Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Please note , low lung volumes limit evaluation . There is subtle opacity at the left lung base which could represent atelectasis or bronchovascular crowding . Please note however in the correct clinical setting and early pneumonia can not be excluded . No large effusion or pneumothorax . Bony structures are intact . No free air below the right hemidiaphragm .
    OUTPUT:
    
Subtle opacity at the left lung base is likely atelectasis , though an early pneumonia in the right clinical setting can not be excluded .