Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest demonstrate normal lung volumes , which accentuate the bronchovascular markings . There is no pleural effusion , focal consolidation or pneumothorax . Hilar and mediastinal silhouettes are unchanged . Heart size is normal . There is no pulmonary edema . Retrocardiac opacity , projecting over spine on the lateral view not seen on prior . Partially imaged upper abdomen is unremarkable . Small hiatal hernia .
    OUTPUT:
    
Retrocardiac opacity , likely atelectasis or infection in the appropriate clinical setting .