Classical appearances of extramedullary hematopoiesis, in this case from thalassemia. The paraspinal regions are a very common site.
The plain films are both abnormal - in particular a good example of the hilum overlay sign and also how one approaches the film to delineate the location of a mass in the mediastinum (anterior, middle, posterior).
The plain radiographs and CT together and the correlation of signs for the definitive diagnosis is the stuff of FRCR 2B and other fellowship examiners dreams.
Hey presto, don't you just love radiology!