Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Since the prior radiograph , there has been interval development of a new left retrocardiac opacity , which silhouettes the left heart border and part of the lower thoracic spine on lateral view . These findings are concerning for pneumonia . There are no pleural effusions or pneumothorax . No pulmonary edema . Cardiomediastinal silhouette is within normal limits . No acute osseous abnormalities .
    OUTPUT:
    
New left lung base opacity , concerning for either a lingular or left lower lobe pneumonia . Recommend repeat CXR in ___ weeks after treatment to document resolution .