Multidetector CT in the Evaluation of
Thoracic Outlet Syndrome in Children
Introduction
Rib Anomalies
Thoracic outlet syndrome (TOS) is an entity often associated with rib anomalies in the pediatric population. Evaluation with Doppler ultrasound and
conventional angiography are complementary tools documenting the significance of vascular compromise related to rib anomalies. Multidetector CT
(MDCT) with multiplanar reformatting can provide additional valuable
information for both diagnosis and surgical planning.
We 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.
Background
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.
J. Noe, MD1, J. H. Kan, MD2, M. Hernanz-Schulman, MD2, and S. M. Stein, MD2
1University
of Tennessee Medical Center, Knoxville TN
2Vanderbilt University Medical Center, Nashville TN
Case 2
3 year old male presents with upper extremity pain and numbness clinically suggestive
of neurogenic TOS. Following diagnosis of TOS, the patient achieved clinical response
with physical therapy and stretching exercises.
Case 1
A 13 year old white male presents with positional right upper extremity pain over the
past year, feeling numbness, tingling, and coldness in his right hand when it is raised
above his shoulder. Clinical examination demonstrates loss of the radial and ulnar artery
pulses with maximal abduction. Palpation revealed a bony prominence above the right
clavicle, with an adjacent pulsatile palpable subclavian artery. Compression of this
structure results in loss of the radial pulse. Doppler ultrasound evaluation with provocative
maneuvers demonstrated absent distal arterial flow on 3 out of 4 trials in the right upper
extremity. Flow persists in the left upper extremity with the same maneuver.
Chest radiograph and MDCT axial images demonstrate a hypoplastic first rib
which terminates in a pseudoarticulation (arrows) with the lateral second rib. 3D
reconstruction from a left anterior oblique projection illustrates the anomalous
pseudoarticulation. Subclavian vessels (SV) and anterior scalene (AS) may be
subtly visualized anterior to the pseudoarticulation.
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.
TOS suspected (pain or paresthesias with
abduction.) Evaluate for pallor, edema, or loss
of pulse with abduction
Vascular symptoms
absent
Vascular symptoms
present
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
Screening
ultrasound with
provocative
maneuvers, chest
radiograph
Arterial or venous
impingement or
aneurysm
Venous thrombosis
Negative US but
bony anomaly on
CXR
MR angiography if no bony
anomaly, MDCT angiography
if bony anomaly is present or
MRA is nondiagnostic
Confirmatory
venography with
possible
thrombolysis
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.
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.
Initial evaluation with chest radiograph demonstrates hypoplasia of the right first rib
which terminates in a pseudoarticulation (arrow) with the right second rib. The right
clavicle also appears bowed anteroinferiorly at this site. CT angiography was performed.
The patient was imaged with the affected extremity maximally abducted, a position that
reproduced the symptoms of concern. 3D renderings of the osseous structures and
vasculature visualize the tortuous course of the right subclavian artery (arrowheads) as it
is first displaced superiorly by the anterior scalene and then anteriorly by the
pseudoarticulation.
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.
Conclusion
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.
Case 3
A 6 year old male presented with a palpable and painless supraclavicular mass. This
patient currently remains asymptomatic, with similar variant anatomy to the prior cases,
emphasizing the importance of clinical history for the accurate diagnosis of TOS.
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.
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.
Evaluation of TOS
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.
Clinical 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.
Axial CT images demonstrate the insertion of the anterior scalene (AS) muscle upon the
first rib displaced lateral and posterior to its anatomic position due to the anomalous
shortening 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.
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.
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.
Chest radiograph and MDCT axial images demonstrate a hypoplastic first rib which
terminates in a pseudoarticulation (arrows) with the lateral second rib. 3D
reconstructions from posterior (top) and anterior (bottom) projections illustrate the
anomalous pseudoarticulation and its relationship with the clavicle. Subclavian vessels
(SV) and anterior scalene (AS) are labeled.
References
Arthur, L. Grier et al. Pediatric Thoracic Outlet Syndrome: a Disorder With Serious Vascular
Complications. Journal of Pediatric Surgery 2008 43:1089-1094
Demondion, Xavier et al. Imaging Assessment of Thoracic Outlet Syndrome. Radiographics 2006
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Demondion, Xavier et al. Thoracic outlet: assessment with MR imaging in asymptomatic and
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Matsumara, J. Letter Re: Helical CT Angiography of Thoracic Outlet Syndrome. AJR 2001; 177:714
Reid, Janet R. et al. Thoracic Outlet Syndrome with Subclavian Aneurysm in a Very Young Child: the
Complementary Value of MRA and 3D-CT in Diagnosis. Pediatr Radiol 2002 32:22-24
Coronal reconstructions more clearly demonstrate the sling formed by the anterior
scalene (AS) muscle. The tortuous course of the right subclavian artery can be
appreciated as it passes posterior to the anterior scalene and is then displaced anteriorly
by the pseudoarthrosis (PA) of the first and second ribs.
Remy-Jardin, Martine et al. Helical CT Angiography of Thoracic Outlet Syndrome: Functional
Anatomy. AJR 2000 174:1667-1674
Rigberg, David A. et al. The Management of Thoracic Outlet Syndrome in Teenaged Patients. Ann
Vasc Surg 2008 Published Online
Lithograph plate from Gray’s Anatomy, 20th Edition (1918) used under public domain.