Keywords
thoracic outlet syndrome - vascular compression - microvascular decompression
Introduction
Thoracic outlet syndrome (TOS) is caused by compression of the brachial plexus and/or
subclavian vessels as they pass through the cervicothoracobrachial region, exiting
the thoracic girdle.[1] There are three main types of TOS: neurogenic TOS, arterial TOS, and venous TOS.
Neurogenic TOS accounts for approximately 95% of all cases, and it is usually caused
by physical trauma (posttraumatic etiology), chronic repetitive motion (functional
etiology), or bone or muscle anomalies (congenital etiology).[2] We present two cases in which neurogenic TOS was elicited by vascular compression
of the inferior portion of the brachial plexus.
Case 1
A 39-year-old left-handed woman presented to the neurosurgery clinic with a history
of right-sided arm and shoulder numbness for almost 5 years. Her occupation involved
desk work. She had been previously diagnosed with neurogenic TOS due to the presence
of numbness in her right shoulder and arm radiating down the hand and fingers in association
with right neck tightness. She underwent physical therapy that included therapeutic
exercise, soft-tissue and joint mobilization, neuromuscular reeducation, and taping,
but these did not alleviate her symptoms. Specific discomfort affected the right shoulder
both anteriorly and posteriorly, radiating down the arm, occasionally affecting either
the medial two digits or the lateral three digits, with sporadic numbness in all digits.
There were no symptoms in the left arm, except very mild infrequent numbness. Symptoms
did not change according to the weather, tended to worsen while sleeping or with overhead
movements, and improved with physical activities in general, except running. She had
a past medical history of migraine.
On physical examination, motor examination showed 5/5 strength in all muscle groups.
Deep tendon reflexes revealed biceps reflex spreading bilaterally, otherwise normal
reflexes were elicited in both upper and lower extremities. She had a right-sided
Hoffmann's sign. All thoracic outlet maneuvers were positive, including Adson's test,
Wright's test, and Roos' test, with sensation of cold and numbness with arm elevation
on the right side. She had a Tinel's sign over the right infraclavicular brachial
plexus and percussion tenderness over the right supraclavicular brachial plexus.
Nerve conduction studies revealed mild right spinal accessory neuropathy, which is
considered to be incidental.
CT scan of the cervical spine showed a cervical rib bilaterally at C7. Doppler vascular
studies showed bilateral impingement on the subclavian artery with thoracic outlet
maneuvers. Magnetic resonance imaging of the cervical spine and of the brachial plexus
ruled out both foraminal stenosis and the presence of any masses.
In light of the failure of conservative therapy, the patient was offered a right thoracic
outlet decompression with removal of the cervical rib.
Surgery was performed through a standard right supraclavicular approach. The anterior
scalene muscle was resected including the fascial band underneath. The C7 rib was
identified and resected with Kerrison rongeurs. The dorsal scapular artery was noticed
coming off of the subclavian artery, and ran directly over the inferior portion of
the brachial plexus, clearly compressing it. It was thought that pulsations from this
artery could add to the compressive pathology on the nerve, and shredded non-adherent
cotton was slipped underneath the artery to separate it from the nerve ([Fig. 1]). Upon detailed examination, the artery felt widely decompressed and free, and vascular
decompression was thought to have been achieved at this point. Closure was performed
per routine.
Fig. 1 First case. (A) Right brachial plexus exposure showing compression of the lower trunk of the brachial
plexus (L) by a branch from the subclavian artery (A) and a vein. Scalenus anterior
muscle edge after partial scalenectomy (S), phrenic nerve (P), upper trunk (U), middle
trunk (blue arrow). (B) A right-angled instrument is used to lift up the vessels off the lower trunk of
the brachial plexus. Shredded Teflon is then used for separation.
At 3-month follow-up, the patient reported a 70% improvement in numbness. At 1 year,
her numbness was almost completely gone, and electromyography performed 2 years after
the surgical procedure was normal. At 30-month follow-up, the patient had complete
resolution of pain.
Case 2
A 46-year-old female presented with pain and numbness in both upper extremities radiating
to the medial two fingers. Thoracic outlet maneuvers were positive bilaterally. She
had a partial response to botulinum toxin injection to the anterior scalene. At surgery,
a branch of the subclavian artery was riding over the middle trunk of the brachial
plexus compressing it before it dove posteriorly between the middle and upper trunks.
This branch was ligated and cut ([Fig. 2]). Postoperatively, her symptoms significantly improved. At 6 weeks, she reported
75% improvement in her preoperative pain.
Fig. 2 Second case. (A) A vessel (arrow) was found to pass between the middle (M) and upper (U) trunks of
the brachial plexus. This was ligated and cut (B). P, phrenic nerve.
Comment
In these two case reports, we describe an unusual cause of neurogenic TOS due to vascular
compression of the lower brachial plexus by a branch from the subclavian artery, likely
the dorsal scapular artery. Recent literature has begun to describe this pathology
both in cadaveric studies and surgical cases.[3]
[4]
[5] The first case is unusual in the use of cushioning instead of ligation in the treatment
of the vascular compression. The technique is adopted from what has been used for
microvascular decompression of the trigeminal nerve. In regards to the overall presentation,
TOS is still often considered a diagnosis of exclusion with neurogenic TOS, the most
challenging variant to diagnose with several clinical maneuvers being developed in
recent years.[6] Initial treatment is rehabilitation physiotherapy, but patients who fail the conservative
treatment are known to frequently benefit from surgical decompression.[7] Our patient followed current standard of practice, initially with physical therapy
and, in the absence of improvement, was offered surgery. She ultimately achieved significant
relief of her symptoms. Special attention should be given by surgeons during the procedures
to identify and treat vascular compressive anatomy that may lead to neurogenic TOS.
