Application of neurite orientation dispersion and density imaging or diffusion tensor imaging to quantify the severity of cervical spondylotic myelopathy and to assess postoperative neurologic recovery

Abstract

Background ContextSurgical outcome and the severity of cervical spondylotic myelopathy (CSM) are unpredictable and cannot be estimated by conventional anatomical magnetic resonance imaging (MRI). The utility of diffusion tensor imaging (DTI) to quantify the severity of CSM and to assess postoperative neurologic recovery has been investigated. However, whether conventional DTI should be applied in a clinical setting remains controversial. Neurite orientation dispersion and density imaging (NODDI) is a recently introduced model-based diffusion-weighted MRI technique that quantifies specific microstructural features related directly to neuronal morphology. However, there are as yet few clinical applications of NODDI reported. Indeed, there are no reports to indicate NODDI is useful for diagnosing CSM. Study DesignThis is a retrospective cohort study using consecutive patients. PurposeThe objective of this study was to evaluate the utility of NODDI and conventional DTI for detecting changes in the spinal cord microstructure. In particular, this study aimed to quantify the preoperative severity of CSM and to assess postoperative neurologic recovery from this myelopathy. Patient SampleWe included 27 consecutive patients with a nontraumatic cervical lesion from CSM who underwent laminoplasty at a single institution between April 2012 and April 2015. The patients underwent MRI before and approximately 2 weeks after surgery. Outcome MeasuresIn addition to conventional DTI metrics, we evaluated the intracellular volume fraction (ICVF) and the orientation dispersion index (ODI), which are metrics derived from NODDI. The 10-second grip and release test and the Japanese Orthopaedic Association scoring system were used before and 1 year after surgery to assess neurologic outcome. Materials and MethodsNeurite orientation dispersion and density imaging and conventional DTI values were measured at the C2–C3 intervertebral level (control value) and at the most compressed levels (C3–C7 intervertebral levels) were measured. The changes in these values pre- and postoperative were demonstrated. Correlations between NODDI and conventional DTI values and clinical outcome were determined. ResultsPreoperative fractional anisotropy was significantly correlated with the severity of neural damage, but not with postoperative neurologic recovery. No significant correlation could be found between the preoperative ICVF, the ODI, the apparent diffusion coefficient, and the severity of the preoperative neurologic dysfunction. Preoperative ICVF was most strongly correlated with the severity of neurologic dysfunction and postoperative neurologic recovery. ConclusionsConventional DTI may be applied clinically to assess the severity of myelopathy. Neurite orientation dispersion and density imaging may be more valuable than conventional DTI to predict outcome following surgery in patients with CSM.