Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Cardiac , mediastinal and hilar contours are unremarkable . The aorta is mildly tortuous . The pulmonary vasculature is normal . Patchy opacity within the left lung base likely reflects an area of atelectasis . No focal consolidation , pleural effusion or pneumothorax is identified . There are no acute osseous abnormalities .
    OUTPUT:
    
Patchy opacity in the left lung base , likely atelectasis .