While diffusion imaging of the brain parenchyma has been in widespread clinical use for nearly 20 years, use of diffusion tensor imaging of the spinal cord has been less enthusiastically embraced by the neuroradiology community. However, this technique can add valuable quantitative information to more standard imaging sequences in a variety of conditions affecting the spinal cord, particularly the cervical spinal cord, including demyelinating diseases, inflammatory myelopathies, spondylotic myelopathies, and scoliosis.

In the first paper featured in this AJNR Digest, Hesseltine, Law, and colleagues utilized DTI in a series of patients with relapsing-remitting multiple sclerosis, to assess regions of the cervical spinal cord that appeared unaffected on conventional imaging sequences. Numerous DTI metrics in their subjects were significantly different from controls, with high sensitivity and specificity, suggesting that DTI could be used to detect otherwise occult disease and provide a quantitative measure of both disease progression and response to treatment.

In the developing spine, DTI has been shown to be useful in the assessment of adolescent idiopathic scoliosis. In the cohort studied by Kong, Chu, Wang, and colleagues, changes in white matter integrity were present in the upper and mid portions of the cervical spine, as well as the medulla oblongata. They hypothesized that significant changes in fractional anisotropy (FA) and mean diffusivity (MD), and an increased incidence of cerebellar tonsillar ectopia, reflect neurophysiologic changes related to subclinical spinal cord tethering from asynchronous osseous and neural growth in this patient population. DTI could well serve as a quantitative method for pre- and posttreatment evaluation, and even for determining treatment options themselves.

Technically, performing DTI of the spinal cord can be challenging. Hodel and colleagues are among those who have applied multiple artifact-reducing strategies simultaneously to reduce distortion and susceptibility effect. The reduced field of view technique combined with pulse-triggering and coronal plane acquisition allowed for tractography-based, rather than the more commonly utilized region-of-interest–based, quantitative analysis in their cohort of patients with demyelinating or inflammatory myelopathies. The higher intra- and interobserver agreement with tractography-based methods may allow for more accurate assessment of changes within the spinal cord prior to and following treatment.

Quantitative evaluation of the exceedingly common cervical spondylotic myelopathy is anticipated to have widespread implications for the management of these patients. Jones, Law, and colleagues have shown how FA correlates with clinical disease severity and may predict surgical outcome. They postulate that quantitative DTI changes in symptomatic patients may precede T2 signal abnormality changes, which may provide the surgeon with a noninvasive, accurate method of determining optimal timing for intervention, prior to irreversible injury.

Although a slight divergence from our topic, a recent publication applying diffusion imaging to the peripheral nervous system warranted inclusion in this edition of the Digest. Yuh, Chin, and colleagues found that adding diffusion-weighted imaging to their MR neurography protocol resulted in additional significant information in the evaluation of peripheral mononeuropathies and plexopathies when mass-like or infiltrative lesions were present. Mean apparent diffusion coefficient values aided in discriminating radiation changes or benign neoplasms from malignant neoplasms. While many neuroradiologists are accustomed to limiting their scope of practice to brain, spine, and head and neck, we are increasingly being called upon to evaluate the brachial and lumbosacral plexi and peripheral nerves as treatment options for peripheral nervous system lesions expand. The inclusion of DWI in your MR neurography examination can increase your diagnostic accuracy.

Quantitative DTI-based metrics add valuable information for a wide variety of conditions affecting the cervical spinal cord, and are anticipated to have significant impacts on treatment. DWI of peripheral nerve lesions improves diagnostic accuracy. If you offer it, they will come—your referring physicians will be grateful and your patients will benefit.

 

Image modified from: Kong Y, Shi L, Hui SCN, et al. Variation in anisotropy and diffusivity along the medulla oblongata and the whole spinal cord in adolescent idiopathic scoliosis: a pilot study using diffusion tensor imaging.