Imaging of the Brachial Plexus using Magnetic Resonance Neurography
A 33-year-old male sustained a high-velocity collision on an electric scooter, resulting in right arm weakness and clinical suspicion of a brachial plexus (BP) nerve root injury. Initial trauma computed tomography (CT) identified a cervical spinal fracture. The patient also reported numbness and weakness in the right upper extremity, while clinical examination demonstrated 0/5 strength in shoulder abduction, external rotation, elbow flexion, and elbow extension.
In such acute, high-velocity traumatic settings, extensive soft tissue edema and hematoma can limit the evaluation of the postganglionic BP on Magnetic Resonance Neurography (MRN). However, the recommended imaging protocol modifications for MRN of the brachial plexus, based on common clinical scenarios, can help optimise visualisation of the brachial plexus structures.
The affected side is scanned only to optimise image focus and reduce scan time. Image planes are adjusted by obliquing images first toward the axial plane to match the angle of the lower half of the cervical spine, then oblique toward the sagittal plane to align with the path of the brachial plexus. The subclavian artery serves as an anatomical reference because the brachial plexus should run parallel to it.
Typical sequences include T1 axial covering from mid C3 to below the shoulder joint (affected side only), STIR axial, T2 fat-suppressed Dixon oblique coronal, T1 sagittal from lateral humerus through the spine, bilateral STIR coronal if contrast is given, scanning posterior spine through the sternoclavicular joints, and post-contrast T1 fat-saturated Dixon axial and oblique coronal sequences.
Contrast administration is used selectively, only when there is a suspicion of a mass or tumour, infection, history of cancer, or prior radiation therapy to the area. This enhances lesion conspicuity in such clinical contexts. The field of view (FOV) and slice thickness are typically set to around 230-240 mm FOV with 3 mm slices at 1 mm spacing for axial and oblique planes, and 5 mm slices at 1 mm spacing for sagittal planes.
These protocols are adaptable to both 1.5T and 3T MRI scanners, with adjustments for image contrast and relaxation times at higher field strengths considered.
When assessing traumatic proximal nerve root injuries, an important differentiation is determining whether the injury is preganglionic versus postganglionic. Preganglionic nerve rootlet avulsion, such as epidural hematoma with pseudomeningocele, can be indicative of preganglionic injury. For clinically suspected or known fractures, a bone-like quality sequence (eg, zero echo-time [ZTE]) or a radio-frequency-spoiled gradient echo sequence can be used to assess osseous pathology.
In the case of a postganglionic nerve injury, the nerve gap should be noted, as well as the viable nerve stump caudal to the foramen, for nerve grafting or transfer planning. Imaging for high-velocity traumatic BP injuries is optimally performed at least 2 to 4 weeks postinjury to allow soft tissue edema to subside.
MRN is requested to assist in diagnosis and surgical planning for this patient. The adaptations in the imaging protocol help optimise visualisation of the brachial plexus structures for different clinical scenarios such as tumours, infection, or post-radiation changes.
- In traumatic settings like the one described, where medical-conditions such as brachial plexus injuries are suspected, Magnetic Resonance Neurography (MRN) may be limited due to extensive soft tissue edema and hematoma.
- When dealing with the effects of cancer, whether it's a history of cancer or a current suspicion of a mass or tumour, contrast administration can be crucial to enhance lesion conspicuity in health-and-wellness assessments.
- In cases of neurological-disorders like postganglionic nerve injuries, imaging is often optimally performed at least 2 to 4 weeks postinjury to reduce the impact of soft tissue edema, allowing for better visualization of the nerve structures. Space-and-astronomy-wise, these imaging techniques are adaptable to both 1.5T and 3T MRI scanners, with adjustments for image contrast and relaxation times at higher field strengths considered.
