Arterial Thoracic Outlet Syndrome (TOS)
Important features of arterial TOS include the following:
- Arterial TOS is rare and the least frequently encountered thoracic outlet compression disorder
- Typically caused by subclavian artery compression in association with a cervical rib or first rib anomaly
- Usually includes narrowing of the subclavian artery and formation of an aneurysm just beyond the narrowed area
- Unique form of arterial TOS occurs with compression of the axillary artery, almost always in overhead throwing athletes
The compression of the subclavian artery caused by the cervical rib leads to turbulent blood flow through the narrowed segment of the artery, and this type of long-standing stress eventually results in degeneration of the arterial wall and formation of an aneurysm in the location of the artery immediately beyond the stenosis, or narrowing. This is often referred to as formation of a “post-stenotic” arterial aneurysm.
A second form of arterial TOS affects the distal axillary artery, beyond the level of the first rib near the shoulder. This form results in either aneurysmal or occlusive lesions, and is a unique condition that appears to occur almost exclusively in baseball pitchers. These lesions are caused by repetitive compression and stretching of the axillary artery by the head of the humerus, as it moves forward during extremes of arm elevation and extension, as seen in the overhead pitching motion.
Prompt recognition of these various forms of arterial TOS is extremely important, as delays in treatment can lead to severe ischemic complications (restricted blood flow), tissue loss requiring debridement or amputation, and permanent disability.
(See story of arterial TOS patient treated by Robert Thompson, MD, at The Washington University Center for Thoracic Outlet Syndrome at Barnes-Jewish Hospital.)
History and Symptoms of Arterial TOS
Unlike other forms of TOS, those with subclavian artery stenosis, occlusions, and aneurysms due to arterial TOS may not exhibit symptoms. In some cases, a significant difference in blood pressure between the arms or a non-tender mass in the lateral lower neck may be present and can be detected upon examination. Patients with arterial TOS will only occasionally have a history of a known cervical rib or previous diagnosis of TOS.
Patients with arterial TOS may have one or more of the following symptoms:
- A sudden onset of hand pain and weakness
- Numbness and tingling in the fingers
- Cold and pale fingers
- Chronic arm fatigue with use or claudication
- Non-healing wounds or ulcerations in the fingers
Physical examination of the patient with suspected arterial TOS is directed toward identifying the presence of a subclavian or axillary artery lesion and evaluating the presence and extent of hand ischemia.
Examination should include inspection of the hand for the presence of:
- Cold and pale fingers with diminished sensation
- Markedly delayed capillary refill
- Diminished handgrip strength may be present because of pain that accompanies use of the hand
- Ischemic arm fatigue may be most evident during maneuvers with the arm elevated overhead
- Signs of digital emboli, such as discolored spots in the fingertips or under the nails
- Ulcerations and non-healing wounds in the fingertips
The arteries of the upper extremity are examined by palpation, with the quality of each pulse compared with that on the asymptomatic side for reference. Arterial examination also includes use of the hand-held Doppler, particularly when the pulses are not palpable.
The neck is also carefully examined and palpated to detect any evidence of a mass, which may represent a cervical rib. The patient’s upper arm is also examined for the presence of aneurysms, but detection of this type of aneurysm by palpation is exceptionally rare given that these lesions are usually quite small.
Standard cuff blood pressure measurements are taken in each arm and compared.
Vascular Laboratory Tests
Vascular laboratory studies are useful in suspected arterial TOS, both to provide initial imaging of the neck and for more accurate definition in functional blood flow in the upper extremity. Duplex ultrasound imaging is used to detect the presence of an aneurysm and may facilitate rapid diagnosis.
Other vascular studies of the upper extremity (such as segmental pulse waveforms and pressure studies) are also valuable in defining any impairment to blood flow.
Plain neck or chest radiographs are important in all patients with suspected arterial TOS, to help define the presence of a cervical rib or first rib anomaly.
Contrast-enhanced arteriography is required to image the extent, location and character of arterial occlusions, and to detect the presence of subclavian artery compression and aneurysm formation.
Arteriography is also critical to visualize the site, extent, and character of the arterial lesions in patients suspected of having arterial TOS affecting the axillary artery.
In current practice, these types of studies are usually performed with CT- or MR-based angiography, although traditional catheter-based (transfemoral) arteriography may also be used in the initial evaluation.
Once a clinical diagnosis of arterial TOS has been confirmed by imaging studies, anticoagulation therapy with intravenous or subcutaneous heparin should be started promptly. . In most cases, treatment with an antiplatelet agent, such as aspirin or clopidogrel (Plavix), is also started soon after diagnosis. These agents are used principally as precursors to surgical treatment.
Continuous infusion of thrombolytic (clot-dissolving) agents into the arteries is also potentially complicated in patients with arterial TOS and carries few benefits compared to direct surgical treatment.
Balloon angioplasty and/or stent placement in the axillary or subclavian arteries is also unsatisfactory treatment, since these approaches do not correct the underlying cause and are known to carry a high likelihood of subsequent failure.
In most cases, prompt operative treatment is more definitive and strongly preferred.
Arterial TOS Surgery
Indications for Surgery
Prompt surgical attention is advised for patients with symptoms:
- Related to an axillary artery or subclavian artery aneurysm
- Associated with a fixed occlusive lesion of either the axillary or subclavian artery
- Symptoms of thromboembolism and acute hand ischemia
Elective surgical treatment is recommended in asymptomatic patients with a cervical rib and a fixed subclavian artery stenosis, or in those with any degree of subclavian artery dilatation.
The first step in thoracic outlet decompression for arterial TOS affecting the subclavian artery is performed through a supraclavicular incision in the front of the neck, parallel to and just above the clavicle, similar to that used for supraclavicular decompression in neurogenic TOS. Through this approach the same initial steps are taken, including mobilization of the scalene fat pad, scalenectomy, and brachial plexus neurolysis.
The cervical rib is identified within the tissue plane of the middle scalene muscle behind the brachial plexus. The posterior portion of the cervical rib is exposed with complete visualization and protection of the brachial plexus nerve roots, and then divided. The posterior portion of the first rib is then exposed and divided in a similar manner. In most patients with arterial TOS the cervical rib attaches directly to the midportion of the first rib, often with formation of a true joint. This junction is maintained while the anterior portion of the first rib is exposed at the level of the scalene tubercle, similar to that described in supraclavicular operations for neurogenic TOS. The anterior first rib is then divided and the cervical rib and first rib are removed together as a single specimen. In the less frequent circumstance where the cervical rib ends in a ligamentous band attached to the first rib, this connection is divided and the cervical rib is removed as a separate specimen before removing the first rib.
If subclavian artery reconstruction is planned and a suitable length of normal artery distal to the lesion cannot be adequately mobilized from the supraclavicular incision alone (see the following section), a second infraclavicular incision is made, parallel to and underneath the lateral aspect of the clavicle. The upper portion of the pectoralis major muscle is separated from the adjacent clavicle without dividing the muscle, and the clavipectoral fascia is opened to expose the underlying pectoralis minor muscle and adjacent neurovascular bundle. The axillary artery is exposed medial to the pectoralis minor muscle, but division of the pectoralis minor tendon is occasionally required to obtain adequate exposure and control of the axillary artery.
Subclavian Artery Reconstruction
Following the initial steps of supraclavicular thoracic outlet decompression outlined above, specific attention is turned to the subclavian artery. The subclavian artery is thoroughly exposed, from the level of the vertebral and internal thoracic artery branches to a level beyond the site of the first rib and just underneath the clavicle. The subclavian artery is visually inspected to evaluate the extent of any aneurysmal dilatation and palpated to detect any wall thickening or fixed occlusive lesions.
When the extent of aneurysmal dilatation is minimal and the need for reconstruction may be in doubt, intraoperative Duplex ultrasound examination may help to verify or exclude the presence of surface ulceration and/or mural thrombus. More recently, we have used intravascular ultrasound for this purpose, guided by an intra-arterial catheter placed from the femoral artery.
Subclavian artery reconstruction is recommended if the extent of aneurysmal dilatation is greater than 50% larger than the adjacent normal subclavian artery, if there has been any evidence of distal thromboembolism, or if evaluation of the artery reveals any evidence of ulceration, excessive wall thickening, or mural thrombus.
In the event that reconstruction is planned, the proximal portion of the normal subclavian artery is controlled at a level immediately beyond the vertebral and internal thoracic artery branches. The distal extent of the subclavian artery lesion is then evaluated to determine the most suitable level for bypass graft reconstruction. In many situations, a segment of the normal axillary-subclavian artery beyond the pathological segment can be mobilized into the supraclavicular incision, allowing reconstruction to be performed entirely from this single exposure. When the diseased segment of the subclavian artery extends further underneath the clavicle, a second infraclavicular incision is made to permit distal control at the level of the axillary artery (see previous section).
After administration of intravenous heparin, the subclavian and axillary arteries are clamped. The diseased segment of the subclavian artery is removed, leaving small portions of normal artery at the proximal and distal clamp sites. An interposition bypass graft of suitable size to match the diameter of the normal subclavian artery is selected for reconstruction, and the length of the graft is carefully measured with the arm at rest and in an elevated position to avoid subsequent tension. The bypass graft is then sutured into position with end-to-end attachments to the proximal and distal arteries, the clamps are removed, and flow is restored through the reconstructed subclavian artery.
The most appropriate conduit for subclavian artery replacement remains open to debate. Although prosthetic bypass grafts may be considered (e.g., Dacron, polytetrafluoroethylene), we strongly prefer tissue-based conduits for arterial reconstruction in this highly mobile position, particularly in the young, active patients who typically develop arterial TOS. Thus, the most frequently used grafts in our experience include autologous saphenous vein, superficial femoral vein, or iliac artery, as well as use of cryopreserved femoral artery.
In patients with evidence of distal arterial obstruction in the lower arm or hands, arising through thromboembolism from an axillary or subclavian artery lesion, an intraoperative arteriogram is performed upon completion of the primary arterial reconstruction. This is usually done through a transfemoral approach under fluoroscopic guidance, with the catheter tip positioned in the brachial artery for contrast injection. Visualization of the arteries throughout the arm is then obtained to localize any sites of arterial occlusion or residual thrombus.
For thromboembolectomy of the brachial, radial, and/or ulnar arteries, a short antecubital incision is initially made in the front midportion of the arm. The brachial artery is identified, exposed, and controlled, and an opening in the artery is created. Any thrombus present in the brachial artery is removed using small forceps and balloon catheters, until there is evidence of normal arterial inflow from the upper arm. Any thrombus in the radial and/or ulnar arteries is also removed using the same techniques as the surgeon periodically evaluates blood return from the distal vessels (“back-bleeding”). The amount of thrombotic material retrieved is compared with that expected from the earlier arteriogram, and care is taken to attempt gentle passage of small balloon catheters to the distal extent of the radial and ulnar arteries when necessary.
In some cases in which the amount of distal thromboembolism is considered extensive, it may also be useful to infuse a thrombolytic agent (such as TPA) and/or a vasodilator (e.g., papaverine or nitroglycerine) into the distal brachial artery. When no additional thrombus can be removed, the brachial arteriotomy is closed, most often with a small patch angioplasty using a short segment of the saphenous vein. Repeat completion arteriography may then be performed. In patients who have severe digital ischemia and fingertip ulcerations, cervical sympathectomy to promote wound healing may also be considered. This can readily be performed at the same time as the thoracic outlet decompression procedure.
Axillary Artery Reconstruction
The axillary artery is approached through an incision along the medial aspect of the upper arm, just below the edge of the pectoralis major muscle. The deep brachial fascia is opened, and the neurovascular bundle is identified. Care is taken in dissecting and mobilizing the axillary vein and nerves of the brachial plexus to avoid injury, and the axillary artery is exposed at a level where the vessel appears normal.
The axillary artery is then traced to a level just above the origin of the circumflex humeral and subscapular branches, and a proximal segment of normal axillary artery is sought. During this process, the axillary artery should be separated from all adjacent tissues to ensure adequate mobility. It is usually necessary to retract the pectoralis minor muscle medially to obtain satisfactory exposure of the underlying proximal axillary artery, and in many situations it is necessary to divide the pectoralis minor tendon to achieve suitable proximal arterial control.
Once intravenous heparin has been administered, the proximal and distal portions of the axillary artery are clamped, along with the adjacent branches. An axillary arteriotomy may be created along the length of the lesion, or the diseased segment may be directly excised with retention of the branch vessel origins. The pathological lesion affecting the vessel is examined, usually demonstrating thickening in the arterial wall, surface ulceration, and intraluminal thrombus. Reconstruction is performed with an interposition bypass graft from the proximal axillary artery to the upper brachial artery just beyond the pathological lesion, using a short reversed saphenous vein graft. Care is taken to measure the length of the graft to ensure that there will be ample mobility of the reconstruction, even in positions of extreme arm elevation. It is also important to preserve or reimplant at least one of the axillary artery branches (usually the posterior circumflex humeral artery).
After axillary artery reconstruction, an intraoperative arteriogram is performed, with the arm at rest and in an elevated position, to ensure that there is satisfactory flow and no positional compression of the bypass graft. Additional steps may then be undertaken if there has been any evidence of thromboembolism to the lower arm and/or hand, as described above.
Potential Complications of Surgery
The potential complications of surgical treatment for arterial TOS involving the subclavian artery are the same as those described above, in the section on neurogenic TOS. There are several additional potential complications that are unique to operations for arterial TOS:
- Postoperative bleeding. Because of the extent of the surgical procedure and the use of anticoagulation, postoperative bleeding can occasionally occur following operations for arterial TOS. This can usually be managed conservatively, with judicious blood transfusions if necessary. In rare situations, reoperation to evacuate blood from the neck or chest may be necessary.
- Early axillary or subclavian artery obstruction or rethrombosis. Although rare, any operative procedure on the axillary or subclavian arteries can be complicated by early postoperative thrombosis. This may be due to suture lines that can serve as sites for thrombus formation, early inflammatory responses in the artery associated with a propensity toward clot formation, or residual areas of arterial stenosis that were not be detected or corrected at the time of the original surgery. Anticoagulation with intravenous heparin can limit the possibility of early postoperative thrombosis, but is usually withheld for at least several days after surgery because of the risks of bleeding. Early postoperative arterial thrombosis usually requires reoperation to correct the occlusion.
- Late axillary or subclavian artery obstruction or rethrombosis. Even when an arterial reconstruction appears to be widely open at the time of surgery and in the early postoperative period, some patients may later develop signs of arterial insufficiency due to intimal hyperplasia, a reactive healing response in the artery wall that can cause stenosis and/or occlusion with thrombosis. Distal emboli can also occur. Prompt recognition is important in order to perform upper extremity arterial studies as a first diagnostic procedure, and if confirmed, to proceed with arteriography. If axillary or subclavian artery stenosis or occlusion is identified, this may be treated with balloon angioplasty and/or reoperative surgical reconstruction.
Expected Outcomes of Surgery
For patients undergoing surgical treatment for arterial TOS with subclavian artery lesions, recovery is similar to those undergoing surgery for neurogenic TOS. Patients are generally kept from returning to work or school for approximately 4 to 6 weeks after surgery, to allow sufficient time for recovery from the operation and to make satisfactory progress with physical therapy. Some may return to limited activities earlier, particularly if their work or school activities are relatively sedentary. Most patients can drive within 2 to 3 weeks of the operation, but in some this can aggravate neck muscle spasm. We have come to appreciate that excessive activity in patients who return to work or other activities too early can lead to flares of neck and back muscle spasm, neurogenic symptoms, and even more prolonged recovery. Some patients may require a longer period of recovery before returning to work, depending on their preoperative levels of symptoms, pre-existing limitations and restrictions, and the nature of their work activities. Recovery is typically complete within 3 months of the operation, and a full return to previous levels of function can usually be expected, including participation in athletics.
For overhead-throwing athletes who have undergone surgery for axillary artery lesions, recovery is expected to be relatively complete within 3 to 4 weeks, at which time general cardiovascular conditioning can resume. We obtain a final positional arteriogram 6 weeks after surgery, at which time the axillary artery reconstruction and the status of the distal arm circulation are reassessed. If the circulation to the upper extremity appears satisfactory and no additional procedures are recommended, patients may then gradually return to full activity including overhead throwing. The majority of patients will have returned to normal levels of activity within 8 to 12 weeks of surgery.
With early surgical treatment and restoration of arterial flow to the hand and digits, excellent outcomes can be anticipated with a full return to function over a period of several months. Unfortunately, because of the insidious clinical presentation of axillary lesions and subclavian aneurysms and delays in surgical treatment, patients with these conditions occasionally have residual difficulties secondary to distal thromboembolism within the hand or digits that cannot be easily resolved, including digital ulcerations, non-healing wounds, and tissue loss requiring amputation.
Patients undergoing surgery for arterial TOS are often maintained on anticoagulation therapy with warfarin (Coumadin) and clopidogrel (Plavix) for approximately 6 to 12 weeks after surgery. In most patients, anticoagulation is thereafter discontinued. For patients who have undergone balloon angioplasty, Plavix is continued for 6 months followed by daily aspirin.