1735 imaging assessment radiographics of thoracic outlet … · 2020. 2. 13. · for an education...

EDUCATION EXHIBIT 1735

Imaging Assessmentof Thoracic OutletSyndrome1

LEARNINGOBJECTIVESFOR TEST 3After reading thisarticle and takingthe test, the reader

will be able to:

� Identify the normaland abnormal anat-omy of the thoracicoutlet on anatomicsections and CT,MR, and US images.

� Describe the use ofvarious imaging tech-niques in assessmentof thoracic outletsyndrome.

� Discuss the useful-ness of postural ma-neuvers in associa-tion with imagingtechniques in assess-ment of thoracic out-let syndrome.

Xavier Demondion, MD ● Pascal Herbinet, MD ● Serge Van Sint Jan, PhDNathalie Boutry, MD ● Christophe Chantelot, MD ● Anne Cotten, MD

The thoracic outlet includes three compartments (the interscalene tri-angle, costoclavicular space, and retropectoralis minor space), whichextend from the cervical spine and mediastinum to the lower border ofthe pectoralis minor muscle. Dynamically induced compression of theneural, arterial, or venous structures crossing these compartmentsleads to thoracic outlet syndrome (TOS). The diagnosis is based on theresults of clinical evaluation, particularly if symptoms can be repro-duced when various dynamic maneuvers, including elevation of thearm, are undertaken. However, clinical diagnosis is often difficult;thus, the use of imaging is required to demonstrate neurovascular com-pression and to determine the nature and location of the structure un-dergoing compression and the structure producing the compression.Cervical plain radiography should be performed first to assess for boneabnormalities and to narrow the differential diagnosis. Computed to-mographic (CT) angiography or magnetic resonance (MR) imagingperformed in association with postural maneuvers is helpful in analyz-ing the dynamically induced compression. B-mode and color duplexultrasonography (US) are good supplementary tools for assessment ofvessel compression in association with postural maneuvers, especiallyin cases with positive clinical features of TOS but negative features ofTOS at CT and MR imaging. US may also allow analysis of the bra-chial plexus. However, MR imaging remains the method of choicewhen searching for neurologic compression.©RSNA, 2006

Abbreviation: TOS � thoracic outlet syndrome

RadioGraphics 2006; 26:1735–1750 ● Published online 10.1148/rg.266055079 ● Content Codes:

1From the Departments of Musculoskeletal Radiology (X.D., P.H., N.B., A.C.) and Orthopedic Surgery B (C.C.), Hôpital Roger Salengro, Bd duProfesseur Jules Leclercq, 59037 Lille Cedex, France; the Anatomy Laboratory, Faculté de Médecine Henri Warembourg, Lille, France (X.D.); andthe Anatomy Laboratory, Faculté de Médecine, Université Libre de Bruxelles, Brussels, Belgium (S.V.S.J.). Recipient of a Certificate of Merit awardfor an education exhibit at the 2004 RSNA Annual Meeting. Received April 6, 2005; revision requested June 1 and received January 12, 2006; ac-cepted February 6. All authors have no financial relationships to disclose. Address correspondence to X.D. (e-mail: [email protected]).

©RSNA, 2006

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TEACHING POINTS

IntroductionThe thoracic outlet includes three confined ana-tomic spaces, the congenital or acquired narrow-ing of which may lead to compression of bloodvessels or nerves or both. Dynamically inducedcompression of the neural, arterial, or venousstructures crossing one of these tunnels leads tothoracic outlet syndrome (TOS). The diagnosis isbased on the results of clinical evaluation, par-ticularly if the patient’s symptoms can be repro-duced when various dynamic maneuvers, includ-ing elevation of the arm, are undertaken.

In this article, we review the anatomy of thethoracic outlet and discuss and illustrate the func-tional anatomy, clinical features, causes, imagingfeatures, and treatment of TOS.

Anatomy of the Thoracic OutletThe thoracic outlet, or cervicothoracobrachialjunction, includes three confined spaces, extend-ing from the cervical spine and the mediastinumto the lower border of the pectoralis minor mus-cle, which are potential sites of neurovascularcompression. These three compartments are theinterscalene triangle, the costoclavicular space,and the retropectoralis minor space (Figs 1, 2)(1, 2).

Figures 1, 2. (1) Diagram shows the three compart-ments of the thoracic outlet and their components.AS � anterior scalene muscle, BP � brachial plexus,C � clavicle, CC � costoclavicular space, IT � inter-scalene triangle, MS � middle and posterior scalenemuscles, Pmi � pectoralis minor muscle, RP � retro-pectoralis minor space, SA � subclavian artery, SM �subclavius muscle, SV � subclavian vein. (2) Anatomicsections show the compartments of the thoracic outlet.(a) Section obtained after removal of the pectoralis ma-jor muscle shows the costoclavicular space (red oval)and retropectoralis minor space (yellow oval). Pmi �pectoralis minor muscle. (b) Section obtained afterremoval of the pectoralis minor muscle shows the neu-rovascular bundle. C � clavicle, straight black arrow �axillary artery, curved black arrow � axillary vein,white arrow � brachial plexus.

1736 November-December 2006 RG f Volume 26 ● Number 6

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TeachingPoint

Teaching PointThe thoracic outlet, or cervicothoracobrachial junction, includes three confined spaces, extending from the cervical spine and the mediastinum to the lower border of the pectoralis minor muscle, which are potential sites of neurovascular compression.

The interscalene triangle is the most medial ofthese compartments. It is limited anteriorly by theanterior scalene muscle, posteriorly by both themiddle and posterior scalene muscles, and inferi-orly by the first rib (Fig 3). The anterior scalenemuscle originates from the anterior tubercle ofC3–C6 and inserts inferiorly onto the scalene tu-bercle of the first rib. The middle scalene muscleoriginates from the posterior tubercle of C2–C7and inserts inferiorly onto the first rib behind thescalene tubercle, from which it is separated by thesubclavian groove. The posterior scalene muscleis the deepest of the three scalene muscles. Itarises from the posterior tubercle of C4–C6 andinserts inferiorly onto the second rib. The inter-scalene triangle is crossed by the subclavian ar-tery, which occupies the floor of the space, and by

the three trunks of the brachial plexus. The upper(C5-C6) and middle (C7) trunks cross the upperpart of the interscalene triangle above the subcla-vian artery. The lower trunk (C8-T1) is located inthe inferior part of the interscalene triangle, be-hind the posterior part of the subclavian artery.The subclavian vein does not cross the inter-scalene triangle but runs beneath the anteriorscalene muscle before joining the internal jugularvein to form the brachiocephalic vein (3).

The intermediate compartment of the thoracicoutlet is the costoclavicular space. This compart-ment is limited superiorly by the clavicle, anteri-orly by the subclavius muscle, and posteriorly by

Figure 3. Assessment of the interscalene triangle with different imaging modalities. Sagittalgross anatomic section (a), computed tomographic (CT) image (b), T1-weighted magnetic reso-nance (MR) image (c), and sonogram (d) show the anterior scalene muscle (AS), clavicle (C),fifth cervical nerve root (C5), sixth cervical nerve root (C6), seventh cervical nerve root (C7),eighth cervical nerve root (C8), first rib (FR), middle and posterior scalene muscles (MS), sub-clavian artery (SA), subclavian vein (SV), and first thoracic nerve root (T1).

RG f Volume 26 ● Number 6 Demondion et al 1737

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both the first rib and the middle scalene muscle(Fig 4). The subclavius muscle originates fromthe junction of the first rib with its costal carti-lage; its fibers run upward and laterally and insertinto the inferior surface of the clavicle. This spacecontains the subclavian vein anteriorly, the sub-clavian artery immediately posterior to it, and thethree cords of the brachial plexus, arranged in atriangular configuration. The lateral cord, formed

by the anterior division of the upper and middletrunks, and the medial cord, formed by the ante-rior division of the lower trunk, are located abovethe subclavian vessels, the lateral cord being an-terior to the medial cord. The posterior cord,formed by the posterior division of the upper,middle, and lower trunks, represents the posterioredge of the triangular configuration. It is locatedabove the medial and lateral cords.

The retropectoralis minor space is the mostlateral of the three compartments. It is limited by

Figure 4. Assessment of the costoclavicular space with different imaging modalities. Sagit-tal gross anatomic section (a), sagittal CT image (b), sagittal T1-weighted MR image (c),and sonogram obtained with a supraclavicular approach (d) show the anterior scalenemuscle (AS), clavicle (C), first rib (FR), lateral nerve cord (LC), medial nerve cord (MC),omohyoid muscle (OH), posterior nerve cord (PC), subclavian artery (SA), subclaviusmuscle (SM), and subclavian vein (SV).


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the posterior border of the pectoralis minormuscle anteriorly, by the subscapularis muscleposteriorly and superiorly, and by the anteriorchest wall posteriorly and inferiorly (Fig 5). Theneurovascular arrangement in this space is quitesimilar to that seen in the costoclavicular space.Just lateral to the pectoralis minor muscle, thecords divide into five terminal branches (mediannerve, ulnar nerve, musculocutaneous nerve, axil-lary nerve, and radial nerve).

Functional Anatomy of TOSTOS is a dynamically induced compression syn-drome that is produced especially by elevation ofthe arm. Several studies that used CT and MRimaging in healthy volunteers have demonstratedthat upper limb elevation does not induce any

Figure 5. Assessment of the retropectoralis minor space with different imaging modalities.Sagittal gross anatomic section (a), CT image (b), T1-weighted MR image (c), and sono-gram (d) show the axillary artery (AA), axillary vein (AV), clavicle (C), lateral nerve cord(LC), medial nerve cord (MC), posterior nerve cord (PC), pectoralis minor muscle (Pmi),pectoralis major muscle (Pmj), serratus anterior muscle (Sea), and scapula (SP).


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obvious change in the interscalene triangle (Fig 6)but does produce narrowing of both the costocla-vicular space and retropectoralis minor space(4–9) (Figs 7, 8). The costoclavicular space is byfar the most frequent site of arterial compression,while the interscalene triangle is the second mostfrequent site (9). Neurologic compression ap-pears to be as frequent in the costoclavicularspace as in the interscalene triangle (9). The ret-ropectoralis minor space has rarely been reportedas a potential site of compression.

Clinical Features of TOSTOS is one of the most controversial subjects inmedicine (10). Although TOS is conceptuallysimple, its diagnosis remains difficult and confus-ing. The term thoracic outlet syndrome was coinedby Peet et al (11) in 1956 to indicate compressionof one or several of the neurovascular structurescrossing the thoracic outlet. The most commonage range for this syndrome is 20–40 years, witha female-to-male ratio of 4:1 (10). The symptomsof TOS are typically reproduced or exacerbatedby activity requiring elevation or sustained use ofthe arms, such as reaching for objects overhead orlifting. Compression of the neurovascular bundle

Figure 6. Effect of arm elevation on the interscalene triangle in an asymptomatic subject.Sagittal T1-weighted MR images obtained with the arm alongside the body (a) and afterarm elevation (b) show narrowing of the space between the anterior scalene muscle and theclavicle with physiologic compression of the subclavian vein (arrow). No other modificationsof the interscalene triangle occurred after arm elevation.

Figure 7. Effect of arm elevation on the costoclavicular space in an asymptomatic subject.Sagittal T1-weighted MR images obtained with the arm alongside the body (a) and afterarm elevation (b) show narrowing of the costoclavicular space.


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may occur in all three compartments of the tho-racic outlet. Three distinct syndromes may beencountered, individually or combined, depend-ing on the injured component of the neurovascu-lar bundle: neurogenic syndrome, arterial syn-drome, and venous syndrome. Clinical signs andsymptoms include pain, numbness, tingling,weakness, and other disorders of the upper ex-tremity. According to the literature, neurogenicTOS is observed in 90%–95% of the cases andvascular TOS in 5%–10% (12,13). However,these percentages may reflect a recruitment bias,as other authors have reported mainly series ofvascular TOS (5,6,9).

Several provocative clinical tests are performedas part of the physical examination. Four basicmaneuvers with several variations have been de-scribed: the Roos test, Adson test, Wright test,and costoclavicular test. The elevated arm stresstest maneuver introduced by Roos and Owens(14) consists of asking the patient to place botharms in 90° abduction and external rotation withthe shoulders braced posteriorly and then to openand close the hands slowly for 3 minutes. Mostpatients with neurogenic TOS are unable to com-plete this test (12). The Adson test is performedby holding the patient’s arm down and checkingthe radial pulse while the patient inhales deeplyand keeps his or her head extended and turnedtoward the involved extremity (15). However, thistest may also be positive in normal subjects and istherefore not very reliable (2,10,16). The costo-clavicular compression test is performed by hav-ing the examiner depress the patient’s shoulderand ask the patient for evidence of symptoms.The Wright test (hyperabduction test) is per-

formed with the patient in a sitting or standingposition with the shoulder hyperabducted androtated externally (17). The patient is askedwhether he or she experiences any symptoms inthe extremity, and any change in pulse is noted.As elevation of the upper limb has been reportedto be relevant in diagnosing TOS (18–21), thismaneuver has been chosen as a postural maneu-ver, combined with imaging techniques such asCT or MR (4–9).

In the case of neurogenic TOS, the symptomsmay be sensory or motor, although subjective sen-sory symptoms of pain and paresthesia predomi-nate (2). Patients may present with upper plexusTOS involving the C5, C6, and C7 nerves. Inupper plexus TOS, pain is generally located in theside of the neck and radiates upward to the earand occipital region. The pain may also radiateposteriorly to the rhomboid area, anteriorly acrossthe clavicle into the upper pectoral region, later-ally through the deltoid and trapezius muscleareas, and down the outer aspect of the arm(10,22). In most cases, however, patients presentwith lower plexus TOS, corresponding to com-pression of the C8 and T1 nerves. Pain is usuallydistributed in the anterior or posterior shoulderregion and radiates down the arm, in the medialbrachial area and along the inner aspect of thearm. Paresthesia affects mainly the ring and littlefingers, with an ulnar nerve distribution (22). Theautonomic innervation of the arm must also beconsidered, as it can account for some autonomicfeatures, such as symptoms of vasomotor distur-bance.

Figure 8. Effect of arm elevation on the retropectoralis minor space in an asymptomaticsubject. Sagittal T1-weighted MR images obtained with the arm alongside the body (a) andafter arm elevation (b) show narrowing of the retropectoralis minor space.


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Teaching PointAs elevation of the upper limb has been reported to be relevant in diagnosing TOS (18-21), this maneuver has been chosen as a postural maneuver, combined with imaging techniques such as CT or MR (4-9).

In arterial TOS, the symptoms are caused byarterial insufficiency. They include weakness,cold, and pain in the extremity, caused by isch-emic neuritis of the brachial plexus. In the case ofsevere compression, subclavian artery thrombosiswith peripheral embolization can be observed(23). Venous TOS consists of swelling and cyano-sis of the extremity, with pain, a feeling of heavi-ness in the upper limb, and venous distention ofthe upper arm and shoulder region (10). Acutesubclavian-axillary vein thrombosis refers to aPaget-Schroetter syndrome or effort thrombosis(2,10).

In many cases, classification as arterial or neu-rologic compression remains difficult. Moreover,arterial and neurologic compression can be ob-served together and some physiopathologicmechanisms are interrelated. For example, nervecompression involves closely related mechanicaland ischemic factors, with disturbance of intra-neural microcirculation (2). In many cases, how-ever, symptoms are vague and nonspecific andclinical diagnosis is often difficult, requiring theuse of imaging methods and electrophysiologiccriteria, such as electromyography or somatosen-sory evoked potentials. This information is veryimportant because treatment for thoracic outletsymptoms is aimed at alleviating or reducing thecompression inside the narrowed space.

Causes of TOSAnatomic abnormalities or acquired disease of theskeletal and soft-tissue structures forming or bor-dering on the three compartments may cause me-chanical compression or direct irritation of theneurovascular structures. These abnormalitiescan be divided into two groups: bone abnormali-ties and soft-tissue abnormalities (12) (Table).

Bone AbnormalitiesSkeletal and bone abnormalities include cervicalribs, elongated transverse process of C7, exostosisof the first rib or clavicle, and excessive callus ofthe clavicle or first rib.

Cervical Rib.—A cervical rib is a supernumeraryrib originating from the seventh cervical vertebra(Fig 9). According to the literature, cervical ribs,which are present in less than 1% of the normalpopulation, have been reported in 5%–9% of pa-tients with TOS (24,25). Cervical ribs may becomplete or incomplete, in association with fi-brous bands (2,16). Complete cervical ribs arefused with a tubercle located on the upper aspect

of the first thoracic rib. This fusion point is usu-ally adjacent to the site of insertion of the anteriorscalene muscle. As a result, the supraclavicularcourse of the subclavian artery is usually dis-placed anteriorly. Incomplete cervical ribs, al-though they do not articulate directly with a tho-racic rib, usually have an associated fibrous bandthat can insert onto the first thoracic rib and com-press adjacent neurovascular structures (Fig 10)(2,16).

Elongated Transverse Process of C7.—A C7transverse process is considered elongated if itextends beyond the tip of the T1 process immedi-ately below it, as seen on cervical radiographs (Fig9). Like a cervical rib, an elongated C7 transverseprocess can lead either directly or indirectly to

Figure 9. Cervical plain radiograph of a 27-year-oldwoman shows both a cervical rib (arrow) and an elon-gated C7 transverse process (arrowhead).

Principal Causes of TOS

Skeletal and bone abnormalitiesCervical rib, elongated C7 transverse processExostosis or tumor of the first rib or clavicleExcess callus of the first rib or clavicle

Soft-tissue abnormalitiesFibrous band*Congenital muscle abnormalities

Insertion variationsSupernumerary muscles

Acquired soft-tissue abnormalitiesPosttraumatic fibrous scarring†

Postoperative scarringPosture and predisposing morphotype

Poor posture and weak muscular support in thinwomen

*With or without an associated cervical rib or elon-gated C7 transverse process.†Due to direct trauma or work-related repetitive mi-crostress.


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neurovascular compression, in association with afibrous band or an abnormal middle scalenemuscle.

Abnormal First Rib or Clavicle.—The first riband clavicle, which form the jaws of the costocla-vicular “pliers,” are important anatomic struc-tures. Abnormal development or orientation of

the first rib may lead to undue neurovascularcompression. Disease processes or acquired ab-normalities, such as exostosis, tumor, callus, orfracture of the first rib or clavicle, may also irritatethe neurovascular structures and in particular thebrachial plexus (Fig 11).

In time, bone abnormalities can lead to severearterial complications. Indeed, repetitive traumaat the site of compression by these abnormalitiescan damage the arterial intima and lead to athero-sclerotic changes, aneurysm, and thrombosis orembolism (5,26). The thickening and fibrosis ofthe arterial wall, as well as the inflammatorychanges in the adventitia, may explain the factthat the dynamically induced symptoms initiallyobserved may later become permanent (fixed ste-nosis).

Soft-Tissue AbnormalitiesIn the soft-tissue group, congenital fibrous bandsand ligaments as well as congenital or acquiredmuscular changes (hypertrophy, fibrosis, etc) andsoft-tissue posttraumatic changes have been re-ported.

Congenital Soft-Tissue Abnormalities.—Several complex anatomic variations of thescalene muscles may be responsible for TOS(1,2,27,28). They include hypertrophy of the an-terior scalene muscle, origin of the anterior andmiddle scalene muscles from a common belly thatdivides in two distally, passage of the brachialplexus through the substance of the anteriorscalene muscle, a broad middle scalene muscleinserting more anteriorly on the first rib than isnormal, interdigitation between the anterior and

Figure 10. Fibrous band in a 42-year-old woman with neurovascular symptoms. Contiguous sagittal (a, b) (b ob-tained lateral to a) and coronal (c) T1-weighted MR images of the interscalene triangle show a tiny fibrous band (ar-rowhead), which pushes forward the subclavian artery (arrow in a and b). Arrow in c � elongated C7 transverse pro-cess.

Figure 11. Excessive callus of the clavicle in a 36-year-old patient with neurologic TOS. Anteroposteriorplain radiograph of the clavicle (a) and sagittal T1-weighted MR images obtained with the arms alongsidethe body (b) and after hyperabduction (c) show exces-sive callus (curved arrow). A close relationship betweenthe posterior part of the brachial plexus (straight arrowin b and c) and the excessive callus is seen after armelevation.


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middle scalene muscles, and supernumerarymuscles (including a possible scalenus minimusmuscle) extending from the transverse processesof C6 and C7 to the first rib behind the scalenetubercle or to the cupola of the lung (Fig 12)(16,22,28). Anomalous fibrous bands, extensivelydescribed by Roos (16), have also been reportedin patients with TOS. They may arise from a cer-vical rib, the first thoracic rib, an elongated C7transverse process, or the anterior and middlescalene muscles. They insert onto the first tho-racic rib or the cupola of the lung. Some of thesebands are fibromuscular in nature and similar tovariations of the scalene muscles.

Acquired Soft-Tissue Abnormalities.—Theseabnormalities include posttraumatic and postop-erative fibrous scarring. As regards posttraumaticcauses, two groups of patients have been differen-tiated (12). Patients who have suffered directtrauma to the brachial plexus or the musclesmake up the first group. The trauma habituallyresults from a whiplash flexion-extension injury tothe neck. The second group consists of patientssuffering from work-related repetitive micro-trauma (activities requiring repeated elevation ofthe upper limb or heavy lifting). It has been hy-pothesized that such trauma may induce fibrosisand spasm of the scalene muscles, leading to el-evation of the first rib and consequently to its im-

pingement on the neurovascular structures. Re-peated microtrauma may also induce local peri-neural inflammation of the soft tissues (12). How-ever, the exact mechanism whereby trauma pre-cipitates TOS is still unclear.

Posture and Predisposing MorphotypeThin women with poor posture and weak muscu-lar support of the shoulder girdle have been re-ported to be predisposed to developing TOS(12). Indeed, drooping and sagging of the shoul-der increase acromioclavicular descent and com-pression of neurovascular structures in the costo-clavicular space.

Imaging Features of TOS

Plain RadiographyRadiographs of both the cervical spine and chestshould be systematically obtained in order tosearch for bone abnormalities that may contributeto the problem (eg, cervical ribs, elongated C7transverse process, degenerative spine disease, orbone destruction related to a primary or second-ary neoplasm) (Fig 9) (2,16).

Arteriography and VenographyConventional arteriography and venography maydemonstrate the presence of extrinsic compres-sion. Unfortunately, they do not allow a clear de-piction of the impinging anatomic structure, andthey tend to be replaced by less invasive proce-dures (CT, MR imaging, sonography).

Figure 12. Scalenus minimus muscle in a 35-year-old woman with neurologic TOS. Sag-ittal gross anatomic section (a) and sagittal T1-weighted MR image (b) show a scalenusminimus muscle (straight arrow), which passes between the C8 nerve root (arrowhead) andsubclavian artery (curved arrow).


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TeachingPoint

Teaching PointRadiographs of both the cervical spine and chest should be systematically obtained in order to search for bone abnormalities that may contribute to the problem (eg, cervical ribs, elongated C7 transverse process, degenerative spine disease, or bone destruction related to a primary or secondary neoplasm) (Fig 9) (2,16).

CT AngiographySpiral CT examination of TOS is performed firstwith the arms alongside the body and then withthe arms elevated in an attempt to reproduce theneurovascular compression (a position intermedi-ate between those of the Roos and Wright maneu-vers). Intravenous injection of contrast medium isoften considered in order to obtain CT angio-graphs (5,6). To opacify the subclavian and axil-lary arteries only without producing any venousartifacts, the contrast medium must be injected

into a vein on the side opposite that being exam-ined. The recommended method consists of be-ginning to scan 15–20 seconds after the start of amonophasic injection of 90 mL of iodinated con-trast medium at a rate of 4 mL/sec (6). By com-paring the images obtained with the arms along-side the body and after elevation, it is possible toassess the narrowing of the various compart-ments, as well as any dynamic compression of theneurovascular structures.

Arterial compression is well assessed with CTby using arterial cross sections produced by sagit-tal reformation of data obtained both in the neu-tral position and after postural maneuvers (Fig13). Whereas sagittal reformation allows assess-ment of the location and severity of the arterialcompression, volume-rendered images of the tho-racic outlet before and after postural maneuversallow simultaneous analysis of bones and vascularbundles, which are well visualized (6). Arterialstenosis has been expressed as the percentage ofreduction of the cross-sectional area or the diam-eter of the artery (6,9). Venous compression isvery difficult to incriminate because such com-pression is frequently observed in asymptomaticindividuals in all the compartments of the tho-racic outlet after arm elevation (5,9,29). Venousthrombosis and collateral circulation are welldemonstrated by means of iodinated contrast me-dia and constitute objective signs of venous TOS(Fig 14). Unfortunately, they are late-stage conse-quences of venous compression (9).

The limitations of CT include the difficulty ofcarrying out a fine analysis of the brachial plexus

Figure 13. Arterial compression in a 37-year-old man. (a, b) Sagittal reformatted CT images, obtained before theentrance to the costoclavicular space (a) and inside the costoclavicular space (b) after arm hyperabduction, show a50% reduction in the cross-sectional area of the subclavian artery (arrow) at the entrance to the costoclavicular space.(c) Three-dimensional reformatted view shows the arterial compression and the relationship of the artery (arrow) tothe surrounding anatomic structures.

Figure 14. Venous compression in a 29-year-oldwoman. Axial CT image obtained after venous admin-istration of contrast material shows collateral pathways(straight arrows), which are a consequence of subcla-vian vein thrombosis (curved arrow). Venous compres-sion is frequently observed in asymptomatic personsafter arm hyperabduction; therefore, this finding mustbe interpreted carefully. Venous thrombosis and collat-eral circulation are objective but delayed signs of patho-logic venous compression.


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Teaching PointVenous compression is very difficult to incriminate because such compression is frequently observed in asymptomatic individuals in all the compartments of the thoracic outlet after arm elevation (5,9,29).

due to the limited CT contrast resolution, towhich must be added two limitations that CTshares with MR imaging. First, abduction of theshoulder is limited by the size of the CT tunnelitself (upper limb elevation of �130° is impos-sible); second, the CT study is carried out withthe patient in the supine position. In fact, the po-sition of the patient undoubtedly has an effect ondynamically induced compression, as demon-strated by Scherrer et al (30) in 1979. In angio-graphic studies performed in 115 patients, theseauthors showed that 32% of false-negative resultswere related to use of the supine position duringthe examination. Finally, CT is an ionizing radia-tion technique, and the administration of iodin-ated contrast medium may be contraindicated orresult in adverse side effects. In our clinical prac-tice, this imaging method has been found to beespecially helpful in analyzing the relationshipbetween the vessels and the surrounding bonystructures.

MR ImagingMR imaging has the advantages of being a nonin-vasive and nonionizing technique offering excel-lent soft-tissue contrast. MR imaging of TOS isclassically performed by using a phased-arraybody coil. Accurate observation of all the ana-tomic components of the thoracic outlet is pos-sible, especially with use of sagittal T1-weightedsequences (7,9,31,32). The sagittal plane hasbeen reported to be especially helpful for the de-piction of vascular and nervous compressions, asthey typically have an anteroposterior and cranio-caudal direction. Coronal sequences can also

supplement the examination, as they may providea good view of the brachial plexus and also dem-onstrate fibrous bands (9). Whatever the plane,the sequences must be performed with the arm ina neutral position and, most of all, after hyperab-duction of the arm. Interestingly, a study reportedthat, except for venous thrombosis, all the formsof neurovascular compression were demonstratedonly with the arm elevated, which highlights theusefulness of this postural maneuver when TOS issuspected.

Arterial and venous compressions may be as-sessed by comparing the arterial cross-sectionalarea at the considered location with the arm in aneutral position (alongside the body) and afterarm elevation (Figs 15, 16). Arterial compressionmay also be detected by analyzing the arterial cali-ber along the course of the vessel (Figs 15–17).MR angiography appears to be complementary toanalysis of the arterial cross-sectional area on sag-ittal MR images (33–35) (Fig 15). This sequencemay be especially helpful in detecting unobtrusivepoststenotic aneurysmal dilatation. When venousTOC is suspected, venous thrombosis and collat-eral circulation must be looked for, but the limita-tions involved are the same as with CT.

MR imaging also allows a good analysis of thebrachial plexus thanks to the excellent soft-tissuecontrast it provides. The criteria used for deter-mining the presence of neurologic compressionare disappearance of the fat surrounding the bra-chial plexus and close contact with the adjacentbony structures (9) (Fig 18). Neurologic com-pressions seem to occur with the same frequencyin the interscalene triangle and in the costocla-vicular space (9).

Finally, MR imaging is also an efficient tech-nique when searching for muscle hypertrophy

Figure 15. Arterial compression in a 24-year-old woman. (a, b) Sagittal T1-weighted MR images, obtained afterarm hyperabduction, show compression of the subclavian artery (arrow) in the costoclavicular space. Compare thecross-sectional area of the artery inside the costoclavicular space (a) with the cross-sectional area at the exit from thecostoclavicular space (b). (c) MR angiogram shows the arterial stenosis (arrow).


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Teaching PointAccurate observation of all the anatomic components of the thoracic outlet is possible, especially with use of sagittal T1-weighted sequences (7,9,31,32).

Figure 16. Arterial compression in a 47-year-old man. Contiguous sagittal T1-weighted MR images, obtained afterarm elevation, show compression of the subclavian artery (arrow) by a cervical rib (arrowhead) in the costoclavicularspace.

Figure 17. Neurovascular TOS in a 20-year-old woman. Consecutive sagittal T1-weighted MR images of the cos-toclavicular space, displayed from medial (a) to lateral (c), show compression of the brachial plexus (arrowhead) in aand b and compression of the subclavian artery (arrow) in a. Compare the caliber of the artery in a and in b and cand the morphology of the brachial plexus in a and b and in c.

Figure 18. Neurogenic TOS in a 44-year-old woman. Sagittal T1-weighted MR images,obtained with the arms alongside the body (a) and after arm elevation (b), show narrowingof the costoclavicular space after hyperabduction and compression of the brachial plexus(straight arrow) between the clavicle (curved arrow) and first rib (arrowhead).


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(scalenus, subclavius, or pectoralis minor mus-cles), abnormal muscles (eg, scalenus minimus)(Fig 12), and fibrous bands (9,32) (Fig 10). Thevisibility of such abnormal structures represents afundamental advantage of MR imaging over otherimaging techniques and may influence treatment.An indirect sign of the presence of a tight fibrousband is elevation of the subclavian artery, which iswell demonstrated on sagittal images (9).

MR imaging has the same practical limitationsas CT, that is, the restriction of arm elevation dueto the size of the tunnel and the supine position ofthe patient. In our experience, another limitationis experienced in very thin individuals with littleadipose tissue, in whom the delineation and indi-vidualization of the anatomic structures may bedifficult.

UltrasonographyContinuous-wave Doppler ultrasonography (US)has the advantage of enabling assessment of bloodflow during performance of the clinical tests usedin clinical practice. This technique is frequentlyused to confirm the clinical suspicion of arterialTOS. However, it is based on indirect signs ofmore proximal arterial stenosis and does notdemonstrate the exact site of the arterial compres-sion. The usefulness of power Doppler US in as-sociation with B-mode scanning has recently beenreported in the assessment of subclavian and axil-lary arterial cross-sectional areas in patients withclinical suspicion of arterial TOS (36). B-modescanning may allow detection of anatomic abnor-malities such as aneurysmal dilatation and devia-tion of vessels. Color duplex sonographic exami-nation associated with postural maneuvers (armin neutral position, 90°, 120°, and 180° of abduc-tion) may demonstrate alterations of the bloodflow, such as complete cessation of blood flow orincrease of blood flow velocity (29,37,38).

The main advantage of this technique is thedirect comparison between dynamically inducedsymptoms and concomitant visualization of thevessels. The other fundamental advantage ofsonography is the possibility of performing theexamination with the patient in an upright orseated position, as in clinical examination, in con-trast to CT and MR imaging, which are per-formed with the patient in a supine position. Un-fortunately, this technique does not allow an ac-curate overview of the thoracic outlet region norin particular an analysis of the region of the pul-monary apex. It must always be kept in mind that

thoracic outlet symptoms may reveal locoregionaldisease such as a superior sulcus lung tumor(Pancoast-Tobias). For this reason, sonographyshould not be used solely to assess TOS; rather, itappears to be a valuable supplementary techniqueto CT or MR imaging in the event of clinical dis-cordance, especially in patients with positive clini-cal features of TOS but negative features of TOSat CT and MR imaging (36).

Sonography also allows delineation of the bra-chial plexus structures (39), but its accuracy de-pends on the experience of the operator, espe-cially as regards the assessment of this complexanatomic region. Moreover, to the best of ourknowledge, the assessment of neurologic com-pression by means of this technique has not yetbeen reported.

Treatment of TOS

Initial ManagementA conservative approach is the rule in the initialtreatment of neurogenic TOS. Therapeutic ef-forts are focused on relaxing the scalene musclesand strengthening the postural muscles throughphysical therapy, combined with hydrotherapyand massage. Pain medication, nonsteroidal anti-inflammatory agents, and muscle relaxants areoften useful adjuncts in treatment.

The initial treatment of arterial TOS is focusedon revascularization in order to remedy acuteischemia if necessary. This step is typically per-formed via brachial artery thromboembolectomy.Demonstration of a fixed arterial lesion, eitherocclusive or aneurysmal in nature, is an indicationfor surgical reconstruction (40). Since these le-sions are secondary to extrinsic compression,there is no significant role for endovascular ap-proaches to their management (41).

The initial treatment of effort thrombosis gen-erally involves contrast venography and catheter-directed thrombolytic therapy. This frequentlyresults in restoration of venous drainage and reso-lution of the acute symptoms. Patients then re-ceive maintenance treatment with intravenousheparin, which is converted to oral anticoagula-tion with warfarin. Most patients with venousTOS are candidates for surgical decompression.

Surgical StrategiesA first-rib resection via a supraclavicular ap-proach represents the predominant treatmentstrategy, but some teams have recently adopted ahighly selective approach in which supraclavicularscalenectomy is the principal surgical strategy andfirst-rib resection is reserved solely for vascularforms of TOS.


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First-rib resection and subclavian artery recon-struction are required when any degree of aneu-rysmal degeneration is present, particularly if thepatient has had preoperative symptoms of digitalthromboembolism, as well as for persistent occlu-sive lesions of the arterial wall that are still presentafter scalenectomy (41).

Patients with disabling neurogenic or arterialTOS may present with symptoms characteristic ofsympathetic overactivity. In these situations, cer-vical sympathectomy may be a useful adjunct tothoracic outlet decompression.

Thoracic outlet decompression for venousTOS includes scalenectomy, brachial plexus neu-rolysis, resection of the first rib, and circumferen-tial venolysis. In situations where external venoly-sis and paraclavicular first-rib resection have notsucceeded in relieving the venous obstruction,additional venous reconstruction may be re-quired.

ConclusionsThe diagnosis of TOS is clinically based. Imagingmay be helpful in informing the clinician as to theanatomic structures undergoing compression, thelocation of that compression, and the anatomicstructures responsible for it (whether normal orabnormal). Indeed, all these features may influ-ence the treatment. Radiographs may demon-strate predisposing bone abnormalities (elongatedC7 transverse process, cervical rib). To the bestof our knowledge, the respective advantages ofthe complementary imaging techniques have notbeen assessed in comparative studies. In the caseof neurogenic or neurovascular symptoms, MRimaging in association with postural maneuvershas proved useful, especially in demonstratingbrachial plexus compression and the existence offibrous bands. CT with contrast medium injec-tion (if not contraindicated) and postural maneu-vers appears effective in demonstrating vascularcompression by means of volume-rendered im-ages, which allow analysis of the relations withbony structures. Color duplex sonographic ex-amination and B-mode scanning, in associationwith postural maneuvers, is a valuable supple-mentary tool to CT and MR imaging when theresults of the latter prove negative.

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This article meets the criteria for 1.0 credit hour in category 1 of the AMA Physician’s Recognition Award. To obtaincredit, see accompanying test at http://www.rsna.org/education/rg_cme.html.

RG Volume 26 • Volume 6 • November-December 2006 Demondion et al

Imaging Assessment of Thoracic Outlet Syndrome Xavier Demondion, MD, et al

Pages 1736 The thoracic outlet, or cervicothoracobrachial junction, includes three confined spaces, extending from the cervical spine and the mediastinum to the lower border of the pectoralis minor muscle, which are potential sites of neurovascular compression. Page 1741 As elevation of the upper limb has been reported to be relevant in diagnosing TOS (18–21), this maneuver has been chosen as a postural maneuver, combined with imaging techniques such as CT or MR (4–9). Page 1744 Radiographs of both the cervical spine and chest should be systematically obtained in order to search for bone abnormalities that may contribute to the problem (eg, cervical ribs, elongated C7 transverse process, degenerative spine disease, or bone destruction related to a primary or secondary neoplasm) (Fig 9) (2,16). Page 1792 Venous compression is very difficult to incriminate because such compression is frequently observed in asymptomatic individuals in all the compartments of the thoracic outlet after arm elevation (5,9,29). Page 1746 Accurate observation of all the anatomic components of the thoracic outlet is possible, especially with use of sagittal T1-weighted sequences (7,9,31,32).

RadioGraphics 2006; 26:1735–1750 ● Published online 10.1148/rg.266055079 ● Content Codes:

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1735 imaging assessment radiographics of thoracic outlet … · 2020. 2. 13. · for an education...

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