Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is improved aeration at the left lung base with persistent retrocardiac opacity , concerning for aspiration or pneumonia . Pulmonary vascular prominence with minimal interstitial haze may be secondary to mild fluid overload . No pneumothorax is detected . Heart size appears mildly enlarged , which may be exaggerated by AP technique and slightly low lung volumes . Mediastinal contours are within normal limits .
    OUTPUT:
    
1 . Improved aeration at the left lung base with persistent retrocardiac opacity , concerning for aspiration or pneumonia . 2 . Mild interstitial pulmonary edema . Viral or atypical infection may also have this appearance .