Mediastinum: The Trachea

10.1055/b-0034-87853

Mediastinum: The Trachea

Fixed Tracheal Stenosis and Tracheomalacia

Tracheal pathology in children generally consists of tracheal narrowing that may be fixed (tracheal stenosis), this can be subdivided in long and short segmental stenosis, or variable (tracheomalacia). Presentation is typically with stridor, which is inspiratory with extrathoracic upper airway problems and biphasic with intrathoracic tracheal narrowing. Expiratory wheeze suggests more distal airway narrowing. Tracheal stenosis is frequently due to extrinsic compression and obstruction, and consequently dysphagia due to coexistent esophageal compression (particularly in the older child eating solids) may be present. In babies, the tracheal diameter is dependent on the respiratory phase, and a decrease in caliber of up to 50% is considered to be normal. This can make the interpretation of the trachea on a conventional radiograph difficult for the inexperienced radiologist.

Tracheal Displacement

Displacement of the trachea as visualized on plain radiographs or other imaging modalities may provide an important clue to pathology in related structures.

**Table 1.47 Displacement and anterior buckling on the lateral radiograph**
Diagnosis	Findings	Comments
Normal Fig. 1.121 Fig. 1.122	Buckling in expiration.	More common in younger children, when r adiograph taken at end of cry.
Esophageal dilatation Fig. 1.123, p. 72 Fig. 1.124, p. 72		Achalasia, foreign body obstruction, esophageal atresia before and after surgery.
Esophageal duplication Fig. 1.125, p. 72	Can present with or without communication to the esophageal lumen.	Can remain undiagnosed for a prolonged period.
Cystic hygroma (cavernous lymphangioma) Fig. 1.126, p. 72	Cervical mass, with possible intrathoracic extension. Narrowed airway (larynx, trachea). Cystic components of variable size; optimal delineation of extend with MRI.	Most common site: neck and flanks. Mostly large and growing tumor. Patients may present with stridor. Diagnosis usually antenatal/clinical.
Bronchogenic cyst Fig. 1.127a, b, p. 73	Mainly near the carina; also in posterior (seldom anterior) mediastinum with narrowing or displacement of the trachea, main bronchi, or esophagus. CT and MRI	Origin: tracheobronchial tree. Content: clear fluid, seldom air (communication with the airway). Growth of the cyst is possible.
Neurogenic tumors Fig. 1.128a–c, p. 73	Posterior mediastinum. Anteriorly displaced esophagus. Calcifications can be seen.	Vanillylmandelic acid elevated in most cases, bone marrow can be involved. Opsoclonus, ataxia (“dancing eyes and feet”) metaiodobenzylguanidine (MIBG) scintigraphy and MRI.
Anomalous vessels with tracheal displacement		(see Table 1.87 )
Pharyngeal diverticulum	Lateral outpouching on upper gastrointestinal (UGI) study	Patients may present with swallowing difficulty.
Foregut duplication cyst	May communicate with esophageal lumen.

**Fig. 1.121 Buckling trachea in expiration.**

**Fig. 1.122 Normal tracheal buckling in expiration.** Chest radio-graph obtained in an uncooperative 18-month-old boy. The diaphragm is at the level of the fourth anterior rib (arrow). The trachea is markedly buckled (circled).

**Fig. 1.123 Tube erroneously positioned in esophagus.**

**Fig. 1.124 Esophageal atresia.** Note the curved NG tube in the proximal blind-ending esophagus.

**Fig. 1.125 Esophageal duplication** in a 15-year-old girl presenting with dysphagia.

**Fig. 1.126 Cystic hygroma** in a 14-year-old girl.

**Fig. 1.127a, b Bronchogenic cyst.** (a) Chest radiograph showing a bronchogenic cyst in a 5-month-old boy. (b) Chest CT of the same patient.

**Fig. 1.128a–c Neurogenic tumor.** (a) Thoracic neuroblastoma in a 5-year-old boy. Note the elevation of the diaphragm as a result of vagus involvement. (b) Axial T1-weighted MRI of the same patient. (c) Coronal T1-weighted contrast-enhanced MRI of the same patient shows intense homogeneous enhancement.

**Table 1.48 Posterior displacement and buckling (anterior impression)**
Diagnosis	Findings	Comments
Enlarged thyroid gland	Posterior displacement of the esophagus. Scout radiograph, barium swallow. US. Thyroid scintigraphy	Anterior swelling in the midcervical region. Mainly prepubertal and pubertal females.
Innominate artery syndrome Fig. 1.129		(see Table 1.87 )
Widened ascending aorta		(see Table 1.86 )
Lymphoma Fig. 1.130a, b	Tumor mass (lymphadenopathy) in superior, anterior, and middle mediastinum. Also pleural effusion, lung parenchyma, and skeletal involvement may be seen. CXR, MRI, and fludeoxyglucose-positron emission tomography (PET)-CT.	External cervical lymph adenopathy, visible or palpable. Splenomegaly, nephromegaly possible at any stage.
Bronchogenic cyst Fig. 1.127, p. 73	Small solitary space-occupying mass may disrupt lung aeration: local overinflation due to air trapping or atelectasis. Air-fluid level in the cyst. CT or MRI for diagnosis.	Asymptomatic or expectoration of fluid contents; stridor to severe dyspnea.
Sternal osteomyelitis or sternal tumor	Osteolysis, periostitis, soft-tissue tumor. US, CT, MRI.	Localized swelling over the sternum, pain, fever.
Teratoma, dermoid mesenchymoma, thymic tumor or cyst Fig. 1.131a, b	Solitary or multicystic. Teratoma may contain teeth, bone, calcification, fat. Pleural effusion suggests malignancy.	Tracheal displacement does not occur with a normal or hyperplastic thymus.
Thymic tumor		Thymic neoplasms all rare in childhood, including thymoma, lymphosarcoma, and primary carcinoma. Large thymic cysts are rare.

**Fig. 1.129 Innominate artery compression.** Sagittal reformat of thoracic CT in infant with stridor and pulsatile compression of the trachea on bronchoscopy. The trachea is significantly narrowed (between arrows) at the level of the innominate artery.

**Fig. 1.130a, b Lymphoma.** (a) Lymphoma in a 14-year-old girl. (b) Note the anterior compression of the trachea by enlarged lymph nodes.

**Fig. 1.131a, b Posterolateral tracheal displacement by teratoma.** (a) CT scout view in an 8-month-old boy with stridor. The trachea is narrowed and markedly displaced laterally (arrows) by an upper mediastinal mass. (b) Axial CT section in same patient demonstrates marked posterior and lateral displacement of the trachea (white arrow) by a cystic mass (black arrow). Histologic examination demonstrated a mature cystic teratoma.

**Table 1.49 Lateral displacement and buckling on the anteroposterior radiograph**
Diagnosis	Findings	Comments
Normal finding: left aortic arch	Deviation and displacement of the trachea to the right and anteriorly.	(see Table 1.81 )
Right aortic arch Fig. 1.132 Fig. 1.133	Trachea displaced to the left. Left-sided indentation of the trachea	(see Table 1.51 )
Aberrant left pulmonary artery (“pulmonary sling”) Fig. 1.134a, b	Displacement of the lower trachea to the left.	(see Table 1.51 )
Mass effect of volume loss	Common imaging findings: displacement of trachea and mediastinum. Upper lobe collapse particularly on right may result in lateral tracheal displacement. P aratracheal mass may displace trachea. If vessels pass behind the esophagus, then the tracheal diameter is unaffected.	Causes: trauma, foreign-body aspiration, postoperative. Differential diagnosis: TB, lymphoma, cysts, tumors, and hygromas. Aberrant vessels may be isolated or associated with congential heart disease.

**Fig. 1.132 Right aortic arch.** Note the Botallian duct clip on the right side of the mediastinum instead of the left.

**Fig. 1.133 Leftward displacement of trachea by right aortic arch.** Chest radiograph in a 13-year-old boy with history of complex congenital heart disease. The lower trachea is displaced to the left due to a right aortic arch (open arrow). Note dextrogastria (white arrow).

**Fig. 1.134a, b Pulmonary artery sling.** (a) Chest radiograph in neonate with stridor. The tracheal angle is wide (arrows). There is diffuse increased opacification in the left hemithorax. (b) Axial CT image in same patient demonstrates retrotracheal course of left pulmonary artery (arrow) with associated tracheal stenosis.

**Table 1.50 Long-segment tracheal stenosis**
Diagnosis	Findings	Comments
Normal finding: expiratory collapse (“floppy trachea”) Fig. 1.135	Caliber fluctuations up to 50% are physiologic.	With or without stridor. Physiologic in first year of life and an example of the softness of the immature tracheal cartilage.
Elastic tracheal stenosis (tracheomalacia)	Mostly associated with hyperlucent lung. Fluoros-copy, bronchography and spot films, bronchoscopy.	Abnormally soft tracheal cartilage (past infancy). Late sequela of endotracheal intubation, tracheostomy, and surgical repair of esophageal atresia (even without dilatation).
(Laryngo-) tracheitis DD: epiglottitis	CXR is unnecessary and possibly dangerous; this is a clinical diagnosis. In epiglottitis, there is marked swelling of the epiglottis, occasionally with subglottic tracheal narrowing.	All the signs of infection. Inspiratory stridor, severe respiratory distress, barking cough, hoarseness, gasping, fever. Epiglottitis is rare today due to inoculation.
Primary tracheal stenosis (intramural) Fig. 1.136	Mainly in combination with unilateral or bilateral pulmonary hypoplasia. Preoperative CT with virtual bronchoscopy.	Congenitally malformed small and nonelastic cartilage rings and absent dorsal membrane. Rigid tracheal wall. Severe respiratory distress. Ninety percent diagnosed in first year of life.
Intramural tracheal tumors	Long-segment narrowing occurs only in papillomatosis as it spreads from the larynx to the trachea. Wartlike excrescences from the tracheal mucosa can be delineated on CXR and CT, proven at endoscopy.	Varying degrees of inspiratory and expiratory stridor.

**Fig. 1.135 Expiratory collapse/buckling of the trachea** on a lateral chest radiograph.

**Fig. 1.136 Tracheal stenosis** on coronal CT.

**Table 1.51 Short-segment tracheal stenosis**
Diagnosis	Findings	Comments
Right aortic arch (also with aberrant left subclavian artery); sometimes caused by asymmetric double aortic arch Fig. 1.137	Tracheal impression on the right, deviated to the left, above the bifurcation at the level of the left aortic arch. CXR: Trachea deviated to left at level of arch and narrowed. Associated oesophageal narrowing. CT/MRI and/or echocardiogram: definitive evaluation.	Vascular ring more common with right arch with aberrant left subclavian than with right arch and mirror image branching. Ductus may be patent or merely a ligamentous remnant (see Table 1.49 ).
Double aortic arch Fig. 1.138 Fig. 1.139a, b	Chest X-ray (CXR): Narrowing of trachea at level of double arch. The right arch is usually dominant, and radiographic appearance may simulate a right arch (i.e., trachea deviates to left). Obstructive overinflation frequent. Associated esophageal narrowing. CT/magnetic resonance imaging (MRI) and/or echocardiogram: definitive evaluation. Bilateral tracheal and esophageal impression above the bifurcation. Impression is ventral on the lateral view (dorsal impressions of the esophagus). MRI.	A segment of either arch may be atretic: this can make distinction from other vascular rings challenging. For example, a double arch with atresia of the distal left arch may be very similar in appearance to a right arch with mirror image branching (see Table 1.87 ).
Left brachiocephalic and common carotid artery (left innominate artery; “innominate artery compression syndrome”) Fig. 1.129, p. 74	Defined by >50% narrowing of trachea at level of innominate artery. The innominate artery may be anatomically normal, be dilated or aneurysmal, or have a distal origin from the arch with an abnormally horizontal course of innominate artery across trachea. Ventral tracheal compression just below the level of the clavicle.	A controversial entity: In many cases, the primary abnormality is tracheomalacia, which allows the innominate artery to take the apparently abnormal course. Mild narrowing of the airway at the level of the innominate artery is a normal finding in many infants. Aortopexy may be beneficial in some symptomatic cases, however (see Table 1.87 ).
Aberrant left pulmonary artery (“pulmonary sling”) Fig. 1.134, p. 76	CXR: The lower trachea is displaced to the left. The carina is often widely splayed and may appear almost horizontal. There may be overinflation, more commonly of the right lung, due to main bronchial compression. CT/MRI: left pulmonary artery arises anomalously from distal pulmonary trunk or right pulmonary artery, and runs between trachea and esophagus.	There is frequently (~50%) associated long-segment congenital tracheal stenosis and an abnormal tracheal branching pattern. Also associated with patent ductus arteriosus (PDA), atrial septal defect (ASD), tetralogy of Fallot, and persistent left-sided superior vena cava.
Tracheal foreign body aspiration	Mimics a stenosis, especially if radiolucent. Mobile foreign bodies can occur. Normal findings on radiography are common. Endoscopy. Fluoroscopy may show asymmetric diaphragmatic motion.	Acute onset. Stridor, especially in young children (“virtual vacuum cleaners”). Localization hint: coins project en face in the esophagus, only laterally as trachea too narrow.
Swallowed foreign bodies (radiopaque or radiolucent) Fig. 1.140	Impacted foreign bodies may compress the trachea dorsally (secondary to edema).	Acute onset of stridor or mild respiratory symptoms in small children. Difficulty in swallowing.
Stenosis after surgical repair of esophageal atresia, compression by the dilated proximal esophagus	Findings resemble those of left-sided brachiocephalic trunk. Stenosis at the height of the anastomosis. UGI with caution.	Typically barking cough, stridor caused by localized tracheomalacia.
Postintubation, tracheostomy, and surgery Fig. 1.141		Usually caused by too large a tube, resulting in pressure ischemia of respiratory mucosa. Accounts for 90% of mature acquired laryngotracheal stenoses. Develops in 1%–5% of patients undergoing prolonged endotracheal intubation. Postesophageal atresia, late sequelae of mucosal granulomas, scarring, or strictures. Stridor following extubation may require reintubation.
Masses—extramural: paratracheal or bronchogenic cysts, goiter, lymph-adenopathy, lymphoma, and localized retropharyngeal abscess Fig. 1.142a–c	Tracheal lumen narrowed at the level of the lesion. US, CT, MRI are most useful. Variable a ppearance according to lesion.	Respiratory symptoms vary with the mass size: stridor, gasping, labored breathing, chronic recurrent infections. Need for endoscopy usually based on clinical findings. Common lesions include lymphoma, bronchogenic cyst, esophageal duplication cyst, neuroenteric cyst, mediastinal teratoma, lymphadenopathy, thyroid lesions, thymic lesions, lymphatic malformation, and hemangioma.
Masses—intramural: hemangioma, polypoid hemangioendothelioma, lymphangioma, cysts, ectopic goiter (subglottic) Fig. 1.143	Endoscopy; CXR, CT, MRI. Soft-tissue density may be visible on CXR. There may be generalized air trapping.	Rare: more common causes include subglottic hemangioma, Wegener granulomatosis, and laryngotracheal papillomatosis.
Segmental tracheal stenosis, segmental tracheomalacia	Seldom an isolated lesion, more commonly in combination with tracheoesophageal fistula or after surgical repair of esophageal atresia, at the site of the anastomosis and fistula repair.
Traumatic		Occasionally occurs following blunt trauma to larynx and trachea. Also occasionally following caustic ingestion and inhalational and thermal injuries.
Congenital tracheal stenosis Fig. 1.144a, b	May be short-segment, long-segment, or even extend into the main bronchi. Often features complete cartilaginous rings, producing an abnormally rounded appearance of the airway on cross-section. Diagnosis usually made at endoscopy ± contrast bronchography. Echocardiography and CT performed to identify extrinsic compression.	Up to 1% of all laryngotracheal stenoses. Frequently associated with cardiac defects, particularly pulmonary artery sling. Also associated with pulmonary agenesis and aplasia.

**Fig. 1.137 Right aortic arch with left-sided ductus arteriosus.** Axial CT image in an infant with stridor: the descending aorta lies posterior to the trachea. A right arch was present (not shown). The ductus arteriosus is patent (arrow), connecting the descending aorta to the left pulmonary artery, completing a vascular ring.

**Fig. 1.138 Double aortic arch** (arrows) on coronal contrast- enhanced CT.

**Fig. 1.139a, b Double aortic arch.** (a) Chest radiograph in an infant with stridor requiring ventilation. The lower trachea deviates slightly to the left (arrow). (b) Axial CT image in same patient following intravenous contrast demonstrates a double aortic arch: the right arch (open arrow) is slightly larger than the left arch (white arrow).

**Fig. 1.140 Coin battery ingestion.** Note the beveled edge that is pathognomonic for a coin battery. This is an indication for emergency bronchoesophagoscopy.

**Fig. 1.141 Acquired tracheal stenosis.** Sagittal reformat of thoracic computed tomography (CT) demonstrating acquired tracheal stenosis (arrows) in a 13-year-old girl following prolonged intubation on an adult intensive care unit after a road traffic accident.

**Fig. 1.142a–c Tracheal compression by neuroenteric cyst.** (a) Chest radiograph in neonate with antenatal diagnosis of congenital lung malformation and respiratory distress. There is a mass extending from the left apex to the right lower zone (white arrows). There are associated midline segmentation defects in the upper thoracic spine (black arrows). The trachea is displaced to the right. (b) Axial short inversion-time inversion-recovery (STIR) MRI in same patient demonstrates water dense structure arising from midline segmentation defect (arrow). (c) Sagittal reformat of CT in same patient. The cystic structure is again demonstrated arising from the region of the segmentation defect (arrow).

**Fig. 1.143 Carcinoid** in the left mainstem bronchus in a 13-year-old boy.

**Fig. 1.144a, b Congenital tracheal stenosis with agenesis of left lung.** (a) Contrast bronchogram in neonate with stridor demonstrates tracheal narrowing with focal narrowing due to complete cartilaginous rings (between arrows). The left main bronchus is absent. (b) Axial CT image in same patient demonstrates absent left lung with herniation of right lung across the midline. The trachea has an unusually rounded morphology (between arrows), in keeping with complete cartilaginous rings.

**Table 1.52 Tracheomalacia**
Diagnosis	Findings	Comments
Primary Fig. 1.145a, b	Diagnosis is based on identifying expiratory collapse of the involved airway. This may be achieved with bronchoscopy, bronchography, or occasionally with dynamic (inspiratory and expiratory) CT.	Most commonly in association with prematurity. May be due to primary cartilage disorders such as polychondritis, chondromalacia, or with metabolic disorders including the mucopolysaccharidoses. Also in association with tracheoesophageal fistula.
Secondary	As primary, but may also have indication of secondary cause.	Most commonly iatrogenic following intubation or tracheostomy. Also following infective tracheobronchitis or due to extrinsic compression: any cause of fixed stenosis due to extrinsic compression may also cause tracheomalacia, particularly those involving vascular compression.
Tracheobronchomegaly (Mounier-Kuhn syndrome)	Marked dilatation of trachea and main bronchi in inspiration, with expiratory airway collapse. Recurrent respiratory infections result in bronchiectasis and lung fibrosis.	Rare. Deficiency of elastin in tracheal walls.

**Fig. 1.145a, b Tracheomalacia following esophageal atresia/tracheoesophageal fistula.** (a) Contrast bronchogram in a 4-year-old boy with persistent stridor following neonatal repair of esophageal atresia with tracheoesophageal fistula. At atmospheric pressure in expiration, there is complete collapse of the upper trachea (between arrows). (b) Contrast bronchogram at positive end expiratory pressure of 20 mm Hg. The airway narrowing is overcome. Note the remnant of the tracheoesophageal fistula (arrow).

**Table 1.53 Widened caliber of the trachea and bronchi**
Diagnosis	Findings	Comments
Previous intubation and suction	Dilatation occurs in the upper trachea above the bifurcation.	In neonates and young infants with chronic disease.
Tracheomegaly, bronchomegaly (Mounier-Kuhn syndrome)	Abnormal width of the trachea and bronchi, later sacklike bronchiectasis. Expiratory collapse of the tracheal wall (trachea dilates in inspiration). Bronchoscopy: abnormal mobility of the posterior tracheal wall, occasionally with mucosal changes (membranous atrophy of the posterior wall), anterior bowing of the intercartilaginous sections.	Congenital malformation with hypoplasia of elastic fibers of the smooth muscle. Predominantly in young and schoolaged children (2–14 y). Noisy bitonal cough, recurrent infections, fever sputum production, pneumonias. May also be asymptomatic. Complication: pneumothorax.