Dynamic MRI delivers in delicate neurovascular cases



Third-year radiology registrar Dr Liam Pugh and senior radiology specialist Dr Thomas Lloyd, both at Princess Alexandra Hospital in Woolloongabba, Brisbane, Queensland.

“Brachial plexus imaging with an MRI protocol with dynamic maneuvers can serve as a valuable tool in the diagnostic pathway and surgical planning of patients with NTOS-compliant clinical features, allowing demonstration of plexus compression in the ‘constricted costoclavicular space’, they reported at last week’s Annual Scientific Meeting of the Royal Australian and New Zealand College of Radiologists (RANZCR), held in Adelaide.

In a poster, they presented a case series involving five patients with positive results after surgical release of such compression.

A 34-year-old man with a clinical picture consistent with NTOS. MRI (sagittal T1-weighted) images show a spacious costoclavicular (CS) space in neutral position measuring 24 mm at the narrowest point. With the arm elevated, this reduces markedly to a minimum distance of 4mm, with the brachial plexus interposed between the clavicle (C) and first rib (R) at this point. Flattening of the subclavian vein (SV) has also been demonstrated. No anatomical variants or other causes of compression were observed either radiographically or surgically. (A) T1-weighted oblique sagittal image at the CS level in neutral position. The CS measures 24 mm in neutral position, and the divisions of the brachial plexus are clearly demarcated by fat (arrows). S = subclavian muscle, SA = subclavian artery. (B) T1-weighted oblique sagittal slice at CS level, arm abducted. The CS is narrowed to 4 mm at the level of the brachial plexus. Arrows = divisions of the brachial plexus. (C) Thick T2 3D SPACE STIR MIP reconstruction in the coronal plane, CS level, arm abducted. The CS is shrunk to 4mm. C5 – T1 nerve roots = labeled. The patient underwent resection of the right first rib with a good clinical response. All figures courtesy of Dr. Liam Pugh and Dr. Tom Lloyd, presented at RANZCR ASM 2022.

Thoracic outlet syndrome consists of neurological and vascular symptoms of the upper limbs due to compression of the neurovascular bundle as it passes through the thoracic outlet, Pugh and Lloyd explained. Compression can occur in the interscalene space, costoclavicular space, and rectopectoral minor space, but is more common in the costoclavicular space and is exacerbated by abduction of the arm, which narrows this space more.

The etiology of NTOS is thought to most likely be due to cervical hyperextension injury – which may be minor – in patients with an underlying predisposition due to anatomical variability, they added.

Diagnostic challenges

Vascular outlet syndrome can be diagnosed by Doppler ultrasound and CT angiography showing compression/stenosis of vascular structures. Although it is the most common subtype, with a neurogenic component present in up to 95% of cases of thoracic outlet syndrome, diagnosing NTOS is often more difficult, the researchers said.

“Clinical features are generally vague and overlap with other causes of nerve compression and pain syndromes,” they point out. “Clinical tests are often positive in asymptomatic volunteers and are often based on arterial compression, which is a poor indicator of neurological compression of the brachial plexus.”

The classic presentation is upper extremity paresthesia and pain exacerbated by certain shoulder movements, including abduction, but the exact location of symptoms varies with the level of compression, and muscle weakness and atrophy are late signs, according to Pugh and Lloyd.

Neurovascular compressions are often not demonstrated in the neutral position, emphasizing the need for dynamic MRI. In contrast, the scalene triangle and minor rectopectoral space exhibit an equal or less degree of compression in patients with thoracic outlet syndrome compared to asymptomatic patients.

A 49-year-old woman with prolonged symptoms of neurogenic thoracic outlet syndrome

A 49-year-old woman with prolonged symptoms of NTOS including neck, chest, upper back and upper extremity pain, paresthesia, muscle weakness and muscle atrophy. MRI demonstrated significant narrowing of the costoclavicular (SC) space with the elevated arm narrowing from 26mm to 5mm. The patient underwent decompressive surgery with resection of the first rib and anterior and middle scalenectomy with thoracic outlet syndrome confirmed by the presence of extensive scar tissue surrounding the brachial plexus. Fibromuscular bands between the anterior and middle scalene muscles have also been identified. The patient showed clinical improvement, but not complete resolution of symptoms, which could be related to the duration of compression before release. (A) T2 3D SPACE STIR 3 shots. CS level in neutral position. C = clavicle, R = first rib, A = subclavian artery, V = subclavian vein, CS = measured (26 mm). (B) T2 3D SPACE STIR 3 shots. CS level with the arm in abduction. The CS is again significantly shrunk to 5mm.

At the Princess Alexandra Hospital, imaging is performed on a 3 tesla scanner with sequences composed of 3D SPACE [sampling perfection with application-optimized contrasts using a different flip angle evolution] STIR [short tau inversion recovery] images in a coronal plane oriented to the neurovascular bundle, sagittal Dixon T2 images, and T-weighted images with the imaged volume extending through the supraclavicular fossa to the humerus.

The sequences are performed with the arm in a neutral position and in abduction with external rotation. Additionally, a T2 sagittal cervical spine is performed to assess the cervical nerve roots.

Origins of the study

Lloyd said AuntMinnieEurope.com that he was initially performing MRI studies of the brachial plexus for a plastic surgeon in the context of trauma. A vascular surgeon then asked Lloyd if it could be used for NTOS.

“When we worked on the protocol, we realized the need to image in more than one position to assess the interval change in anatomical spaces, and we had some good clinical results,” he said. points out.

The project remains a work in progress. Lloyd – who is director of network training at his hospital, visiting radiologist at BreastScreen Queensland and adjunct professor at Queensland University of Technology (QUT) School of Health – said he was happy to share the protocol with other sites and radiologists. He hopes this will lead to a larger project.

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