A diagnostic approach to mediastinal abnormalities.

A number of mediastinal reflections are visible at conventional radiography that represent points of contact between the mediastinum and adjacent lung. The presence or distortion of these reflections is the key to the detection and interpretation of mediastinal abnormalities. Anterior mediastinal masses can be identified when the hilum overlay sign is present and the posterior mediastinal lines are preserved. Widening of the right paratracheal stripe and convexity relative to the aortopulmonary window reflection indicate a middle mediastinal abnormality. Disruption of the azygoesophageal recess can result from disease in either the middle or posterior mediastinum. Paravertebral masses disrupt the paraspinal lines, and the location of masses above the level of the clavicles can be inferred by their lateral margins, which are sharp in posterior masses but not in anterior masses. The divisions of the mediastinum are not absolute; however, referring to the local anatomy of the mediastinal reflections in an attempt to more accurately localize an abnormality may help narrow the differential diagnosis. Identification of the involved mediastinal compartment helps determine which imaging modality might be appropriate for further study. (c) RSNA, 2007.