The Thoracic Outlet Syndrome

Annie S. Dubuisson, MD

Department of Neurosurgery, CHU Liege, Belgium

(Dr. Dubuisson was a peripheral nerve fellow at LSUMC)

Thoracic outlet syndrome (TOS) is due to compression/irritation of brachial plexus (BP) elements ("neurogenic TOS") and/or subclavian vessels ("vascular TOS") in their passage from the cervical area toward the axilla. The usual site of entrapment is the interscalenic triangle. TOS is a source of disagreement among clinicians regarding its incidence, diagnostic criteria and optimal treatment. Constitutional factors, like a cervical rib, predispose to the development of TOS. The syndrome often develops during the 3rd or 4th decade, following external factors such as trauma, weight excess, incorrect shoulder posture.

The clinical picture can be varied: pain in the cervical region and arm, paresthesias (medial side of arm predilected) aggravated by overhead positions of the arms, hand intrinsic muscle deficit/atrophy, easy fatiguability, paleness, coldness of hand.

The clinical examination may be entirely normal or show cervical muscle spasm, tenderness of BP in the supraclavicular area, radial pulse attenuation and occurence of symptoms upon positional maneuvers, sensory or motor deficit. The diagnosis is based upon clinical evaluation and absence of other relevant pathology. Therefore, the cervical spine and distal peripheral nerves are studied by radiological and electrophysiological studies. There is no laboratory test confirming TOS: most of the time, there is no anatomic variation seen radiologically and electrophysiological testing is normal. The scalene muscle block appears a helpful diagnostic tool if used with the other clinical data.

Unless there is significant motor deficit or subclavian artery compression, the treatment should be kept conservative as long as possible, by an individually tailored physical therapy program. In case of neurological deficit or symptoms unresponsive to medical treatment, the patients will be helped by decompressive operation in the thoracic outlet. Transaxillary first rib resection (TAR) has been the most popular surgical approach but nowadays, the supraclavicular approach has superseded TAR in many centers. The anterior approach provides a good access to the BP elements and subclavian artery, allowing their adequate relief from constrictive/irritative anatomic structures. The posterior subscapular approach is indicated in rare cases of TOS associated with severe obesity, a large cervical rib or recurrent TOS with residual first rib following TAR. (NerveCenter 4(2), 1999)

[Introduction | Anatomy | Case Illustrations | Discussion | References]

Thoracic outlet syndrome (TOS) can be defined as a set of symptoms existing due to compression/irritation of the brachial plexus (BP) and/or subclavian vessels in the cervical area. The thoracic outlet lies in a region concerning general, neurological, thoracic and vascular surgeons. A confusing terminology is used to describe the syndrome: scalenus anticus syndrome, cervical rib syndrome, costoclavicular syndrome, hyperabduction syndrome, thoracic outlet syndrome. The last one is nowadays the accepted one in the english literature whereas the syndrome is usually named "syndrome du défilé cervico-thoracique" in the french-speaking literature.
TOS is a highly controversial subject. Some clinicians even doubt the existence of the syndrome. It was first described by Galenus and Vesalius in the 2nd century AD in a patient presenting compression of neural and vascular elements by a cervical rib- the rare situation where most authors accept the diagnosis of TOS. However, objective confirmatory tests are often lacking. Hence the exact incidence of the syndrome is not known and the syndrome is said to be underdiagnosed by some (14) and overdiagnosed by others (19). The issue of treatment is also a source of much disagreement: conservative or operative? If conservative, for how long a time? If operative, by what surgical approach?

Anatomy of the thoracic outlet region is schematized in figure 1:

Figure 1: Schematic representation of the anatomy at the thoracic outlet. C5, C6, C7, C8, T1: spinal nerves; A: subclavian artery; V: subclavian vein. Download a larger image of above.

1. the C5, C6, C7, C8 and T1 spinal nerves emerging from the foramina recombine to form the 3 trunks of the BP. These elements pass between the anterior and middle scalenes which, along with the first rib to which they attach, form the interscalenic triangle. The second portion of the subclavian artery accompanies the BP while the subclavian vein is located in front of the anterior scalene. 2. The trunks of the BP divide into anterior and posterior divisions which travel under the clavicle, in the costoclavicular space. 3. The divisions recombine into 3 cords which enter the axilla by passing beneath the pectoralis minor insertion on the coracoid process of the scapula.
The neurovascular bundle can be compressed or irritated by repetitive movements in one or other of these 3 locations-the interscalenic triangle, the costoclavicular space and/or the subcoracoid tunnel. The interscalenic triangle is by far the most frequent site of entrapment. Several anatomic variations exist in this region which can compromise an already narrow passage (5). Predisposing constitutional factors are osseous (cervical rib or hypertrophic C7 transverse process (figure 2)) or more often fibromuscular (scalene muscle anomalies, cervical bands).

Figure 2: C-spine X-Rays (A-P view) of a patient operated for cervical radiculopathy by anterior cervical discectomy and fusion, with a good result. One year postoperatively, he began to complain of bilateral arm pain and heaviness. The X-Rays show bilateral C7 transversomegaly. The transverse processes of C7 extend beyond the ones of T1 (arrows).

A cervical rib occurs in 1% of people in the general population; 7 types of cervical bands have been described. The most frequent is the type III band extending from the neck to the scalene tubercle of the first rib, crossing the concavity of the rib. Another frequent finding is a thickened medial edge of middle scalene muscle acting as a chopper for the lower BP elements (5).

Case Illustrations:
Case 1: This 34-year-old, right-handed man had been followed for 2 years in another institution for a right "atypical cervicobrachialgia". He complained of right arm heaviness and palmar paraesthesias. He had been suffering from right-sided headaches for many years. The "standard" neurological examination was non contributory. Mild C4-5 and C5-6 discopathies were diagnosed. The patient was treated with antiinflammatory drugs, analgesics, cervical collar, muscular and 2 cervical epidural infiltrations. There was no improvement following these treatments and the patient sought medical consult in our institution. His complaints were pain in the cervical posterior region, radiating toward the right side of the head and the right shoulder, and right arm diffuse numbness upon exercise or maintained positions. On clinical examination, the upper third of the trapezius was tender on palpation; palpation of the supraclavicular area was negative; the right radial pulse was reduced at 60 degrees of arm abduction and disappeared at 90 degrees; concomitantly, the patient complained of right upper extremity numbness; the test was negative on the left side. The hands-up test produced right arm heaviness after 25 movements and was negative on the left. The neurological examination showed no motor, sensory nor deep tendon reflexes deficit. The subclavian artery doppler confirmed the clinical findings of complete disappearance of flux in the right artery upon arm elevation; no abnormality was seen on the left. The diagnosis of right TOS was made and the patient underwent an appropriate physical therapy program without any change of his symptoms. The patient was operated for BP/subclavian artery decompression at the thoracic outlet, by a supraclavicular approach. The vascular and lower neural elements were relieved from the knife-like action exerted by the medial edge of the middle scalene. Postoperatively, all the patient's symptoms disappeared, including the chronic "migraines" he had been suffering for many years.

Case 2: This male patient progressively developed left hand weakness and paresthesias in 1980, at age 20. Examination at this time revealed left thenar muscle atrophy and subclavian artery bruit on hyperabduction of the arm. The diagnosis of left TOS was made and the patient was operated in January 1981 by transaxillary first rib resection in another institution. The patient gained a good result postoperatively and led a normal life for 12 years. In 1993, he progressively developed shoulder and arm pain along with numbness of upper limb down to 4th and 5th digits. He had gained 10 kgs since the operation. On examination, the patient looked stocky; there was tenderness on left trapezius palpation; hyperabduction at 110 degrees resulted in diminished radial pulse on the left; no neurological deficit was present. Radiological work-up showed a left residual 1st rib (figure 3 left- see below); a cervical CT scan disclosed a goitre; MRI of cervical spine was normal; electrophysiologic studies detected a slight impairment of F-wave at C7 and C8 on the left. A recurrent TOS was diagnosed. The patient was treated conservatively for 6 months; physical therapy and 2 scalenic infiltrations yielded little improvement. The thyroid pathology was treated operatively in June 1994. The now 34-year-old patient continued to complain of left shoulder pain, numbness, heaviness and weakness of the left upper extremity that were invalidating. He had been unable to work for 12 months. BP exploration by a posterior subscapular approach was thought indicated and was performed in May 1995. The approach allowed BP neurolysis and decompression from the 1st rib stump which was resected (figure 3 right- see below). The patient obtained an excellent outcome: he was painfree and able to work again in September 1995.

Figure 3: C-spine X-Rays (Case 2, A-P view). Left: following TAR on the left side, the patient gained an excellent result for 12 years. Recurrence of TOS symptoms were not relieved by conservative management. A posterior stump of the 1st rib is well-visualized (arrow). Right: the posterior subscapular approach permitted BP neurolysis and removal of the rib stump. Metallic clips seen on the midline were placed during a previous thyroid operation. The patient obtained an excellent result.



[Epidemiology | Clinical Presentation | Clinical Examination | Diagnostic Management | Therapeutic Management]

TOS commonly develops during the 3rd or 4th decade, more often in women, under the combination of a peculiar cervical anatomy and of external factors. Some morphotypes predispose to the syndrome: poor muscular development, droop of scapula, obesity and breast hypertrophy. The patient psychological status may sometimes play an important role in the development of the syndrome: stress and depression can lead to chronic muscle spasm in the neck region and there to decompensation of a previously asymptomatic predisposing anatomy. Other precipitating factors are work-related (static work posture). An antecedent of neck or shoulder trauma is noted in approximately half of the cases (15).

Clinical Presentation:
Two types of TOS are commonly described. 1. In the vascular form of TOS ( about 10% of cases), the compression mostly exerts on the subclavian artery. The patient complains of aching pain diffusely distributed in the upper extremity, easy fatiguability, coldness and paleness of the hand. In the extreme form, microemboli may cause acute digit ischemia and ulcerations. Rarely is it the subclavian vein which is compressed by the pectoralis minor tendon; intermittent or constant arm swelling and cyanosis develop or exceptionnally subclavian vein thrombosis. 2. The neurogenic type of TOS is by far the most frequent ( about 90% of cases). The BP, especially the lower elements, C8 and T1 spinal nerves and lower trunk, becomes compressed/irritated in the interscalenic triangle. Pain and sensory changes (numbness, tingling) in a BP distribution, aggravated with use of the upper extremity, especially on elevation are the main complaints. The medial side of limb and ulnar fingers are predilected. Pain may radiate toward the cervical region, chest or head. Motor deficit is seldom significant but a neurogenic TOS may present as isolated hand intrinsic muscle atrophy without any pain (Gilliat-Sumner hand).

Clinical Examination:
The clinical examination must include both a neurologic and a locomotor examination, looking for positive and negative diagnostic clues. Palpation and percussion over the supraclavicular area may elicit dysesthesias radiating distally. Palpation and percussion of peripheral nerves (ulnar nerve at elbow, median nerve at wrist) should be negative. Inspection of patient posture may reveal obesity, breast hypertrophy, droop of scapula. There is often tenderness of the periscapular musculature. Many provocative maneuvers have been described, that aim to demonstrate subclavian artery compression in extreme neck, shoulder or thorax positions. To be considered as positive, the maneuver must elicit both reduced radial pulse intensity at the wrist and reproduction of the patient's symptoms. The test is particularly valuable if positive unilaterally, on the side of the affected upper extremity. Indeed, provocative maneuvers are found positive in a high percentage of asymptomatic volunteers, especially the hyperabduction maneuver (10). The neurological response (paresthesias) appears more valuable than the vascular response (reduced radial pulse intensity). The most predictive maneuver seems to be the abduction/external rotation of the arm. The repetitive fist closing-opening movements in that position during 3 minutes (hands-up test) is also a good test; often, the patient describes a deep, diffuse upper extremity pain after 10, 20 or 30 movements.

Diagnostic Management:
In the majority of cases, TOS remains a diagnosis of exclusion. The main differential diagnoses include a cervical radiculopathy by soft cervical disk herniation or uncoarthrosis and a distal compression neuropathy. Syringomyelia, Pancoast's tumor and brachial plexitis are rarer pathologies which should be kept in mind. The cervical spine is best studied by standard X-Rays and MRI. Electrophysiological testing should easily rule out ulnar nerve or median nerve entrapments. In a neurogenic TOS, electrophysiological testing is often entirely normal. EMG can sometimes detect neurogenic C8/T1 signs; by electrostimulation, abnormal sensory conduction from ulnar nerve coupled with abnormal median motor conduction may suggest TOS. The diagnosis may also be suggested by somatosensory evoked potentials findings like prolonged conduction latencies between axilla and C-spine (17). On the other hand, the F-wave impairment is not constant: it analyses conduction along a long segment of nerve so that a localized slowing of conduction at the thoracic outlet is easily overlooked. At last, the Erb point stimulation test is inaccurate, usually performed distal to the site of compression.

In some rare cases, diagnosis of TOS is approached on the ground of positive findings. A cervical rib or C7 transversomegaly is a strong argument for the diagnosis of TOS in the adequate clinical context. Some authors have attempted to study the thoracic outlet region by CT scan or MRI/MRA, comparing both the affected and the contralateral sides (2,11). One of the limitations is that the compromise of the neurovascular bundle is often positional and intermittent. Duplex ultrasonography of subclavian artery with positional maneuvers is useful in confirming the clinical impression of artery compression under specific arm conditions. Arteriography/venography are indicated only in the evaluation of vascular types of TOS. An interesting test used by Sanders et al (15) is the scalene muscle block: temporary relief of symptoms following anterior scalene muscle infiltration with 4 cc of 1% lidocaine appears a useful diagnostic tool for TOS. Furthermore, the authors find a high correlation between good response to the block and improvement following scalenectomy.

Therapeutic Management:
1/ Conservative: General measures include reduction of weight and proper breast support when indicated. Medications such as muscle relaxants and tranquilizers or antiinflammatory drugs can help some patients. The key point of the treatment is an individually tailored physical therapy program (7,9). The patient should be examined by a physical therapist well aware of the TOS pathology. The physician will prescribe a 3 to 6-week program including postural correction, stretching exercises of some muscles and stengthening exercises of others. More than half of the patients will significantly improve under this therapeutic regimen (9); if so, the patient must be encouraged to continue a home-exercise program on a long-term basis.
2/ Operative: Operative treatment is often indicated in the vascular forms of TOS which appear resistant to conservative treatment. In the neurogenic TOS, surgical treatment is indicated in all cases of significant neurological-especially motor- deficit and in the painful syndrome which remains invalidating despite a well-conducted conservative treatment. The thoracic outlet region can be approached by 3 routes: "by underneath" (transaxillary approach), "in front" (supraclavicular approach) and "from behind" (posterior subscapular approach).

a) The transaxillary first rib resection (TAR) is the most popular by history. It has been popularized by Roos (13) in 1966 and has been the approach preferred by thoracic surgeons. With the patient in a lateral position, a transverse incision is made over the 3rd rib just inferior to the axillary hairline and deepened between the pectoralis major and the latissimus dorsi to the chest wall. Scalene muscle attachments to the 1st rib are released and the rib is excised extraperiosteally from the chondrosternal articulation to the costotransverse articulation. The rationale for this approach is that 1st rib resection permits the widening of both the interscalenic triangle and the costoclavicular space. Good to excellent results have been published in about 80% of cases following this procedure (8,13). On the other hand, Dale (3) has reported in 1982 the occurence of complete paralysis of the upper extremity following an uneventful TAR in a 43-year-old patient, who fortunately obtained complete return of the upper extremity function at 4 months postoperatively. Thereafter, a national inquiry among the members of the International Cardiovascular Society in April 1981 revealed a 2.6% occurence of plexus injuries after TAR. Nerve injury may occur during TAR by either stretching the plexus or cutting one of its elements. Following description of these complications with TAR, there was a progressive loss of interest among surgeons for TAR, in favor of the supraclavicular route.

b) The supraclavicular route is the classical anterior supraclavicular approach well-known by neurosurgeons and surgeons who routinely expose the supraclavicular part of the BP in case of BP trauma or tumors. In case of TOS, an horizontal incision is made parallel and one fingerbreadth above the clavicle, extending from the sterno-cleido-mastoid muscle (SCM) to the anterior border of the trapezius. After platysma incision, the clavicular head of SCM is either retracted medially or incised and then repaired at the end of operation. The supraclavicular pad of fat, of varying bulk, is dissected from below upward; the omo-hyoid muscle is incised; the cervical transverse vessels may be ligated. One reaches the plane of the anterior scalene muscle; the phrenic nerve coursing obliquely on the surface of the muscle must be protected in order to perform the anterior scalenectomy. Optimally, the muscle is excised in toto from its insertion on the 1st rib to its attachments on the cervical tranverse processes. The subclavian artery and BP are exposed; BP elements are neurolyzed, ie individualized and placed on Penrose drains; any compressing element is released: cervical rib, elongated C7 transverse process, fascial band; as much of the medial portion of the middle scalene as possible should be resected. The anterior approach allows perfect visualization/decompression of the supraclavicular plexus (figure 4).

Figure 4: Operative view of the supraclavicular exposure/decompression of the right BP/subclavian artery complex. UT: upper trunk, MT: middle trunk, LT: lower trunk, A: subclavian artery, p: phrenic nerve. Download a larger image of above.

Intraoperative nerve action potential recordings have shown abnormalities in 62 out of 70 instances (6). Of interest is the fact that the electrical changes are recorded close to the spine, distant to the first rib. Good to excellent results after an anterior approach average 80% (6,16,18). Morbidity is minimal; a phrenic nerve paralysis occurs in a few % of cases (up to 7% in Sanders et al's series (15) of 239 scalenectomies). The paralysis is temporary and asymptomatic in most of the cases. The supraclavicular approach without resection of the 1st rib appears the current procedure of choice for treating vascular and neurogenic forms of TOS. TOS is a soft-tissue disease. Surgery should concentrate on the fibromuscular anomalies. There is no need to resect a normal-appearing 1st rib (1,12,16,18).

c) The BP can be approached by a posterior subscapular approach. The procedure includes incision between the medial border of the scapula and the cervicodorsal spinous processes, division of trapezius and rhomboid muscles, exposure of the posterior upper rib cage, resection of 1st rib and of posterior and middle scalene muscles. The BP is approached from behind, at the level of spinal nerves and trunks. This approach, rather extensive in regard to muscle incision, is reserved to "complicated TOS": half of the indications for the procedure in Dubuisson and Kline's series (4) were TOS complicated by severe obesity, a large cervical rib or recurrence following TAR. A 5% incidence of scapular winging occurs postoperatively.

Download a management plan flowchart for TOS


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