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The thoracic outlet comprises the anatomical spaces through which the brachial plexus passes, from the cervical foramina to the emergence of its terminal branches in the axillary region. It can be divided into three parts: the interscalene space, the costoclavicular space, and the retropectoralis minor space.
Interscalene Triangle:
The interscalene triangle is the space defined by the muscular masses of the anterior and middle scalene muscles, above the clavicle.
Costoclavicular Space:
The costoclavicular space is bounded anteriorly and superiorly by the clavicle and the subclavius muscle, and inferiorly by the first rib where the subclavian vein joins the course of the subclavian artery and the trunks of the brachial plexus.
Retropectoralis Minor Space:
The retropectoralis minor space is defined anteriorly by the pectoralis minor muscle and posteriorly by the thoracic wall and the subscapularis muscle.
Dynamic Assessment of the Thoracic Outlet in Magnetic Resonance Imaging:
The imaging protocol for the study of the thoracic outlet is traditionally carried out with the arms at rest and then with the abduction and external rotation maneuver, aiming to assess possible points of restriction and entrapment of the neurovascular structures.
In our experience, neurological compression seems to be more frequent in the costoclavicular space than in the interscalene triangle.
The costoclavicular space is by far the most common site of arterial compression, while the interscalene triangle is the second most frequent site for this condition.
Thoracic Outlet Syndrome:
The dynamically induced compression of neural, arterial, or venous structures that cross the thoracic outlet is termed thoracic outlet syndrome.
Bone Causes
Cervical Rib.
Elongated Transverse Process of C7.
Abnormal First Rib or Clavicle.
Soft Tissue Causes
Variations in the Subclavius Muscle.
Variations of the Scalene Muscle.
Supernumerary Muscle Bellies: Several supernumerary muscle bellies can occur, with the scalenus minimus being the most common.
Anomalous Fibrous Bands.
Acquired Abnormalities:
These include post-traumatic and post-operative changes with fibrosis formation. Repetitive microtraumas related to work (activities requiring repeated elevation of the upper limb or heavy lifting) can also lead to TOS, inducing fibrosis and spasm of the scalene muscles, resulting in the elevation of the first rib. In my opinion, acquired compression in the costoclavicular space has been the main cause and site of compression in most cases of Thoracic Outlet Syndrome, mainly in the neurogenic or neurological form. Our clinical findings lead us to conclude that the narrowing of the costoclavicular space may result from current postural changes in the population, attributed to the use of computers and cell phones.
Indeed, cases of cervicobrachial pain have increased in parallel with the rise in cell phone use. The main changes seem to involve the shortening of the pectoralis minor and subclavius muscles due to these postural changes. This shortening generally does not affect the retropectoralis minor space; however, it has implications for the costoclavicular space. Persistent tension due to shortening tends to induce hypertrophy in these two muscles and, in some cases, even fibrosis. The subclavius muscle is a natural depressor of the clavicle, originating from the clavicle and inserting into the first rib, where it can also slightly pull this rib upwards.
Indeed, pulling the ribs upwards seems to be a chain of mechanisms involving the pectoralis minor (insertion in the 3rd to 5th ribs), subclavius (insertion in the 1st rib), and scalenes (insertion in the 1st and 2nd ribs), consequently narrowing the costoclavicular space. Mechanisms of Clavicle Depression can also occur through Scapular Protraction and Anterior Tilt of the Scapula. Muscles such as the pectoralis minor, the conjoined tendon (coracobrachialis + short head of the biceps), and the subclavius are responsible for this. Chronic use of cell phones and computers in positions where the shoulder is elevated for long periods, even at small degrees, can be part of this postural problem. Therefore, Thoracic Outlet Syndrome (TOS) is a complex problem with combined multifactorial causes.
Clinical Picture:
After excluding cervical spine diseases, Thoracic Outlet Syndrome should be considered. The classification of Thoracic Outlet Syndrome is based on the pathophysiology of the symptoms, encompassing subgroups that include neurogenic, venous, and arterial etiologies. Moreover, each of these subgroups can be associated with congenital, traumatic, or functionally acquired causes. Neurogenic Thoracic Outlet Syndrome alone results from the compression of the nerves of the brachial plexus, accounting for over 90% of all cases of Thoracic Outlet Syndrome. In fact, over 90% of all cases of Thoracic Outlet Syndrome manifest as purely neurological symptoms, while almost all cases of vascular Thoracic Outlet Syndrome present with associated Neurogenic Thoracic Outlet Syndrome.
The diagnosis is based on clinical assessment, particularly if symptoms can be reproduced by dynamic maneuvers, including shoulder abduction and external rotation. However, clinical diagnosis is often challenging, requiring the use of imaging to demonstrate neurovascular compression and determine the nature and location of the compressing structure.
In cases of Neurogenic Thoracic Outlet Syndrome, patients often present with sensory or motor symptoms, with pain and paresthesias being the most prevalent manifestations. The pain is commonly located on the side of the neck, radiating towards the ear and the nape. Additionally, it can radiate posteriorly to involve the Rhomboid muscles (mainly along the path of the dorsal scapular nerve), anteriorly towards the clavicle and upper pectoral region, laterally affecting the deltoid and trapezius muscles, and even distally towards the lateral side of the arm. However, patients can also present with symptoms associated with the lower plexus, corresponding to the compression of the C8 and T1 nerves. In these cases, the pain tends to extend along the arm on the inner surface. In this case, paresthesia predominantly affects the fourth and fifth fingers, following the distribution of the ulnar nerve. Additionally, the autonomic innervation of the arm can also be affected with vasomotor symptoms.
In the context of Neurogenic Thoracic Outlet Syndrome, I strongly advocate for a diagnostic approach involving direct digital compression of the three main sites for 30 seconds. This method aims to accurately identify the exact location of nerve compression: between the scalenes, subclavius, and pectoralis minor muscle.
The Tinel sign and scratching collapse test may also be present at these same locations.
Furthermore, it is essential to consider the potential involvement of the Suprascapular Nerve, which, if compressed, can have long-term implications, primarily affecting the rotator cuff.
Preferred Treatment by the Author:
Care should be taken to differentiate nTOS from cervical problems in patients before starting treatment.
The incidence of Neurogenic Thoracic Outlet Syndrome has been increasing in recent years. This trend may be correlated with the postural changes people are experiencing due to the growing use of smartphones and computers; therefore, postural reeducation in using these devices is part of the treatment.
The chronic protration of the scapula resulting from these postural changes can play a significant role in the development of this pathology. The underlying mechanism for the compression of the brachial plexus is the chronic protration of the scapula. The protration leads to the stretching of the posterior muscles, including the Rhomboids and Trapezius, as well as the shortening of the Pectoralis Minor and Subclavius muscles, causing the clavicle to descend and, consequently, the costoclavicular space to become narrower.
Most patients will present with mild clinical symptoms that can be treated through physiotherapy, including stretching of the pectoralis minor and subclavius, strengthening of the rhomboids and trapezius, and correction of postural habits.
Medications targeted at the nerve should be considered. Most patients will experience symptom relief following these basic clinical cares.
In cases where patients do not improve or have significant impairment, brachial plexus release surgery may be necessary.
It is crucial to understand the main nerves involved and the sites of compression, as this knowledge guides the physician to the most appropriate treatment.
Surgical techniques should target the structures causing the compression. The most common procedures include cervical rib resection, scalenectomy, and release of the tendon of the pectoralis minor muscle near the coracoid.
When cervical ribs are present, open or robotic approaches can be used. In other cases, an endoscopic approach is viable.
I prefer the endoscopic surgical method because it is faster, has a shorter recovery time, involves less bleeding, and results in fewer scars and adhesions.
Currently, endoscopic decompression of the brachial plexus is possible at all compression sites between the neck and arm to treat patients with Thoracic Outlet Syndrome.
In our opinion, the endoscopic technique is easier, faster, safer, more aesthetic, with less bleeding, and less scar formation.
The post-operative protocol involves the use of a sling for 1-2 weeks. After this initial period, the stitches are removed, and the patient is free to engage in all activities with restrictions. 2 months after surgery, patient is free for all activities. We recommend a gradual progression of strength during the first month.
The endoscopic surgery presents very good results in cases of neurogenic thoracic outlet syndrome. However, for vascular thoracic outlet an open or robotic transaxillary approach can be necessary.
To learn more about Neurogenic Thoracic Outlet Syndrome, you can refer to the following book chapters and scientific studies authored by Dr. José Carlos Garcia: