Original contribution
Diffusion tensor imaging of lumbar spinal nerve in subjects with degenerative lumbar disorders,☆☆

https://doi.org/10.1016/j.mri.2015.05.002Get rights and content

Abstract

Recently several authors have reported that diffusion tensor imaging (DTI) might provide a new understanding of sciatica. The purpose of this study was to investigate the clinical feasibility of DTI for the evaluation of lumbar spinal nerve of patients with sciatica associated with lumbar degenerative disorders. Thirty-four patients (25men, mean age63. 3 years) with degenerated lumbar disease, 14 patients with lumbar spinal stenosis with foraminal stenosis, 12 with lumbar spinal stenosis without foraminal stenosis, five with lumbar disc herniation, two with discogenic low back pain, and one with spondylolysis who underwent 3.0 T magnetic resonance (MR) imaging and surgical treatment were included in the present study. Fractional anisotropy (FA) was calculated from an FA map, and tractography was investigated. In asymptomatic nerves, tractography showed all L3–S1 spinal nerve roots clearly. Abnormalities of tractography were classified into three types by shape; “Disrupted”, “Narrowing”, and “Tapering”. More abnormalities of tractography were found in patients with lumbar spinal stenosis, and especially in patients with foraminal stenosis. The disrupted type was the most common. The mean FA of entrapped symptomatic nerves was less than seen on the intact side. This study demonstrates that tractography shows abnormal findings for nerve roots in lumbar spinal degeneration and that FA decreases in symptomatic roots. DTI may offer not only morphological evaluation, but also quantitative evaluation. We believe that DTI can be used as a tool for the diagnosis of lumbar spinal degenerative disease.

Introduction

Imaging plays an important role in the diagnosis of degenerative lumbar diseases with sciatica and radicular symptoms affecting leg pain. However, discrepancies between clinical symptoms and imaging are often found. Although conventional imaging modalities for the lumbar spinal degenerative disease, such as radiography, computed tomography (CT), myelography and magnetic resonance (MR) imaging, have a good potential for morphological evaluation, these conventional imaging techniques do not provide any effective means for quantitative evaluation of nerve damage.

Diffusion-weighted imaging (DWI) can provide valuable information regarding the microstructure of tissues by applying a motion probing gradient (MPG) in some directions to monitor the random movement of water molecules, which is restricted in tissues [1], [2], [3], [4]. DWI has been widely used in the clinic to evaluate the central nervous system for the diagnosis of diseases such as acute brain stroke [5]. If there is no directional variation rate in tissues, diffusion is said to be isotropic. By contrast, water molecules tend to move along the nerve fibers in neural tissue, and this is called anisotropic diffusion. The diffusion data can be used to determine quantitative diffusion values such as the apparent diffusion coefficient (ADC) and a scalar fractional anisotropy (FA) value that reflects the directionality of molecular diffusion.

Diffusion tensor tractography (DTT) uses diffusion tensor imaging (DTI) to visualize highly anisotropic nerve fiber tracts [15]. Several studies have shown that DTI is useful for the evaluation and visualization of peripheral nerves [6] and the measurement of axon regeneration in rat [7] and mouse [8] sciatic nerves, demonstrating that a decrease in mean FA is observed in injured nerves with demyelination [6], [7], [8], [9]. Recently, several authors reported that DTI could visualize lumbar spinal nerves [10], [11], [12], [13], [14]. To our knowledge, this is the first study to evaluate DTI and FA values of lumbar spinal nerve of consecutive patients with lumbar degenerative disorders including lumbar spinal canal stenosis. The purpose of this study was to investigate the clinical feasibility of DTI for the evaluation of lumbar spinal nerve of patients with sciatica associated with lumbar degenerative disorders.

Section snippets

Subjects

Our study received prior approval from our institutional review board and ethics committee. Thirty-four consecutive patients (25 men; mean age, 63.3 years) with the degenerated lumbar disease who underwent 3.0 T MR imaging and surgical treatment were included. Patients with a previous history of spinal trauma, surgery, neurological disease, or contraindication to MR imaging were excluded. Fourteen patients with lumbar spinal stenosis (LSS) with foraminal stenosis (FS), 12 with LSS without FS,

Tractography of healthy subjects

In healthy volunteers, the tractography clearly showed all L3–S1 spinal nerves.

L3–S1 spinal nerves coursed symmetrically and obliquely downward, and merged with T2-WI; it could be clearly observed that spinal nerves from intra-spinal canal to extra-foraminal zone were successive (Fig. 2).

Classification of the tractography

By contrast with the normal spinal nerves, there are some abnormalities of tractography in patients with asymptomatic spinal nerves. Abnormalities of tractographies were classified into three types by the

Discussion

Developmental narrowing of the lumbar vertebral canal causes radicular syndrome [16], which is usually related to the level of the responsible lesion. However, in some patients the level of stenosis on the image does not correlate with the neurological findings, and the origin of radiculopathy remains complicated and controversial. Furthermore, lumbar foraminal stenosis often unfortunately results in failed back surgery syndrome because of the difficulty in making a correct diagnosis [17], [18]

Conclusion

This study demonstrates that tractography shows abnormal findings for spinal nerves in lumbar spinal degeneration and so DTI may offer not only morphological evaluation, but also quantitative evaluation. We believe that DTI is a potential tool for the diagnosis of lumbar spinal degenerative disorders.

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    All subjects were studied after informed consent, and the study had prior approval of the Chiba University Ethics Committee.

    ☆☆

    This study was supported by a medical research grant on traffic accident from The General Insurance Association of Japan. We did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

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