Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest were obtained . Subtle left base opacity is seen , which could be due to an early infectious process . The right lung is clear . There is no pleural effusion or pneumothorax . Cardiac and mediastinal silhouettes are unremarkable .
    OUTPUT:
    
Subtle left base retrocardiac opacity , can not exclude infection in the appropriate clinical setting .