Vascular causes of vertebral asymmetry and the laterality of scoliosis.

The aetiology of idiopathic scoliosis is multifactorial and complex, but the direction (laterality) of the curvature may depend on normal growth factors. It is postulated that vascular asymmetries are responsible for the left laterality of infantile thoracic scoliosis and the right laterality of adolescent thoracic scoliosis. Two hypotheses are presented. The left laterality of thoracic scoliosis in infancy may be due to the streaming of blood from the aortic arch to the right and streaming of blood from the ductus arteriosus to the left so that right vertebral arches receive better oxygenated blood, develop faster and grow larger. It is also suggested that, at a later stage, spontaneous resolution of infantile scoliosis and the right laterality of adolescent thoracic curvatures are due to the rotational force that is exerted on growing thoracic vertebrae by the asymmetrically situated descending thoracic aorta. It is emphasized that the normal growth factors that tend to a slight left thoracic scoliosis in infancy, and to a right thoracic scoliosis in adolescence, by themselves produce only a minimal scoliosis, and that progressive scoliosis involves additional unknown factors.