Non-degenerative Disease of the Peripheral Nerves

Clinical History: A 30 year-old male who was involved in a high-speed motor vehicle accident 10 months prior. Axial T2-weighted (1A) and T1-weighted (1B) images are provided. What are the findings? What is your diagnosis?

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Figure 1

Findings

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Figure 2:

The right-sided nerve root sheath at C2-3 appears featureless and dilated (arrowheads) on the axial T2-weighted image(2A). The right-sided nerve root is not identified. The normal left-sided nerve root (arrow) is seen on the axial T1-weighted (2B) image.

Diagnosis

Traumatic avulsion of the right C2 nerve root.

Introduction

The peripheral nerves are frequently compromised due to degenerative disc and facet disease in the spine. However, there are other less common causes of peripheral nerve disease that can present with similar clinical findings. This web clinic reviews several non-degenerative causes of peripheral nerve pathology.

Trauma

Nerve root avulsion is a severe injury which occurs when the nerve roots are subjected to significant traction. In adults, avulsion is usually due to direct trauma or high-speed motor vehicle accidents, with motorcycle accidents commonly cited. In children, avulsion is most frequently seen as a result of birth trauma. When the nerve root is torn, the meninges are also frequently torn, resulting in leakage of CSF and an associated pseudomeningocele.¹On MRI, these changes result in an “empty” or featureless nerve root sheath which is fluid-filled with no neural elements; expansion and remodeling of the neural foramen is common. In some cases, a post-traumatic reactive neuroma can develop at the end of the damaged nerve.^2,3

Nerve root avulsion presents clinically with variable neurological deficits, including partial or complete motor loss, and can significantly impact activities of daily living. Cervical nerve root avulsion is associated with brachial plexus dysfunction, as the C5 through C7 nerve roots are part of the brachial plexus. If recovery of function does not occur within 3 months, surgical repair is indicated in an attempt to preserve or restore function.^4,5

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Figure 3:

44 year-old female with history of birth trauma and limited use of the left arm. Axial T1-weighted (3A) and fat-suppressed proton density-weighted (3B) images show a fusiform mass in the left interscalene triangle (asterisks), consistent with a neuroma. A chronic left C7 nerve root avulsion with pseudomeningocele (arrowheads) is seen on sagittal (3C) and axial (3D) T2-weighted images of the cervical spine.

Inflammatory/demyelinating

Chronic inflammatory demyelinating polyneuropathy (CIDP) is an acquired demyelinating disease of the peripheral nerve roots. Patients typically present with gradual onset of weakness and loss of reflexes. The clinical presentation can mimic Guillian-Barre syndrome, but CIDP has a more chronic course. Over time, inflammation results in significant thickening of the nerve roots. On MRI, the nerve roots demonstrate fusiform enlargement and generally enhance; associated changes of denervation, such as atrophy or enhancement, can be seen in the paraspinous musculature, and abnormal signal can also be seen in the adjacent spinal cord. Treatment for CIDP consists of steroids and other immunosuppressive drugs.^6,7

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Figure 4:

73 year-old male with progressive weakness and upper motor neuron signs. Sagittal post-gadolinium contrast T1-weighted (4A) and axial T2-weighted (4B) images show massive, fusiform enlargement of the C2 nerve roots bilaterally (arrowheads) with mild heterogenous enhancement. On a midline sagittal T2-weighted image (4C), hyperintensity is seen in the spinal cord at the C2 level (arrow), consistent with demyelination.

Congenital

The hereditary motor and sensory neuropathies (HMSN) are a group of genetic disorders that present as variable progressive motor weakness and sensory deficits. Charcot-Marie-Tooth (CMT) disease is one of the more common HMSNs and is usually transmitted via an autosomal dominant inheritance pattern. In CMT, increased myelination causes hypertrophy of the peripheral nerves with a classic “onion bulb” appearance, described originally as a histopathologic finding but also seen on MRI. Associated muscle atrophy and scoliosis can be present. Enhancement is not usually a common finding. There is currently no treatment for CMT.^8,9

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Figure 5:

Asymptomatic 13 year-old male with known diagnosis of Charcot-Marie-Tooth. Sagittal T1-weighted (5A) and T2-weighted (5B) images demonstrate enlargement of the L2, L3 and L4 nerve roots (arrowheads). The L5 nerve root is normal(arrows).

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Figure 6:

26 year-old female with sensory deficit. An axial T2-weighted image (6A) shows symmetric enlargement of the L5 nerve roots (asterisks). A sagittal T2-weighted image (6B) shows the characteristic “onion bulb” pattern of nerve root enlargement seen in CMT (arrowheads).

Benign neoplasm

Schwannoma is a common benign neoplasm of the peripheral nerve which can present with pain or parasthesias. On MRI imaging, schwannomas are well-circumscribed masses that are hyperintense on T2-weighted images and hypointense on T1-weighted images. They may have a rim of peripheral fat or T2 hyperintensity and are not associated with significant edema. Schwannomas can mimic perineural cysts but are generally more heterogeneous on T2-weighted imaging and enhance after the administration of gadolinium. Schwannomas can be intradural, extradural, or peripheral.¹⁰

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Figure 7:

56 year-old female with right-sided radiculopathy. Sagittal T1-weighted (7A) and T2-weighted (7B) and post-contrast fat-suppressed T1-weighted (7C) images reveal a well-circumscribed lobulated mass involving the right S1 nerve root (arrows). The mass is slightly hyperintense to CSF on T1 weighted sequences, mildly heterogeneous on T2 weighted sequences, and intensely enhances after the administration of gadolinium.

Malignant neoplasm

The peripheral nerves can be involved by leptomeningeal spread of a primary malignancy, most commonly breast cancer, lung cancer, or melanoma. Leptomeningeal spread of cancer is a late-stage complication that is generally associated with a poor prognosis. Although CSF cytology is needed for definitive diagnosis of leptomeningeal disease, T1-weighted post gadolinium images are abnormal in 70-80% of patients with leptomeningeal disease and are helpful in diagnosis. Enhancement, nodularity, and clumping of peripheral nerve roots are seen on MR imaging.¹¹

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Figure 8:

59 year-old female with a history of lung cancer. An axial post-contrast T1 weighted image (8A) shows symmetric enlargement and enhancement of the L5 nerve roots (arrowheads). A sagittal post-contrast fat-suppressed T1-weighted image (8B) demonstrates nodular fusiform enhancement along the L5 nerve roots (arrowheads) with additional areas of nodular enhancement in the cauda equina (arrows).

Perineural cyst

A perineural cyst is a benign meningeal cyst of the nerve root sheath. Perineural cysts in the sacrum are usually referred to as Tarlov cysts and can uncommonly cause back pain. On MRI, perineural cysts are thin-walled and follow CSF signal intensity on all sequences; the nerve roots are closely associated with the cyst and are preserved. Remodeling of the neural foramen can be seen. Perineural cysts are very common and should not be mistaken for nerve root avulsion or tumors.¹²,¹³

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Figure 9:

76 year-old female with back pain. Sequential axial T2-weighted images (9a and 9b) show a perineural (Tarlov) cyst involving the right S1 nerve root (arrowheads). The nerve is intact and seen at the periphery of the cyst (arrows).

Conclusion

In addition to degenerative disease, a variety of processes can involve the nerves in the spine, including trauma, inflammation/demyelination, congenital disease, benign or malignant neoplasm, and non-pathologic cysts. Proper identification of these different entities on MRI examinations has significant clinical implications for treatment and prognosis.

References