The Azygos Vein Is at Potential Risk of Injury From Malpositioning of Left Thoracic Pedicle Screw in Thoracic Adolescent Idiopathic Scoliosis Patients

Study Design. A computed tomography study. Objective. To evaluate the changed position of azygos vein in patients with thoracic adolescent idiopathic scoliosis (AIS) and to analyze the potential risk of injury of azygos vein from thoracic pedicle screw placement in these patients. Summary of Background Data. It has been widely recognized that the anatomic positions of structures adjacent to the vertebrae may change in patients with AIS. To date, no study had evaluated such change of azygos vein in patients with AIS. Methods. Twenty-five patients with thoracic AIS and 17 age-matched normal teenagers were included in the present study. Axial computed tomography images from T7 to T10 level were obtained to evaluate azygos vein-vertebral angle (defined as 08 when the azygos vein was located directly laterally to the left and 1808 when directly laterally to the right). The percentage of azygos vein located in the direction of left screw passage was calculated to analyze the potential risk of injury from left pedicle screw placement. Results. The azygos vein-vertebral angles were significantly smaller in patients with AIS when compared with normal teenagers from T7 to T10 level (P< 0.001). The percentage of azygos vein at high risk of injury from left pedicle screw placement was 80% (20/25) at T7 level, 84% (21/25) at T8 level, 76% (19/25) at T9 level, and 72% (18/25) at T10 level in patients with AIS. No azygos vein was found to be at risk of injury from right pedicle screw placement in patients with AIS. The azygos vein was safe from pedicle screw placement on both sides in normal teenagers. Conclusion. The changed relative anatomic position of azygos vein in patients with thoracic AIS places the azygos vein at high potential risk of injury from excessively long left pedicle screw placement. Spine surgeons should choose appropriate screw length to avoid anterior cortex perforation.