Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low . Cardiomediastinal silhouette is normal . There is no large pleural effusion . There is no pneumothorax . There is a focal left retrocardiac opacity . Views of the upper abdomen are unremarkable .
    OUTPUT:
    
Focal left retrocardiac opacity , which may represent atelectasis or pneumonia in the correct clinical setting .