Hi, Thanks for writing in. If your swelling is stable in size, painless, not associated with lymph nodes and not growing fast then it is most likely a benign condition. Ultrasound scan shows muscles and subcutaneous structures in great details but will not show much bone related lesions. X ray on the other had shows bones well and less about fat and soft tissues. Both the above problems can be solved by doing a CT scan of the chest. It will show the exact size, origin and content of the lesion. It will also show if there are more lesions and if there is any extension of the lesion. A small amount of contrast given during CT scan will be able to tell about any rich blood supply to the lesion. Meeting up with a surgical oncologist is equally important. They will see your report and advise you if biopsy is required. Nowadays biopsy is done with minimal invasive techniques under guidance of CT scan and it is a almost painless office procedure. Even the primary doctors suspicion of a lipoma and if it is adherent to the structures below will be known on CT. Biopsy will be done only if necessary. If it is a clear benign lesion then nothing needs to be done unless you are having any discomfort. Hope this helps