Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Patchy opacity is present at the left lung base . The cardiomediastinal silhouette and hilar contours are stable . Calcifications of the aortic arch are again noted . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
Patchy opacity at the left lung base may represent atelectasis , although a superimposed infection can not be excluded in the appropriate clinical setting .