The trachea: normal anatomic features, imaging and causes of displacement.

Radiologists have long regarded the trachea as one of their "blind spots," even though this structure can be visualized as well as, if not better than, any other intrathoracic component because of the excellent intrinsic contrast provided by air within the trachea and by the tracheal interfaces with the mediastinum and the lung. Despite this ease of visualization, radiologists may overlook tracheal abnormalities in their diligence in examining the pulmonary parenchyma and the heart. The trachea can be imaged by a variety of techniques, including plain radiography, computed tomography (CT) and magnetic resonance imaging. Important tracheal interfaces include the right and left paratracheal stripes and the tracheoesophageal stripe. The right posterolateral tracheal band is best seen with CT. The trachea is generally a midline structure displaced slightly to the right by the aortic arch. Various conditions, including mediastinal masses and vascular anomalies, may bow, displace or indent the trachea. Such appearances are most commonly seen in patients with thyroid masses or a right-sided aortic arch. Enlarged nodes do not usually narrow the trachea unless they are much harder than the cartilaginous rings, as occurs in nodular sclerosing Hodgkin's disease, or the rings are soft, as is the case in children.