The position of the aorta relative to the spine: A comparison of patients with and without idiopathic scoliosis

Background: There is little information documenting the relationship of the aorta to the thoracic scoliotic spine. Recent studies have suggested that the ends of screws placed during an anterior spinal arthrodesis, and pedicle screws used for the treatment of right thoracic scoliosis, may be in proximity to the aorta. The purpose of this study was to analyze the anatomical relationship between the aorta and the spine in a comparison of patients with idiopathic right thoracic scoliosis and patients with a normal spine. Methods: Thirty-six patients with adolescent idiopathic scoliosis with a right thoracic curve and forty-three with a normal straight spine were studied. Radiographs were analyzed to determine the Cobb angle, the apex of the curve, and the apical vertebral rotation for the patients with scoliosis. Axial magnetic resonance images from the fourth thoracic vertebra to the third lumbar vertebra at the midvertebral body level were used to measure the distance from the aorta to the closest point of the vertebral body cortex, the distance from the posterior edge of the aorta to the spinal canal, and the aorta-vertebral angle. Results: No differences were found between the groups with respect to age or sex distribution. For the scoliosis and normal groups, boys had greater average vertebral body width and depth for all levels than did girls (p < 0.05). For the scoliosis group, the most common apical vertebra was the eighth thoracic vertebra, the average coronal curve measurement was 55.2°, and the average apical rotation was 17.3°. The average distance from the aortic wall to the vertebral body cortex at the apex of the curve was greater in the patients with scoliosis (4.0 mm) than at similar levels in the normal group (2.5 mm) (p < 0.05). The distance from the posterior aspect of the aorta to the anterior aspect of the spinal canal was less in the scoliosis group (11.1 mm) than in the normal group (19.2 mm) for the fifth to the twelfth thoracic level (p < 0.05). The aorta was positioned more laterally and posteriorly adjacent to the vertebral body at the fifth to the twelfth thoracic level in patients with scoliosis compared with that in normal patients as reflected in a smaller aorta-vertebral angle (p < 0.05). With an increasing coronal Cobb angle in the thoracic curve and apical vertebral rotation, the aorta was positioned more laterally and posteriorly (p < 0.05). Conclusion: In patients with right thoracic idiopathic scoliosis, the aorta is positioned more laterally and posteriorly relative to the vertebral body compared with that in patients without spinal deformity. Clinical Relevance: The altered position of the aorta and its proximity to the vertebral cortex pose challenges for safe placement of anterior screws or left posterior pedicle screws in patients with right thoracic idiopathic scoliosis. Surgeons should be wary of the position of the aorta when placing these screws. Preoperative magnetic resonance imaging may be helpful in planning surgery.