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
ARTICLE HIGHLIGHTS
Research background

Redundant nerve roots (RNRs) of the cauda equina are often defined as the development of elongated, enlarged, and tortuous nerve roots at the superior and/or inferior of the lumbar canal stenosis and as secondary to it due to degenerative processes. Clinically, they can lead to lower back and leg pain, paresthesia, and neurogenic claudication in patients.

Research motivation

The radiological diagnosis of RNRs of the cauda equina was previously made with conventional myelography, while magnetic resonance imaging (MRI) findings have been more commonly defined in recent years. Nevertheless, this condition has been relatively under-recognized in radiological practice. Therefore, there is a need to keep this issue on the agenda by discussing it in light of the literature.

Research objectives

In this study, lumbar MRI findings of RNRs of the cauda equina were evaluated in spinal stenosis patients. Cross-sectional area (CSA) of the dural sac at the stenosis level that could lead to RNRs of the cauda equina and how the cauda equina nerve roots are affected by this stenosis (redundant segment length and extensions, etc.) were investigated.

Research methods

On lumbar MRI of patients with stenosis, dural sac CSA levels of less than 100 mm2 at the intervertebral disc space were considered stenosis, and levels leading to lumbar stenosis were determined. Statistical differences between the CSA levels that led to RNRs of the cauda equina and those that did not lead to RNRs were investigated. Relative length (RL) was calculated by dividing the length of RNRs on sagittal T2-weighted images by the vertebrae corpus height adjacent to the stenotic segment superior. The relationships of herniation type into the dural sac (soft or sharp margins) and spondylolisthesis with CSA and RL were investigated.

Research results

RNRs of the cauda equina were observed in 42% of patients with spinal stenosis. Mean 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 (P < 0.001). Using a cut-off value of 55.22 mm2 for CSA leading to RNRs of the cauda equina, the sensitivity was 96.4%, specificity 96.1%, positive predictive value (PPV) 89.4%, and negative predictive value (NPV) 98.7%. RL varied from 0.93 to 6.01 (mean: 3.39 ± 1.31). Of all RNRs, 54.5% were at the superior of stenosis level, 32.8% at both superior and inferior of stenosis level, and 7% at inferior of stenosis. Soft margin disc type was observed in 29 and sharp margin type was found in 26 of the disc herniations at the stenosis levels that led to RNRs of the cauda equina. Disc herniation type and spondylolisthesis were not significantly associated with RL or CSA of the dural sac with stenotic levels (P > 0.05). As the CSA of the dural sac decreased, the frequency of RNRs at the superior of the stenosis level increased (P < 0.001).

Research conclusions

RNRs of the cauda equina are not uncommon in patients with lumbar spinal canal stenosis. Although RNRs of the cauda equina are frequently observed at the superior of stenosis level, a considerable percentage of them can also be found at both superior and inferior, and at a lower rate at the inferior localization. The possibility of RNRs of the cauda equina is high in patients with dural sac CSA of 55 mm2 or less.

Research perspectives

Although clinical and treatment outcomes are controversial, lumbar stenosis patients with marked reductions in CSA of the dural sac on MRI should be carefully evaluated for RNRs of the cauda equina. In these patients, tortuosity, elongation, and extension findings indicating redundancy in nerve roots should be reported as this could contribute to efficient treatment of the patients.