Retrospective Study
Copyright ©The Author(s) 2021. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Radiol. Jan 28, 2021; 13(1): 29-39
Published online Jan 28, 2021. doi: 10.4329/wjr.v13.i1.29
Magnetic resonance imaging findings of redundant nerve roots of the cauda equina
Erkan Gökçe, Murat Beyhan
Erkan Gökçe, Murat Beyhan, Department of Radiology, Tokat Gaziosmanpasa University, Faculty of Medicine, Tokat 60100, Turkey
Author contributions: Gökçe E designed and supervised the study; Beyhan M collected the data; Gökçe E and Beyhan M participated in literature research and manuscript preparation, and read and approved the final version.
Institutional review board statement: This study was reviewed and approved by the Ethics Committee of the Tokat Gaziosmanpasa University Faculty of Medicine (No. 19- KAEK-099).
Informed consent statement: Patients were not required to give informed consent for the study as the figures from the picture archiving and communication system were studied retrospectively.
Conflict-of-interest statement: All authors declare no conflicts-of-interest related to this article.
Data sharing statement: No additional data are available.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Corresponding author: Erkan Gökçe, MD, Chief Doctor, Department of Radiology, Tokat Gaziosmanpasa University, Faculty of Medicine, Kaleardı Mah., Muhittin Fisunoglu Cad., Tokat 60100, Turkey. drerkangokce@gmail.com
Received: July 24, 2020
Peer-review started: July 24, 2020
First decision: November 14, 2020
Revised: November 26, 2020
Accepted: December 4, 2020
Article in press: December 4, 2020
Published online: January 28, 2021
Processing time: 186 Days and 22.7 Hours
Abstract
BACKGROUND

Redundant nerve roots (RNRs) of the cauda equina are often a natural evolutionary part of lumbar spinal canal stenosis secondary to degenerative processes characterized by elongated, enlarged, and tortuous nerve roots in the superior and/or inferior of the stenotic segment. Although magnetic resonance imaging (MRI) findings have been defined more frequently in recent years, this condition has been relatively under-recognized in radiological practice. In this study, lumbar MRI findings of RNRs of the cauda equina were evaluated in spinal stenosis patients.

AIM

To evaluate RNRs of the cauda equina in spinal stenosis patients.

METHODS

One-hundred and thirty-one patients who underwent lumbar MRI and were found to have spinal stenosis between March 2010 and February 2019 were included in the study. On axial T2-weighted images (T2WI), the cross-sectional area (CSA) of the dural sac was measured at L2-3, L3-4, L4-5, and L5-S1 levels in the axial plane. CSA levels below 100 mm2 were considered stenosis. Elongation, expansion, and tortuosity in cauda equina fibers in the superior and/or inferior of the stenotic segment were evaluated as RNRs. The patients were divided into two groups: Those with RNRs and those without RNRs. The CSA cut-off value resulting in RNRs of cauda equina was calculated. Relative length (RL) of RNRs was calculated by dividing the length of RNRs at mid-sagittal T2WI by the height of the vertebral body superior to the stenosis level. The associations of CSA leading to RNRs with RL, disc herniation type, and spondylolisthesis were evaluated.

RESULTS

Fifty-five patients (42%) with spinal stenosis had RNRs of the cauda equina. The average CSA was 40.99 ± 12.76 mm2 in patients with RNRs of the cauda equina and 66.83 ± 19.32 mm2 in patients without RNRs. A significant difference was found between the two groups for CSA values (P < 0.001). Using a cut-off value of 55.22 mm2 for RNRs of the cauda equina, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) values of 96.4%, 96.1%, 89.4%, and 98.7% were obtained, respectively. RL was 3.39 ± 1.31 (range: 0.93-6.01). When the extension of RNRs into the superior and/or inferior of the spinal canal stenosis level was evaluated, it was superior in 54.5%, both superior and inferior in 32.8%, and inferior in 12.7%. At stenosis levels leading to RNRs of the cauda equina, 29 disc herniations with soft margins and 26 with sharp margins were detected. Disc herniation type and spondylolisthesis had no significant relationship with RL or CSA of the dural sac with stenotic levels (P > 0.05). As the CSA of the dural sac decreased, the incidence of RNRs observed at the superior of the stenosis level increased (P < 0.001).

CONCLUSION

RNRs of the cauda equina are frequently observed in patients with spinal stenosis. When the CSA of the dural sac is < 55 mm2, lumbar MRIs should be carefully examined for this condition.

Keywords: Cauda equina; Dural sac; Lumbar spine; Magnetic resonance imaging; Redundant nerve roots; Spinal stenosis

Core Tip: In this study, magnetic resonance imaging findings of redundant nerve roots (RNRs) of the cauda equina were evaluated in patients with lumbar stenosis. The stenotic segment cross-sectional area (CSA) cut-off value that could lead to RNRs of the cauda equina was detected as 55.22 mm2. In patients with RNRs of the cauda equina, the average CSA was significantly lower than in patients who did not have RNRs. Disc herniation type and spondylolisthesis were not significantly associated with the relative length or CSA of the dural sac. It was found that the incidence of RNRs observed at the superior of the stenosis level increased as the CSA decreased.