The term thoracic outlet syndrome (TOS) describes a condition arising from compression of the subclavian artery, the subclavian vein, and the brachial plexus between the scalene muscles and the first rib (Fig. 122-1). There exists a wide spectrum of patient symptoms, which include vascular and/or neurologic signs. Neurogenic TOS accounts for most cases, whereas venous (2–3%) and arterial TOS (1%) are relatively rare. Objective vascular studies such as venograms and arteriograms may identify signs of vascular compromise to aid in the diagnosis of arterial or venous TOS, but neurologic findings are more varied, and there is no single specific test to diagnose neurogenic TOS.

The neurologic signs and symptoms of neurogenic TOS can range from mild paresthesias and numbness to intrinsic hand muscle atrophy. There is little controversy in this latter group of patients regarding diagnosis or treatment. However, the diagnosis of TOS is controversial in patients with the neurologic-type complaints of paresthesias, numbness, and pain but with no positive objective test to identify the cause. This chapter focuses on the management and surgical therapy of neurogenic TOS.

GENERAL PRINCIPLES

Many surgeons are highly skeptical of the merits of surgical intervention for patients with TOS because of the high incidence of major complications and the variable reports of successful outcome. Exceptions to this rule include uncommon cases involving vascular compromise and even rarer cases involving severe neurologic muscle atrophy in the hand.¹ Patients with intrinsic hand muscle atrophy that localizes to the level of the brachial plexus with no distal sites of nerve compression are likely to have a cervical rib or anomalous ligamentous band(s) that compresses the lower trunk of the brachial plexus. Compression of the artery may lead to poststenotic dilatation and subsequent thrombosis and embolization. Patients with symptomatic arterial TOS may present with signs and symptoms of microembolization in the digits on the affected side. Venous compression, which usually occurs at the junction of the clavicle and first rib, leads to occlusion and thrombosis. Patients characteristically become symptomatic with evidence of venous congestion after a precipitating physical activity (Paget-Schroetter syndrome; see Chap. 125).

The clinical syndrome (TOS) derives from three anatomic areas in which compression of the neurovascular structures may occur: the scalene triangle, the costoclavicular space, and the subcoracoid space (Fig. 122-2). The scalene triangle is the region bordered by the anterior scalene muscle, the middle scalene muscle, and the first rib. The brachial plexus and subclavian artery pass over the first rib between the scalene muscles, and the subclavian vein also passes over the first rib but external to the scalene triangle. The costoclavicular space is bordered by the clavicle and the first rib, with the costoclavicular ligament located anteriorly and the edge of the middle scalene muscle posteriorly. This space contains the brachial plexus, the subclavian artery and vein, and the subclavius muscle. The subcoracoid space is beneath the pectoralis muscle, the coracoid process, and the ribs posteriorly. The brachial plexus courses through this space and can become tethered with arm elevation, abduction, or abnormal depression of the coracoid. Anomalous cervical ribs are found in fewer than 1% of the population. They may compress the neurovascular structures in this region. The most common sites of compression in patients with TOS are the scalene triangle and the subcoracoid space, although it is clinically difficult to determine the exact location of the compression.

PATIENT SELECTION AND PREOPERATIVE ASSESSMENT

There is no single test or examination finding that establishes the diagnosis of neurogenic TOS. Rather, the clinical diagnosis is based on the history, physical examination findings, and objective tests, such as electrodiagnostic studies of the peripheral nerves, that are used to rule out other more distal compression neuropathies. Chest and neck x-rays are obtained routinely to look for cervical ribs or other bony abnormalities. Paresthesias in the upper extremity may be the result of either compression at the brachial plexus or compression more distally. The pain associated with TOS usually results from a muscle imbalance in the cervical, thoracic, and scapular regions.² Patients with TOS-related pain often assume an abnormal posture with forward position of the head and neck, thoracic kyphosis, and scapulae abduction (Fig. 122-3). This posture results from a weakness of the lower scapular stabilizers (i.e., middle and lower trapezius and serratus anterior) that leads to overuse and hypertrophy of other muscle groups (e.g., levator scapulae, upper rhomboids and trapezius, and scalene muscles). Upper extremity activities (e.g., arm abduction or elevation) often exacerbate the symptoms. The onset of symptoms is usually insidious without a defined traumatic event.

Chronic nerve compression is associated with a continuum of symptoms. Initially, the patient may complain of aching in the muscles innervated by the compressed nerve. Later, the patient complains of muscle weakness and, finally, muscle atrophy. With sensory nerve compression, patients complain first of intermittent paresthesias, then persistent paresthesias, and eventually numbness. Clinical sensory testing follows a similar continuum; therefore, not all sensory tests are equally effective for detecting nerve compression at all stages of TOS. Initially, patients may have symptoms only with positional changes or provocative maneuvers. Sensory testing in a resting position will be normal, only becoming abnormal when the patient is tested in positions of provocation (e.g., with the arms elevated). With continued nerve compression, axonal involvement, and wallerian degeneration, the innervation density of the sensory receptors decreases, and sensory testing with two-point discrimination is abnormal.

It has been hypothesized that proximal compression of a nerve increases its susceptibility to compression injury more distally. Thus, in treating upper extremity neuropathic symptoms, it is important to identify and treat all sites of compression.³ Distal sites of nerve entrapment, for example, the elbow, forearm, and wrist, should be evaluated carefully and managed conservatively. Clinical evaluation using pressure and positional provocative testing is key to making the diagnosis because electrodiagnostic studies usually do not detect these dynamic sites of nerve compression.⁴ Conservative treatment often effectively relieves these distal symptoms, but when surgical intervention is required, surgery at the carpal or cubital tunnel levels is usually more effective than surgical decompression of the thoracic outlet for complete relief of hand paresthesias and numbness. Overlapping symptoms from the cervical disc level or the shoulder are common.

Loss of radial pulse with arm movement on physical examination forms the basis of several clinical tests designed to detect vascular insufficiency, although not effective for the evaluation of neurogenic TOS. In Adson's test, the patient is asked to turn his or her head toward the affected side, extend the neck, and inspire deeply. Obliteration of the radial pulse suggests compression. In Roos's test, the subject elevates his or her arm to 90 degrees of shoulder abduction and then rotates the arm externally and flexes the elbow for 3 minutes. The patient then is asked to rapidly open and close the hand. A positive test will reproduce the patient's symptoms.

The physical examination of patients with TOS should include documentation of pinch and grip and two-point discrimination, as well as examination of the upper extremity for other compression issues. The cervical spine and rotator cuff are examined as well as the muscles of the parascapular area. Standard tests performed at the wrist are used to assess carpal tunnel syndrome, including Tinel's sign, the pressure provocative test, and Phalen's test. Care is taken to keep the forearm in a neutral position during testing because extreme supination of the forearm will cause median nerve compression at the pronator teres and lead to a false-positive result. The elbows also must remain extended so as not to provoke signs of cubital tunnel syndrome. One test for median nerve compression in the proximal forearm is to maximally supinate the forearm with pressure applied just proximal to the pronator teres while keeping the wrist in neutral position. If this maneuver produces paresthesias in the distribution of the median nerve, it suggests median nerve compression in the proximal forearm. The radial sensory nerve is provoked by extreme forearm pronation and wrist ulnar deviation. A Tinel's sign between the tendons of the extensor carpi radialis longus and the brachioradialis indicates radial sensory nerve compression in the forearm.

The evaluation for cubital tunnel syndrome or ulnar nerve compression at the elbow involves elbow flexion and pressure over the ulnar nerve at the cubital tunnel. The wrist and the forearm are kept in neutral position so as not to provoke median nerve symptoms. Brachial plexus compression in the region of the thoracic outlet is tested by elevating the arms over the head while keeping the wrist neutral, the elbows extended, and the forearms neutral. The examiner evaluates for change in pulse and color while the patient reports any new or increased sensory disturbance in the upper extremity.

Patients with neurogenic TOS typically have an associated muscle imbalance in the cervical scapular area. To evaluate these muscles, the examiner stands behind the patient while the patient slowly elevates the arms above the head. Elbows are kept extended, and the shoulders are forward flexed. The arms then are lowered to the sides from this forward-flexed, elevated position while the examiner observes for winging of the scapula. Winging of the scapula suggests weakness of the serratus anterior muscle. Middle and lower trapezius muscle function is tested by abducting the shoulders with the extremities extended while the arms are elevated above the head from an abducted position. Once again, the arms are lowered slowly to the side. Winging of the scapula suggests a weakness of the middle and lower trapezius muscles. Patients with muscle imbalance in the scapular areas typically have abducted scapulae. Instead of rotating normally with movement of the arms, the scapulae tend to move "up and down" on the back because of overuse of the upper trapezius muscle.

We have recently described a new test, the scratch collapse test, that can be used to identify areas of nerve irritation and/or muscle weakness. To perform this maneuver, the examiner scratches the patient's skin lightly over the area of nerve compression while the patient performs sustained resisted movement of both arms. If the patient has allodynia owing to compression neuropathy, a brief loss of muscle resistance will be elicited. Patients with TOS-related muscle weakness will respond if the examiner just touches along the posteromedial border of the scapula. This test does not rely on patient report and hence is a more objective evaluation method than most clinical tests for nerve compression.⁵

We also rely on a pain questionnaire to assess each patient's symptoms. The questionnaire consists of visual analog scales of pain, questions for patients to describe their pain, and a body diagram for the patient to indicate the location(s) of pain. Responses are considered positive if more than three descriptors are chosen, the body diagram does not follow an anatomic pattern, or if the questionnaire score exceeds 20. Patients who score positive in more than two of these areas are referred for psychological assessment and are not offered immediate surgical intervention. An example of this questionnaire is provided by Novak and Mackinnon in their review.⁶

Specific physical therapy protocols that address postural abnormalities, neural mobility, and muscle imbalance relieve the neurologic and muscular symptoms of most neurogenic TOS patients.³ In our experience, few patients require surgical decompression. When one is evaluating a patient who has "failed" physical therapy, it is important to review the physical therapy regimen. In our experience, a faulty physical therapy program actually can exacerbate the patient's symptoms.

TECHNIQUE

All patients should have an extensive course of appropriate physical therapy before being considered as a surgical candidate. Given the potential for litigation and the controversial nature of the procedure, the patient must be adequately informed of the complexity of the operation and its potential significant surgical complications even with the best surgical technique and care.

The two favored approaches to the treatment of TOS are the transaxillary approach for first rib resection (see Chap. 123) and the supraclavicular approach for anterior and middle scalenectomies with or without first rib resection, the subject of this chapter.^7,8 Reported "good" success rates vary from 75% to 99% when all surgical approaches are considered. In contrast, reoperation on patients in whom the primary operation failed yields improved results in only approximately 15%. There are no randomized clinical trials that compare the transaxillary and supraclavicular approach for TOS decompression. Numerous authors have reported similar results with both approaches, and some have compared outcomes of scalenectomy with and without first rib resection. In a review of the literature, the best long-term outcomes appear to be the result of strict adherence to surgical principles: removal of the first rib, decompression of the artery and vein, and resection of the scalene muscles.

Supraclavicular First Rib Resection

Our preference for patients who do require operation is to perform a first rib resection with decompression of the brachial plexus followed by anterior and middle scalenectomies. Because complications increase with recurrent or secondary operations, a case can be made for first rib resection and scalenectomy in most patients, with care taken to remove the entire posterior aspect of the first rib. This philosophy ensures that a failure to relieve symptoms with scalenectomy alone will not be followed by the recommendation for a secondary thoracic procedure to remove the first rib.

The supraclavicular surgical approach to excise the first rib and release the scalene muscles is our preferred approach. This approach permits direct visualization of the brachial plexus and removal of the cervical rib, if present. Under general anesthesia, the patient is positioned supinely, with a Roho inflatable sandbag placed between the scapulae and the neck slightly extended toward the nonoperative side. Loupe magnification and microbipolar cautery and a portable nerve stimulator are used. Long-acting paralytic agents are avoided to facilitate intraoperative nerve stimulation. The operative incision is made parallel to and approximately 2 cm above the clavicle in the supraclavicular fossa.

The supraclavicular nerves are identified immediately below the platysma muscle. These nerves are mobilized carefully both proximally and distally, and a vessel loop is placed around them to permit retraction across the operative site throughout the procedure (Fig. 122-4). If these cutaneous nerves are divided inadvertently, the proximal end should be cauterized and placed in a deep site, preferably in a muscle bed away from the overlying skin and scar to prevent postoperative neuromatous pain. The omohyoid muscle is identified and divided, and the supraclavicular fat pad is elevated and mobilized proximally. The most lateral portion of the sternocleidomastoid muscle then is divided and, at the conclusion of the procedure, is reapproximated. At this point, the brachial plexus can be palpated between the scalene muscles (Fig. 122-5). The phrenic nerve is identified on the anterior surface of the anterior scalene muscle. There can be an accessory branch of the phrenic nerve that runs within the muscle. The scalene muscle is divided without mobilizing the phrenic nerve to try to avoid excessive manipulation. If the nerve is divided inadvertently, it can be repaired; however, it is unlikely that recovery of diaphragmatic function will be forthcoming because of the long distance to the denervated diaphragm. If the patient experiences respiratory compromise, then consideration can be given for a transfer of a motor intercostal/rectus nerve to the phrenic nerve just above the diaphragm. The long thoracic nerve is located on the posterior aspect or within the middle scalene muscle (Fig. 122-6). A nerve stimulator can be used to identify the nerve, and frequently, two branches of the long thoracic nerve are noted. A vessel loop can be placed around the long thoracic nerve once it is identified (Fig. 122-7). The disposable nerve stimulator is set at its highest stimulation. Even at this setting, if a likely neurologic structure does not respond to direct stimulation, then the tip of the stimulator should be tapped several times on the structure because this maneuver usually will elicit a response. Once the anterior scalene muscle has been divided, the subclavian artery is immediately identified. An umbilical tape is placed around the artery. In patients with TOS, the artery often will be encountered in an elevated position; once it is mobilized and the anterior scalene muscle is divided, it will drop to a more normal location. The middle scalene muscle often will have a fibrous anterior edge. The middle scalene muscle is dissected sharply from the first rib. Care is taken to protect the long thoracic nerve within or behind the middle scalene muscle. The upper, middle, and lower trunks of the brachial plexus can be mobilized as a single unit. Only one branch divides at the trunk level (the suprascapular nerve from the upper trunk). The upper, middle, and lower trunks then are mobilized proximally and distally so that they can be retracted while the first rib is resected. With anterior retraction of the artery and brachial plexus, the first intercostal muscles are sharply dissected, and the midpoint of the first rib is divided. Anterior retraction provides excellent exposure for resection of the posterior first rib back to the spine. Posterior retraction of the plexus and anterior retraction of the artery provide excellent exposure for resection of the anterior portion of the first rib to a point anterior to the subclavian vein. Care is taken to mobilize the C8 and T1 roots because they course above and below the first rib, respectively (Fig. 122-8). Any congenital fibrous bands or thickening of Sibson's fascia will be excised.

A neurolysis of the brachial plexus is needed infrequently, usually only in the cases of a traumatic injury or at the time of recurrent operation. Microinstrumentation and magnification are necessary. Microforceps will hold the epineurium, and straight microspring scissors then will be used to spread and release the epineurium. Care is taken not to damage or breech the perineurium. If the perineurium is violated, then a typical outpouching or herniating of the nerve tissue will be noted.

The first rib is isolated in the midportion of the exposure, where it is visualized most easily, and it is divided under direct vision with the use of a rib cutter. Rongeurs then are used to remove the posterior aspect of the first rib in a piecemeal fashion (see Fig. 122-8). Care is taken to make sure that the most critical portion of the first rib with respect to nerve compression (i.e., the most posterior aspect of the first rib) is totally removed from its spinal attachments. A fine elevator is used to separate the soft tissue attachments from the first rib. The posterior cut edge of the first rib will be held with a rongeur, and in a twisting, rocking motion, the entire posterior portion of the first rib will be removed so that the cartilaginous components of the first rib articular facets (the costotransverse and costovertebral joints) are identified in the specimen. If periosteum or bony fragments are left at the posterior site, a callus will form subsequently to produce new bone formation, which may result in recurrent compression. If a prolonged transverse process or a cervical rib is present, it is removed with the same technique. The anterior portion of the first rib is removed under direct vision to decompress the neural and vascular elements. An opening of approximately 3 cm then is made in the pleura to facilitate drainage of any postoperative blood away from the brachial plexus into the pleural cavity (Fig. 122-9). Care is taken with this maneuver not to injure the intercostal brachial nerve, which courses across the surface of the dome of the pleura. A Marcaine infusion pump is placed in the incision for postoperative comfort. A simple suction drain in the operative site is used and sealed after wound closure and maximum inflation of the lungs by the anesthesiologist. We have not had to routinely place a chest tube for pneumothorax using this strategy.

POSTOPERATIVE CARE

In the immediate postoperative period, a chest x-ray should be obtained to rule out a pneumothorax. If present, it is typically small and usually does not require a chest tube for drainage. The surgical drain placed during the operation is usually removed on the first postoperative day. The patient should be reexamined to document motor or sensory deficits to the upper extremity. The patient is counseled to resume physical therapy exercises, with emphasis on range of motion. By 6 weeks, the patient should resume a supervised physical therapy program.

PROCEDURE-SPECIFIC COMPLICATIONS

The most significant complications associated with surgical decompression of the thoracic outlet include injuries to the major neurovascular structures. Injury to the artery and vein are best avoided by careful manipulation and by obtaining proximal control. The surgeon should be prepared to extend the incision or even perform a median sternotomy (e.g., for right-sided innominate artery injury) or thoracotomy (e.g., for left subclavian artery injury) in the event of a difficult-to-control vascular injury.

Injury to nerves may be due to excessive traction or transection. Injury to the phrenic nerve may result in long-term or even permanent paralysis of the diaphragm. Surgical plication of the diaphragm has been used in a patient with respiratory compromise. Injury to the long thoracic nerve may result in a winged scapula. Injury to the sympathetic chain may result in a Horner's syndrome. The most devastating injury may be to the lower trunk of the brachial plexus. This may cause constant pain or weakness and significant sensory and motor deficits to the hand. A temporary palsy has been reported to be as high as 10%. We believe that the supraclavicular approach provides for the best visualization of these structures, avoiding unintentional injury.

Even with careful preservation of the supraclavicular nerves (i.e., sensory nerves deep to the platysma), patients routinely will describe diminished sensation in the distribution of the supraclavicular nerves for approximately 6 weeks. To minimize irritation of this area, female patients are discouraged from wearing a bra strap across their surgical site for approximately 1 month after the operation. However, with inadvertent laceration of these small sensory nerves, severe postoperative neuropathic pain can result. In these cases of laceration, the nerve should be mobilized, the distal end should be cauterized, and the nerve should be buried away from the incision region.

Resection of the left first rib can be associated with injury to the thoracic duct. Increased drainage from the wound, or from the drain placed at the time of surgery, or the presence of a large effusion should raise concern for a cervical chyle leak. If conservative management by having the patient fast does not alleviate the problem, the wound should be explored. Often an injury to the thoracic duct or a tributary can be identified and repaired. In our experience, one patient required thoracic duct ligation.

SUMMARY

Neurogenic TOS presents the clinician with a complex array of symptoms and physical signs. Clinical judgment must be used to exclude non thoracic outlet compression etiology and to confirm the diagnosis. Most patients respond to nonoperative intervention with physical therapy. In the appropriately selected and well-counseled patient, a supraclavicular exposure with scalenectomy, first rib resection, and brachial plexus neurolysis offers an effective and durable treatment for neurogenic TOS.

REFERENCES