Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is increased opacity in the retrosternal region on the lateral view , correspond to possibly the left upper lung . Mild increase in retrocardiac atelectasis is noted . Otherwise , the lungs are clear . The heart size is normal . No pneumothorax , pulmonary edema , or pleural effusion .
    OUTPUT:
    
Increased opacity in the retrosternal region on the lateral view , possibly corresponding to the left upper lobe , is concerning for pneumonia .