Thoracic Outlet Canada
Menu
|
Anatomy With respect to the anatomy of the thoracic outlet region, I refer you to my 1998 article (Appendix 3). This article shows that fibro-osseous anomalies at the level of the thoracic outlet are very common in an otherwise 'normal' population (45%). We also noticed that the same anomalies are universally present in all of our patients with TOS who came to surgery. In other words, these anomalies occur in nearly one-half of the general public. These anomalies do not in and of themselves necessarily cause symptoms. The anomalies have the effect, however, of 'setting the patient up' for the development of TOS. They predispose the patient to the development of TOS. In my experience, about half of the patients with symptomatic TOS will develop the syndrome following a specific traumatic event, whilst the other half do so spontaneously over time as result of the repetitive activities at work or of daily living. We know that anomalies posterior to the brachial plexus can often be shown by radiological means by the presence of true cervical ribs, vestigial cervical ribs or elongation of the C7 transverse processes. These elongated C7 transverse processes become continuous with a fibrous band that extends down to the superior aspect of the first rib. We also know that anomalies anterior to the plexus can seldom be identified by radiological means because they are entirely fibrous in nature and not imageable. It is for this reason that normal x-rays do not exclude the diagnosis of TOS. It is not uncommon to find both posterior and anterior bands in TOS patients coming to surgical exploration. These bands have the effect of narrowing the anatomical thoracic outlet (the space between first rib and clavicle). The brachial plexus and the subclavian vessels pass through the thoracic outlet. The narrowing caused by bands makes the neuro-vascular bundle more susceptible to compression. The clavicle presses backwards on this bundle when the arm is elevated or extended. The clavicle presses downwards when patients lift heavy objects. This drawing below is copied from my 1991 article and illustrates the band associated with an elongated transverse process of C7. This band is found posterior the plexus. 
The photograph below, with overlays, shown below illustrates a completely removed first rib. The arrow points to an anteriorly positioned non-imageable band that can trap the T1 nerve root. 
[arterial] | [venous] | [neurogenic] | [symptomatic] |