Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Left chest wall port catheter terminates over the right atrium . Heart size and mediastinal contours are stable . There is moderate heterogeneous retrocardiac opacification which may represent atelectasis , however pneumonia is a possibility . Mild linear opacification at the right lung base has the appearance of atelectasis . No pleural effusion or pneumothorax .
    OUTPUT:
    
Retrocardiac opacity , possibly representing atelectasis or pneumonia .