Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Low lung volumes leads to crowding of the bronchovascular structures . Retrocardiac airspace opacities likely reflect atelectasis . The upper lungs are grossly clear . Mild tortuosity to the descending thoracic aorta is present . The cardiomediastinal silhouette is otherwise within normal limits .
    OUTPUT:
    
Retrocardiac atelectasis without overt pneumonia or pulmonary edema .