The three compartments are interscalene triangle, costoclavicular space, and retropectoralis minor space.
MRI confirmed compression in her right subclavian artery within the interscalene triangle triangle distally (Figure 1).
Particularly, the brachial plexus components can be affected at the interscalene triangle
, costoclavicular space, or less commonly, the pectoralis minor space.
 The majority of cases result from anatomical distortion at the interscalene triangle
.  For various reasons, the described anatomical spaces transform and evolve into 'entrapment spaces'.
TOS is one such general term used for problems stemming from nerve or blood vessel compression in their passage from the cervical area toward the axilla and proximal arm either at the interscalene triangle
, the costoclavicular triangle, or the subcoracoid space.
The brachial plexus, namely the ventral rami of the fifth cervical and first thoracic (C5-T1) spinal nerves, exit the vertebral column and pass through the interscalene triangle
to enter the axilla.
The roots unite to form the upper (C5 and C6 roots), middle (C7 root), and lower (C8 and T1 roots) "trunks" in or near the cleft between the anterior and middle scalene muscles known as the interscalene triangle
. The subclavian artery travels through the interscalene triangle
with the plexus, while the subclavian vein courses anteriorly to the anterior scalene muscle.