Relative shortening and functional tethering of spinal cord in adolescent idiopathic scoliosis? Study with multiplanar reformat magnetic resonance imaging and somatosensory evoked potential

Study Design. MR imaging and multiplanar reconstruction were used to evaluate relative length of the spinal cord to the vertebral column in adolescent idiopathic scoliosis (AIS). Objectives. Ratio of spinal cord length to vertebral column length and position of the cerebellar tonsils were evaluated and correlated with somatosensory cortical evoked potentials (SSEP). Summary of Background Data. Tonsillar herniation, abnormal anthropometric growth, relative spinal overgrowth, and abnormal somatosensory function have been reported in AIS. All these observations suggest a possible neural origin of the etiopathogenesis of AIS, which can be linked to a disproportional growth between spinal column and cord. Methods. Two-dimensional sagittal MRI of the spine was performed in 28 AIS patients (14 mild curve; 14 severe curve) and 14 age-matched controls. Measurements of spinal cord, vertebral column length, and tonsillar position were made on reformat images and correlated with SSEP studies. Results. No significant differences in the absolute spinal cord length were found. However, there was significant relative segmental lengthening of the spinal column at the thoracic level in AIS patients with severe curve; hence, ratios of cord to vertebral column length were significantly reduced (P < 0.01). There was high interobserver reliability (0.9); 28% (8 of 28) scoliosis patients had low-lying cerebellar tonsils and abnormal SSEP, respectively. Conclusion. There was significantly reduced spinal cord to vertebral column ratios in the AIS patients with severe curve, suggesting a disproportional growth between the skeletal and the neural systems. The relative shortening and functional tethering of spinal cord may play an important role in the etiopathogenesis of AIS.