There is no ‘gold standard’ for the diagnosis of neurogenic TOS. Clinical tests such as Adson’s test are known to have low accuracy. No lab test or electrophysiologic test has proven accuracy. This article references a publication by Thompson, et al that states, “…the diagnosis is based largely on the exclusion of other conditions and a recognition of stereotypical clinical patterns.” Well, that is no gold standard, either.
It should be obvious that I am an advocate of modern diagnostic imaging in patients with TOS. However, there remains a lot of resistance to such imaging, despite the lack of a gold standard. As an example, in 2016, the Reporting standards of the Society for Vascular Surgery for thoracic outlet syndrome: Executive summary stated the following regarding diagnostic imaging of patients with neurogenic TOS:
“A chest radiograph or cervical spine series should be performed in all patients and the presence or absence of a cervical rib or elongated C7 transverse process reported”
Researchers first demonstrated congenital soft tissue variations in the thoracic outlet more than a century ago. TOS authorities widely accept the fact that such variations may cause compression or tension on the brachial plexus, resulting in neurogenic TOS. This mechanism of nerve entrapment is well-known in other areas of the body.
Can you see any congenital soft tissue variations in this radiograph? I can’t.
Cervical ribs and elongated C7 transverse processes are relatively common in humans. About o.5 to 1% of people have them, and most of these people do not have TOS. Looked at another way, most TOS patients do not have these bony variations. The presence of a cervical rib does not rule in or rule out TOS.
Radiographs were first performed in 1895. They show bones with good detail. They cannot demonstrate congenital soft tissue variations or compression of the brachial plexus.
Today, we use MRI for almost all diagnostic imaging involving soft tissue structures. MRI is widely used for assessing knee ligaments, the rotator cuff of the shoulder, or elbow ligament damage in baseball pitchers. MRI has been proven accurate in assessing the soft tissues of the thoracic outlet.
Scalene muscles may become ‘tight,’ but the stated effect of pulling “the first rib closer to the collar bone.” is purely conjecture. The anterior scalene muscle originates on the cervical spine and inserts on the first rib. While the cervical spine is flexible, the first rib is rather tightly bound to the entire rib cage. Should the anterior scalene muscle contract, it is far more likely that the neck would flex forward than the entire rib cage would elevate. Additionally, the position of the clavicle is independent of the anterior scalene muscle. To the best of my knowledge, there is no published evidence of the first rib being elevated by a ‘tight’ anterior scalene muscle. Nonetheless, radiographs cannot show the space between the first rib and clavicle. MRI has been proven to show this space, as well as the brachial plexus that passes through this space.