 Bronchiectasis is defined as irreversible abnormal bronchial dilatation, with patients most commonly presenting with chronic productive cough. Although a wide range of congenital and acquired conditions can be associated with bronchiectasis, a common etiologic pathway is thought to be impairment of normal bronchial clearance and airway immune mechanisms, resulting in recurrent infections and chronic bronchial inflammation that cause bronchial injury and dilatation [9,10]. The prevalence of bronchiectasis has increased worldwide over the last few decades; in the United States, prevalence has been estimated as approximately 139 per 100,000 individuals [9]. Treatment includes preventive airway clearance therapies, anti-inflammatory agents, prophylactic or therapeutic antibiotics, and, in severe cases, surgical resection or lung transplantation. Special Imaging Considerations In cases of tracheal stenosis and central airway lesions in general, special CT reformatting techniques such as 2-D multiplanar, 3-D volume-rendered, and virtual bronchoscopic images may be helpful for illustration of findings and preprocedural planning [11-13]. For example, coronal and sagittal 2-D reformatted images and 3-D volume reformatted images can depict the craniocaudal extent of lesions and distance from landmarks such as the vocal cords and carina, and virtual bronchoscopic images can illustrate the expected endoluminal appearance of lesions and provide guidance for bronchoscopy and procedures by demonstrating local airway anatomy. Minimum intensity projection reformatted images can also display central airway abnormalities and bronchiectasis [10]. Modern multidetector CT can be used to image the entire trachea at end expiration or during forced expiration (dynamic expiratory imaging). More recently, 320-row multidetector CT scanners have enabled cinematic 4-D volumetric images of the trachea, allowing time-resolved coverage of the entire trachea throughout an inspiratory/expiratory cycle [14,15].
Tracheobronchial Disease.  Bronchiectasis is defined as irreversible abnormal bronchial dilatation, with patients most commonly presenting with chronic productive cough. Although a wide range of congenital and acquired conditions can be associated with bronchiectasis, a common etiologic pathway is thought to be impairment of normal bronchial clearance and airway immune mechanisms, resulting in recurrent infections and chronic bronchial inflammation that cause bronchial injury and dilatation [9,10]. The prevalence of bronchiectasis has increased worldwide over the last few decades; in the United States, prevalence has been estimated as approximately 139 per 100,000 individuals [9]. Treatment includes preventive airway clearance therapies, anti-inflammatory agents, prophylactic or therapeutic antibiotics, and, in severe cases, surgical resection or lung transplantation. Special Imaging Considerations In cases of tracheal stenosis and central airway lesions in general, special CT reformatting techniques such as 2-D multiplanar, 3-D volume-rendered, and virtual bronchoscopic images may be helpful for illustration of findings and preprocedural planning [11-13]. For example, coronal and sagittal 2-D reformatted images and 3-D volume reformatted images can depict the craniocaudal extent of lesions and distance from landmarks such as the vocal cords and carina, and virtual bronchoscopic images can illustrate the expected endoluminal appearance of lesions and provide guidance for bronchoscopy and procedures by demonstrating local airway anatomy. Minimum intensity projection reformatted images can also display central airway abnormalities and bronchiectasis [10]. Modern multidetector CT can be used to image the entire trachea at end expiration or during forced expiration (dynamic expiratory imaging). More recently, 320-row multidetector CT scanners have enabled cinematic 4-D volumetric images of the trachea, allowing time-resolved coverage of the entire trachea throughout an inspiratory/expiratory cycle [14,15].