Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Several displaced left rib fractures are again noted . Persistent opacity at the left lung base is most compatible with small pleural effusion and compressive lower lobe atelectasis . Difficult to exclude a superimposed pneumonia . The right lung is clear . There is no pneumothorax . The heart normal . Mediastinal contour unremarkable .
    OUTPUT:
    
Persistent small left pleural effusion with compressive lower lobe atelectasis , difficult to exclude a superimposed pneumonia . Multiple displaced left rib fractures again noted .