From the Guidelines
For patients with long thoracic nerve (LTN) palsy or spinal accessory nerve (SAN) palsy, MRI is the recommended imaging modality of choice. This recommendation is based on the most recent and highest quality study available, which suggests that MRI provides excellent soft tissue contrast to directly image features of neuritis or nerve sheath tumors, as well as fully characterize the carotid space and posterior cervical space 1.
Key Considerations for Imaging
- MRI orbits, face, and neck or MRI orbits, face, and neck performed simultaneously in conjunction with complementary MRI head can be used to investigate the high cervical and intracranial portions of the accessory nerve, as well as the brainstem and extracranial course of the accessory nerve innervating the sternocleidomastoid and trapezius muscles 1.
- Imaging protocols should use applicable thin-cut high-resolution techniques and focus on the posterior fossa, posterior skull base, and neck through the course of CN XI and its innervated structures.
- Pre- and postcontrast imaging provides the best opportunity to identify and characterize a lesion, although non-contrast MRI may also be an alternate option for this clinical scenario 1.
Advantages of MRI
- MRI offers excellent soft tissue contrast to directly image features of neuritis or nerve sheath tumors, as well as fully characterize the carotid space and posterior cervical space 1.
- MRI can help identify atrophy and denervation signal changes in the trapezius muscle in patients with accessory nerve palsy 1.
- Contrast-enhanced modified balanced SSFP sequences and MRA focused on the posterior skull provide detailed imaging of the lower CNs within the jugular foramen and as they exit the skull base 1.
Clinical Implications
- Early imaging with MRI can help determine whether the palsy is due to reversible causes that might benefit from timely intervention, such as surgical decompression for entrapment or targeted treatment for inflammatory conditions.
- Electromyography (EMG) and nerve conduction studies should complement imaging to confirm the diagnosis and assess the severity of nerve dysfunction.
From the Research
Recommended Imaging for Long Thoracic Nerve Palsy or Spinal Accessory Nerve Palsy
- The recommended imaging modality for patients with long thoracic nerve (LTN) palsy or spinal accessory nerve (SAN) palsy is magnetic resonance (MR) imaging 2, 3.
- High-resolution MR imaging can reveal secondary signs that can confirm a clinical suspicion of LTN injury, such as skeletal muscle denervation in the serratus anterior, trapezius, and rhomboid muscles 2.
- MR imaging may also show neurogenic fatty infiltration or atrophy in patients with LTN palsy or SAN palsy 3.
- However, high-resolution MR imaging is limited in its ability to visualize the long thoracic nerve directly 2.
Diagnostic Tests
- Electrodiagnostic testing, such as electromyography (EMG) and nerve conduction studies, can be used to confirm the diagnosis of LTN palsy or SAN palsy 3, 4.
- Bilateral nerve conduction studies of the LTN and SAN, and needle EMG of their target muscles, can be useful in diagnosing LTN palsy or SAN palsy 4.