Posttraumatic Neurogenic Thoracic Outlet Syndrome and Immediate Effects of Decompressive Surgery: A Case Report

Abstract

Neurogenic thoracic outlet syndrome (TOS) results from a combination of trauma and congenital anatomical predisposition. Although trauma is recognized as a significant contributor to neurogenic TOS, it is predominantly linked to injuries such as whiplash-type neck injuries in individuals with predisposing congenital anatomical structures. Reports on neurogenic TOS resulting from major trauma, including fractures and dislocations near the brachial plexus pathway, are rare. We report a rare case of a patient with persistent paralysis in the right shoulder, preventing abduction, extension, and elbow flexion following a contusion and soft tissue trauma to the right side of the neck. The initial diagnosis of post-traumatic neurogenic TOS following soft tissue trauma was missed until magnetic resonance imaging was conducted 8 months after injury, which revealed unexplained paralysis in the right upper extremity. Decompression of the right brachial plexus with scalenectomy resulted in immediate alleviation of paralysis of the shoulder and elbow. The diagnosis of post-traumatic neurogenic TOS should be considered when a patient who has sustained significant neck trauma presents with symptoms of weakness, heaviness, numbness, and tingling paresthesia in the ipsilateral upper extremity, and these symptoms are not attributable to cervical spine pathology.

INTRODUCTION

Thoracic outlet syndrome (TOS) is characterized by a variety of clinical manifestations in the neck, shoulder, and upper extremity, resulting from compression of neurovascular structures in the thoracic outlet region.²,⁶,¹³⁾ The 3 neurovascular components implicated in TOS are the subclavian vein, the subclavian artery, and the brachial plexus. Specifically, symptoms of nerve compression are differ from those of arterial or venous compression. Neurogenic TOS, which is far more prevalent than arterial or venous TOS, accounts for up to 98% of cases.²,⁶,¹³⁾ Neurogenic TOS is often caused by combination of a congenital anatomical predisposition and trauma.⁶,²³,²⁴⁾ The most prevalent trauma leading to neurogenic TOS is neck trauma, typically resulting from motor vehicle accidents.¹²,¹⁶⁾ Nonetheless, poor posture of the neck, upper back, and shoulder has also been suggested as the most frequent cause of primary neurogenic TOS.⁶,¹⁶⁾

The criteria for post-traumatic neurogenic TOS remain undefined. Discussion about post-traumatic neurogenic TOS typically begin with the consideration of brachial plexus compression due to clear, singular musculoskeletal trauma such as fractures of the clavicle, neck, or thorax’s first rib.⁴,¹⁴,¹⁵⁾ However, most reports cases detail gradual onset of neurogenic TOS following trauma, examples include whiplash injury from a motor vehicle accident (MVA) or a fall,¹¹,¹²,²³,²⁴,²⁷,²⁹⁾ or repetitive misuse or abuse of the neck, shoulder, and upper extremity muscles related to occupational activities.²⁴⁾ Cases of post-traumatic neurogenic TOS resulting from a single major trauma, such as a fracture or dislocation impacting the bones around the brachial plexus, are infrequent. Furthermore, there is an absence of reports concerning neurogenic TOS arising from trauma to neck’s soft tissues.

This report documents a case of post-traumatic neurogenic TOS secondary to traumatic soft tissue injury in the neck. The patients consequent chronic upper extremity paralysis was effectively treated with brachial plexus decompression surgery.

CASE REPORT

A 26-year-old male patient was assessed for monoplegia of the right arm. Approximately eight months before this evaluation, he sustained an injury at work where his right arm was entrapped in machinery, leading to significant soft tissue contusion on the right side of his neck. He developed severe respiratory distress from the contusion and swelling in his neck’s soft tissues. He underwent intubation, sedation, respiratory therapy for 2 weeks in the intensive care unit. Once extubated and conscious, he was transferred to a general ward and discovered that his right arm was immobile. Computed tomography (CT) of the brain indicated no traumatic or ischemic changes. An magnetic resonance imaging (MRI) of the cervical spine revealed substantial neck soft tissue swelling due to injury (FIGURE 1A). It was concluded that nerve damage on the right side of his neck had caused paralysis of his right arm, necessitating ongoing rehabilitation to assess potential improvement.

FIGURE 1. Weakness of the right upper extremity and radiologic findings.

(A) An axial T2-weighted image of the cervical spine MRI at the level of the C7 vertebral body taken 3 days after injury. This image shows diffuse swelling and edema in the soft tissue and scalene muscles of the right cervical paravertebral space, indicated by white arrows. No abnormalities were observed in the cervical cord and roots. (B) A clinical photograph displays limited extension and abduction of the patient’s right shoulder. (C) An axial T2-weighted image corresponding to figure (B) from an MRI of the brachial plexus taken 8 months post-injury. This image shows that compared to the iso-signal intensity of the left cervical roots (white arrowhead), the right roots (white arrow) are swollen and exhibit high signal intensity. (D) A coronal T2-weighted image of the right brachial plexus revealing diffusely thickened and swollen brachial plexus and scalene muscles, marked by white arrows. (E) A coronal T1-weighted maximum intensity projection image depicting pronounced swelling of the right brachial plexus relative to the left, illustrated with white arrows and white arrowheads respectively. (F) An axial T2-weighted image shows diffuse hyperintensity and mild atrophy in the supra- and infraspinatus muscle, indicative of denervation myopathy.

MRI: magnetic resonance imaging.

Subsequent to his initial treatment, the patient underwent rehabilitation for 7 months at 2 different facilities. An electromyography (EMG) performed at three months post-injury diagnosed brachial plexus plexopathy, predominantly affecting the upper and middle trunks. Movement of the patient’s right wrist and fingers began to return three months, but there was no sign of improvement in shoulder and elbow mobility, aside from slight movement restoration in his wrist and fingers. Due to the persistent paralysis of his right arm, he was referred to the author for further evaluation by a physician from a fourth hospital.

On physical examination, extension and abduction of his shoulder were not possible (FIGURE 1B). Flexion of the right elbow was limited to only 10 degrees. Extension of the elbow was feasible, yet, the associated motor power was weak (Medical Research Council [MRC] grade 3). His right wrist allowed for 90 degrees of both flexion and extension, and his right fingers exhibited full range of motion in both actions. Hand grasping and pinching with the right hand and fingers were achievable, although strength was not fully intact (MRC grade 4). There were no significant abnormalities in sensation in the right arm, except for mild numbness on the side of the right thumb and the back of the hand. Deep tendon reflexes in the right biceps and triceps were absent. He reported no pain in his right arm or hand. Mild muscle atrophy was observed in the supraspinatus and deltoid muscles. His right upper and lower arms appeared compared to his left arm. No tenderness was noted in his right neck region. His laboratory findings showed no abnormalities. He expressed concern about the loss of function in his arm and hand, attributing it to an inability to use his right shoulder and elbow regardless of the duration.

MRI of the cervical spine was performed to evaluate for traumatic changes in the cervical cord and roots, which might explain the right arm weakness, but the spinal cord and roots exhibited no remarkable abnormalities. However, swelling of the extraforaminal cervical roots was observed (FIGURE 1C). With suspicion of a traumatic injury to the right brachial plexus, an MRI of the brachial plexus was conducted. This revealed diffuse swelling and thickening of the brachial plexus, which extended along the C5-7 nerve roots to the level of the division of the right brachial plexus (FIGURE 1D & E). There was no interruption in the continuity of the right brachial plexus. Additionally, signs of chronic denervation myopathy were noted, including increased signal intensity with contrast enhancement and mild atrophy involving the right-sided supra- and infraspinatus muscles (FIGURE 1F). Considering the persistent paralysis of the right shoulder and elbow with diffuse swelling of the right brachial plexus, the condition was diagnosed as traumatic right brachial plexus injury. Since the paralysis of the right arm showed no improvement, a right brachial plexus decompression was performed through a supraclavicular approach.

After dissecting the supraclavicular nerve and the external jugular vein and elevating the supraclavicular fat pad, the right brachial plexus adjacent to the scalene muscle was exposed (FIGURE 2). The anterior scalene muscle was unexpectedly swollen and firm (FIGURE 2A & B). Furthermore, the brachial plexus, swollen, was compressed between the anterior and middle scalene muscles (FIGURE 2C). Under microscopic surgical vision, the scalene muscles were detached from the nerve, and the fibrous adhesions between the brachial plexus and the scalene muscles were excised. Intraoperative nerve stimulation facilitated identification of the upper, middle, and lower trunks. The long thoracic nerve, located neath the middle scalene muscle, was dissected and preserved (FIGURE 2D). After a comprehensive circumferential dissection of the right brachial plexus, accompanied by scalenectomy (FIGURE 2E), the surgical wound was meticulously sutured in layers, as no abnormal findings were observed during the intraoperative monitoring.

FIGURE 2. Surgical findings of traumatic brachial plexus entrapment.

(A) An intraoperative photograph depicting severe adhesions between the scalene anterior muscle (black arrows) and the upper trunk of the brachial plexus (white arrows) following the elevation of the supraclavicular fat pad. The demarcation between the scalene anterior muscle and the upper trunk of the brachial plexus is unclear. The white arrowhead represents the right phrenic nerve traversing the scalene anterior muscle. (B) An intraoperative photograph illustrates the upper trunk of the brachial plexus (white arrows), initially exposed by dissecting the lateral margin of the scalene anterior muscle (black arrows). The white arrowhead denotes the right phrenic nerve traversing the scalene anterior muscle. (C) An intraoperative photograph illustrating the middle trunk (white arrows) of the brachial plexus at it becomes visible with the progressive resection of the scalene anterior muscle. The scalene anterior muscle, presenting as stiff and tense, exerted pressure on the brachial plexus. The white arrowhead identifies the upper trunk, which has previously been dissected and decompressed. (D) An intraoperative photograph demonstrating the scalene medius muscle (black arrows) being separated from its adhesion on the lateral inferior aspect of the upper trunk (white arrows). The white arrowhead represents the long thoracic nerve, which courses between the fibers of the scalene medius muscle. Additionally, the scalene medius muscle exhibits stiffness and severe adhesions due to intramuscular hemorrhage sustained from trauma. (E) An intraoperative photograph showing complete decompression of the upper (white arrows), middle (black arrows), and lower trunks of the brachial plexus with the resection of the anterior and middle scalene muscles. The white arrowhead indicates the supraclavicular nerve, and the black arrowhead denotes the phrenic nerve.

Starting from the second day post-surgery, mobility in his right shoulder began to improve. Initially, his right shoulder achieved 45 degrees of abduction and 30 degrees of extension (FIGURE 3A). One month post-surgery, his right shoulder attained an abduction of 90 degrees and an extension of 150 degrees. His right elbow could flex up to 90 degrees. No tenderness was present in the neck above the right clavicle, and no sensory alterations were noted at the surgical site, the right arm, or the hand. Three months post-surgery, full range of motion was restored in his right shoulder and elbow (FIGURE 3B). The previous clumsiness in the right hand and fingers had resolved, allowing him to use his right hand for daily tasks and to resume his prior employment. No variations were found in the numbness or paresthesia on the radial side of the right thumb and on the dorsum of the hand. Yet, he declined to take the medicine, asserting that the pain was manageable. He returned to his regular employment 4 months after the surgery.

FIGURE 3. Surgical findings of traumatic brachial plexus entrapment.

(A) This clinical photograph depicts improved abduction and extension of the right shoulder immediately after surgery, captured on the second day post-surgery. Flexion of the right elbow still appears limited. (B) A clinical photograph illustrates unrestricted abduction and extension of the right shoulder and the flexion of the right elbow 3 months post-brachial plexus decompression.

DISCUSSION

Neurogenic TOS

TOS was first defined by Peet et al.²¹⁾ and it is now commonly used to describe patients with symptoms resulting from the compression of the brachial plexus, and subclavian vein and artery in the thoracic inlet.¹⁹⁾ TOS encompasses condition involving compression in the thoracic outlet, affecting the subclavian artery, subclavian vein, and the brachial plexus. Depending on the structures compressed, TOS is classified as neurogenic TOS, venous TOS, and arterial TOS.⁶⁾ Identifying vascular compression is relatively straightforward with objective vascular imaging.⁶⁾ Neurogenic TOS is the most prevalent form, accounting for up to 98% of cases.³⁾ A major controversy among patients with TOS concerns those with neurologic-type symptoms such as paresthesia, numbness, and pain, yet lack positive objective tests confirming the cause.⁶⁾ The absence of professional consensus, combined with the broad variability of symptoms and the lack of a gold standard for diagnosis, often leads to misdiagnosis or oversight of this condition.²²⁾

Posttraumatic neurogenic TOS

Trauma has been established as a significant cause of neurogenic TOS.⁴,¹⁴,¹⁵,²⁸⁾ However, reviews of the literature on trauma-induced neurogenic TOS reveal a scarcity of cases attributed to major neck injuries. In the 1970s and 1980s, numerous reports linked neurogenic TOS to traumatic events.⁴,¹⁴,¹⁵⁾ Consequently, trauma continues to be regarded as a significant factor in neurogenic TOS. Ochsner and colleagues²⁰⁾ initially associated TOS with injuries to the scalene muscles, suggesting that neck trauma caused a spasm in the scalene anterior muscle, which mechanically elevated the first rib and irritated the brachial plexus. Aynesworth¹⁾ described 20 cases of scalene anticus syndrome, observing that 80% of cases involved a history of trauma; the majority of these patients achieved relief through scalenotomy. The pathophysiology was thought to involve secondary contracture and fibrosis of the scalene muscles, leading to compression of the brachial plexus.²⁸⁾ Wood²⁸⁾ examined 1,958 patients with soft tissue injuries of the neck and found that 23% presented with neurogenic TOS. Although numerous researchers documented the incidence of trauma in their TOS patients in the 1970s and 1980s, many did not differentiated between neurogenic TOS arising from intense prolonged muscular efforts or repetitive tasks and TOS resulting from a solitary traumatic event such as a motor vehicle accident.⁹⁾

Another controversy regarding the link between neurogenic TOS and trauma stems from work-related injuries such as repetitive physical stress and minor traumas like whiplash injury, which can lead to development of neurogenic TOS.¹⁶⁾ A higher incidence of TOS has been reported in workers whose jobs require their arms to be in a supinated position.²⁶⁾ Such work-related injuries are linked to secondary gain and symptom magnification, complicating the diagnosis and treatment of traumatic neurogenic TOS.¹⁶⁾ Neurogenic TOS related to whiplash injuries from minor traffic accidents is often challenging to directly relate to trauma and can create medico-legal issues. To explain the association between neurogenic TOS and a history of minor trauma, Sanders et al.²⁴⁾ proposed that overstretching of the scalene muscles due to hyperextension injury to the neck lead to microscopic changes, such as an increase in type I muscle fiber increases, atrophy of type II fibers, and an increase in connective tissue.

Severe trauma to the musculoskeletal system in the thoracic outlet can clearly result in secondary neurogenic TOS. Instances where neurogenic TOS arose from a single traumatic event include fractures of the clavicle or first rib, C7 transverse process, shoulder dislocation, and gunshot wounds to the chest.⁴,¹⁴,¹⁵,¹⁸⁾ Compromise of the brachial plexus may be due to hemorrhage and edema or direct compression from bone fragments. In later stages, pseudoarthrosis or bone callus formation can cause progressive narrowing of the costoclavicular space.⁸⁾ Neurogenic TOS in this instance was caused by adhesions involving the brachial plexus due to contusion-hemorrhage of the anterior and middle scalene muscles, which were severely spastic, rigid, and exhibited significant adhesions with the brachial plexus. This condition is thought to increase pressure on the brachial plexus in the interscalene triangle, thereby leading to immediate improvement in the right upper extremity following the decompression of the brachial plexus.

The findings of T2 hyper-intensity of the brachial plexus noted in this MRI case (FIGURE 1) are noteworthy. The understanding of MRI findings of the brachial plexus post-trauma is less well understood than previously anticipated. The majority of earlier studies on posttraumatic TOS resulting from severe thoracic outlet trauma were authored primarily by thoracic or vascular surgeons, many prior to the widespread adoption of advanced MRI techniques for the brachial plexus in the 2000s. In the current case, only CT and MRI evaluation of the cervical spine were conducted to assess right arm paralysis without imaging examinations of the brachial plexus. The late diagnosis of posttraumatic neurogenic TOS in these case series indicates that there is still insufficient awareness of brachial plexus injuries resulting from neck trauma among clinicians.

Decompression of posttraumatic neurogenic TOS

Although there is no universally accepted definition or criteria for the timing of brachial plexus decompression surgery after posttraumactic neurogenic TOS, surgical intervention is necessary for cases with medically refractory neuropathic pain or paralysis of the affected nerves, similar to peripheral nerve compression syndromes. The preferred surgical method for neurogenic TOS, endorsed by most authors, involves an anterior supraclavicular approach coupled with anterior and middle scalenotomy, and the removal of any compressive osseous or soft tissue elements.⁶,⁷,⁸⁾ This procedure is particularly beneficial for posttraumatic neurogenic TOS, as the scalene muscles significantly contribute to its pathophysiology.⁸,²⁴,²⁵⁾ The anterior approach facilitates excellent visualization of the brachial plexus from the spinal nerve to the division level and is associated with minimal morbidity.⁵,⁶,⁸,¹³,²⁵,²⁷⁾ In the current case, a scalenectomy was performed through a supraclavicular approach due to posttraumatic TOS caused by adhesions following hemorrhage and fibrosis in the scalene muscle, forming the interscalene triangle without evident bony pathology.

The most frequently cited issue in the diagnosis and management of posttraumatic TOS is the delay in diagnosis.⁸⁾ The primary controversy surrounding patients with spontaneous neurogenic TOS involves those presenting with neurological-type symptoms such as paresthesia, numbness, and pain, absent positive objective tests to confirm the cause.⁶,¹³,¹⁷,¹⁹⁾ Due to professional disagreement, the wide variability of symptoms, and the lack of a diagnostic gold standard, diagnoses are often missed in patients with spontaneous neurogenic TOS.⁶⁾ These observations pertain to post-traumatic neurogenic TOS resulting from whiplash-type injuries.¹⁰⁾ However, neurogenic TOS following significant trauma that definitely compromises the brachial plexus, such as bony fractures of the thoracic outlet with subsequent pseudoarthrosis, is not challenging to diagnose when it presents with neurogenic pain or weakness. Despite this, as confirmed in this case, only cervical MRI was conducted, and imaging of the brachial plexus was not neglected. A lack of awareness regarding neurogenic TOS can result in delayed diagnosis and treatment failures, potentially leading to chronic neuropathic pain, weakness, hand atrophy in the affected limb, and unnecessary cervical or peripheral nerve surgeries.⁸⁾ The immediate improvement in right arm paralysis post-surgery underscores the importance of early diagnosis and surgical decompression of the brachial plexus in posttraumatic neurogenic TOS.

CONCLUSION

Trauma to the neck or shoulder area can lead to the development of posttraumatic neurogenic TOS through direct or indirect pathophysiological mechanisms, with the scalene muscles playing a critical role. When a patient exhibits weakness and heaviness, numbness, and tingling paresthesia in the ipsilateral upper extremity after significant trauma to the neck, and these symptoms are not due cervical spine pathology, the diagnosis of posttraumatic neurogenic TOS should be considered. If a neurologic deficit continues despite optimal conservative treatment, surgical decompression of the brachial plexus should be undertaken promptly.