MDCT in the Evaluation of Thoracic Outlet Syndrome in … · The second passageway is the...
Transcript of MDCT in the Evaluation of Thoracic Outlet Syndrome in … · The second passageway is the...
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
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 26:1735-1750
Demondion, Xavier et al. Thoracic outlet: assessment with MR imaging in asymptomatic and symptomatic populations. Radiology 2003;227:461-468
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
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.
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.