Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is o pacitiy at the left lung base , but is unchanged since ___ when patient was asymptomatic . This suggests chronic scarring . Otherwise , there are no focal consolidations , pleural effusions or pneumothorax . No evidence of hilar lymphadenopathy . Cardiomediastinal silhouette is within normal limits . No acute osseous abnormalities .
    OUTPUT:
    
Left lung base opacity , likely due to chronic atelectasis . No hilar lymphadenopathy .