Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Previously described right basilar focal opacity has resolved . There is decreased aeration at the left lung base , which could be due to a combination of atelectasis , effusion , or consolidation . Accounting for patient positioning , the cardiomediastinal contours are unchanged . No pneumothorax . Old healed left upper posterior rib fractures are unchanged .
    OUTPUT:
    
Left basilar opacity could be any combination of atelectasis , infection , or effusion . Consider PA / lateral chest radiograph if patient is amenable .