Imaging description

The approach to non-traumatic, non-hemorrhagic causes of mediastinal widening on emergency radiographs can be divided into broad diagnostic categories. Imaging findings will vary depending on the cause, but CT will invariably be diagnostic.

Mediastinal widening is perhaps the best known radiographic sign of blunt thoracic aortic injury (BTAI). However, the definition of a widened mediastinum varies. Quantitatively, it refers to a mediastinal width of 8 cm at the level of the aortic arch on a supine (or erect) chest anterior-posterior radiograph [1]. Due to variation in patient size, mediastinum to chest-width ratios of (>0.25 [and >0.38]) have been suggested as more accurate measures, but these have not been found to be consistently sensitive [2]. Supine radiography has a poor specificity for aortic injury [2]. Although it offers greater specificity, an erect chest radiograph often cannot be obtained in unstable trauma patients and in the setting of a potential spine injury. No single radiographic sign has adequate specificity or sensitivity for the diagnosis or exclusion of aortic injury in patients with a BTAI. The specificity and sensitivity of radiographic evaluation is increased by considering a combination of other suggested signs. These include an abnormal aortic knob contour, shift of the tracheal wall to the right of the T4 transverse process, rightward deviation of the nasogastric tube, an apical pleural cap, widened paraspinal lines, or depression of the left main bronchus [2]. For a detailed discussion of the signs of aortic injury see Case 41.