Keywords
thoracic outlet syndrome - eighth cervical vertebra - cervical rib - brachial plexus
Background
Thoracic outlet syndrome (TOS) is caused by compression of neurovascular structures
passing through the cervicoaxillary canal. Symptoms can include pain, paraesthesia,
weakness, coldness, pallor, or venous congestion depending on the compromised structure.
Neurological symptoms (95%) are much more common than vascular symptoms (5%).[1] Neurological and vascular symptoms can certainly coexist and often have overlapping
presentations. Compression levels are commonly divided into three areas: the interscalene
triangle between anterior, middle scalenes, and first rib, the costoclavicular space
between clavicle and first rib, and the subcoracoid space inferior to pectoralis minor.[2] As a dynamic space, compression of the neurovascular bundle and symptoms are often
worse with use of the upper limb.
A range of anatomical anomalies have been reported associated with TOS.[3]
[4] Cervical ribs are usually an incidental finding on chest X-ray, arising from the
transverse process of the 7th cervical vertebra. They exist in 1% of the general population,
with most patients being asymptomatic and 10% manifesting compressive symptoms.[5] Of patients with TOS, a cervical rib has been reported to be present in almost 30%.[2]
[6]
We report the first case in the literature of neurogenic TOS from a cervical rib arising
from an anomalous supernumerary 8th cervical vertebra.
Case Report
A 27-year-old female presented with symptoms of bilateral neurogenic TOS. She was
otherwise well but described 5 years of symptoms with upper limb numbness particularly
in the C8/T1 dermatomal distribution, and pain in both shoulders, neck, and scapulae.
All symptoms were worse with activity and limb elevation. She had no obvious precipitating
trauma. As a result of her symptoms she was unable to work.
On examination she had bilateral flattened thenar eminences and reduced power in her
first dorsal interosseous and abductor digiti minimi muscles. She failed the elevated
arm stress test bilaterally, right earlier than left sides, and lost the right radial
pulse at 90 degrees shoulder abduction with 50 degrees external rotation and the left
radial pulse at 90 degrees shoulder abduction with 90 degrees external rotation.
She underwent neurophysiology tests and imaging including magnetic resonance imaging
of the brachial plexus and cervical spine X-rays and computed tomography. All were
unremarkable except for the finding of a supernumerary C8 vertebra with bilateral
cervical ribs arising from this C8, with the right larger than left ([Fig. 1A, B]).
Fig. 1 (A) Cervical rib with subclavian artery and middle and inferior trunks overlying following
anterior scalenotomy. (B) Blue dash line indicating insertion of anterior scalene to cervical rib.
In terms of patient-reported measures, she scored 42/93 in Brachial Assessment Tool
and had a QuickDASH score of 61.36. She was consented and scheduled to undergo staged
thoracic outlet decompression, starting with the more severe right side.
The patient underwent release of the right thoracic outlet with multiple neurolyses,
scalenotomies, and resection of both the anomalous C8 cervical rib as well as resection
of the first thoracic rib segment subjacent to the clavicle. This was done via a supraclavicular
approach ([Fig. 2A, B]). Intraoperatively, a long upper trunk of the brachial plexus was found with an
atypical contribution to the phrenic nerve from its anterior surface. The anterior
scalene was inserting into the cervical rib, compressing the subclavian artery and
middle and inferior trunks of the brachial plexus. These neurovascular structures
were running tautly over the cervical rib. Fibrinous scar in the region was consistent
with long-standing local inflammation. Once an anterior scalenotomy had been performed
releasing its insertion, the anterior and middle portions of cervical rib were removed.
On shoulder motion with abduction and external rotation, there was ongoing costoclavicular
impingement. The scalenus medius insertion was therefore released off the first rib
and the relevant portion of this rib was segmentally resected to decompress the costoclavicular
impingement ([Fig. 3]). The patient had immediate and sustained postoperative improvement in symptoms
with arm activities including high elevation of the limb.
Fig. 2 Cervical spine computed tomography (CT) demonstrating C8 vertebrae with bilateral
ribs, right larger than left. (A) Anterior view. (B) Superior view.
Fig. 3 Portions of resected cervical rib and first rib as labeled.
Discussion
Embryologically, cervical vertebrae formation is controlled by Hox genes and seven
cervical vertebrae is remarkably consistent across all mammals.[7] This consistency is proposed to be due to Hox genes also being responsible for neural
defects, neonatal malignancies, or stillbirth. A range of mild anomalies of the cervical
spine exist, commonly fusion as seen in Klippel-Feil syndrome and cervical ribs.[8]
[9] There is only one other report of an eighth cervical vertebra[10] in the literature. This was in an 11-year-old boy, with an incidental finding of
8 cervical and 13 thoracic vertebrae, when X-rays were performed due to neck trauma.
There were no compressive thoracic outlet symptoms reported in this case.
Gruber classified the cervical rib anomaly in 1869 into four types.[5] The cervical rib in type 1 extends just beyond the transverse process of C7; in
type 2 beyond the transverse process but not connected to the first rib; in type 3
the cervical rib is partially fused through fibrous bands or cartilage to the first
rib; and in type 4 the cervical rib is united with the first rib. Cervical ribs are
positioned such that they narrow the interscalene interval through which the subclavian
artery and trunks of the brachial plexus are transmitted from neck to axilla. The
mere presence of cervical ribs certainly does not mandate removal. Despite the existence
of the anatomical variation, more than the bony anomaly alone is commonly required
to cause symptoms. In 80% of patients a supervening trauma will bring on TOS symptoms
where none existed prior to the trauma.[11] Spontaneous symptoms (with no known trauma or other precipitant) are however more
likely in complete, type 4 cervical ribs with 50% incidence of spontaneous symptoms
compared with a 20% incidence with incomplete ribs. In our patient, with incomplete
cervical ribs, the spontaneous and severe symptoms could be attributed to traction
and compression of the neurovascular structures across the cervical rib with an additional
cervical vertebra.
First-line treatment for TOS is nonsurgical with posture modification, exercises,
and strengthening. After a period of 3 to 12 months, failing sufficient symptom improvement,
surgical management is considered. In the presence of cervical ribs requiring operative
management for TOS, Chang et al and Sanders and Hammond now advocate for the removal
of cervical and first ribs to avoid need for revisionary surgery, without increased
morbidity.[5]
[11] Sanders and Hammond report 24% failure of TOS surgery on cervical ribs including
first rib removal but 41% failure without first rib removal.[11]
Conclusion
We report the first case of a supernumerary 8th cervical vertebra with its anomalous
cervical rib being associated with TOS.
