Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is complete opacification at the left lung base obscuring the left costophrenic angle , which is new from the prior study . A small left pleural effusion is difficult to exclude on this single AP view . The right lung is relatively clear . No pneumothorax is detected . The pulmonary vasculature is not engorged . The cardiac silhouette is incompletely evaluated due to opacification of the left lung base . The mediastinum appears prominent compared to the most recent prior study , which is in part related to technique ; however , there is indistinctness at the aortic knob for which further evaluation with chest CTA is warranted .
    OUTPUT:
    
1 . Prominent mediastinum in part related to technique with indistinct aortic knob . Further evaluation with chest CTA is pending . 2 . Left basilar opacification may represent pneumonia or lung collapse .