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Directions in Clinical Research on ATOS

  • Ali Azizzadeh
  • Louis L. Nguyen
  • Robert W. Thompson
Chapter

Abstract

Arterial thoracic outlet syndrome (TOS) is the least frequent but likely most complex form of TOS. It most frequently occurs in relatively young, active, and otherwise healthy individuals. It is primarily caused by bony abnormalities, such as cervical ribs and anomalous first ribs. In this condition, longstanding subclavian artery compression leads to poststenotic dilatation and ulceration or aneurysmal degeneration, followed by occlusive thrombosis or mural thrombus formation with distal embolization to the arm and/or hand. Many clinical questions regarding diagnosis and optimal management of arterial TOS remain unanswered. The development of an international registry for patients with arterial TOS, along with standards for characterizing patients and reporting clinical outcomes, would provide useful data to help guide the optimal management of this rare and challenging clinical condition.

Keywords

Computerize Tomography Angiography Magnetic Resonance Angiography Subclavian Artery Distal Embolization Great Saphenous Vein 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Introduction

Arterial TOS is the most rare form of TOS and is most frequently observed in relatively young, active, and otherwise healthy individuals [1, 2, 3, 4]. The condition is often caused by osseous structures, such as cervical ribs, anomalous first ribs, fibrocartilagenous bands and hypertrophic callus from healed first rib or clavicular fractures [2, 5, 6]. The pathophysiology is related to longstanding subclavian artery compression, poststenotic dilatation, and ulceration or aneurysmal degeneration, followed by occlusive thrombosis or mural thrombus formation with distal embolization to the arm and/or hand. Due to the rarity of this condition, there are no large prospective clinical trials involving patients with arterial TOS. Therefore, the diagnosis and care of patients with arterial TOS is largely based on principles derived from caring for other types of TOS, as well as standard vascular surgical techniques in dealing with the complications of arterial TOS. In this chapter, we explore some of the clinical questions related to arterial TOS that need further study and organize these questions into the stage of care at which these issues arise.

Diagnosis and Imaging

Among patients who present with acute upper extremity ischemia, arterial TOS is only one of many possible causes. A high suspicion for the diagnosis should be considered, however, in young patients, especially those who participate in athletics or in occupations with repetitive arm motion. Initial imaging studies should include plain chest and cervical spine x-rays to evaluate for osseous abnormalities. Additional imaging obtained in the course of treatment for these patients should include visualization of the subclavian artery for the presence of an aneurysm. The choice of imaging modality may depend on the urgency of the presentation. Computerized tomography angiography (CTA) and magnetic resonance angiography (MRA) both provide excellent imaging of the aortic arch, subclavian artery and axillary artery, though anomalous bony structures are better viewed with CTA and soft tissue structures are better seen with MRA.

Traditional angiography provides detailed imaging of the proximal vessels and the distal extremity vessels that are otherwise difficult to image with conventional CTA and MRA. Visualization of the distal vasculature is particularly important in patients suspected of having thromboembolism. A recently published series reported that the incidence of arterial compression at the thoracic outlet may actually be underreported [4]. The authors recommend routine arterial imaging for patients evaluated with TOS who have a bony abnormality or an examination that shows an arterial abnormality.

Uncertainty exists for patients who present with incidentally discovered cervical ribs or ­elongation of the C7 transverse process (apophy­somegaly). The estimated prevalence of cervical ribs and C7 apophysomegaly is approximately 0.75 % and 2.2 %, respectively [7]. In the absence of symptoms of arterial TOS, it is unclear what imaging or follow up is needed for patients who present with incidental cervical ribs and apophysomegaly. Since arterial TOS is usually asymptomatic until the clinical sequelae of aneurysmal degeneration, thrombus formation, and distal embolization occur, it is prudent to follow these patients with serial imaging. Future research, through observational studies, is needed to determine the time-course over which arterial abnormalities develop and the optimal type and frequency of surveillance imaging in this patient population.

Research Directions

  • Who should be screened for or suspected of having ATOS?

  • What is the most appropriate diagnostic test to screen for cervical ribs or other osseous abnormatilities?

  • What is the appropriate follow up for patients with asymptomatic cervical ribs or C7 apophysomegaly?

  • What is the most appropriate imaging modality to screen for subclavian artery aneurysms?

  • Do all patients diagnosed with ATOS require angiography?

  • What are the implications of arterial signs in a patient with neurogenic TOS?

Treatment

A selection of published case series of patients undergoing surgery for arterial TOS are listed in Table 89.1 [1, 2, 4, 5, 8, 9, 10, 11, 12, 13, 14, 15, 16]. This review of the literature revealed fewer than 450 cases of arterial TOS reported over three decades. This signifies the rarity of this pathology and the importance of relying on the clinical experience with other types of TOS for the best management of these patients. There appears to be a significant correlation between arterial TOS and the presence of osseus abnormalities, especially cervical ribs and anomalous first ribs [4, 6]. Although the transaxillary approach has been utilized by many authors to effectively decompress the thoracic outlet for neurogenic and venous TOS, exposure and reconstruction of the subclavian artery is best achieved with the patient supine through supraclavicular or paraclavicular exposure [4, 17]. This allows for the greatest surgical access to the subclavian and axillary vessels, the brachial plexus, and the relevant musculoskeletal structures. Using a combination of transaxillary and supraclavicular approaches has also been reported [10].
Table 89.1

Selected case series on treatment of arterial TOS

Author

Type of TOS, # of patients

F/U years

Treatment

Ex/Good results (%)

A

V

N

C

R

TA

SC

Dunwayri [8]

47

178

347

1.2

527

89

Sanders [21]

11

75

2,375

Degeorges [9]

38

27

15

96

7.5

107

69

84

Urschel and Razzuk [10]

240

264

2,210

1,221

2,714

Jamieson and Chinnick [11]

29

12

368

4

380

29

72

Hempel et al. [12]

18

47

705

>2

770

86

Lindgren et al. [13]

3

2

146

24

2

175

59

Wood et al. [15]

20

20

81

2

5.5

123

89

Kieffer et al. [16]

38

3.6

33

87

Type of TOS: A arterial, V venous, N neurogenic, C combined, R recurrent, F/U followup in years. Treatment: TA transaxillary, SC supraclavicular, Ex/Good percent of patients with excellent or good results

Surgical decompression with removal of osseus abnormalities is recommended for patients with arterial TOS. In the presence of a cervical rib, removal of both the first and cervical rib is often recommended [4, 6, 10, 17], but it is still unclear whether removal of the cervical rib alone provides adequate decompression. Studies of cadavers with cervical ribs have revealed histological changes of fibrosis in the lower brachial plexus nerve trunks [18]. This evidence suggests that neurolysis of the brachial plexus and first rib resection may be beneficial in patients who undergo decompression for arterial TOS, since at least some proportion of symptoms in these patients may be attributable to concomitant neurogenic TOS. For patients with distal emboli and compromised circulation in the hand, concomitant dorsal (cervical) sympathectomy has also been advocated [10, 19].

For patients with minimal poststenotic dilation of the subclavian artery, relief of the proximal stenosis without arterial reconstruction is usually sufficient [10]. However, no long-term studies exist that have followed these dilated segments to see if they are prone to later aneurysmal dilation or thrombosis, and it is worth emphasis that surface ulceration and mural thrombus formation can occur even with minimal arterial dilatation. It appears well established that when authentic aneurysmal degeneration of the subclavian artery is present, excision of the affected segment with interposition grafting is required. However, the choice of the optimal conduit for this type of bypass is debatable, and use of both autogenous and prosthetic conduits has been reported. Long-term comparative studies regarding the patency rates of different conduits in patients with arterial TOS is lacking. Extrapolating the data from other anatomical beds, however, it would appear that autogenous conduits would be preferable. It is notable that there is often a size mismatch between the greater saphenous vein (GSV) and the subclavian artery, making reversed GSV a less than ideal choice. Spiral grafts of the GSV may correct the size mismatch, but are often cumbersome and time-consuming to construct. Use of the autogenous iliac artery has been described for subclavian artery repair [20], and other suitable options for bypass graft conduits include the superficial femoral vein or cryopreserved femoropopliteal artery. The use of prosthetic grafts, constructed from either Dacron or polytetrafluoroethylene (PTFE), has also been reported, and these widely used conduits have excellent outcomes in carotid-subclavian bypass procedures for atherosclerosis. At present, the choice of conduit for subclavian artery reconstruction in arterial TOS appears to be largely based on surgeon preference. The use and duration of postoperative anticoagulation is also widely variable among published studies, but for patients with extensive distal embolization who undergo thrombectomy and vascular reconstruction, a significant period of anticoagulation seems advisable.

Research Directions

  • Does removal of a cervical rib or other osseous abnormality constitute adequate ATOS decompression? Do first ribs always need to be resected as well?

  • What is the most appropriate conduit for subclavian artery aneurysm repair? Autogenous or prosthetic?

  • What is the most suitable autogenous conduit for repair of the subclavian artery? Greater saphenous vein, femoral vein, external iliac artery, or cryopreserved femoral artery?

  • If autogenous conduits are preferred, is a greater saphenous vein with a significant size mismatch appropriate?

  • What is the proper management of distal upper extremity embolization? Open thrombectomy or thrombolysis prior to decompression?

  • How soon after thrombolysis should the ATOS decompression procedure be performed? Same admission, or electively?

Outcomes and Follow-Up

The reported results of surgery for arterial TOS reveal excellent or good outcomes in the majority of patients. Following decompression and arterial reconstruction at the thoracic outlet, the status of the distal vasculature plays the most important role in the functional recovery of the patient. Extensive emboli that have led to chronic occlusion of the forearm and hand vessels are often irreversible. Revascularization of the distal ­vasculature using thrombolysis or open thrombectomy following thoracic outlet decompression is recommended in this setting, especially in the presence of acute ischemia. Simultaneous dorsal (cervical) sympathectomy has also been recommended by some authors, as a means to optimize microvascular circulation and lower the risk for digital ulceration or tissue loss [10]. A relatively simple classification system has been used by most authors to assess functional outcomes, graded as follows: (1) excellent results characterized by no pain and an easy return to preoperative professional and leisure daily activities; (2) good results with intermittent pain that is well tolerated, and a possible return to preoperative professional and leisure daily activities; (3) fair results with intermittent or permanent pain that is poorly tolerated, as well as a difficult return to preoperative professional and leisure daily activities; and (4) poor results when symptoms are not improved or are aggravated. The reported follow-up regimen for patients undergoing decompression for arterial TOS is unfortunately widely variable. It nonetheless seems prudent that patients undergoing arterial reconstruction for arterial TOS should be followed on a regular basis with physical examination and noninvasive ultrasound assessment of upper extremity circulation, and perhaps intermittent imaging evaluation.

Research Directions

  • What is the appropriate medical therapy (anticoagulation, clopidogrel, or aspirin) after ATOS decompression and subclavian artery aneurysm repair? How long should it be continued?

  • What is the natural history of a subclavian artery poststenotic dilation after ATOS decompression?

  • What is the follow-up regimen of patients after ATOS decompression? How often should they be seen? What diagnostic tests should be ordered?

Conclusion

Arterial TOS is the least frequent but likely most complex form of TOS. The diagnosis and management of these patients is based on the cumulative experience of physicians who have expertise in the care for patients with all forms of TOS. Many clinical questions regarding this condition remain unanswered, yet randomized clinical trials and even satisfactory observational studies are not feasible. The development of an international registry for patients with arterial TOS, along with more uniformly-applied standards for characterizing patients and reporting clinical outcomes, would be an immense step in collecting more useful data to help guide the optimal management of this challenging clinical condition.

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Copyright information

© Springer-Verlag London 2013

Authors and Affiliations

  • Ali Azizzadeh
    • 1
  • Louis L. Nguyen
    • 2
  • Robert W. Thompson
    • 3
  1. 1.Department of Cardiothoracic and Vascular SurgeryUniversity of Texas Medical School, Memorial Hermann Heart and Vascular InstituteHoustonUSA
  2. 2.Department of Vascular and Endovascular SurgeryBrigham and Women’s HospitalBostonUSA
  3. 3.Department of Surgery, Section of Vascular Surgery, Center for Thoracic Outlet SyndromeWashington University, Barnes-Jewish HospitalSt. LouisUSA

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