Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiomediastinal and hilar contours are within normal limits . There is a focal patchy opacity at the base of the left lung seen only on the frontal view . There is no evidence of pleural effusion or pneumothorax .
    OUTPUT:
    
Patchy left lower lobe opacity , which could represent a small / early focus of infection or atelectasis .