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A Valuable Addition to the Lumbar Search Pattern: Examining the L5 Nerve Root When Evaluating Chronic Radiculopathy 2007

General Spine

Nicholas Wickersham, MD
James Taylor, DO, Non ASSR Member
William Keyes, MD, Non ASSR Member
Phil Chapman, MD, Non ASSR Member

Scientific Poster

Exhibit Panels: 1

Purpose

MRI findings commonly encountered in the assessment of patients with back pain, including disc protrusions, nerve root contact by discs, and even nerve root deviation by discs can also be seen in asymptomatic patients. Over 20% of randomly imaged asymptomatic patients show nerve root contact by disc material on MRI, most commonly at L5-S1 (1). A reliable, direct imaging indicator of nerve root injury is important to improve diagnostic accuracy when evaluating the lumbar spine. In a recent study, radiologists at our institution demonstrated an association between radicular pain and L5 nerve root enlargement, fascicular distortion and T2 signal abnormalities, recognized signs of nerve pathology on MR neurography (2). The L5 nerve root is a rapid and useful addition to the neuroradiologist's search pattern, indicating chronic, potentially irreversible, nerve injury in addition to acute nerve injury in the setting of trauma, as well as drawing attention to other pathology that could be easily overlooked. These cases are reviewed and characteristic images are selected to facilitate recognition of this sign and rare mimics.

Methods & Materials

The L5 nerve roots of 43 patients on MRI were reviewed by a neuroradiology fellow and two neuroradiologists. Radiculopathy on the side of the L5 nerve root abnormality was documented by questionnaire, interview, or physician diagnosis. Images were selected from the cases to demonstrate the typical MRI appearance of chronic L5 nerve injury, including enlargement, T2 hyperintensity, and distortion. Selected images of the spine from the same patients were included to show the characteristic appearance of L5 enlargement. Additional images from cases collected during the review process, involving acute enlargement of L5 due to trauma and pathologic enlargement by a ganglioneuroma were included. Since the time of the original series, the sign has been observed in an additional 50 patients.

Results

43 patients showed relative T2 hyperintensity, enlargement, or architectural distortion of a unilateral L5 nerve on conventional T1/T2 weighted axial MRI. The majority (81%) of patients had severe L5-S1 neuroforaminal stenosis with impingement of the L5 nerve, although the impingement was occasionally related to lateral spinal stenosis at the L4-5 level. 38 of 43 (88%) patients had L5 radicular symptoms as their chief complaint or as part of the total pain syndrome. 22 patients had additional follow up images ranging from 1-10 years, with an average of 1.5 years. At follow up all 22 patients continued to exhibit the L5 nerve root sign, regardless of treatment. The majority of these patients continued to have persistent or intermittent L5 radicular pain.

These images demonstrate the characteristic appearance of abnormal and normal L5 nerve roots, readily visible on axial images L5 nerves lying ventral to the sacral ala. There is normal signal intensity on T1 weighted images with variable enhancement following Gadolinium administration. The symptomatic, chronically injured nerve roots are visibly enlarged, with abnormally increased T2 signal. Normal nerve roots should be isointense to adjacent muscle tissue on T2 weighted images. (3) Images from additional patients observed to have enlarged L5 nerve roots shows enlargement due to acute injury stemming from a sacral fracture and pathologic enlargement from a ganglioneuroma.

Image 1: The L5 nerve root sign. The L5 nerve roots are readily visible anterior to the sacral alae. Note the asymmetric enlargement and T2 hyperintensity of the left L5 nerve root in this patient with left sided radiculopathy.

Image 2: Patient with 4 years of left L5 radiculopathy and a positive left L5 nerve root sign, who subsequently underwent foraminotomy.

Image 3: Two years later, MRI in the same patient showed no significant change in appearance of the L5 nerve root and the patient had no significant change in symptoms.

Image 4: Patient with enlargement of the left L5 nerve root, distinguished from the typical L5 nerve root sign by lack of foraminal stenosis and enlargement of the root in the foramen. The lesion was a biopsy proven ganglioneuroma.

Conclusion

Given the frequency of abnormal MRI findings involving the L5-S1 level in both symptomatic and asymptomatic patients, attention to characteristic signs of nerve root injury can improve the accuracy of MRI in correlating imaging findings with patient symptoms. The L5 nerve roots are readily visible and standard T2 sequences are sufficient for visualization, making the L5 nerve root sign a simple and useful addition to routine lumbar imaging evaluation. With increased awareness of and attention to this sign, we believe neuroradiologists can increase sensitivity for detecting symptomatic nerve injury and potentially diagnose patients whose chronic pain may not improve with surgical intervention.

References

There are no financial disclosures to make. All studies were performed through Inland Imaging, PS either at one of its outpatient imaging centers, or through one of its partner hospitals, Holy Family Hospital or Sacred Heart Hospital in Spokane, Washington.

1. D Weishaupt, M Zanetti, J Hodler, and N Boos. MR imaging of the lumbar spine: prevalence of intervertebral disk extrusion and sequestration, nerve root compression, end plate abnormalities, and osteoarthritis of the facet joints in asymptomatic volunteers. Radiology 1998; 209: 661.
2. Filler, AG, MD, PhD, Maravilla, KR, MD, Tsuruda, JS, MD. MR neurography and muscle MR imaging for image diagnosis of disorders affecting the peripheral nerves and musculature. Neurologic Clinics 2004; 22:643-682.
3. Aagaard, BD, Lazar, DA, et al. High-Resolution Magnetic Resonance Imaging Is A Noninvasive Method of Observing Injury and Recovery in the Peripheral Nervous System. Neurosurgery 2003, 53: 199-204.

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