Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Bronchovascular markings are accentuated by low lung volumes . There is an opacity at the left lung base . A small pleural effusion is likely also present . Right lung field is essentially clear . No pneumothorax . Heart size is top - normal . No acute osseous abnormalities identified . Old left - sided rib fractures are redemonstrated .
    OUTPUT:
    
1 . Left lung base opacity , potentially atelectasis in the setting of low lung volumes although pneumonia is entirely possible . 2 . Small left pleural effusion .