Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is a linear opacity at the left lung base , which appears to be discoid atelectasis when also examined on the subsequent CT . The lungs are otherwise clear . The hilar and cardiomediastinal contours are normal . There is no pneumothorax or pleural effusion . Pulmonary vascularity is normal .
    OUTPUT:
    
No acute intrathoracic process .