MRI Helps Predict Curve Progression in AIS Patients

March 1, 2015 – Magnetic resonance imaging (MRI) measures cord-vertebral length ratio and LCS ratio, which are new significant independent predictors for curve progression in adolescent idiopathic scoliosis (AIS), according to a new study published in The Spine Journal.1

Studies have shown significant associations between curve severity and morphological evidences of relative shorter spinal cord tethering in AIS. In conjunction with increased prevalence of abnormal somatosensory cortical evoked potentials (SSEP) and low-lying cerebellar tonsil in severe AIS, suggest that there might be neural morphological predictors for curve progression. The investigators sought to identify any morphological predictors associated with cord tethering, as measured by magnetic resonance imaging (MRI), for curve progression in AIS patients.

In the study, the clinicians performed MRI scans of hindbrain and whole spine, and areal bone mineral density (BMD) at bilateral femoral necks on 81 female AIS subjects between 10 and 14 years, without surgical intervention during the follow up period.

Side-view MRI showing syrinx (abnormal collection of fluid within the spinal cord) in a  7-year-old boy with a 30o neuromuscular scoliosis. Source: Scoliosis Research Society.

All AIS patients were longitudinally followed up starting from initiation of bracing beyond skeletal maturity in 6-monthly interval. Clinical and radiographic data were recorded at each clinic visit. BMD and MRI measurements including ratio of spinal cord to vertebral column length, ratio of anteroposterior (AP) and transverse (TS) diameter of cord, lateral cord space (LCS) ratio, cerebellar tonsil level, and conus medullaris position were obtained at baseline. Only compliant patients with a minimum 2-year follow-up were analyzed. AIS girls were assigned into three groups according to bracing outcome: (A) Non-Progression (curvature increase ≤5°); (B) Progression (curvature increase ≥6°); (C) Progression with surgery indication (Cobb angle ≥50° after skeletal maturity despite bracing). The predictors for curve progression were evaluated using univariate analysis and multivariate ordinal regression model.

There were 46 girls (57%) in group A, 19 girls (23%) in group B and 16 girls (20%) in group C. No significant intergroup differences were found in spinal cord length, tonsil level and conus position. Group C had significantly longer vertebral column length, smaller cord-vertebral length ratio, and higher AP/TS cord ratio as compared to group A, while LCS ratio in group C was significantly increased when compared with both group A and group B. In regression model, five significant independent predictors including cord-vertebral length ratio, LCS ratio , initial Cobb angle, menarche age, BMD, and a marginally significant predictor namely AP/TS cord ratio.  

The author concluded On baseline MRI measurement, cord-vertebral length ratio and LCS ratio are identified as new significant independent predictors for curve progression in AIS while AP/TS cord ratio is suggested as a potential predictor requiring further validations.

Sources. 1. Deng M, Hui SC, Yu FW, et al. MRI-based Morphological Evidence of Spinal Cord Tethering Predicts Curve Progression in Adolescent Idiopathic Scoliosis. The Spine Journal. 2015 Feb 25. pii: S1529-9430(15)00199-0. doi: 10.1016/j.spinee.2015.02.033. [Epub ahead of print]