A young women has swelling in her lower neck, which is biops…

A young women has swelling in her lower neck, which is biopsied and diagnosed as Hodgkin disease.  A chest x-ray also reveals a mediastinal mass, which correlates with a positive PET/CT scan with increased SUV uptake in the same area. She has not experienced any fever, night sweats, or weight loss.  The most likely staging would be: