Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP portable upright chest film ___ at 18 51 is submitted .
    OUTPUT:
    
There is persistent but improving mild interstitial edema . More focal opacity in the retrocardiac region is seen with an associated effusion most likely reflecting partial lower lobe atelectasis , although pneumonia or aspiration should also be considered . A smaller right effusion is also present . No pneumothorax . Overall cardiac and mediastinal contours are stable .