Winnie Chu

Defend Wang

This topic was chosen because our group has a long history of research interest in the etiopathogenesis of adolescent idiopathic scoliosis (AIS). In our previous work, which evaluated the morphologic aspect of the spinal cord in AIS using MRI, we found that patients with AIS had increased total vertebral column length, predominantly affecting the thoracic segment, without corresponding lengthening of the spinal cord; hence, there is a reduced cord-vertebral length ratio in AIS, associated with distortion of cross-sectional shape of the cord at the level of scoliotic apex and resulting low-lying cerebellar tonsils. The above observations support the hypothesis of asynchronous or uncoupled neuro-osseous growth, first proposed by Roth and rediscovered by Porter. It is hypothesized that when spurts of elongation of the spine are too rapid for the slower growth rate of the spinal cord and nerve roots, an abnormal rotator anatomy is observed at the apex in scoliosis. As a result, lordosis and adaptive scoliotic curvature develop in the otherwise normally growing spine. According to the above theory, the spinal cord might fail to stretch in response to vertebral growth, and there will be damage to the white matter tract at the molecular level. Findings of our current study provide further support to the above theory. By using advanced diffusion tensor imaging, we have demonstrated significantly decreased fractional anisotropy (FA) values and increased mean diffusivity (MD) values at the medulla oblongata and upper cervical segment (C1–C5) of the spinal cord in patients with AIS when compared with healthy controls.

This renewed finding indicates possible microstructural change in the neural pathway of AIS, which also accounts for the clinical observation of abnormal somatosensory-evoked potential (SEP) commonly reported in AIS. This new observation opens a new direction for research on etiopathogenesis of AIS. Recently, our group has also found that the cord-vertebral length ratio is a significant independent predictor for curve progression in AIS in a 2-year longitudinal study (The Spine Journal, in press). In clinical practice, when resources are available, we strongly recommend including DTI as part of the spinal cord MR imaging protocol of patients with AIS. We postulate that the degree of changes in FA at the medulla oblongata and cervical spine might provide quantitative data for assessment of microstructural change of the neural pathway in AIS, which may add prognostic value to curve progression, though the above proposed relationship requires further validation.

Our group has presented our new findings in this area during the 10^th Biennial Meeting of the International Research Society for Spinal Deformities (IRSSD), held from June 30 – July 3, 2014, in Sapporo, Japan, and the 14^th Asian Oceanic Society of Paediatric Radiology (AOSPR) and ANZPR Congress held September 7–10, 2014, in Vue Grand, Australia. We are also going to present our findings at the Annual Meeting of the Pediatric Orthopaedic Society of North America (POSNA) on April 29 – May 2, 2015, in Atlanta.

We have received positive feedback and interest on this topic. Audiences have made further enquiries about any difference in FA/MD within the hemicord, respectively on the convex and concave side of the scoliosis curve, which is a question of interest, as the degree of stretching of the spinal cord might be different between the convex and concave side of the scoliotic curve, hence there might be asymmetry in the extent of microstructural change at different halves of the cord.

Our group is currently expanding the spinal cord research in AIS. We are going to continue our pilot work by increasing the size of the cohort and employing the emerging diffusional kurtosis imaging (DKI) technique, which is capable of inferring tissue microstructures by measuring the diffusion of water molecules. DKI has been demonstrated to be of higher sensitivity than DTI in detecting alteration of tissues. It is appealing to employ the advanced DKI technique to analyze the central nervous system to identify detailed neuroanatomic changes in AIS. To supplement the limitation of the current pilot study, we are going to conduct SEP in all subjects who have DKI assessment, so that SEP abnormalities can be further quantified and correlated with the FA/MD values. The above measure will enhance our understanding about the relationships between anatomic and electrophysiologic derangement within the cord in AIS with different curve severity and resulting cord tethering.

 

Read this article at AJNR.org …