Multidetector CT in the Evaluation ofThoracic Outlet Syndrome in Children

Thoracic outlet syndrome (TOS) is an entity often associated with rib anoma-

lies in the pediatric population. Evaluation with Doppler ultrasound and

conventional angiography are complementary tools documenting the signifi-

cance of vascular compromise related to rib anomalies. Multidetector CT

(MDCT) with multiplanar reformatting can provide additional valuable

information for both diagnosis and surgical planning.

Introduction

MDCT with provocative maneuvers as a primary diagnostic modality for TOS has been well

documented in the adult population. Pediatric literature largely focuses upon doppler

sonography and MR angiography in evaluating suspected vascular etiologies of thoracic outlet

syndrome.

As seen in adults, however, MDCT with 3D reconstruction and multiplanar reformats offers

several advantages for diagnosis and surgical planning with its more complete depiction of the

intricate anatomy of this complex space. In the pediatric population, these advantages may

prove more significant. The current literature suggests that TOS is more often due to vascular

compromise related to congenital anomalies of the first and second ribs compared with the

adult population.

In the presented cases, congenital rib deformities were frequently associated with abnormal

course of the scalene muscles. Though this anomaly is asymptomatic in some patients, two of

our patients presented with symptoms of TOS. MDCT with multiplanar reformats depicted the

narrowing of the spaces of the thoracic outlet by osseous and muscular structures. The degree

of osseous detail depicted by MDCT is difficult to obtain by MR. 3D reconstructions delineated

the anatomy and allowed the surgical team to plan a corrective procedure before surgical

exploration was pursued, as conventional surgical techniques for TOS may need modification

for these bony anomalies.

MDCT can play a key role in the evaluation and management of pediatric TOS. In those

cases of suspected vascular TOS, MDCT can play a valuable role because both vascular and

congenital osseous deformities can be exquisitely delineated. MDCT can provide benefits over

other commonly used modalities.

Conclusion

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Lithograph plate from Gray’s Anatomy, 20th Edition (1918) used under public domain.

References

Background

In adults, the majority of patients present with neurogenic symptoms (>90%). Venous

compression contributes 2% to 5% of cases and arterial compression contributes 1% to 2%.

Data for the pediatric population is less well reported. One series of 25 patients between the

ages of 12 and 18 years reported 11 patients with venous manifestations, 11 with neurological

symptoms, and 2 with arterial abnormalities. A second pediatric case series reported venous

manifestations in 6 of 8 patients.

In adults, TOS is most associated with occupational activity involving overhead work or

computer use in non-ergonomic postures, as well as prior trauma. In older teenagers, TOS is

most commonly found in athletes who engage in repetitive overhead maneuvers such as

swimmers and baseball pitchers. In younger patients, congenital anomalies of the skeletal and

muscular structures play a more prominent role.

The subclavian vessels and trunks of the brachial plexus pass through three narrow

passageways. The most proximal of these is the interscalene triangle, which is bordered by

the anterior scalene muscle anteriorly, the middle scalene muscle posteriorly, and the medial

surface of the first rib inferiorly. This area may be small at rest and may become smaller with

provocative maneuvers. Anomalous structures, such as fibrous bands, cervical ribs, and

abnormal muscles, may constrict this triangle further.

The second passageway is the costoclavicular triangle, which is bordered anteriorly by the

middle third of the clavicle, posteromedially by the first rib, and posterolaterally by the upper

border of the scapula. The last passageway is the subcoracoid space beneath the coracoid

process just deep to the pectoralis minor tendon.

Anatomy of the Thoracic Outlet, Gray’s Anatomy 20th Edition

Anatomic and schematic depiction of the thoracic outlet. The interscalene and costoclavicular triangles are indicated by green and blue shading, respectively.

Rib AnomaliesWe have encountered multiple patients with similar first rib anomalies. In these cases, the first

rib is hypoplastic and terminates in a pseudoarticulation with the lateral portion of the second

rib. Three successive cases from our institution are presented here. Two of these patients

ultimately received clinical diagnoses of TOS.

J. Noe, MD1, J. H. Kan, MD2, M. Hernanz-Schulman, MD2, and S. M. Stein, MD2

1University of Tennessee Medical Center, Knoxville TN2Vanderbilt University Medical Center, Nashville TN

Evaluation of TOSClinical history should direct the approach to diagnosis of TOS. Chest radiography may

demonstrate a cervical rib, first rib anomaly, or clavicle deformity.

Continuous wave Doppler ultrasonography is useful to evaluate arterial compromise in

postures which produce the symptoms of concern. US is effective in confirming vascular

compression, and allows more flexibility in patient positioning in order to more accurately

replicate the symptomatic posture. US does not adequately define the osseous and muscular

anatomy of the thoracic outlet, however, and does not precisely localize the location of

vascular compression.

MR imaging, with its excellent soft tissue contrast, is ideal for the evaluation of neurogenic

TOS. Sequences may be performed with the arm in neutral and maximally abducted

positions. Loss of fat planes between the brachial plexus and surrounding structures on

provocative maneuver is considered evidence for TOS.

CT Angiography has been performed in the adult population for suspected vascular

compromise, with arteriographic phase contrast enhanced imaging of the thoracic outlet in

both relaxed and maximally abducted positions of the upper extremities. The reduction in

cross sectional area of the subclavian artery with hyperabduction is taken as a quantitative

measurement of the degree of arterial compression. Venous compression may be similarly

characterized, but is considered less specific due to the high incidence of venous

compression in asymptomatic patients with postural maneuvers. The CT data may also be

used for volume rendering for surgical planning.

A 13 year old white male presents with positional right upper extremity pain over thepast year, feeling numbness, tingling, and coldness in his right hand when it is raisedabove his shoulder. Clinical examination demonstrates loss of the radial and ulnar arterypulses with maximal abduction. Palpation revealed a bony prominence above the rightclavicle, with an adjacent pulsatile palpable subclavian artery. Compression of thisstructure results in loss of the radial pulse. Doppler ultrasound evaluation with provocativemaneuvers demonstrated absent distal arterial flow on 3 out of 4 trials in the right upperextremity. Flow persists in the left upper extremity with the same maneuver.

Axial CT images demonstrate the insertion of the anterior scalene (AS) muscle upon thefirst rib displaced lateral and posterior to its anatomic position due to the anomalousshortening of the first rib with pseudoarticulation (PA) between the first and second ribs.The abnormal course of the AS forms a sling around the subclavian artery (arrowheads).The subclavian artery is also displaced anteriorly.

Case 1

Initial evaluation with chest radiograph demonstrates hypoplasia of the right first ribwhich terminates in a pseudoarticulation (arrow) with the right second rib. The rightclavicle also appears bowed anteroinferiorly at this site. CT angiography was performed.The patient was imaged with the affected extremity maximally abducted, a position thatreproduced the symptoms of concern. 3D renderings of the osseous structures andvasculature visualize the tortuous course of the right subclavian artery (arrowheads) as itis first displaced superiorly by the anterior scalene and then anteriorly by thepseudoarticulation.

A 6 year old male presented with a palpable and painless supraclavicular mass. Thispatient currently remains asymptomatic, with similar variant anatomy to the prior cases,emphasizing the importance of clinical history for the accurate diagnosis of TOS.

Case 3

3 year old male presents with upper extremity pain and numbness clinically suggestiveof neurogenic TOS. Following diagnosis of TOS, the patient achieved clinical responsewith physical therapy and stretching exercises.

Chest radiograph and MDCT axial images demonstrate a hypoplastic first ribwhich terminates in a pseudoarticulation (arrows) with the lateral second rib. 3Dreconstruction from a left anterior oblique projection illustrates the anomalouspseudoarticulation. Subclavian vessels (SV) and anterior scalene (AS) may besubtly visualized anterior to the pseudoarticulation.

Case 2

Coronal reconstructions more clearly demonstrate the sling formed by the anteriorscalene (AS) muscle. The tortuous course of the right subclavian artery can beappreciated as it passes posterior to the anterior scalene and is then displaced anteriorlyby the pseudoarthrosis (PA) of the first and second ribs.

Chest radiograph and MDCT axial images demonstrate a hypoplastic first rib whichterminates in a pseudoarticulation (arrows) with the lateral second rib. 3Dreconstructions from posterior (top) and anterior (bottom) projections illustrate theanomalous pseudoarticulation and its relationship with the clavicle. Subclavian vessels(SV) and anterior scalene (AS) are labeled.

TOS suspected (pain or paresthesias with abduction.) Evaluate for pallor, edema, or loss

of pulse with abduction

Vascular symptoms absent

Presumed neurogenic TOS, evaluate with chest radiograph and MRI of the neck.

EMG may be helpful for equivocal cases. MDCT if bony anomaly is present and

surgery is considered

Vascular symptoms present

Screening ultrasound with

provocative maneuvers, chest

radiograph

Arterial or venous impingement or

aneurysm

MR angiography if no bony anomaly, MDCT angiography if bony anomaly is present or

MRA is nondiagnostic

Venous thrombosis

Confirmatory venography with

possible thrombolysis

Negative US but bony anomaly on

CXR

MDCT angiography

A proposed modification to the diagnostic algorithm for evaluation of TOS, taking into account the benefit of MDCT in delineating variant osseous and muscular anatomy.