Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is a mild interstitial abnormality similar to the prior study , but no focal opacification . There is no pleural effusion or pneumothorax . The cardiac , mediastinal and hilar contours appear unchanged .
    OUTPUT:
    
Mild interstitial abnormality , possibly due to slight vascular congestion or airway inflammation , but not significantly changed .