Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . The mediastinal and hilar contours are unremarkable . The pulmonary vascularity is normal . There is a linear area of opacification within the left lung base which likely reflects an area of atelectasis . No pleural effusion or pneumothorax is present . There are mild degenerative changes of the thoracic spine . A subcentimeter granuloma within the left upper lung field is unchanged .
    OUTPUT:
    
Subsegmental atelectasis in the left lung base .