AJR 2000; 175:417-422
© American Roentgen Ray Society
Thoracic Outlet
Anatomic Correlation with MR Imaging
X. Demondion1,2,
N. Boutry1,
A. Drizenko2,
C. Paul1,
J. P. Francke2 and
A. Cotten1
1
Department of Musculoskeletal Radiology, Roger Salengro Hospital, 59037, Lille
Cedex, France.
2
Anatomy Department, Faculty of Medicine, University of Lille 2, Pl. de Verdun,
59037, Lille Cedex, France.
Received July 12, 1999;
accepted after revision January 11, 2000.
Address correspondence to X. Demondion, Service de Radiologie
Ostéo-Articulaire,
Hôpital Roger Salengro, Blvd. du Pr. J.
Leclercq, 59037, Lille Cedex, France.
Abstract
OBJECTIVE. The purpose of this report is to describe the normal MR
anatomy of the thoracic outlet and its modification after postural maneuvers
using an anatomic—MR imaging correlation.
CONCLUSION. MR imaging appears to be a useful technique to study the
thoracic outlet and its contents because of its excellent soft-tissue
depiction and its multiplanar capabilities. T1-weighted images obtained in the
sagittal plane clearly depicted the different compartments of the
cervicothoracic—brachial junction. Hyperabduction maneuvers may have
potential applications in the assessment of the thoracic outlet syndrome by
showing the location of compression.
Introduction
The thoracic outlet or cervicothoracic—brachial junction consists of
several confined spaces extending from the cervical spine and the mediastinum
up to the lower border of the pectoralis minor muscle. It is divided into
three tunnels: the interscalene triangle, the costoclavicular space, and the
retropectoralis minor space
[1].
Symptoms and signs of thoracic outlet syndrome result from the compression
or irritation of the neurovascular bundle at various levels of the
cervicothoracic—brachial passages. Compression usually occurs as a
result of congenital or acquired changes in the surrounding fibroosseous and
fibromuscular structures [2].
There is potential for static or dynamic compression or both. Moreover, in an
already "tight" thoracic outlet, dynamic movements such as holding
the arm overhead and backward (hyperabduction) can further compress the
enclosed structures and bring on symptoms
[2,3,4].
The usefulness of MR imaging for the assessment of the thoracic outlet
[5] and brachial plexus
[6,7,8]
has yet to be fully defined. To the best of our knowledge, only two case
reports about MR imaging of patients with arms in hyperabduction have been
published [9,
10]; no MR imaging and
anatomic correlation of the thoracic outlet spaces with arms alongside the
body and with arms hyperabducted has been reported. The purpose of this report
is to describe the normal MR anatomy of the thoracic outlet and its
modifications after postural maneuvers using an anatomic—MR imaging
correlation.
Subjects and Methods
Five fresh cadavers (two men and three women; age range, 76-85 years; mean,
81.4 years) were examined. Two were injected bilaterally into the brachial
artery with a mixture of warm gelatin, gadolinium (Dotarem; Laboratoire
Guerbet, Aulnay-sous-Bois, France), and red stain to visualize arterial
structures during MR and anatomic studies. All cadavers were examined with a
1.5-T imager (Magnetom Vision; Siemens, Erlangen, Germany) and a body coil.
Sagittal images were obtained bilaterally using a T1-weighted spin-echo
sequence. Imaging parameters were as follows: TR/TE, 500/14; slice thickness,
3 mm; interslice gap, 0.3 mm; matrix, 366 x 512; and field of view, 175
x 200 mm. Thereafter, the specimens were frozen and sawed into
3-mm-thick contiguous sagittal sections with a band saw. Four cadavers were
positioned with the arms alongside the body; one cadaver, with the arms
hyperabducted.
Twelve volunteers (three men and nine women; age range, 22-40 years; mean,
31.5 years) were also examined bilaterally with a 1.5-T imager (Magnetom
Vision; Siemens) and a body coil. Sagittal T1-weighted spin-echo sequences
were performed in all volunteers. Imaging parameters were as follows: 500/14;
slice thickness, 3 mm; interslice gap, 0.3 mm; imaging matrix, 224 x
256; and field of view, 263 x 350 mm. These sequences were performed
first with the arms alongside the body and then with the arms hyperabducted
(135°). The study was approved by our institutional review board and
informed consent was obtained from each volunteer.
To determine a radioanatomic correlation, first the gross anatomic sections
and the corresponding MR images were evaluated in consensus by two
musculoskeletal radiologists. The reviewers were asked to identify the
clavicle, the first rib, the subclavian vein and artery, the dorsal scapular
artery, the trunks and cords of the brachial plexus, the scalene muscles, the
subclavius muscle, the serratus anterior muscle, the subscapularis muscle, and
the pectoralis minor and major muscles. Then the same radiologists identified
these structures on MR images of the volunteers in both arm positions. They
were also asked to assess the compression of vessels, the presence of fat
surrounding the vascular or nervous structures, and the modifications of the
different tunnels after hyperabduction.
Results
In two volunteers, the MR images were slightly blurred because of large
respiratory movements during the examination. However, the different spaces of
the thoracic outlet (i.e., interscalene triangle, prescalene space,
costoclavicular space, and retropectoralis minor space) were identified in all
cadavers and volunteers. In each of these spaces, the different components of
the neurovascular bundle could be seen with the arms alongside the body or
hyperabducted (Figs.
1A,1B,1C,2A,2B,3A,3B,4A,4B,5A,5B).
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Fig. 1A. —Interscalene triangle. 1 = clavicle, 2 = subclavian artery, 3 =
subclavian vein, 4u = upper trunk of brachial plexus, 4m = middle trunk of
brachial plexus, 4l = lower trunk of brachial plexus, 5 = first rib, 6 =
anterior scalene muscle, 7 = middle scalene muscle, 8 = dorsal scapular
artery, 9 = lung. Photograph of sagittal gross anatomic slice shows
interscalene triangle in 76-year-old male cadaver with arms positioned
alongside body. Interscalene triangle is bordered by anterior scalene muscle
anteriorly and by middle and posterior scalene muscles posteriorly.
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Fig. 1B. —Interscalene triangle. 1 = clavicle, 2 = subclavian artery, 3 =
subclavian vein, 4u = upper trunk of brachial plexus, 4m = middle trunk of
brachial plexus, 4l = lower trunk of brachial plexus, 5 = first rib, 6 =
anterior scalene muscle, 7 = middle scalene muscle, 8 = dorsal scapular
artery, 9 = lung. Sagittal T1-weighted MR images of 32-year-old male volunteer
with arms positioned alongside body (B) and with arms hyperabducted
(C) show interscalene triangle. In C, note narrowing of space
between posterior side of clavicle and anterior side of anterior scalene
muscle (prescalene space) when compared with B.
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Fig. 1C. —Interscalene triangle. 1 = clavicle, 2 = subclavian artery, 3 =
subclavian vein, 4u = upper trunk of brachial plexus, 4m = middle trunk of
brachial plexus, 4l = lower trunk of brachial plexus, 5 = first rib, 6 =
anterior scalene muscle, 7 = middle scalene muscle, 8 = dorsal scapular
artery, 9 = lung. Sagittal T1-weighted MR images of 32-year-old male volunteer
with arms positioned alongside body (B) and with arms hyperabducted
(C) show interscalene triangle. In C, note narrowing of space
between posterior side of clavicle and anterior side of anterior scalene
muscle (prescalene space) when compared with B.
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Fig. 2A. —Costoclavicular space with arms positioned alongside body. 1 =
clavicle, 2 = subclavian artery, 3 = subclavian vein, 4L = lateral nerve cord
of brachial plexus, 4M = medial nerve cord of brachial plexus, 4P = posterior
nerve cord of brachial plexus, 5 = first rib, 6 = subclavius muscle, 7 =
pectoralis major muscle, 8 = pectoralis minor muscle, 9 = serratus anterior
muscle, 10 = lung. Photograph of gross sagittal anatomic slice of 80-year-old
female cadaver shows costoclavicular space.
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Fig. 2B. —Costoclavicular space with arms positioned alongside body. 1 =
clavicle, 2 = subclavian artery, 3 = subclavian vein, 4L = lateral nerve cord
of brachial plexus, 4M = medial nerve cord of brachial plexus, 4P = posterior
nerve cord of brachial plexus, 5 = first rib, 6 = subclavius muscle, 7 =
pectoralis major muscle, 8 = pectoralis minor muscle, 9 = serratus anterior
muscle, 10 = lung. Sagittal T1-weighted MR image of 31-year-old male volunteer
shows costoclavicular space. Note costoclavicular space bordered anteriorly by
inner half of clavicle and posteriorly by first rib.
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Fig. 3A. —Costoclavicular space with arms hyperaducted. 1 = clavicle, 2 =
subclavian artery, 3 = subclavian vein, 4 = cords of brachial plexus, 5 =
first rib, 6 = subclavius muscle, 7 = lung. Gross sagittal anatomic slice of
85-year-old female cadaver shows costoclavicular space.
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Fig. 3B. —Costoclavicular space with arms hyperabducted. 1 = clavicle, 2 =
subclavian artery, 3 = subclavian vein, 4 = cords of brachial plexus, 5 =
first rib, 6 = subclavius muscle, 7 = lung. Sagittal T1-weighted MR image of
31-year-old female volunteer shows costoclavicular space. Note narrowing of
costoclavicular space when compared with that in Figure
2A,2B.
Note also slight compression of subclavian vein.
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Fig. 4A. —Retropectoralis minor space with arms positioned alongside body. 1 =
clavicle, 2 = axillary artery, 3 = axillary vein, 4L = lateral nerve cord of
brachial plexus, 4M = medial nerve cord of brachial plexus, 4P = posterior
nerve cord of brachial plexus, 5 = scapula, 6 = subclavius muscle, 7 =
pectoralis major muscle, 8 = pectoralis minor muscle, 9 = subscapularis
muscle, 10 = lung. Gross sagittal anatomic slice of 80-year-old female cadaver
shows retropectoralis minor space.
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Fig. 4B. —Retropectoralis minor space with arms positioned alongside body. 1 =
clavicle, 2 = axillary artery, 3 = axillary vein, 4L = lateral nerve cord of
brachial plexus, 4M = medial nerve cord of brachial plexus, 4P = posterior
nerve cord of brachial plexus, 5 = scapula, 6 = subclavius muscle, 7 =
pectoralis major muscle, 8 = pectoralis minor muscle, 9 = subscapularis
muscle, 10 = lung. Sagittal T1-weighted MR image of 36-year-old female
volunteer shows retropectoralis minor space. Note retropectoralis minor space
defined anteriorly by posterior border of pectoralis minor muscle and
posteriorly by subscapularis muscle.
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Fig. 5A. —Retropectoralis minor space with arms hyperabducted. 1 = coracoid
process, 2 = axillary artery, 3 = axillary vein, 4L = lateral nerve cord of
brachial plexus, 4M = medial nerve cord of brachial plexus, 4P = posterior
nerve cord of brachial plexus, 5 = pectoralis minor muscle, 6 = serratus
anterior muscle, 7 = subscapularis muscle, 8 = lung. Gross sagittal anatomic
slice of 85-year-old female cadaver shows retropectoralis minor space.
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Fig. 5B. —Retropectoralis minor space with arms hyperabducted. 1 = coracoid
process, 2 = axillary artery, 3 = axillary vein, 4L = lateral nerve cord of
brachial plexus, 4M = medial nerve cord of brachial plexus, 4P = posterior
nerve cord of brachial plexus, 5 = pectoralis minor muscle, 6 = serratus
anterior muscle, 7 = subscapularis muscle, 8 = lung. Sagittal T1-weighted MR
image of 36-year-old female volunteer shows retropectoralis minor space. Note
narrowing of retropectoralis minor space when compared with that in Figure
4A,4B.
Note also contact between neurovascular structures and posterior side of
pectoralis minor muscle and anteroposterior compression of axillary vein.
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The Interscalene Triangle
This triangle is bordered by the anterior scalene muscle anteriorly, the
middle and the posterior scalene muscles posteriorly, and the first rib
inferiorly. The posterior scalene muscle was rarely identified as a separate
structure from the middle scalene muscle on MR images. The subclavian artery
always passed through the lower part of this space. The superior (C5-C6) and
middle (C7) trunk of the brachial plexus passed through the upper part of this
space. The lower (C8-T1) trunk crossed the inferior part of the interscalene
triangle behind the subclavian artery. The dorsal scapular artery (Fig.
1A,1B,1C)
was identified in all cadavers and in eight volunteers bilaterally between the
middle and the lower trunks. No apparent modification of the interscalene
triangle was noticed after hyperabduction in cadavers and volunteers.
The Prescalene Space
In all cases, the subclavian vein coursed between the clavicle anteriorly
and the anterior scalene muscle posteriorly (prescalene space). In each
volunteer, we observed a narrowing of the prescalene space after upper limb
elevation and concomitantly noticed a compression of the subclavian vein (Fig.
1A,1B,1C).
The Costoclavicular Space
The limits of this space and its neurovascular contents were particularly
well depicted on sagittal images. This triangular space is bordered anteriorly
by the inner half of the clavicle and posteromedially by the first rib. On
sagittal images, the nerve cords maintained a constant relationship with the
axillary vessels as they coursed through this space. The axillary vein was
anteroinferior to the axillary artery (Fig.
2A,2B).
During hyperabduction the clavicle moved backward, narrowing the space between
the posterior side of the clavicle and the first rib (Fig.
3A,3B).
In eight of the 12 volunteers, the anteroposterior diameter of the right and
left costoclavicular spaces narrowed by more than 50% after hyperabduction. A
compression of the subclavian vein at the costoclavicular space was observed
bilaterally in each volunteer after hyperabduction, and a slight compression
of the subclavian artery was noticed unilaterally in one of them. In all
volunteers, fat surrounding the vascular or nervous structures was
present.
The Retropectoralis Minor Space
This passage was also well depicted on sagittal planes. It was defined
anteriorly by the posterior border of the pectoralis minor muscle and
posteriorly by the subscapularis muscle. In this anatomic tunnel, the nerve
cords course just above and posterior to the axillary artery. The lateral
nerve cord was the most anterior cord. The posterior nerve cord was above the
lateral and medial nerve cords.
The axillary vein was found beneath the artery in each cadaver and
volunteer (Fig.
4A,4B).
The retropectoralis minor space also narrowed with upper limb elevation with
the nerve cords leaning tightly against the posterior side of the pectoralis
minor muscle (Fig.
5A,5B).
An anteroposterior compression of the axillary vein was observed in this space
in four of the 12 volunteers after hyperabduction.
Discussion
MR imaging appears to be an interesting technique by which to further study
the thoracic outlet and its contents because of this technique's excellent
soft-tissue depiction and its multiplanar capabilities. Images obtained in the
sagittal plane depicted the nervous or vascular structures in cross-section as
they pass through the different spaces of the thoracic outlet, and this plane
appears suitable for evaluation of compression within these spaces. To our
knowledge, this investigation is the first to correlate MR and anatomic slices
of the thoracic outlet compartments before and after upper limb
hyperabduction. This postural maneuver reproduced "Wright's
maneuver," a clinical hyperabduction test used to diagnose thoracic
outlet syndrome [4]. Knowledge
of the modifications of thoracic outlet and its content in the cadavers
allowed a more confident and detailed analysis of the MR images obtained of
volunteers.
In most of our volunteers, we observed an important narrowing of the
prescalene and costoclavicular spaces after arm hyperabduction. A compression
of the subclavian vein also occurred frequently in our study at the prescalene
and costoclavicular spaces after upper limb elevation. A compression of the
axillary vein was not rare at the retropectoralis minor space; it was observed
in one third of our volunteers. Compression of the subclavian vein in healthy
people has already been outlined on phlebography at the prescalene space or at
the costoclavicular space after arm elevation
[11]. As previously reported
in anatomic studies [12], we
also observed dynamic modifications of the different spaces of the
cervicothoracic—brachial junction. Thus, the pathologic significance of
dynamic modifications or vascular compression must be interpreted carefully. A
larger study should be performed in both symptomatic and asymptomatic
populations to assess the normal range of sizes of the tunnels in the thoracic
outlet and to further define variation with hyperabduction.
In conclusion, a complete understanding of the normal relationship between
the components of the thoracic outlet and the neurovascular bundle is
essential for interpreting signs of compression in thoracic outlet syndrome.
This study explores modifications of the thoracic outlet after postural
maneuvers that may be helpful in assessment of thoracic outlet syndrome. In
our series, hyperabduction caused some venous compression in all 12
asymptomatic volunteers. The morphology and size of the different anatomic
tunnels and neurovascular structures need to be defined in a larger population
of volunteers.
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Abstract
Introduction
