Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Heart size is top normal , exaggerated by low lung volumes . Cardiomediastinal contours are stable . Increased retrocardiac opacity may represent atelectasis , but is compatible with infection in the appropriate clinical setting . No substantial pleural effusion or pneumothorax . Right PICC terminates in the upper SVC . Left humeral head screws are in stable position .
    OUTPUT:
    
New retrocardiac opacity may represent atelectasis but could represent infection in the appropriate clinical setting .