eMedicine Specialties > Radiology > Vascular/Interventional
Thoracic Outlet Syndrome: Imaging
Updated: Jun 10, 2008
Radiography
Findings
Plain images, such as chest radiographs and upper thoracic and cervical spine studies, can effectively depict congenital or acquired bony anomalies (eg, cervical ribs, healed fractures). Radiography is important if prior images are not available. Such findings may help focus subsequent more complex and more invasive radiologic studies of a particular region. In addition, unsuspected findings such as a Pancoast tumor of the lung may be identified on these initial studies.
False Positives/Negatives
Although plain radiography is relatively inexpensive as a radiologic screening test, it is highly limited in its ability to depict the fine anatomic details that contribute to the symptoms of thoracic outlet syndrome. Plain radiography has a lower sensitivity for these findings than other modalities, such as CT.
Computed Tomography
Findings
CT is most helpful when plain radiographs show abnormal findings involving the thoracic outlet. CT performed both before and after intravenous administration of contrast agent and CT angiography are useful in identifying lesions (eg, cervical disks, neoplasms, bony spurs) that encroach on the structures of the thoracic outlet.
Investigators have reported the use of various sophisticated protocols for spiral CT angiography. After a prospective analysis, Remy-Jardin et al concluded that reconstructed volume-rendering images have the highest sensitivity (95%) and specificity (100%), compared with cross-sectional imaging and image reconstruction with multiplanar and 3-dimensional-shaded surface display techniques.13 In another article, Remy-Jardin et al describe changes in the functional anatomy of the thoracic outlet in 79 patients with symptomatic thoracic outlet syndrome who underwent CT angiography.14,15,16
Degree of Confidence
Most clinicians consider arteriography or venography to be the definitive tests for identifying vascular lesions and their associated complications. Both CT and MR angiography are relatively new and promising techniques for the vascular evaluation of the thoracic inlet that continue to evolve.
Magnetic Resonance Imaging
Findings
Multiple MR angiographic sequences and protocols can be used to obtain images of the arterial and venous anatomy of the body, including 2-dimensional (2D) and 3-dimensional (3D) time-of-flight, pulse-echo, and phase-contrast imaging. Compared with conventional angiography, MR imaging combined with MR angiography has the added advantage of enabling visualization of adjacent soft tissue abnormalities; it is particularly useful in evaluating fibromuscular causes of narrowing. Additionally, the specific application of MR angiography to the thoracic outlet has been reported.
Dymarkowski et al reported the use of 3D time-resolved contrast-enhanced MR angiography and T1-weighted spin-echo MR imaging for the evaluation of vascular causes of thoracic outlet syndrome. Five patients with symptoms and clinical examination findings suggestive of arterial or venous thoracic outlet syndrome were studied during ipsilateral arm adduction and hyperabduction. In all patients, 3D MR angiography during hyperabduction revealed the location of the vascular compression, while the images obtained during adduction showed normal vessel patency. The stenoses were precisely located with the maximum intensity projection images.17
In 3 patients in the Dymarkowski study, the results of conventional angiography performed within a 2-day interval confirmed the location. The T1-weighted images showed the anatomic etiology of the vascular compression, which was confirmed during surgery. The findings of this small study demonstrate the potential of MR angiography in the diagnosis of vascular causes of thoracic outlet syndrome.17
Demondion et al also described the normal MR anatomy of the thoracic outlet and its alteration with positional maneuvers by correlating the gross anatomic images with the corresponding MR images.18
Degree of Confidence
As discussed above, MRI is a promising noninvasive technique for the diagnosis of vascular causes of thoracic outlet syndrome, allowing the evaluation of both the vascular and soft-tissue anatomy of the thoracic inlet. Potential drawbacks of MR imaging include factors that may limit the image quality (see False Positives/Negatives below) and the relatively time-consuming process of obtaining images. Dymarkowski et al noted that the need for a time interval between the acquisitions of the 2 series of images was a potential drawback to their approach.17 Additional larger trials are needed to compare the accuracy of MR imaging with that of conventional angiography, as well as to confirm the clinical utility of MR angiography.
False Positives/Negatives
Several factors may limit the image quality of MR imaging and contribute to artifacts that reduce its sensitivity. These factors include abrupt changes in the path of a vessel, turbulent flow, changes in the direction of flow relative to the plane of imaging, and patient motion. As MR angiography continues to evolve, newer techniques may be able to overcome many of these pitfalls.
The need to study the patient in different positions (eg, in abduction or in adduction) is important for the physician performing the MR imaging study because a simple image obtained in the anatomic position may obscure unprovoked vascular compression.
Ultrasonography
Findings
The arterial system and the venous system of both upper extremities are usually studied during duplex ultrasonography. The patient lies supine with his or her head turned to the side opposite to that being examined. The arm is initially examined in a neutral position and then at varying degrees of abduction, such as 90°, 135°, and 180°. The subclavian artery and the entire venous circulation, including the internal jugular vein, subclavian vein, axillary vein, and innominate vein (in which the portion just above the superior vena cava may not be visualized), are examined.
The criteria for hemodynamically significant venous compression include the obliteration of flow through the subclavian vein or the loss of normal cardiac pulsatility or respiratory phasicity. The criteria for hemodynamically significant arterial narrowing include a 2-fold or greater increase in the peak systolic velocity compared with that measured with the arm in the neutral position or the obliteration of flow. Duplex ultrasonography has been useful in the follow-up care of patients after surgical or radiologic intervention, and a baseline postprocedural examination is routinely performed.19
Degree of Confidence
See False Positives/Negatives below.
False Positives/Negatives
Although ultrasonography is a useful noninvasive test, the false-positive rate with the arterial criteria is 20%, and the false-positive rate with the venous criteria is 10%. Another limitation of duplex ultrasonography is the incorrect identification of a large collateral vein as the subclavian vein in subclavian vein thrombosis. Careful delineation of the entire course of the vessel and its relationship to the artery, which normally is posterior to the subclavian vein, is necessary in order to avoid this mistake. At the present time, another study (eg, conventional angiography) is usually performed to confirm abnormalities identified with ultrasonography.
Angiography
Findings
Arteriography
Arteriography is the most specific diagnostic examination for thoracic outlet syndrome, and it is indicated in a patient with ischemic upper extremity symptoms. The entire arterial circulation of the upper extremity is examined from the aortic arch to the distal arteries of the fingers. Access through the common femoral artery is preferred to evaluate both upper extremities, if necessary, and to evaluate various stress positions. In addition, in the presence of subclavian artery occlusion, delayed imaging after injection may be useful to demonstrate antegrade collateral circulation, with distal reconstitution of the artery beyond the point of obstruction (see Image 1).
Examination in a minimum of 3 positions may be required to demonstrate findings that may not be present in 1 position but are evident in another. In many patients, smooth extrinsic arterial narrowing is seen only on images obtained during stress.
The examination is begun with the patient in the completely adducted neutral position. Although the findings are often limited to minimal narrowing at most (or no findings are seen at all), the neutral position is best for evaluating intrinsic arterial diseases, arterial thrombosis, and poststenotic dilatation or aneurysms.
The Lang maneuver is then performed, with the arm abducted to 90° and with the patient lifting a 2-lb weight 2 cm above a tabletop. Images are obtained during deep inspiration and with the patient's head turned sharply to the opposite side. The Lang maneuver, also called the modified Allen maneuver, elicits sites of compression in the costoclavicular space, the scalene triangle, and the costocoracoid space inferior to the pectoralis minor tendon, a site of compression of the axillary artery; however, evidence of minor compression with this exaggerated stress position has also been shown in persons without thoracic outlet syndrome.
The Adson maneuver consists of depression of the patient's shoulder with his or her head turned to the symptomatic side.
Other positions for imaging include hyperabduction of the arm and the costoclavicular maneuver; the clinical examinations with these positions are equivalent (see Preferred Examination and Images 2-3).
If technically feasible, an evaluation of the patient under conditions that produce the symptoms should be considered. These conditions may include various sitting positions with the arm abducted.
Frequently, findings are readily apparent, with severe narrowing of the subclavian artery accompanied by poststenotic dilatation or a subclavian artery aneurysm. Such findings are strong indicators of a hemodynamically significant lesion. Other findings that may indicate extrinsic compression of the subclavian artery include a ridgelike defect of the inferior margin, which indicates compression against the first rib; a similar defect combined with an impression along its superior margin, which indicates narrowing of both the scalene triangle and the costoclavicular space; or a tapered cutoff of the artery as it emerges from the scalene tunnel, which indicates compression within the scalene triangle and the scalene tunnel.
Another finding that is not accepted as a strong indicator of a hemodynamically significant lesion includes an oblique compression defect or a twist of the subclavian artery as it passes through the scalene tunnel.20,21
Venography
Ascending brachial venography is the preferred and most definitive examination for diagnosing venous thrombosis. Collateral veins are more evident with venography than with ultrasonography, and therapeutic techniques, such as thrombolysis, can be readily performed if necessary. Venography is indicated in patients with definite symptoms of venous obstruction or when a duplex ultrasonography finding suggests venous abnormalities.
During the procedure, the patient's arm is placed in slight abduction to prevent artificial venous occlusion. Because the cephalic vein may lead to collateral vessels that bypass the site of thrombosis in the subclavian or axillary veins, the basilic vein is injected to ensure complete opacification around the venous thrombosis. One potential drawback of venography is that the proximal extent of the thrombus may be difficult to accurately identify.
Two major findings of upper extremity venous thrombosis are described. The first finding is a short area of obstruction at the subclavian-axillary vein junction between the first rib and the clavicle at the thoracic inlet. A variable number of adjacent collateral veins are visualized. This finding is often seen with acute obstruction. The second finding is a long area of obstruction extending distally from the axillary vein and possibly into the brachial vein. Approximately 75% of cases also involve the subclavian vein, though innominate vein involvement is rare (see Image 4). Chronic and intermittent venous obstruction with or without a thrombus may be seen as an area of scarring or narrowing at the subclavian-axillary vein junction.22
Degree of Confidence
At the present time, most clinicians consider catheter-based arteriography or venography to be the criterion standard for evaluating the vascular anatomy of the thoracic outlet; however, MR angiography and CT angiography are 2 promising and relatively new techniques that may be able to replace many diagnostic conventional angiographic examinations. Further clinical trials are required to compare the accuracy of these new techniques with that of conventional angiography before they can be considered acceptable alternatives in clinical decision-making.
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| Overview: Thoracic Outlet Syndrome |
 Imaging: Thoracic Outlet Syndrome |
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Further Reading
Keywords
Paget-von Schrötter syndrome, effort thrombosis, spontaneous thrombosis, traumatic thrombosis
