Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: On the frontal view , there is an apparent focal left base opacity , which may represent overlap of structures and is not well seen on the lateral view ; however , a small focus of infection is not excluded . The right lung is clear . There is no pleural or pericardial effusion . The cardiac and mediastinal silhouettes are unremarkable .
    OUTPUT:
    
Subtle left base opacity may be due to overlap of structures ; however , a small focus of infection is not excluded in the appropriate clinical setting .