Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Portable AP upright chest radiograph is obtained . The lungs are clear bilaterally without focal consolidation , effusion , or pneumothorax . Clips are noted in the right axilla . The heart size is normal . There is an unusual configuration of the mediastinum which is stable from prior exams and likely reflects the extensive collateral vessels due to known left subclavian and brachiocephalic venous stenosis . Bony structures are intact . No free air below the right hemidiaphragm .
    OUTPUT:
    
No acute intrathoracic process .