Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is a persistent opacity at the left lung base which likely reflects atelectasis , as seen on prior chest CT . There is persistent mild cardiomegaly . No pneumothorax is identified . Calcifications of the aortic arch and descending aorta are again noted . Rounded opacity projecting over the right apex is likely external to the patient .
    OUTPUT:
    
Opacity at the left lung base which likely reflects atelectasis , unchanged since CT chest from ___ .