Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Cardiac , mediastinal and hilar contours are normal . Pulmonary vasculature is not engorged . Streaky opacity in the retrocardiac region likely reflects left lower lobe atelectasis . No focal consolidation , pleural effusion or pneumothorax is present . There is no acute osseous abnormality identified .
    OUTPUT:
    
Streaky retrocardiac opacity , likely atelectasis .