Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Low lung volumes cause bronchovascular crowding and accentuation of the cardiac silhouette . There is moderate retrocardiac opacity . There may be a small left effusion . There is no pneumothorax . Cardiomegaly is moderate . Imaged osseous structures are intact . No free air below the right hemidiaphragm is seen .
    OUTPUT:
    
1 . Apparent widening of the mediastinum is likely due to low lung volumes , patient positioning , and AP technique . 2 . No pneumothorax or pulmonary edema . 3 . Retrocardiac opacity is likely due to atelectasis , but in the appropriate clinical setting , infection could be a possibility .