Nonacquired diffuse tracheal widening is much less common than tracheal narrowing and has a more limited differential diagnosis. The Mounier-Kuhn syndrome, primarily affecting men in the fourth and fifth decades, accounts for almost all cases of nonacquired tracheal widening.19 Mounier-Kuhn syndrome, thought to be congenital but possibly acquired,9 is an abnormality of the trachea and main bronchi characterized by atrophy or absence of elastic fibers and thinning of muscle, which allows the trachea and main bronchi to become flaccid and markedly dilated on inspiration, with narrowing or collapse on expiration or cough. The abnormal airway dynamics and pooling of secretions in broad outpouchings (diverticula) of redundant musculomembranous tissue between the cartilaginous rings predispose to the development of chronic pulmonary suppuration, bronchiectasis, emphysema, and pulmonary fibrosis.174 Patients may be asymptomatic, have minimal disease with good preservation of pulmonary function, or have progressive disease that leads to respiratory failure and death. The trachea is involved from the subglottic region to the carina, and although a tracheal diameter greater than 3 cm is required for diagnosis, tracheal widths up to 5.5 cm have been recorded.19 The radiographic features of the condition include marked dilatation of the trachea and main stem bronchi, tracheal diverticulosis, and a variable incidence of bronchiectasis and chronic pulmonary parenchymal disease. The CT scan features are similar.31,133 Many cases of this disorder probably go undiagnosed or are not recognized clinically or radiographically, but only on CT scanning.133 Roditi and coworkers126 studied 75 adults referred for CT assessment of possible bronchiectasis and a control group of 75 patients being staged for lymphoma and found that 7 (17%) of 42 patients with bronchiectasis had tracheomegaly and 2 of 33 patients without bronchiectasis had tracheomegaly on high-resolution computed tomography (HRCT). Tracheomegaly, therefore, may be a frequent finding in bronchiectasis. People with large tracheas, which may be overlooked unless tracheal dimensions are measured, may be at risk for development of bronchiectasis.

Several conditions can result in acquired tracheobronchomegaly that may closely resemble that seen in Mounier-Kuhn syndrome. Some degree of tracheal dilatation may be seen with aging38,49 and with certain occupations (musicians who play wind instruments, drill sergeants, and Moslem muezzins).38 Chronic infection, cigarette smoking, chronic bronchitis, emphysema, cystic fibrosis (CF), inhalation of noxious fumes, chronic intubation, and diffuse pulmonary fibrosis can also result in tracheobronchomegaly.13,173,174 Other conditions associated with tracheal widening, which may in fact be related to Mounier-Kuhn syndrome, are Ehlers-Danlos syndrome and cutis laxa.18,166 Finally, although tracheal narrowing is the usual end result in relapsing polychondritis, a disorder of cartilaginous inflammation involving the nose, ear, trachea, and joints, diffuse tracheal widening has occasionally developed.35 Nasal and ear cartilage abnormalities are absent in Mounier-Kuhn syndrome. Tracheobronchomalacia (Williams-Campbell syndrome), a disorder of cartilage deficiency, is an uncommon cause of tracheomegaly.

Tracheal narrowing is seen with saber-sheath deformity, amyloidosis, relapsing polychondritis, tracheobronchopathia osteochondroplastica, complete cartilage rings (“napkin ring” anomaly or congenital tracheal stenosis), scleroma, sarcoidosis, Wegener’s granulomatosis, tracheobronchitis associated with ulcerative colitis, tracheomalacia and bronchomalacia, trauma (including postintubation stricture and surgical trauma), neoplasms, infectious disorders, extrinsic processes (vessels, nodes, thyroid and other mediastinal masses) (Fig. 26-1), and mediastinal fibrosis; it can also be idiopathic.5,75,131,149

Strictures of the trachea are usually caused by damage from a cuffed endotracheal or tracheostomy tube or trauma to the neck.47 Postintubation tracheal injuries remain the most common indication for tracheal resection and reconstruction, despite identification of the causes of these lesions and development of techniques for their avoidance.55 CT scans can demonstrate the site of narrowing in most cases, although a web or stenosis that involves a short segment may be missed because of volume averaging, and CT may overestimate the severity of a fixed stenotic segment and underestimate the length of the abnormal trachea.75 Quint and colleagues116 evaluated 27 patients who underwent lung transplantation and 17 nontransplantation patients with suspected airway abnormalities and found helical CT with multiplanar reconstructions to be more accurate than thin-section axial CT in the demonstration of mild stenosis, the length of a stenosis, and horizontal webs. Tracheomalacia, diagnosed when the trachea collapses more than 50% on expiration, can also result from trauma; it may be recognized only on expiratory CT scanning.116,147

Saber-sheath trachea is an intrathoracic narrowing of the trachea, with the coronal diameter equal to or less than two thirds of the sagittal diameter when measured 1.0 cm above
the top of the aortic arch.51 More than 95% of patients with this deformity have clinical evidence of chronic obstructive pulmonary disease (COPD), and saber-sheath trachea is considered a valuable sensitive and specific sign for COPD on standard chest radiography.51,52 The CT diagnosis of saber-sheath trachea has been correlated with various functional, clinical, and radiographic signs of COPD.157

Relapsing polychondritis is a systemic autoimmune connective tissue disease in which cartilage is affected diffusely by recurrent episodes of inflammation. The pinnal, nasal, laryngeal, and tracheal cartilages are most commonly involved. The major airways are involved in more than 50% of cases, and recurrent pneumonia is the most common cause of death in these patients.19,43 Collapsibility of the major airways is seen in conjunction with softening and destruction of the cartilaginous rings. On CT scanning, a fixed narrowing of the tracheobronchial lumen with associated thickening of the wall is seen.29,99 Dense calcium deposits may be seen in the thickened tracheal cartilage.65 Rarely, diffuse tracheal widening can result.

Amyloidosis of the respiratory tract, both primary and secondary, is a rare condition that produces irregular narrowing of the airway by submucosal deposits of amyloid in a focal or diffuse distribution.47 Both chest radiography and CT scanning may demonstrate diffuse narrowing or show nodular protrusions into the tracheal lumen that may show calcification.19 The average patient age is 53 years, and men are affected twice as frequently as women.19

Tracheobronchopathia osteochondroplastica is a benign condition characterized by multiple submucosal osteocartilaginous growths along the inner anterolateral surfaces of the trachea.81,130 Men are more frequently affected than women (3:1), and the average age is more than 50 years (range, 11 to 78 years).19 Although the cause is unknown, theories have linked this disorder to chronic inflammation, degenerative processes, amyloidosis, and neoplasia.3,167,177 Chest radiography and CT scanning show multiple sessile nodular tumors, with or without calcification, extending over a long segment of the trachea. The nodules in amyloidosis may be circumferential, but those of tracheobronchopathia osteochondroplastica spare the posterior membranous wall.

Wegener’s granulomatosis is characterized by granulomatous vasculitis of the upper and lower respiratory tract, usually in conjunction with renal and other organ involvement. The CT appearance includes circumferential narrowing of the airway lumen, abnormal soft tissue within the tracheal rings, and dense irregular calcification of the tracheal cartilages.145 Sarcoidosis is another granulomatous disorder that may involve the trachea and bronchi. Granulomatous lesions may exist intrinsically in the airway, or enlarged hilar nodes may compress the bronchi extrinsically. CT scanning may show extrinsic compression by adenopathy and bronchial wall thickening.88,171

Ulcerative colitis has a rare association with bronchitis, bronchiectasis, and bronchiolitis.163 On CT scans, the tracheobronchial walls are thickened, producing irregular narrowing, and bronchiectasis may be seen.75 Finally, the major airways may be involved in viral, bacterial, fungal, or other infectious disease processes. In North America, most cases of laryngotracheobronchitis are viral in nature; subglottic or laryngeal narrowing is common, but radiographically demonstrable tracheal narrowing is unusual.75