Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Extensive airspace opacification within the left lung with minimal subpleural sparing has improved slightly compared with the immediate prior study but remains extensive . There is similar airspace opacification of the medial right lung base with new subsegmental atelectasis adjacent to the minor fissure . There is no pleural effusion , pneumothorax , or pulmonary edema . The cardiomediastinal silhouette is within normal limits .
    OUTPUT:
    
Slight interval improvement in extensive airspace opacity involving the left lung and medial right lung base , differential etiologies include aspiration , aspiration pneumonitis , or pneumonia .