Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac , mediastinal and hilar contours appear stable . There is bilateral heterogeneous opacification which is again worse on the right than left but substantially improved , probably indicating improvement in background pulmonary edema . However patchy opacities persist and there is volume loss with persistent opacification at the lung bases , greater on the left than right .
    OUTPUT:
    
Persistent opacity at the left lung base , with a configuration that is commonly due to atelectasis although pneumonia is not excluded . Improvement in diffuse lung opacification suggesting decreased fluid overload . However , differential considerations for persistent patchy asymmetric opacities include resolving alveolar edema or possibly pneumonia .