What is the role of MRI (Magnetic Resonance Imaging) and MR (Magnetic Resonance) Neurography in diagnosing and managing brachial plexus injuries?

Role of MRI and MR Neurography in Brachial Plexus Injuries

MRI of the brachial plexus is the gold standard first-line imaging modality for evaluating brachial plexus injuries, with superior soft-tissue contrast and spatial resolution that allows detection of nerve root avulsions, differentiation of preganglionic from postganglionic injuries, and assessment of nerve integrity—all of which are crucial for surgical planning and determining prognosis. 1, 2, 3

Primary Diagnostic Role

MRI/MR neurography serves as the definitive imaging test because it can:

• Identify traumatic nerve root avulsions, which are critical to detect for surgical reconstruction planning and prognostic determination 1
• Differentiate preganglionic injuries (involving intraspinal nerve roots) from postganglionic injuries (involving plexus lateral to dorsal root ganglion), as these require completely different reconstruction approaches and have different prognoses 1, 2, 3
• Distinguish between minor stretching injuries and complete nerve disruptions, directly assessing whether nerve integrity is maintained 1
• Detect pseudomeningoceles as surrogate markers for root avulsion, though this finding has lower diagnostic accuracy (68%) compared to direct visualization of nerve root avulsion (79% accuracy) 1

Diagnostic Performance

The evidence demonstrates strong diagnostic accuracy:

• Overall sensitivity of 84%, specificity of 91%, and accuracy of 87% when compared to surgical findings and clinical follow-up 1
• 79% diagnostic accuracy for detecting C5 to T1 nerve root avulsion specifically 1
• MRI provides additional diagnostic information beyond clinical evaluation and electrodiagnostic studies in approximately 45% of patients 3

Optimal Timing and Protocol

Critical timing consideration: Imaging should ideally be delayed until approximately 1 month after the initial trauma to allow time for:

• Resolution of hemorrhage and edema 1, 2, 3
• Formation of pseudomeningocele 1

Essential protocol requirements:

• Dedicated brachial plexus MRI protocols are mandatory—standard neck, chest, or spine MRI protocols are inadequate 2, 3, 4
• Include orthogonal views through the oblique planes of the plexus 2, 3, 4
• Sequences should include T1-weighted, T2-weighted, fat-saturated T2-weighted or STIR sequences 2, 3, 4
• Contrast is usually not necessary for initial traumatic injury evaluation, though it can help differentiate vascular structures from nerves 1, 3

Beyond Acute Injury Detection

MRI/MR neurography also identifies:

• Post-traumatic complications including regional soft-tissue hematomas, traumatic neuromas, and scarring 1, 3, 4
• Extrinsic compression from displaced fractures or hematomas that may compress the brachial plexus 1
• Secondary signs of neuropathy such as degenerative muscular atrophy 1, 4
• Post-surgical assessment of repaired nerves and complications following surgical nerve repair 1, 3

Comparison to Alternative Imaging

MRI is definitively superior to other modalities:

• CT cervical spine cannot visualize preganglionic nerve roots and has limited soft-tissue contrast resolution relative to MRI 1, 3
• CT myelography can only evaluate preganglionic nerve root injury and does not directly visualize the postganglionic brachial plexus 1
• FDG-PET/CT has no role in traumatic brachial plexopathy evaluation 1

Clinical Impact on Management

MRI findings directly influence surgical decision-making:

• Complete nerve ruptures identified on MRI generally require early operative intervention and have worse prognosis 2, 4
• Preganglionic injuries (root avulsions) require different reconstruction approaches than postganglionic injuries 1, 2, 3
• Penetrating and open injuries typically require early surgical exploration, while blunt injuries may be managed operatively or non-operatively based on MRI severity assessment 2, 4

Important Caveats

Methodological limitations exist: A systematic review found that studies on MRI diagnostic accuracy for traumatic brachial plexus injury lacked methodological rigor, indicating the need for more rigorous research 1

Emerging techniques: Diffusion tensor imaging and tractography show promise for evaluating nerve injury and microstructural disruption, but these are not routinely performed outside research settings 1

Clinical correlation remains essential: Even with optimal protocols, some nerve injuries may not demonstrate visible abnormalities on conventional MRI despite causing clinical dysfunction 3