Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral chest radiographs again demonstrate sternal wires and a partially imaged cervical and lumbar fixation hardware . Lung volumes are low , with increased prominence of the cardiac silhouette and bronchovascular crowding . A retrocardiac opacity is unchanged and again may represent atelectasis .
    OUTPUT:
    
1 . Retrocardiac opacity may represent atelectasis , but superimposed infection can not be excluded . 2 . Low lung volumes with increased prominence of the cardiac silhouette and bronchovascular crowding .