Thoracic Outlet Syndrome: Arterial

Arterial complications from subclavian artery compression represent the least common type of thoracic outlet syndrome (TOS) in adults, but they also represent the strongest indication for operative intervention. Arterial manifestations usually follow a progressive course characterized by extrinsic compression, poststenotic dilatation, aneurysmal degeneration, thrombus formation, and secondary embolization. Because arterial TOS is typically associated with anomalous osseous structures, this form of TOS has a more easily definable clinical picture. In fact, arterial TOS was probably the first form to be described as early as 1831. The first reported resection of a bone abnormality causing a subclavian aneurysm was by Coote in 1861. Compression of the subclavian artery and brachial plexus was first termed Naffziger syndrome and evolved to the modern term thoracic outlet syndrome after a 1956 publication by Peet and coworkers.

Pathophysiology

Arterial complications of TOS are associated with bone abnormalities in almost all cases. Cervical ribs that cause subclavian artery damage tend to extend beyond the transverse process with partial or complete fusion to the first rib by a bony pseudarthrosis. This differs from the longer, thinner, and incomplete cervical ribs usually associated with neurogenic TOS. The cervical rib pushes the subclavian artery forward, angulating and compressing it between the first rib and the anterior scalene muscle. This compression causes injury to the inferior wall of the third segment of the subclavian artery, which may lead to localized intimal damage or poststenotic dilatation. Less common causes of arterial TOS include anomalous first ribs, fibrocartilaginous bands associated with the anterior scalene muscle, muscular hypertrophy in athletes, and hypertrophic callus from healed clavicle or first rib fractures. Poststenotic dilatation associated with chronic arterial compression may progress to aneurysmal change, whereas localized intimal damage may lead to embolization or thrombosis. The relative frequencies of anatomic abnormalities are shown in Table 125.1 .

TABLE 125.1

Relative Frequency of Anatomic Abnormalities Causing Arterial Thoracic Outlet Syndrome

Abnormality	Frequency (%) ^a
Cervical rib	64
Anomalous first rib	17
Fibrocartilaginous band	11
Clavicular fracture	7
Enlarged C7 transverse process	1

a Percentages represent a compendium of 162 patients from six large series. ^, ^,

Epidemiology

The frequency of arterial TOS in the general population is undefined, but it represents a small subset of patients undergoing operative treatment for TOS. In the largest single-institution experience of 5102 patients treated for all varieties of TOS, Urschel and Kourlis performed primary neurovascular decompression on 294 (6%) for arterial TOS. Orlando et al. reported that 25 (4%) of 594 consecutive first rib resections were performed for arterial TOS. Similarly, Rinehardt et al. reported that 44 (3%) of 1431 TOS cases from the NSQIP database were performed for arterial TOS. In contrast, arterial TOS is a relatively more common form in children and adolescents, accounting for 12% to 32% of cases. ^,

Most patients presenting with symptoms of arterial TOS are young, active adults. The mean age in recent published series ranges from 32 to 45 years, with proportionately more women than men. ^, ^, No familial predisposition has been described. The condition appears to be related to bone abnormalities or trauma in nearly every circumstance. ^, ^, Orlando et al. reported arterial TOS is significantly more likely to be associated with a cervical rib than either venous TOS or neurogenic TOS: in their series, 60% of arterial TOS patients had a cervical rib versus 2.3% of venous TOS and 9.4% of neurogenic TOS. Vemuri et al. reported that only one (3%) of 40 patients with arterial TOS had no identifiable bony abnormality.

Clinical Presentation

Patients with arterial TOS have a characteristic history and physical examination, but diagnosis requires confirmation with objective testing.

Signs and Symptoms

The most common presentation is hand ischemia due to brachial artery embolus or distal microembolization. However, arterial TOS can be associated with less dramatic symptoms, and many cases go unrecognized because the condition tends to occur in young patients without atherosclerotic risk factors. Early in the disease process, patients may present with mild symptoms of exertional arm pain or unilateral Raynaud syndrome. Moderate to severe exertional pain may be associated with subclavian artery thrombosis. On occasion, a subclavian artery aneurysm may be discovered in an asymptomatic patient. Although rare, stroke from retrograde propagation of subclavian thrombus has been reported. ^,

Clinical Assessment

Although acute hand ischemia with absent brachial and radial pulses is a common presentation, the clinical picture of arterial TOS may be more chronic and subtle. Clues to the diagnosis include the young age of the patient and the tendency for symptoms to be unilateral, which helps differentiate the condition from systemic pathologic states. The directed physical examination should consist of assessing upper extremity pulses, measuring bilateral arm blood pressures, and auscultating for bruits in the supraclavicular fossa. A bruit may be elicited on shoulder abduction or the overhead arm position if it is not present in the relaxed position. Specific findings on physical examination include a palpable cervical rib and a pulsatile supraclavicular mass. Evidence of microembolization to the hand, including digital ischemia and splinter hemorrhages, may also be present.

Diagnostic Evaluation

Arterial TOS is a clinical diagnosis made by combining important elements from the history and physical examination. The following adjuncts may help support the diagnosis or suggest an alternative cause of the patient’s symptoms.

Compression Maneuvers

Compression maneuvers such as the Adson test, costoclavicular maneuver (exaggerated military position), and hyperabduction maneuver (shoulder abduction beyond 90 degrees) have historically been used to aid in the diagnosis of TOS, but none is accurate. Ablation or reduction of the radial pulse with these maneuvers is considered a positive test result, but the incidence of false-positives in normal, healthy volunteers ranges from 9% to 57%. Another compression maneuver is the abduction–external rotation test, also referred to as the elevated arm stress test popularized by Roos and Owens. Development of hand pain or paresthesias within 60 seconds is considered a positive test result. This test is used in the diagnosis of neurogenic TOS but is not helpful in arterial TOS (see Ch. 124 , Thoracic Outlet Syndrome: Neurogenic).

Noninvasive Vascular Laboratory Studies

Duplex Ultrasonography

Duplex ultrasound examination of the subclavian and axillary arteries may demonstrate aneurysmal change, blunted waveforms, or elevated flow velocities correlating with a compressive stenosis (see Ch. 22 , Vascular Laboratory: Arterial Duplex Scanning). The clavicle may interfere with complete ultrasound imaging of the subclavian artery, but significant ulcerations and intimal disruption may be visible. A subclavian artery flow velocity exceeding 240 cm/s may be considered evidence of a hemodynamically significant fixed stenosis. In patients without a fixed stenosis, compression maneuvers during sonographic evaluation have been recommended, with decreased subclavian artery diameter or changes in peak systolic velocity thought to be diagnostic of arterial TOS. However, as with the pulse-monitored compression maneuvers described before, there are a high number of false-positives in normal, healthy volunteers. Studies have shown that compression maneuvers are associated with complete occlusion or significant stenosis of the subclavian artery in approximately 20% of normal subjects. ^, Therefore an abnormality detected on ultrasound during compression maneuvers should be used only to confirm a suspected diagnosis of arterial TOS.

Pulse Volume or Segmental Pressure Recording

Pulse volume or Doppler segmental pressure recordings taken at multiple levels in the upper extremities can help localize the level of arterial obstruction if embolization has occurred from arterial TOS (see Ch. 21 , Vascular Laboratory: Arterial Physiologic Assessment). Diminished digital waveforms in the affected extremity during compression maneuvers coupled with normal findings in the contralateral extremity suggest dynamic subclavian artery compression in the symptomatic patient ( Fig. 125.1 ). Fixed waveform dampening is indicative of arterial insufficiency consistent with stenosis or distal embolism.

Figure 125.1, Digital photoplethysmography studies showing left upper extremity arterial waveform reduction with selected compression maneuvers.

Radiologic Studies

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