Imaging of Large and Small Airways

Large airways or the central airways are composed of trachea and bronchi. The human tracheobronchial tree has 23 generations with the lobar bronchi being the first generation. The proximal, approximately, 16 generations of bronchi have conductive function, while the distal airways take part in gas exchange with a transition zone between the two where the bronchioles have both functions (Fig. 2.1). The respiratory bronchiole, alveolar duct, and alveolar sac have pure gas exchange function. The measurements of the trachea are described in Table 2.1 [1, 2]. The tracheal wall is composed of multiple rigid C-shaped hyaline cartilages covering the anterolateral wall and a collapsible membrane in posterior wall composed of muscle (trachealis) and connective tissue. CT plays an essential role in the identification of lobar and segmental bronchi as well as fissures. This is important in preoperative localization of the endobronchial and parenchymal lesion. The right bronchus is wider, shorter, and more vertical than the left lung. This leads to higher chances of right endobronchial intubation. The right bronchus, after giving rise to upper lobe bronchus, continues as bronchus intermedius and bifurcates into longer right middle lobe bronchus and shorter right lower lobe bronchus. The left bronchus divides into an upper lobe and lower lobe bronchus and subsequently to their segmental bronchi. Lingular bronchus arises from the left upper lobe bronchus. The segmental bronchi help in localizing the bronchopulmonary segments (Table 2.2).