Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post sternotomy . The cardiac , mediastinal and hilar contours appear unchanged . There is streaky opacity in the left lower lobe , partly effacing the left diaphragmatic contour , not significantly changed . There is no definite pleural effusion or pneumothorax . Mild degenerative changes are present along the thoracic spine .
    OUTPUT:
    
Patchy retrocardiac opacity , probably due to minor scarring or atelectasis .