Thoracic outlet syndrome (TOS), a term coined by Rob and Standeven,¹ refers to symptomatic compression of the structures of the thoracic outlet (subclavian vessels and brachial plexus) at the superior opening of the chest. It was previously designated as scalenus anticus, costoclavicular, hyperabduction, cervical rib, and first thoracic rib syndromes according to presumed etiologies. The various syndromes are similar, and the compression mechanism is often difficult to identify. Most compressive factors operate against an osseous structure, most commonly the first rib.^2,3

At the superior aspect of the thoracic cage, the subclavian vessels and the brachial plexus traverse the cervicoaxillary canal to reach the upper extremity. The cervicoaxillary canal is divided into two sections by the first rib: the proximal division, composed of the scalene triangle and the costoclavicular space, and the distal division, composed of the axilla (Fig. 144-1). The proximal division is important to achieve acceptable neurovascular decompression. It is bounded superiorly by the clavicle, inferiorly by the first rib, anteromedially by the costoclavicular ligament, and posterolaterally by the scalenus medius (middle scalene) muscle and the long thoracic nerve. The scalenus anticus (anterior scalene) muscle, which inserts on the scalene tubercle of the first rib, divides the costoclavicular space into two compartments: The anteromedial compartment contains the subclavian vein, and the posterolateral compartment contains the subclavian artery and the brachial plexus. The latter compartment, which is bounded by the scalenus anticus (anterior scalene) muscle anteriorly, the scalenus medius (middle scalene) muscle posteriorly, and the first rib inferiorly, is called the scalene triangle.

The cervicoaxillary canal, particularly its proximal division, also termed the costoclavicular area, normally has ample space for the passage of the neurovascular bundle without compression. Narrowing of this space occurs during functional motions of the upper extremities. It narrows during abduction of the arm because the clavicle rotates backward toward the first rib and the insertion of the scalenus anticus (anterior scalene) muscle. In hyperabduction, the neurovascular bundle is pulled around the pectoralis minor tendon, the coracoid process, and the head of the humerus. During this maneuver, the coracoid process tilts downward and thus exaggerates the tension on the bundle. The sternoclavicular joint, which ordinarily forms an angle of 15 to 20 degrees, forms a smaller angle when the outer end of the clavicle descends (as in drooping of the shoulders in poor posture), and narrowing of the costoclavicular space may occur. Normally, during inspiration, the scalenus anticus muscle raises the first rib and, thus, narrows the costoclavicular space. This muscle may cause an abnormal lift of the first rib, as in cases of severe emphysema or excessive muscular development, which is seen in young adults.

The scalene triangle, demarcated by the scalenus anticus anteriorly, the scalenus medius posteriorly, and first rib inferiorly, permits passage of the subclavian artery and the brachial plexus, which are in direct contact with the first rib. The space of the triangle is 1.2 cm at its base and approximately 6.7 cm in height. There is a close-fitting relationship between the neurovascular bundle and this triangular space. Anatomic variations may narrow the superior angle of the triangle, cause impingement on the upper components of the brachial plexus, and produce the upper type of TOS that involves the trunk containing elements of C5 and C6. If the base of the triangle is raised, compression of the subclavian artery and the trunk containing components of C7, C8, and T1 results in the lower type of thoracic outlet syndrome, as described by Swank and Simeone in 1944 (Fig. 144-2).⁴

Many factors may cause compression of the neurovascular bundle at the thoracic outlet, but the common denominator is deranged anatomy, to which congenital, traumatic, and occasionally, atherosclerotic factors may contribute (Table 144-1).⁵ Bony abnormalities are present in approximately 30% of patients, either as cervical rib, bifid first rib and fusion of first and second ribs, clavicular deformities, or previous thoracoplasties.³ These abnormalities can be visualized on a plain posteroanterior chest film, but special x-ray views of the lower cervical spine may be required in some cases of cervical ribs. A more comprehensive theory of multiple sites of compression was proposed by Upton and McComas in 1973,⁶ which suggests that a proximal site of nerve compression would render the distal nerve more susceptible to a second site of compression. This theory supports the well-recognized association between the carpal and cubital tunnel syndromes and TOS.

The symptoms of TOS depend on whether the nerves or blood vessels or both are compressed in the cervicoaxillary canal. Neurogenic manifestations are observed more frequently than vascular ones. Symptoms of pain and paresthesias are present in approximately 95% of patients. Motor weakness and occasionally atrophy of hypothenar and interosseous muscles, which is the ulnar type of atrophy, are present in less than 10%. The symptoms occur most commonly in areas supplied by the ulnar nerve, which include the medial aspects of the arm and hand, the fifth finger, and the lateral aspects of the fourth finger. The onset of pain is usually insidious and commonly involves the neck, shoulder, arm, and hand. The pain and paresthesias may be precipitated by strenuous physical exercise or sustained physical effort with the arm in abduction and the neck in hyperextension. Symptoms may be initiated by sleeping with the arms abducted and the hands clasped behind the neck. In other cases, trauma to the upper extremities or the cervical spine is a precipitating factor. Physical examination may be noncontributory and largely unreliable. A triad of signs including supraclavicular tenderness, hand pallor or paresthesias upon elevation, and adduction/abduction weakness of digits 4 and 5 (ulnar distribution) has been proposed but is uncommonly obvious and is largely subjective.⁷ When present, objective physical findings usually consist of hypesthesia along the medial aspects of the forearm and hand. Atrophy, when evident, is usually described in the hypothenar and interosseous muscles with clawing of the fourth and fifth fingers. In the upper type of TOS, in which components of C5 and C6 are involved in the compression (see Fig. 144-2), pain is usually in the deltoid area and the lateral aspects of the arm. The presence of this pain should raise concern to exclude a herniated cervical disk. Entrapment of C7 and C8 components that contribute to the median nerve produces symptoms in the index and sometimes middle fingers. Compression of components of C5, C6, C7, C8, and T1 can occur at the thoracic outlet by a cervical rib and produce symptoms of various degrees in the distribution of these nerves.

In some patients, the pain is atypical, involving the anterior chest wall or parascapular area, and is termed pseudoangina because it simulates angina pectoris. These patients may have normal coronary arteriograms and ulnar nerve conduction velocities decreased to values of 48 m/s and less, which strongly suggests the diagnosis of thoracic outlet syndrome. The shoulder, arm, and hand symptoms that usually provide clues for the diagnosis of TOS may be minimal or absent when compared with the severity of the chest pain, requiring a high index of suspicion. In these patients, the diagnosis of TOS frequently is overlooked, causing significant patient frustration.⁸

Symptoms of arterial compression include temperature changes (usually in the cool range), weakness, easy fatigability of the arm and hand, and pain that is usually diffuse.^3,9 Raynaud phenomenon is noted in approximately 7.5% of patients with TOS.³ Unlike Raynaud disease, which is usually bilateral, symmetric, and elicited by cold or emotion, Raynaud phenomenon in neurovascular compression usually is unilateral and is more likely to be precipitated by hyperabduction of the involved arm, turning of the head, or carrying heavy objects. Sensitivity to cold also may be present. Symptoms include sudden onset of cold and blanching of one or more fingers, followed slowly by cyanosis and persistent rubor. Vascular symptoms in neurovascular compression may be precursors of permanent arterial thrombosis.⁵ When present, arterial occlusion, usually of the subclavian artery, is manifest by persistent coolness, cyanosis, or pallor of the fingers, and in some instances ulceration or gangrene. Palpation in the parascapular area may reveal prominent pulsation, which indicates poststenotic dilatation or aneurysm of the subclavian artery.¹⁰

Less frequently, the symptoms are those of venous obstruction or occlusion, commonly recognized as effort thrombosis, or Paget–Schroetter syndrome. The condition characteristically results in edema, discoloration of the arm, distention of the superficial veins of the limb and shoulder, and some degree of pain or discomfort. In some patients, the condition is observed on waking; in others, it follows sustained efforts with the arm in abduction. Sudden backward and downward bracing of the shoulders, heavy lifting, or strenuous physical activity involving the arm may constrict the vein and initiate venospasm, with or without subsequent thrombosis. On examination, in patients with definite venous thrombosis, there is usually moderate tenderness over the axillary vein, and a cordlike structure may be felt that corresponds to the course of the vein. The acute symptoms may subside in a few weeks or days as the collateral circulation develops. Recurrence follows with inadequacy of the collateral circulation.

Objective physical findings are more common in patients with primarily vascular as opposed to neural compression. Loss or diminution of radial pulse and reproduction of symptoms can be elicited by the three classic clinical maneuvers (described below)—the Adson or scalene test,¹¹ the costoclavicular test, and the hyperabduction test.¹²

The diagnosis of TOS includes history, physical and neurologic examinations, radiographic surveys of the chest and cervical spine, electromyogram, and ulnar nerve conduction velocity (UNCV). In some patients with atypical manifestations, other diagnostic procedures, such as cervical myelography, peripheral or coronary arteriography, and phlebography should be considered. A detailed history and physical examination, together with neurologic examination, often can result in a tentative diagnosis of neurovascular compression. This diagnosis is strengthened when one or more of the classic clinical maneuvers is positive and is confirmed by the finding of decreased UNCV.⁹

Clinical Maneuvers

The clinical evaluation is best based on the physical findings of loss or decrease of radial pulses and reproduction of symptoms that can be elicited by four classic maneuvers (see also Chapter 143).

Adson or Scalene Test

This maneuver tightens the anterior and middle scalene muscles and thus decreases the interspace and magnifies any preexisting compression of the subclavian artery and brachial plexus.¹¹ The patient is instructed to take and hold a deep breath, extend the neck fully, and turn the head toward the side. Obliteration or decrease of the radial pulse suggests compression.^5,12

Costoclavicular Test (Military Position, Halstead Maneuver)

This maneuver narrows the costoclavicular space by approximating the clavicle to the first rib and thus tends to compress the neurovascular bundle. Changes in the radial pulse with production of symptoms indicate compression. The shoulders are drawn downward and backward.^5,12

Roos Test

This maneuver is performed by holding both arms at 90 degrees of abduction and external rotation with the shoulders drawn back. The patient is instructed to open and close the hands slowly for 3 minutes. The test result is positive if the patient experiences numbness or pain in the hands and forearms, or fatigue and heaviness in the shoulders.

Hyperabduction Test (Wright)

When the arm is hyperabducted to 180 degrees, the components of the neurovascular bundle are pulled around the pectoralis minor tendon, the coracoid process, and the head of the humerus. If the radial pulse is decreased, compression should be suspected.^5,12

Radiographic Findings

Films of the chest and cervical spine are helpful in revealing bone structure-related abnormalities, particularly cervical ribs and bony degenerative changes. If osteophytic changes and intervertebral disk space narrowing are present on plain cervical films, a cervical CT scan or MRI should be performed to rule out bony encroachment and narrowing of the spinal canal and the intervertebral foramina.

Sensory Testing

The range of findings in sensory testing varies according to the severity, chronicity, and degree of functionality required by the patient. Initially, patients may be completely asymptomatic during rest and develop symptoms only during exertion. As the degree of injury increases, these symptoms can become more persistent and severe in nature. Eventually, nerve injury and loss of fibers result in loss of discriminatory function as measured by the two-point discrimination test. The greatest challenge is to be able to diagnose the condition before nerve injury becomes permanent. Provocative testing is used to elicit symptoms in otherwise asymptomatic patients at rest. These include nerve percussion at common entrapment sites (Tinel’s test), arm elevation, elbow flexion and wrist flexion (Phalen’s sign). Finally, measurements of vibration thresholds, pressure thresholds and innervation density can be used to detect slight degrees of impairment that could be early signs of compression injury. somatosensory evoked potentials (SSEP) have had mixed results in the early diagnosis of TOS and are generally regarded as not useful for early diagnosis.^13,14

Nerve Conduction Velocity and Electromyography

This test is used widely in the differential diagnosis of the causes of arm pain, tingling, and numbness with or without motor weakness of the hand. Such symptoms may result from compression at various sites: in the spine; at the thoracic outlet; around the elbow, where it causes tardy ulnar nerve palsy; or on the flexor aspects of the wrist, where it produces carpal tunnel syndrome. For diagnosis and localization of the site of compression, cathode-based stimulation is applied at various points along the course of the nerve. Motor conduction velocities of the ulnar, median, radial, and musculocutaneous nerves can be measured reliably. Caldwell et al. ¹⁵have improved the technique of measuring UNCV for evaluation of patients with thoracic outlet compression. Conduction velocities over proximal and distal segments of the ulnar nerve are determined by recording the action potentials generated in the hypothenar or first dorsal interosseous muscles. The points of stimulation are the supraclavicular fossa, middle upper arm, below the elbow, and at the wrist.⁹

Equipment

Electromyographic examination of each upper extremity and determination of the conduction velocities are done with the Meditron 201 AD or 312 or the TECA-3 electromyograph; coaxial cable with three needles or surface electrodes are used to record muscle potentials, which appear as tracings on the fluorescent screen.