What is the mass likely made of? How would you confirm this?
The mass is high on both T1 and T2 weighted images, most likely representing fat. This can be confirmed with a fat saturated sequence.
What is the differential for a well circumscribed fatty mass in the anterior mediastinum?
Lipoma, liposarcoma, thymolipoma and mature teratoma (the latter three usually have solid components).
Limited images of an MRI of the chest demonstrate the mass to be of fat density (confirmed on fat saturated sequences - not shown).