Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A portable frontal chest radiograph demonstrates low lung volumes with increased prominence of the cardiac silhouette and bronchovascular crowding . There is bibasilar atelectasis . A retrocardiac opacity is again seen and probably unchanged compared to the prior radiograph , again possibly representing atelectasis , but superimposed pneumonia can not be excluded . No pleural effusion or pneumothorax is identified .
    OUTPUT:
    
Low lung volumes , with bronchovascular crowding and bibasilar atelectasis . A retrocardiac opacity is redemonstrated , likely unchanged compared to the prior exam . This again may represent atelectasis , but superimposed pneumonia can not be excluded .