Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiomediastinal and hilar contours are normal . Trace left pneumothorax is not seen on the current study . Vague increased density along the left lower lung likely correlates to previously seen hemothorax , although lung contusion is possible . New left retrocardiac opacity not seen on the prior CT is present . Known rib fractures are better assessed on the recent chest CT .
    OUTPUT:
    
1 . No left pneumothorax . 2 . New left retrocardiac opacity , which may represent atelectasis , aspiration , or pneumonia in the correct clinical setting .