The position of the aorta relative to the spine in patients with left thoracic scoliosis: A comparison with normal patients

STUDY DESIGN. Analysis axial magnetic resonance images (MRIs) identifying the position of the aorta in left thoracic scoliosis and normal patients. OBJECTIVES. To determine the position of the aorta in patients with left thoracic scoliosis and to compare these findings with those seen in normal patients. SUMMARY OF BACKGROUND DATA. Screws placed during an anterior spinal fusion and instrumentation for right thoracic scoliosis are in proximity to the aorta, which is primarily due to the position of the aorta on the posterolateral left aspect of the vertebra. There are no studies that have evaluated the aorta in left thoracic scoliosis. METHODS. A retrospective review of all patients with an MRI with left thoracic scoliosis (Group LTS) was performed and compared with patients with a normal straight spine (Group N). Axial MRI images from T4 to L3 in both groups were analyzed to include the aorta-vertebral angle (AVA), where 0° = aorta directly lateral to the left and 180° = directly lateral to the right. RESULTS. There were 20 patients in Group LTS and 43 patients in Group N. There were no differences in age (13.1 vs. 14.0 years) or gender (52% vs. 62% females) between the LTS and N groups. The aorta was positioned more anterior (larger AVA) to the vertebral body at levels T4 thru T11 (average, 70.1° vs. 40.6°) and L3 (77.1° vs. 70.9°) in Group LTS compared with group N (P < 0.05). With increasing thoracic coronal Cobb angle, the aorta was positioned more laterally to the right (larger AVA) at T8 and T10 (P < 0.05). In the LTS group, curves greater than 40° had a larger AVA (91.4° vs. 57.7°) at apical levels (T7-T10) than for curves ≤40° (P < 0.05). CONCLUSIONS. In left thoracic LTS, the aorta is positioned more anteriorly and to the right (toward the concavity) compared with patients with a straight spine. This position will allow full access to the convexity of the left curve to perform an anterior fusion/release as well as instrumentation and is not in the trajectory of a well-placed anterior screw. This relative safety was not seen at the apex of larger curves (>40°).