Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Relatively low lung volumes are seen with secondary crowding of the bronchovascular markings and a retrocardiac opacity which is likely atelectasis . Superiorly , the lungs are clear . The cardiomediastinal silhouette is within normal limits . No acute osseous abnormalities . Free intraperitoneal air is again noted .
    OUTPUT:
    
1 . Low lung volumes with left basilar opacity which could be atelectasis noting that infection can not be excluded . 2 . Persistent free intraperitoneal air . Although significantly decreased in amount since prior CT scan given differences in technique , this is somewhat unexpected this far out from intervention from several weeks prior .