Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Chest PA and lateral radiographs demonstrate unremarkable mediastinal , hilar , and cardiac contours . Bibasilar atelectasis is identified . Retrocardiac opacity likely represents atelectasis exaggerated by low lung volumes , though can not exclude developing infectious process . No pleural effusion or pneumothorax evident .
    OUTPUT:
    
Bibasilar opacities , more pronounced in retrocardiac space , are likely atelectasis but can not exclude developing infectious process .