Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: An interstitial abnormality has improved substantially . There is suggestion of persistent reticulation in the lower lungs , however , which suggests underlying interstitial disease , as was reported previously . There is no focal opacification suggestive of pneumonia . The cardiac , mediastinal and hilar contours appear unchanged . Although difficult to exclude , there are no definite pleural effusions . There is no pneumothorax .
    OUTPUT:
    
No definite evidence of acute abnormality , although a persistent heterogeneous predominantly peripheral interstitial abnormality suggests underlying interstitial lung disease .