Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Since prior , there has been persistence of a left retrocardiac opacity with obscuration of the left hemidiaphragm . The right lung is unchanged and grossly clear . There is a probable small left pleural effusion . There is no pneumothorax . Hemodialysis catheter and left PICC are unchanged in position .
    OUTPUT:
    
Persistent retrocardiac opacity with obscuration of the left hemidiaphragm , most likely represents progressive left lower lobe atelectasis .