Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The appearance of the left retrocardiac opacity has significantly improved , likely due to improved aeration on the current exam . Right lung is clear . No pleural effusion or pneumothorax . Hilar structures and cardiomediastinal silhouette is normal . There are chronic resorptive changes in the distal right clavicle .
    OUTPUT:
    
Significant improvement in left basilar opacity , likely due the improved aeration on the current exam . Residual left basilar opacity may be atelectasis , although infection can not be ruled out .