Sorry to hear that you got new issues to tackle, @KoolDude…
I’d still suggest to reconsider physiotherapy approach to put the ribcage/shoulders/scapula/neck curvature in better shape.
My reasoning is that if you have straight neck, the ribcage might be staying at a different angle than if you had proper curvature.
Also, if you expand the ribcage by deeply inhaling (so that the chest “puffs out”), the sternum also moves to a different spot in relation to the spinal column.
Not to forget that as you said, the compression wasn’t present in your CT when you kept your arms above the head.
Another important point, relaxed shoulders should naturally hang slightly higher than “military stance” which has been popularized by some folks including mediocre physiotherapists, stating that “you should pull your scapulae down to the back pockets”.
Finally, I somehow relate the “hands up” CT scan with the old topic:
All that leads to possibilities, that it’s fixable without the surgical intervention.
Ah, one more thing: lifting the arms above the head indeed may change a lot of blood flow paths, like in this TOS example:
