Neurologic Imaging

Should You Order MRI for Suspected Traumatic Brachial Plexus Injury? An ACR-Guided Workflow

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Should You Order MRI for Suspected Traumatic Brachial Plexus Injury? An ACR-Guided Workflow

A 24-year-old male is brought to the emergency department after a high-speed motorcycle accident. He has a clavicle fracture and complains of severe pain, weakness, and numbness in his right arm and hand. On examination, he has profound weakness in a C5-T1 distribution. You suspect a traumatic brachial plexus injury, a potentially devastating diagnosis with a narrow window for optimal intervention. The immediate clinical question is which imaging study will most accurately define the extent of the injury to guide management. This article provides a focused workflow for this exact scenario, based on the American College of Radiology (ACR) Appropriateness Criteria. For suspected traumatic brachial plexopathy, the ACR rates MRI brachial plexus without IV contrast as Usually Appropriate.

Who Fits This Clinical Scenario?

This guidance applies specifically to the initial imaging of adult or pediatric patients with a suspected traumatic brachial plexopathy. The classic mechanism is a high-energy traction injury, such as those seen in motorcycle accidents, falls from height, or contact sports, where the head and neck are forced away from the ipsilateral shoulder. It also includes direct trauma, such as a clavicle or first rib fracture that injures the plexus, or iatrogenic injury during a surgical procedure. This is not for perinatal brachial plexus injuries (e.g., Erb’s palsy), which have a distinct pathophysiology and imaging approach.

This workflow should be distinguished from several related but distinct clinical presentations:

  • Nontraumatic Plexopathy: If the patient presents with progressive arm weakness without a clear traumatic event, the differential shifts toward causes like inflammatory conditions or compression from a mass. This follows the nontraumatic brachial plexopathy guidelines.
  • Known Malignancy: If the patient has a history of cancer (e.g., lung, breast) or has received radiation therapy to the region, the workup must differentiate between tumor infiltration and radiation-induced plexopathy, a separate ACR scenario.
  • Lumbosacral Plexopathy: If the symptoms involve the leg and pelvis, the injury is to the lumbosacral plexus, which requires a different imaging protocol and clinical evaluation.

What Diagnoses Are You Working Up in This Scenario?

In traumatic brachial plexopathy, imaging is critical for distinguishing between injuries that may recover spontaneously and those requiring urgent surgical intervention. The differential diagnosis is a spectrum of nerve injury severity, and the primary goal of imaging is to locate the injury and classify its type.

Nerve Root Avulsion: This is the most severe injury, where the nerve rootlets are torn directly from the spinal cord (a preganglionic injury). There is no potential for spontaneous recovery, and it often requires nerve transfer surgery. Imaging signs include pseudomeningoceles, spinal cord displacement, and lack of visualization of the ventral or dorsal nerve roots.

Nerve Rupture: This involves a complete transection of the nerve distal to the dorsal root ganglion (a postganglionic injury). While severe, it is potentially repairable with nerve grafting. MRI may show a clear gap in the nerve or a neuroma-in-continuity at the injury site.

Stretch Injury (Neuropraxia/Axonotmesis): This is the most common type of injury, where the nerve is stretched but remains in continuity. Neuropraxia is a temporary conduction block that typically recovers fully, while axonotmesis involves axonal damage with the nerve sheath intact, allowing for potential regeneration. MRI findings can range from normal-appearing nerves to diffuse thickening and T2 signal hyperintensity (edema).

Compressive Hematoma or Pseudoaneurysm: The trauma may cause a hematoma or vascular injury (e.g., subclavian artery pseudoaneurysm) that externally compresses the brachial plexus. These are critical to identify as they may be treatable, leading to neurologic recovery.

Why Is MRI of the Brachial Plexus the Recommended Initial Study?

The ACR designates MRI brachial plexus without IV contrast as Usually Appropriate for the initial evaluation of traumatic brachial plexopathy because of its unparalleled soft-tissue resolution and ability to directly visualize the nerves and surrounding structures without ionizing radiation.

A dedicated brachial plexus MRI protocol uses high-resolution, thin-section 2D and 3D sequences to meticulously evaluate the anatomy from the spinal cord nerve roots to the terminal branches in the axilla. It can reliably identify key prognostic findings like pseudomeningoceles (indicating root avulsion), nerve discontinuity, neuroma formation, and surrounding muscle denervation changes. The use of IV contrast is also rated Usually Appropriate when performed with a non-contrast study, but the non-contrast portion is the essential component. Contrast can be helpful to assess for active inflammation, vascular injury, or an unexpected mass, but it is not mandatory for the primary goal of anatomical assessment in trauma.

Alternative studies are rated lower for specific reasons in this initial workup:

  • CT Myelography cervical spine: Rated as May be appropriate, this invasive study involves injecting intrathecal contrast. It is considered the gold standard for detecting pseudomeningoceles and confirming nerve root avulsion. However, its invasiveness, use of significant ionizing radiation (☢☢☢☢ 10-30 mSv), and inability to visualize the postganglionic plexus as well as MRI make it a secondary, problem-solving tool rather than the initial study of choice.
  • US neck: Rated as Usually not appropriate, ultrasound has a limited role. While it can visualize portions of the supraclavicular plexus, it is highly operator-dependent and cannot adequately assess the crucial preganglionic nerve roots within the spinal canal. It is insufficient for the comprehensive evaluation required in a significant traumatic injury.

The primary advantage of MRI is its ability to provide a comprehensive, non-invasive road map of the injury. This directly informs the crucial decision between conservative management and surgical exploration. The radiation dose for MRI is O 0 mSv, a critical consideration, especially in younger trauma patients.

What’s Next After MRI? Downstream Workflow

The results of the brachial plexus MRI will guide the subsequent clinical pathway, which almost always involves collaboration with neurosurgery and/or peripheral nerve specialists, as well as physical medicine and rehabilitation.

  • If the MRI shows definitive nerve root avulsion: This finding necessitates an urgent neurosurgical consultation. Surgical intervention, often involving nerve transfers from donor nerves, is typically considered within 3 to 6 months of the injury for optimal outcomes. Further workup may include electrodiagnostic studies (EMG/NCS) to confirm the functional deficit, but the imaging findings are paramount for surgical planning.
  • If the MRI is negative or shows only nerve edema (stretch injury): The likely diagnosis is neuropraxia or a low-grade axonotmesis. The recommended course is typically conservative management with physical and occupational therapy. Serial clinical examinations and electrodiagnostic studies performed 3-4 weeks post-injury (allowing time for Wallerian degeneration to occur) are crucial to monitor for signs of recovery. If no clinical or electrophysiologic recovery is seen by 3-6 months, a repeat MRI or surgical exploration may be considered.
  • If the MRI shows nerve rupture or a neuroma-in-continuity: This also warrants neurosurgical consultation. The decision to operate depends on the clinical picture and electrodiagnostic findings. Intraoperative nerve action potential recording may be needed to determine if the neuroma should be resected and grafted or if neurolysis (freeing the nerve from scar tissue) is sufficient.

In all cases, electrodiagnostic studies serve as a critical functional complement to the anatomical information provided by MRI, helping to confirm the severity and location of the injury and track recovery over time.

Pitfalls to Avoid (and When to Get Help)

Navigating the workup for traumatic brachial plexopathy requires careful attention to detail to avoid common errors that can impact patient outcomes.

  1. Ordering the Wrong MRI: A “routine MRI of the cervical spine” is not sufficient. You must specifically order an “MRI of the brachial plexus,” which uses a dedicated protocol with a different field of view and specialized sequences designed to visualize the nerves.
  2. Delaying the Initial Imaging: While not always an emergent, middle-of-the-night study, obtaining the MRI within a few days to weeks is important. Early, accurate diagnosis of an avulsion injury is critical, as the window for successful surgical repair is time-limited.
  3. Overlooking Associated Injuries: High-energy trauma is a multisystem event. Always consider and evaluate for concurrent vascular injuries (e.g., subclavian artery dissection or pseudoaneurysm), fractures (clavicle, scapula, first rib), and spinal cord injury.
  4. Relying Solely on Imaging: MRI provides the anatomical map, but the clinical examination and electrodiagnostic studies provide the functional data. Management decisions should integrate all three components. If there is a discrepancy between a severe clinical deficit and a “normal” MRI, escalate to a peripheral nerve specialist for further evaluation.

Related ACR Topics and Tools

This article focuses on a single, specific clinical scenario. For a comprehensive overview of imaging for all types of brachial and lumbosacral plexopathy, refer to the parent topic article. For additional tools to help with ordering and interpreting imaging, see the resources below.

Frequently Asked Questions

Since this is a trauma case, why not start with a CT scan?

While a CT of the cervical spine is excellent for evaluating fractures and is often performed as part of a primary trauma survey, it does not directly visualize the nerves of the brachial plexus. MRI is the superior modality for assessing soft tissue and nerve injury, which is the primary concern in a suspected plexopathy. CT myelography is a secondary, more invasive option for specific questions like confirming a nerve root avulsion.

Is intravenous contrast necessary for the initial MRI?

Not always. The ACR rates both ‘MRI brachial plexus without IV contrast’ and ‘MRI brachial plexus without and with IV contrast’ as ‘Usually Appropriate.’ The non-contrast sequences provide the essential anatomical detail. Contrast may be added if there is a specific concern for a vascular injury, an underlying mass, or an inflammatory process, but it is not mandatory for the initial evaluation of traumatic changes like edema, nerve rupture, or avulsion.

What is the role of electrodiagnostic studies (EMG/NCS) relative to imaging?

EMG (electromyography) and NCS (nerve conduction studies) are functional tests that complement the anatomical information from an MRI. They are typically performed 3-4 weeks after the injury to allow for electrophysiologic changes to manifest. They help confirm the location and severity of the nerve injury, distinguish between preganglionic and postganglionic injuries, and provide a baseline for monitoring recovery. The two tests are used together to make critical management decisions.

How does the workup change for a penetrating injury, like a stab wound?

The fundamental question is the same: is the nerve in continuity? MRI remains the primary imaging modality to assess for nerve transection. However, in penetrating trauma, there is a higher suspicion for associated vascular injury. Therefore, a CTA (CT Angiography) of the neck and chest may be performed first or in conjunction with the MRI to urgently rule out an arterial or venous injury that requires immediate surgical intervention.

My patient has a pacemaker or other non-MRI-conditional implant. What is the alternative?

If a patient has an absolute contraindication to MRI, the next best imaging study is CT myelography. It is rated ‘May be appropriate’ by the ACR. While it is invasive and involves radiation, it is the most effective alternative for assessing the preganglionic nerve roots and identifying avulsion injuries. A peripheral nerve specialist and radiologist should be consulted to determine the best imaging strategy in these complex cases.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 26, 2026