a. A large left pleural effusion
b. A large right pneumothorax
c. Atelectasis of the left lung
d. Pneumonia in the left lung
e. Unilateral pulmonary edema
The correct answer
Pneumonia in the left lung
Explanation
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There is opacification of the left hemithorax. There is no shift of the heart and mediastinal structures (i.e. the trachea). This eliminates pleural effusion and atelectasis as possibilities. A tension pneumothorax would displace the heart and mediastinal structures away from the side of the pneumothorax and would not cause complete opacification of the opposite lung. In addition, there should be no lung markings visible in the hemithorax which contains the pneumothorax. Either pneumonia or pulmonary edema could cause the findings shown, but pneumonia is a much more common cause.
