Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Chest PA and lateral radiograph demonstrates abnormal rounded contour of the left upper mediastinum which is likely related to known mediastinal mass , better evaluated on the ___ CT , though mass appears larger than those depicted on CT . Hilar and cardiac contours are unremarkable . Lungs are clear . No pleural effusion or pneumothorax evident . No osseous abnormality evident .
    OUTPUT:
    
Rounded border of upper mediastinum may correlate with known anterior mediastinal mass . If this border does in fact correspond with mass , it appears larger than on chest CT performed ___ .