Diffusion tensor imaging and tractography of the sciatic nerve: assessment of fractional anisotropy and apparent diffusion coefficient values relative to the piriformis muscle, a preliminary study.

Abstract

Piriformis muscle syndrome (PMS) is underdiagnosed. To evaluate the potential of diffusion tensor imaging and diffusion tensor tractography as innovative tools for the diagnosis of PMS by functional assessment of the sciatic nerve, the aims of this study are to assess the reproducibility and to evaluate the changes in the parameters at levels proximal and distal to the piriformis. Fractional anisotropy (FA) and the apparent diffusion coefficient (ADC) of the sciatic nerve at three levels were quantified twice each by two examiners using the fiber-tracking method. In the first part of the study, laterality and reproducibility were evaluated using intraclass correlation coefficients (ICC) in ten healthy volunteers. In the second part of the study, the healthy side and symptomatic side were assessed in ten consecutive patients with sciatica. There were three patients with no findings on lumbar magnetic resonance imaging (MRI). There was no laterality in either FA or ADC values in asymptomatic patients at any level. The mean intra-rater ICC was 0.90 and the mean inter-rater ICC was 0.87. FA was significantly lower and ADC significantly higher on the symptomatic side at each level in patients with sciatica. In the three sciatica patients with no findings on lumbar MRI, FA was significantly lower and ADC was significantly higher only at levels distal to the piriformis. These patients experienced full pain relief after ultrasound-guided injection of local anesthesia. Diffusion tensor imaging and diffusion tensor tractography might be innovative tools for the diagnosis of PMS.