Reevaluation of plain radiographic findings in the diagnosis of aortic rupture: the role of inspiration and positioning on mediastinal width.

Despite the advent of newer imaging modalities, conventional radiography and clinical examination remain the primary screening method in evaluation of the mediastinum following blunt thoracic trauma. Mediastinal width (MW) is generally considered an important finding in assessing for aortic rupture. The degree of inspiration and patient positioning clearly affects MW, but is largely ignored in the literature. This study investigates the mediastinal widths of normal volunteers with differing degrees of inspiration and positioning, and compares them to radiographs of patients with known aortic ruptures. Mediastinal widths were obtained from chest radiographs of 16 patients with known aortic rupture, and from 50 volunteers using AP-inspiratory-supine, AP-expiratory-supine, and PA-inspiratory-upright technique. Upper 95% confidence limits were obtained for normals. A statistically significant difference in MW of normals was found between inspiratory-supine, expiratory-supine, and upright-inspiratory techniques. Compared to the same degree of inspiration in normals, 12 of 16 patients with aortic rupture had a MW above the upper 95% confidence limits. It is concluded that mediastinal width in normals is significantly affected by the degree of inspiration and positioning. When comparing mediastinal widths for normals and ruptures, there was a significant difference in MW for most degrees of inspiration. As depth of inspiration increased, differences between MW in controls and rupture patients increased. We conclude that patient positioning and degree of inspiration are important factors in assessing the mediastinum, and every effort should thus be made to obtain an upright-inspiratory film if clinically feasible prior to declaring a mediastinum as abnormal.