Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright and lateral views of the chest provided . Subtle opacity in the left lower lung could represent atelectasis versus an early pneumonia in the correct clinical setting . No large effusion or pneumothorax . Right lung is clear . Heart size appears grossly within normal limits . The mediastinal contour is unchanged with slightly unfolded thoracic aorta . Bony structures are intact . No free air below the right hemidiaphragm .
    OUTPUT:
    
Subtle opacity at the left lung base is concerning for atelectasis versus an early pneumonia in the correct clinical setting .