Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Cardiac silhouette size is normal . The aortic knob appears dilated to 4 .5 cm , more pronounced than that seen on the prior CT of the chest from ___ . Hilar contours are normal . Pulmonary vasculature is normal . Lungs are clear . No pleural effusion or pneumothorax is seen . No acute osseous abnormalities detected .
    OUTPUT:
    
1 . Dilatation of the aortic knob , more pronounced than on the prior CT . Chest CTA is recommended for further assessment given the history of chest pain . 2 . No evidence for pneumonia .