Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Subtle left base retrocardiac opacity most likely represents atelectasis , scarring , and vascular structures . Previously noted left upper lobe opacity appears to have resolved in the interval . No pleural effusion or pneumothorax is seen . Cardiac and mediastinal silhouettes are grossly stable .
    OUTPUT:
    
No acute cardiopulmonary process .