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figure 4-9 Right-sided aortic arch. A, Anteroposterior view of the trachea demonstrates marked tracheal narrowing adjacent to the right aortic arch. B, Axial T1-weighted magnetic resonance imaging reveals compression of the mid-trachea by a slightly dilated right-sided aortic arch.

figure 4-9 Right-sided aortic arch. A, Anteroposterior view of the trachea demonstrates marked tracheal narrowing adjacent to the right aortic arch. B, Axial T1-weighted magnetic resonance imaging reveals compression of the mid-trachea by a slightly dilated right-sided aortic arch.

and are usually asymptomatic. Tracheal bronchi are classified into four different types: 1) rudimentary tracheal bronchus, typically arising as a blind outpouching of the right lower side of the trachea; 2) displaced bronchus, the most common anomaly in which one or two of the upper lobe segments are aerated by the tracheal bronchus; 3) supernumerary accessory bronchus, which arises from the trachea in addition to the normal right upper lobe (Figure 4-10); and 4) right upper lobe bronchus, with three normal segments arising above the tracheal bifurcation, sometimes a duplicate of a normal right upper lobe bronchus.

Congenital Tracheal Stenosis

Congenital tracheal stenosis is a rare developmental abnormality of the trachea that may affect any or all parts of the trachea, in which the tracheal cartilages are hypoplastic, forming complete rings without a membranous posterior wall.23 As a result, the trachea is rigid and nondistensible. On CT scans, the trachea is narrowed, with identifiable calcified complete cartilaginous rings (Figure 4-11). Associated congenital anomalies are present in 80% of cases, including H-type tracheoesophageal fistula, laryngomalacia, subglottic stenosis, bronchial stenosis, hypoplasia or agenesis of the lungs, and other skeletal, cardiovascular, and intestinal anomalies.

Congenital Vascular Anomalies and Rings and Vascular Compression

Vascular rings, slings, or mediastinal great vessels may compress the trachea and/or esophagus.24-27 In adults, most vascular compressions are related to acquired aneurysmal dilation of the great vessels. Contrast CT, magnetic resonance angiography, and/or angiography is indicated to establish a diagnosis. A barium swallow is necessary in the work-up of a child with respiratory symptoms, because the esophagus is frequently involved in compression syndromes.

figure 4-10 Tracheal bronchus. Computed tomography examination demonstrates a tracheal bronchus (A) arising from the distal trachea just above the carina (B). The normal right upper lobe bronchus is noted (C).

figure 4-10 Tracheal bronchus. Computed tomography examination demonstrates a tracheal bronchus (A) arising from the distal trachea just above the carina (B). The normal right upper lobe bronchus is noted (C).

Vascular rings are the most common symptomatic anomalies causing tracheal and esophageal compression and are classified as 1) double aortic arch or 2) right aortic arch with left ligamentum arteriosum, patent ductus, or aberrant left subclavian artery. The absence of an aortic arch on the left and the presence of a tracheal indentation by the right-sided aorta are critical findings. The distal trachea may be deviated to the left on the frontal view, and anteriorly on the lateral view. A double aortic arch causes both anterior and posterior compression of the trachea.

A pulmonary artery sling occurs when an anomalous left pulmonary artery courses over the right main stem bronchus, near its origin from the trachea, and crosses posteriorly and to the left between the esophagus and the trachea, reaching the left hilum above the bronchus. As a result, it may compress the trachea and right main stem bronchus. A strong association exists with both tracheobronchial defects and cardiovascular anomalies. Diagnostic findings on barium swallow, CT, and MRI include indentation of the anterior aspect of the esophagus as well as tracheal deviation to the left just above the carina, by the aberrant pulmonary artery. The left hilum is situated more caudal than normal.27

Anterior compression of the trachea may occur by the innominate artery. The degree of compression is usually most severe in expiration. In children, the innominate artery often originates partially or totally to the left of the trachea and crosses in front of it, and clinical symptoms result because of crowding in the mediastinum. The lateral chest radiograph usually demonstrates a typical anterior compression of the trachea. The esophagus is usually not affected on an esophagogram.26

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