[The first structure compromised in these compression syndromes is the subclavian artery (five percent of all cases).
This great vessel leaves the thorax by arching over the first rib from behind the scalenus anticus muscle and in front of the scalenus medius muscle.

This egress of the artery through the interscalene triangle places it at high risk for compression by the scalenes whenever there is muscular hypertrophy. Compression of the subclavian artery gives rise to ischemia, decreased peripheral pulses, coolness, pallor, and possible cyanosis of the upper extremity.

Running directly beside the subclavian artery, with the exception of passage anterior to the scalenus anticus muscle, is the subclavian vein. Due to the vein’s escape from inter-muscular passage, venous compression syndromes are much less common (one percent), but involve swelling in the hands whenever the vein is involved.

The third component of the neurovascular bundle, the brachial plexus, also follows the same course as the subclavian artery through the interscalene triangle, only slightly more posterior and lateral. It is the most frequently involved structure in TOS (95 percent of all cases) and produces paresthesias, anesthesias, pain, weakness, and atrophy in the upper extremity as a result of its compression.

Finally, the great lymph channels also pass through Sibson’s fascia, following the course of the neurovascular bundle, but are rarely compressed.
] http://spinetalk.conforums.com/index...num=1153540139

Chart of symptoms and causes -
http://tos-syndrome.com/newpage12.htm