Diagnostic Imaging of Brachial Plexopathy

Introduction to Brachial Plexus MRI

• The American College of Radiology recommends MRI of the brachial plexus as the gold standard imaging modality for diagnosing brachial plexopathy due to its superior soft-tissue contrast and spatial resolution, providing detailed definition of intraneural anatomy and localization of pathologic lesions when clinical and electrodiagnostic findings are nonspecific 1, 2, 3

Diagnostic Capabilities

• MRI can detect and characterize various etiologies of brachial plexopathy including tumors, inflammatory conditions, and compressive lesions with high accuracy (sensitivity 81%, specificity 91%, accuracy 88%) 1, 2
• MRI provides additional diagnostic information beyond clinical evaluation and electrodiagnostic studies in approximately 45% of patients 2
• MRI can reliably differentiate compressive from non-compressive plexopathy 2
• MRI allows visualization of the entire course of the brachial plexus from the spinal cord to the axilla, which other imaging modalities cannot fully evaluate 1, 4

Technical Considerations

• Dedicated brachial plexus MRI protocols are essential and differ significantly from routine neck, chest, or spine MRI protocols 5, 3
• Optimal protocols include orthogonal views through the oblique planes of the plexus with T1, T2, fat-saturated T2 or STIR, and fat-saturated T1 postcontrast sequences 4, 3
• MRI with IV contrast can provide additional information over non-contrast studies, particularly for detecting and characterizing masses, tumors, and inflammatory conditions 2, 6
• 1.5 Tesla MRI may be preferable when metal is present in the area to reduce artifact 4, 3

Clinical Applications

• MRI helps identify and characterize intrinsic nerve sheath tumors (neurofibromas, schwannomas) 4
• MRI helps identify and characterize inflammatory/autoimmune conditions (brachial neuritis, chronic inflammatory demyelinating polyneuropathy) 4
• MRI helps identify and characterize extrinsic compression from adjacent structures or masses 1, 2
• MRI can differentiate pre-ganglionic (root avulsion) from post-ganglionic injuries 7
• MRI can identify pseudomeningoceles as surrogate markers for root avulsion 7
• MRI can assess nerve integrity to differentiate minor stretching injuries from complete nerve disruptions 7
• MRI can detect post-traumatic complications like hematomas, neuromas, and scarring 7
• MRI can evaluate surgical repairs in the post-treatment setting 7

Comparison to Other Imaging Modalities

• MRI is superior to CT cervical spine for brachial plexopathy as CT cannot fully visualize preganglionic nerve roots and has limited soft-tissue contrast resolution 1
• MRI is superior to cervical spine MRI for brachial plexopathy as cervical spine MRI does not evaluate the plexus lateral to the neural foramina 2
• Ultrasound has limited utility as a primary imaging modality for brachial plexopathy but may serve as a useful supplemental test in selected centers 2
• FDG-PET/CT is not recommended for non-traumatic brachial plexopathy unless there is a known malignancy 1, 4

Common Pitfalls and Caveats

• For traumatic plexopathy, imaging should ideally be delayed until approximately one month after trauma to allow for resolution of hemorrhage and edema 7, 3
• Clinical overlap between radiculopathy and plexopathy can be challenging; in cases of diagnostic uncertainty, cervical spine MRI may be complementary to brachial plexus MRI 2, 6
• Standard MRI protocols for the neck, chest, or spine are inadequate for proper evaluation of the brachial plexus; specialized brachial plexus protocols are required 5, 3
• The appropriate CPT code for brachial plexus MRI depends on the clinical indication and may vary across institutions 4, 5

MRI Findings in Brachial Plexus Injury

Imaging Limitations in Brachial Plexus Injuries

• The American College of Radiology acknowledges that standard MRI has limitations in detecting certain types of nerve injuries, particularly those involving microstructural changes that may not be visible on conventional sequences, and research into brachial plexus imaging is ongoing, with newer techniques like diffusion tensor imaging showing promise but not yet routinely performed outside research settings 8
• The American College of Radiology notes that even with dedicated brachial plexus MRI protocols, some nerve injuries may not demonstrate visible abnormalities despite causing clinical dysfunction, and post-traumatic complications like hematomas, neuromas, and scarring may be visible on MRI even when the nerves themselves appear normal 8

Factors Affecting MRI Visibility of Nerve Injuries

• Post-traumatic complications like hematomas, neuromas, and scarring may be visible on MRI even when the nerves themselves appear normal, according to the American College of Radiology 8

Imaging Protocol Considerations

• Even with optimal protocols, some nerve injuries may not be detectable on conventional MRI, as stated by the American College of Radiology 8

MRI Ordering for Cervical Radiculopathy vs. Brachial Plexus Pain

Initial Imaging Strategy

• The American College of Radiology recommends starting with MRI cervical spine without contrast because radiculopathy is far more common than plexopathy, with cervical spine MRI having 88% accuracy in correctly predicting lesions in cervical radiculopathy 9, 10, 11

When to Add Dedicated Brachial Plexus MRI

• Proceed to MRI brachial plexus with and without contrast if cervical spine MRI is negative or shows only asymptomatic findings, or if clinical examination suggests plexus involvement, with dedicated brachial plexus imaging requiring different sequences including orthogonal views through the oblique planes of the plexus 9, 12

Contrast Considerations

• The American College of Radiology suggests that contrast is usually not necessary for initial evaluation of radiculopathy, but for brachial plexus MRI, use both with and without contrast to detect and characterize tumors, inflammatory conditions, and masses 9, 11

Common Pitfalls to Avoid

• Don't assume cervical spine MRI adequately evaluates the plexus, as it only shows the nerve roots within and immediately adjacent to the neural foramina, and don't over-interpret asymptomatic findings, as 45% of cervical radiculopathy patients show root compression on MRI without clinical substrate 9, 13

Alternative if MRI Contraindicated

• If the patient cannot undergo MRI, CT myelography cervical spine is the next best option for radiculopathy evaluation, though it cannot evaluate the plexus itself beyond the neural foramina, according to the American College of Radiology 10, 13, 14