The retrotracheal space.
The retrotracheal space may be abnormal when a frontal chest radiograph is normal. Common abnormalities, seen usually on the lateral view, are widening of the anterior soft tissue stripe separating the tracheal air column from the clear space behind it, and a mass density overlying the space. A barium esophagram generally facilitates the diagnosis.
D011859:Radiography; D014132:Trachea / Q000000981:diagnostic imaging*