Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Subtle retrocardiac basilar opacity , better seen on the lateral view , most likely is due to overlapping structures and mild atelectasis , however , underlying aspiration or less likely infection are not excluded , but felt less likely . No pleural effusion or pneumothorax is seen . The cardiac silhouette is top - normal to mildly enlarged . The aortic knob is calcified . No overt pulmonary edema is seen .
    OUTPUT:
    
Subtle retrocardiac basilar opacity , better seen on the lateral view , most likely is due to overlapping structures and mild atelectasis , however , underlying aspiration or less likely infection are not excluded , but felt less likely . No pleural effusion or pneumothorax is seen . The cardiac silhouette is top - normal to mildly enlarged . The aortic knob is calcified . No overt pulmonary edema is seen .