Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Compared to the prior study , there is a new retrocardiac and left lower lobe opacity opacity which may represent atelectasis , aspiration or pneumonia in the appropriate clinical setting . The cardiac , hilar and mediastinal contours are normal . No pneumothorax .
    OUTPUT:
    
New left lower lobe and retrocardiac opacities may represent atelectasis or pneumonia .