Was it just the standard MRI that was done -or a special MRA or MVA?

Generally a standard MRI doesn't really show TOS anyway, unless there is some obvious anomalies in the in the bones or ligaments or other solid structures.
It's basically used to rule out the neck or c spine or any other structural causes for the pain and symptoms.

The hard nodule in armpit could be a triggerpoint or blocked lymph node.
Of course you should have it checked for something more serious also.
Is it there all the time or does it come and go?

Swelling can be a symptom of vascular compressions as well as color changes.
I'll bump up or testing suggestions for you.
a thread on testing and discussions-
http://neurotalk.psychcentral.com/sh...2184#post92184