Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is suggestion of a left retrocardiac opacity which may represent pneumonia in the appropriate clinical setting . No pleural effusion or pneumothorax . Cardiomediastinal silhouette is within normal limits . No acute osseous abnormalities are identified .
    OUTPUT:
    
Left retrocardiac opacity which could represent atelectasis or pneumonia in the appropriate clinical setting .