Quantitative Evaluation of the Compressed L5 and S1 Nerve Roots in Unilateral Lumbar Disc Herniation by Using Diffusion Tensor Imaging

Abstract

Background and purpose: Nerve root compression by lumbar disc herniation (LDH) induces a series of clinical symptoms, seriously affecting the patient's life and work. The purpose of this study is to investigate microstructural changes and fiber bundle abnormalities of the compressed L5 and S1 nerve roots in young patients with unilateral LDH by using diffusion tensor imaging (DTI).

Methods: Forty young patients with unilateral LDH and 17 healthy volunteers participated in the study, and 33 patients received follow-up DTI examination after one month of conservative treatment. Fractional anisotropy (FA), apparent diffusion coefficient (ADC) and trace weight (TraceW) values of the L5 and S1 nerve roots were measured on FA maps.

Results: The mean FA, ADC and TraceW values of the affected nerve roots were 0.259 ± 0.047, 1.79 ± 0.252 and 0.076 ± 0.025, respectively. Compared to the contralateral side and volunteers, the affected nerve roots showed a decreased FA (P < 0.01), an increased ADC (P < 0.01) and TraceW (P < 0.05). The compression severity had a moderately negative correlation with FA (r = -0.646, P < 0.01) and positive correlation with ADC (r = 0.408, P < 0.01) but not with TraceW (r = 0.298, P = 0.06). For 33 patients with follow-up study after conservative treatment, FA (0.286 ± 0.06) and ADC (1.630 ± 0.046) in the affected nerve roots showed an increasing and a decreasing trend, respectively. Moreover, FA values (14 cases; 0.246 ± 0.015, P = 0.213) in the severe compression group had no significant changes between initial and follow-up data.

Conclusions: DTI is able to assess microstructural abnormalities of the compressed nerve roots and has potentially practical value for prognostic evaluation after treatment in patients with LDH.

Keywords: Apparent diffusion coefficient; Diffusion tensor imaging; Fractional anisotropy; Lumbar disc herniation; Nerve roots.