': 'assistant'}]