The Trachea

Chapter 12 The Trachea


Plain Films

Several radiographic studies are used to evaluate the trachea and main bronchi (Table 12-1). The plain chest radiograph in the posteroanterior and lateral projections is the most frequently used screening study. A high-kilovoltage (140-kVp) technique is preferred because it reduces the visibility of the bony thorax and improves imaging of the various mediastinal interfaces. However, it is easy to miss a tracheal or main bronchial lesion on standard posteroanterior and lateral chest radiographs because there is considerable overlap of the trachea with the mediastinum and bony thorax. Bilateral, oblique chest radiographs improve visibility of the trachea and main bronchi by rotating the spine so that it is not superimposed on the central airways (Fig. 12-1). In most cases, additional imaging is usually indicated.

Table 12-1 Approach to Diagnostic Imaging of the Trachea

Study Clinical Indications
Chest radiographs (posteroanterior, lateral, oblique projections) Screening study
Conventional tomography (anteroposterior, lateral, 55-degree posterior oblique projections) Postintubation tracheal stenosis
Preoperative assessment of length of lesion
Postoperative assessment of bronchial anastomosis
Computed tomography Tracheobronchial tumor location and extent
Density determination
Vascularity of tumor
Airway diameter
Wall thickness
Compression of airway by mediastinal mass or vessel
Tracheobronchial rupture
Tracheobronchial dehiscence
Magnetic resonance imaging Multiplanar imaging
Mediastinal invasion by airway, neoplasm
Airway obstruction by vascular rings
Fluoroscopy Tracheomalacia
Air trapping due to bronchial obstruction

Computed Tomography

Computed tomography (CT) has become the imaging modality of choice for most tracheobronchial lesions. Because of the clarity of anatomic detail on cross-sectional imaging, there is a direct display of tracheobronchial anatomy. The superior contrast resolution compared with conventional radiography permits evaluation of adjacent mediastinal soft tissues. This is particularly important in cases of tracheal neoplasms, which may invade the adjacent mediastinum, or in cases of mediastinal masses such as goiters or vascular rings, which may compress the trachea. CT can identify calcific and fatty densities and vascular enhancement of tumors and aneurysms after intravenous contrast administration. Paired inspiratory and expiratory CT scans can identify abnormal collapsibility of the trachea and main bronchi in cases of tracheobronchomalacia. High-resolution computed tomography (HRCT) can be obtained with the use of thin (1- to 1.5-mm) sections and a bone reconstruction algorithm. The major disadvantage of conventional CT is that craniocaudally oriented trachea and bronchi are not imaged in the long axis. Although images may be reconstructed in sagittal and coronal planes, the resolution is limited by the inherent scan thickness on conventional CT scans.

Multidetector CT (MDCT) has significantly improved the way the trachea is imaged. MDCT increases the capacity to register data and significantly shortens the scan time. The entire trachea and major bronchi can be imaged in a single breath hold of a few seconds. The isometric data set obtained with MDCT has equal resolution in all the imaging planes, and artifacts seen with multiplanar reformats in conventional CT can be avoided. High-quality, multiplanar images are possible if thin sections (1 to 2.5 mm) and an overlapping image reconstruction algorithm are used (Fig. 12-2). The image reconstruction thickness can be selected prospectively or retrospectively after raw data set is acquired. The same data can be transferred to a dedicated workstation to obtain three-dimensional images. The two commonly used three-dimensional techniques are external volume rendering of the airways (Fig. 12-3A) and internal rendering or virtual bronchoscopic views (see Fig. 12-3B). These imaging techniques supplement but do not replace conventional axial images. There are several advantages of using these techniques. The craniocaudal extent and shape of the lesion is better displayed, complex and subtle lesions can be better demonstrated (Fig. 12-4), and simulated bronchoscopic views can be used as a guide in planning interventional procedures.

Because of high temporal resolution, MDCT allows dynamic CT imaging during expiration and coughing. These techniques are more sensitive in demonstrating malacia than paired inspiratory and expiratory images.

Historically, conventional tomography in the anteroposterior, lateral, and oblique projections was routinely used to evaluate the trachea and central bronchi. With refinements in CT scanning, conventional airway tomography is no longer routinely employed. However, it does permit an accurate assessment of patency or the degree of obstruction in the central airways and provides a direct image of the airways in the long axis. Conventional tomograms can determine accurately the length of tracheal lesions relative to the larynx or carina. The major disadvantage of conventional tomography is the inability to visualize adjacent mediastinal structures.


Tracheal diverticula are outpouchings from the tracheal wall. They are seen in up to 1% of population. They can be congenital or acquired. The congenital diverticula are single, located 4 to 5 cm below the vocal cords or just above the carina, and contain all the layers of tracheal wall. The acquired diverticula are outpouchings from a weak posterior wall and are lined by respiratory epithelium. They lack other layers of the tracheal wall, such as smooth muscle and cartilage. The acquired diverticula may be single or multiple and are thought to be associated with increased intraluminal pressure and chronic cough.

Most tracheal diverticula are asymptomatic and are discovered incidentally. They can manifest with recurrent episodes of airway infection and chronic cough because the diverticula may act as reservoirs of infection.

On standard radiographs, small diverticula are often missed. Thin-section CT with multiplanar and three-dimensional reconstructions establishes the relation to the trachea, and further imaging is usually not required (Fig. 12-6; see Fig. 12-4).

The differential diagnosis of a paratracheal air collection includes laryngocele, pharyngocele, Zenker’s diverticula, and apical paraseptal blebs or bullae. These entities can be easily distinguished by CT and barium swallow occasionally is required.


Diffuse tracheal narrowing is seen in several conditions, including chronic obstructive pulmonary disease (COPD); after tracheal trauma; as the result of viral, fungal, tuberculous, or bacterial infections; and in other diseases, such as sarcoidosis, Wegener’s granulomatosis, relapsing polychondritis, amyloidosis, and tracheobronchopathia osteochondroplastica. The narrowing may be idiopathic and may involve the larynx (Table 12-2).

Table 12-2 Diffuse Tracheal Stenosis

Causative Conditions Tracheobronchial Findings Other Findings
Idiopathic Smooth, tapered, irregular, lobulated, or eccentric morphology 2-4 cm long, usually subglottic ±Laryngeal involvement
Postintubation cuff injury Smooth narrowing with hourglass configuration  
Posttraumatic Smooth narrowing with hourglass configuration ±Upper rib and sternal fractures
Saber-sheath trachea Smooth narrowing of intrathoracic trachea
Coronal diameter ≤ one half of sagittal diameter
Hyperinflated lungs
Tracheopathia osteochondroplastica Submucosal nodularity of anterolateral walls of trachea and main bronchi with ossification
Membranous wall is spared
Relapsing polychondritis Diffusely thickened tracheobronchial walls with diffuse narrowing of trachea and main bronchi
±Calcification of wall
Auricular and nasal chondritis, arthritis
Wegener’s granulomatosis Focal or diffuse tracheobronchial wall thickening and narrowing
±Enlarged calcified cartilages
Renal involvement
Amyloidosis Diffuse tracheobronchial wall-thickening and narrowing
Focal nodular masses
Contrast enhancement of masses on CT or MRI
Slowly progressive
±Lymphadenopathy, may calcify
Sarcoidosis Smooth, irregular, or nodular stenosis
Tracheobronchial wall thickening
Bronchial compression by lymph node
±Lymphadenopathy, ±calcification
±Reticular/nodular interstitial lung disease
Tracheobronchial papillomatosis Diffuse nodules or masses in trachea and bronchi Laryngeal involvement
±Multiple pulmonary nodules, may cavitate
Complicated by squamous cell carcinoma
Rhinosclerosis Nodular masses or diffuse, symmetric narrowing of trachea and bronchi
Slowly progressive
Hyperplastic stage Irregular tracheobronchial wall thickening and narrowing Hilar/mediastinal lymphadenopathy
Parenchymal cavitation and consolidation
Fibrostenotic stage Smooth tracheobronchial narrowing Atelectasis and scarring
Calcified lymph nodes

Idiopathic Laryngotracheal Stenosis

Idiopathic laryngotracheal stenosis is an uncommon cause of narrowing in the larynx and subglottic trachea. It typically affects middle-aged women who have no history of intubation, trauma, infection, or other underlying systemic disease. Clinically, patients experience progressive shortness of breath accompanied by wheezing, stridor, or hoarseness. The average duration of symptoms is approximately 2 years.

The radiologic appearance of idiopathic laryngotracheal stenosis varies, including lesions that may be smooth and tapered (Fig. 12-7) or irregular, lobulated, and eccentric (Fig. 12-8). The stenosis is 2 to 4 cm long, with severe compromise of the lumen measuring no more than 5 mm at the narrowest point.

Histologically, the stenotic areas show dense keloid fibrosis involving the adventitia and the lamina propria and sparing the mucosa, muscularis propria, and the cartilage. Small areas of spindle cell proliferation are similar to fibrosing mediastinitis or retroperitoneal fibrosis. The mucosa may show squamous metaplasia without dysplastic changes. The lesions may be treated surgically or conservatively with dilation, intubation, stenting, steroid injection, cryotherapy, or electrocoagulation.

Postintubation Injuries

Most long-term complications of intubation are related to cuff injury. Cuffed endotracheal tubes became commonplace only after the introduction of intermittent positive-pressure breathing for the treatment of respiratory failure during the poliomyelitis epidemic of 1952. As patients survived for longer periods with respiratory assistance, new long-term complications arose, including tracheal stenosis, tracheoesophageal fistula, and tracheoinnominate artery fistula (Box 12-1).

A stenosis may occur at the level of the tracheostomy stoma or rarely where the tip of the tube impinges on the tracheal mucosa. However, pressure necrosis at the cuff site is responsible for most long-term postintubation complications. If the cuff pressure exceeds capillary pressure, blood supply to the mucosa is compromised, leading to ischemic necrosis. Initially, the mucosa becomes inflamed, followed by ulceration in the mucosa overlying the cartilaginous rings. As the ulcers enlarge, there is increasing exposure of the cartilage, which becomes colonized with bacteria. With further pressure on the wall, necrosis develops, and softening and dissolution of the cartilage lead to tracheomalacia or to scarring and stenosis formation. Radiographically, the stenosis has a smooth, gradual narrowing with an hourglass configuration (Fig. 12-9). Typically, symptoms of stenosis develop in 2 to 6 weeks after extubation and, in some patients, months later. Most stenoses are appropriately treated with resection of the damaged segment and end-to-end anastomosis. In the past 20 years, most tracheostomy and endotracheal tubes have been designed with large-volume, low-pressure cuffs, which has dramatically reduced the incidence of tracheal stricture. Postintubation tracheal strictures continue to occur but at a much reduced rate.

Tracheoesophageal fistula

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Feb 28, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on The Trachea

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