Applied Radiology, November 2014
David A. Lawrence, MD, Brittany Branson, MD, Isabel Oliva, MD, and Ami Rubinowitz, MD
A variety of neoplastic, inflammatory and congenital diseases may affect the trachea and mainstem bronchi. The clinical manifestations of these diseases are frequently protean, including symptoms such as cough, hemoptysis, dyspnea and wheezing. Often, patients with these diseases are misdiagnosed with asthma or chronic obstructive pulmonary disease (COPD).
The central airways can be evaluated with computed tomography (CT), which can detect widening or narrowing of the airway, airway wall thickening, the location of an abnormality to guide interventions, and associated findings in the mediastinum or lung parenchyma. CT is inferior to bronchoscopy in evaluating mucosal abnormalities and may underestimate disease extent.
In this article, we review the anatomy of the central airways and describe different pathologic conditions. We group central-airway abnormalities by diffuse or focal tracheal wall thickening and morphologic abnormalities.Central airway anatomy
The trachea consists of 4 layers: an inner mucosal layer, a submucosal layer, cartilage and muscle, and an outer adventitial layer (Figure 1). The anterior trachea is composed of 16 to 22 C-shaped, cartilaginous rings linked by annular ligaments of fibroconnective tissue (Figure 2).1 The function of the rings is to support the trachea during expiration. The posterior tracheal wall lacks cartilaginous support, which is provided only by the thin band of the trachealis muscle. The posterior aspect of the trachea is also known as the membranous portion.
The trachea is approximately 10-12 cm in craniocaudal length, extending from the inferior aspect of the cricoid cartilage to the carina. The normal coronal diameter is 13-25 mm in men and 10-21 mm in women. The normal sagittal diameter is 13-27 mm in men and 10-23 mm in women.2 On CT, the normal tracheal wall is 1-3 mm thick, delineated by luminal air and the mediastinal fat or lungs. Calcification of the cartilage can be associated with senescent changes, particularly in older women.3
The superior aspect of the manubrium separates the extrathoracic and intrathoracic portions of the trachea.4 During expiration, CT images will demonstrate physiologic anterior bowing of the posterior non-cartilaginous aspect of the intrathoracic trachea with little change in contour of the anterolateral tracheal wall (Figure 3).
The mainstem bronchi are histologically similar, but have different morphologic features. The right mainstem bronchus courses posteriorly and superiorly to the right pulmonary artery (epaterial), while the left mainstem bronchus courses laterally and inferiorly in relation tothe left pulmonary artery (hyparterial). The right mainstem bronchus is shorter, has a more vertical course and originates more superiorly than the left. - See more at: http://www.appliedradiology.com/articles/mdct-of-the-central-airways-anatomy-and-pathology#sthash.T6u21Qoq.dpuf