Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Linear density in the retrocardiac region appears to project over the spine on the lateral view . The morphology suggests subsegmental atelectasis in the left lower lobe , however , pneumonia is also a possibility in the appropriate clinical circumstance . MInimal blunting of the right cp angle is present . The remainder of the lungs are clear . There is no vascular congestion or pleural effusion . The cardiomediastinal and hilar contours are within normal limits .
    OUTPUT:
    
Linear opacity in the left lower lobe , likely atelectasis , though pneumonia is possible in the appropriate clinical circumstance .