Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: An opacity in the left lower lung base and retrocardiac area is likely a combination of atelectasis and pleural effusion , although pneumonia can not be ruled out . The right lung appears clear . No significant pulmonary edema . No free air . Bony structures are intact .
    OUTPUT:
    
Increased left lower lobe opacity , likely combination of effusion and atelectasis .