There are many reasons for superior mediastinal widening. If this was seen on a plain chest xray it must be compared with any older chest xrays to see if it was present before. There are many structures in this area and some of them are normal. At times there can be lymph nodes that enlarge in this area for many reasons including infection, lymphoma and inflammation. Also, the thymus gland may cause mediastinal enlargement. The thyroid can sometimes cause the abnormalities here. If not done a chest CT scan can help define the anatomy better and help guide next steps. You may consider seeing a lung specialist or a thoracic surgeon to discuss the implications of your abnormal chest xray finding and also correlate with the cough and throat pain you have had. I hope this information is helpful and you find some relief soon.