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Radiology of the trachea

Paul Stark, MD
Section Editor
Nestor L Muller, MD, PhD
Deputy Editors
Geraldine Finlay, MD
Susanna I Lee, MD, PhD


Most clinicians quickly recognize a variety of abnormal patterns of diffuse parenchymal lung disease on conventional chest radiographs. However, anomalies of the upper respiratory tract, some of which can cause acute respiratory failure, are often overlooked during the initial assessment. Imaging of the trachea will be reviewed here. The radiologic manifestations of diffuse parenchymal lung disease, and the management of central airway obstruction, are discussed separately. (See "Evaluation of diffuse lung disease by conventional chest radiography" and "Clinical presentation, diagnostic evaluation, and management of central airway obstruction in adults".)


The trachea extends from the lower border of the larynx (2 cm below the vocal cords) to the carina, where it bifurcates into the mainstem bronchi. The average tracheal length is 10 to 12 cm, and the normal angle of the tracheal bifurcation is 70 ± 20 degrees (image 1A-B). With deep inspiration, the tracheal length increases by as much as 2 cm and the angle of the tracheal bifurcation decreases by up to 10 degrees [1,2].The superior border of the manubrium sterni separates the extrathoracic cervical trachea from the intrathoracic trachea.

The trachea consists of four layers: an inner mucosal layer, a submucosal layer, cartilage, and muscle as well as an outer adventitia. It is supported anteriorly and laterally by 18 to 22 semicircular incomplete rings of cartilage connected by annular ligaments of fibroconnective tissue; this corresponds to two cartilage elements per centimeter of tracheal length. Tracheal cartilages can calcify in elderly patients with a predilection for women and patients on longstanding warfarin therapy. The posterior (membranous) tracheal wall is devoid of cartilage and consists of longitudinally aligned smooth muscle, called trachealis muscle and fibrous connective tissue. The tracheal wall has a thickness of 1 to 3 mm and is delineated by intraluminal gas and mediastinal fatty tissue, as determined on CT scans.

The normal transverse internal diameter of the trachea ranges between 15 and 25 mm in men and 10 to 21 mm in women, with a cross-sectional area of 250 to 350 mm2 and a volume of 30 to 40 cm3 at total lung capacity (TLC) [1,3]. The transverse diameter of the trachea increases by 10 percent with inspiration and can decrease by 30 percent with coughing. During expiration, CT images display physiologic anterior bowing of the posterior non-cartilaginous membranous wall of the intrathoracic trachea while the anterolateral tracheal wall remains unchanged in its configuration.

The radiographic appearance of the tracheal air column should be assessed routinely when chest radiographs are obtained. If an endotracheal tube is present, proper position must be confirmed (figure 1). Aspiration of sand, food, secretions, or other particulates may create a radiopaque outline of the trachea and large bronchi (image 2). Three-dimensional CT imaging and perspective rendering or virtual bronchoscopy are useful additional imaging tools [4].

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Literature review current through: Nov 2017. | This topic last updated: Jun 15, 2017.
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