Timothy C. Hain, MD • Page last modified: July 19, 2015
Thoracic outlet syndrome (TOS) is an uncommon condition arising from compression of either the subclavian artery and/or the brachial plexus as the structures travel from the thoracic outlet to the axilla (arm pit). There are two forms -- vascular (from compression or other alteration of blood flow in the subclavian) and neurogenic (from compression of the brachial plexus). Neither one would be expected to cause any dizziness.
About 95% of TOS are neurogenic -- i.e. cause numbness/tingling/weakness symptoms in the arms, and don't cause any dizziness at all (Klassen et al, 2013). This leaves only 5% left that have any potential of causing dizziness.
Dizziness would seem very unlikely from TOS as the vertebral arteries ordinarily take off from the subclavians prior to any presumed compression in the TOS.
The thoracic outlet consists of three areas; the interscalene triangle, the costoclavicular space, and the pectoralis minor space or the subcoracoid space. (Klassen et al, 2013). With respect to the subclavian arteries, they typically ascend into the neck before arching laterally. They cross under the clavicle and over the first rib. They travel behind the anterior scalene muscle (and in front of the posterior scalene), and then descend to the outer border of the first rib at which point they become the axillary arteries (that go to the arms). The scalene muscles are located between the neck and ribs.
Anatomical variations in the thoracic outlet are the main cause. Common anomalies involve variations in insertion of the scalene muscles, presence of an (extra) cervical rib (Chang et al, 2013; Weber et al, 2013) fibrous or muscular bands, variations in insertion of the pectoralis minor, and anomalies in the course of neurovascular structures.
Cervical ribs are said to be more commonly found in the subclavian compression patients (i.e. dizzy patients), and various muscular anomalies more common in the neurogenic (i.e. non-dizzy) patients. Cervical ribs occur in about 1-6% of the general population, and are slightly more common in persons with TOS (about 10%).
Usually there is initially an attempt to improve posture. If this doesn't work, surgical treatment is the mainstay to treat anatomical variations such as extra ribs.
For overuse syndromes -- such as hypertrophy of the scalenes from exercise the obvious solution is to stop exercises or occupations that make the scalenes or pectoral musles enlarge.