Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lungs are well - expanded with a heterogeneous left lower lobe opacity . No additional opacity . No pleural effusion or pneumothorax . Heart size , mediastinal contour , and hila are unremarkable .
    OUTPUT:
    
1 . No pneumothorax . 2 . Patchy left retrocardiac opacity is likely due to atelectasis or aspiration in the absence of infectious symptoms . Early or resolving infectious pneumonia is also possible in the appropriate clinical setting .