Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest demonstrate hyperinflation of the lungs , with no evidence of pleural effusion , pneumothorax or focal consolidation concerning for pneumonia . There is relative paucity of lung markings in the bilateral upper lobes , compatible with underlying emphysema . Bibasilar insterstitial abnormality is again seen . The cardiomediastinal silhouette is unremarkable . Tracheal narrowing is again seen at the level of the aortic arch , unchanged compared to prior studies .
    OUTPUT:
    
Severe emphysema . Bibasilar interstitial abnormality , possibly due to mild superimposed edema . This finding may be chronic , as it is not significantly changed from prior studies , although this could be acute exacerbation seen at multiple time points .