Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Linear opacity at the left lung base likely represents atelectasis , otherwise , normal heart , lungs , pleural and mediastinal surfaces . No rib fracture is identified . If there are focal areas of pain , dedicated views of those areas are recommended .
    OUTPUT:
    
Opacity in the left lung base is new since ___ and most likely represents atelectasis , however , aspiration could have a similar appearance .