Medical Challenge

For my non medical readers, this is an abnormal CT scan.  The CT scan takes a transverse image sliced through, so you are looking at the patient sliced in half transversely.  This is the chest area. I will orient you:

The whitish circle and v-shaped part is the vertebral column.  So you know that is the back.   Bone shows up whiter than organs.  The small whitish lines in a circle are the