A radiographic sign of left sided mediastinal lymph node enlargement

This report draws attention to an apparent clear space, which is normally present on routine chest posterior-anterior roentgenograms, composed of the descending aorta, pulmonary outflow tract and left upper lobe vessels which form its medial, inferior and lateral boundaries respectively. The medial margin of this space has a concave outer border. Lymph nodes of the ligamentum group lie in close proximity to this space. In the absence of other processes involving structures of the middle mediastinum, encroachment of this space from the medial direction, with formation of a convex outer border is a reliable and frequently the first radiographic sign of left-sided mediastinal lymph node enlargement.