My understanding from talking to my doctor is that the primary cause of TOS is something called perineural fiberous. which is very small, otfen to small to see on an MRI. The other common causes listed (which are easier to see on imaging) are often really secondary causes that only start to be a problem when you have the first problem.

Essentially the perineural fiberous is scar tissue around and in your nerves has had abnormal nerve growth into it. This cause your nerves to not be able to move normally and causes them to be stretched when they should not be,

That say, any nerve blocks offered can help isolate problems, it a good idea to do them.

In my case, the ortho though my reflex problems (in my hands) were from the spine (on exam before an MRI) but the reflexes became normal after a special brachial plexsus block. The neck MRI was pretty normal, just small nerinations typically of middle aged spines.

In my low back the spine nerve blocks made it really clear what the three causes of my low back pain were. My spine is pretty crumbled there so it's helpful to know what exactly is causing the problem