David R. White, H. Biemann Othersen, Jr. and André Hebra

Practical Embryology and Anatomy

A working knowledge of the embryonic development of the mediastinal structures aids in understanding the etiology and associated anomalies of tracheal obstruction. Malformations of the great vessels (vascular rings) should be suspected and investigated when evaluating a child with complete tracheal rings. The most common vascular malformation associated with complete tracheal rings is a pulmonary vascular sling. This anomaly occurs when the left pulmonary artery arises to the right of the trachea, around which it curves and compresses just above the carina, and then passes between the trachea and esophagus before reaching the left lung (Fig. 21-1).³ Other vascular ring malformations may produce varying degrees of tracheal, bronchial, and esophageal compression.

Subglottic and Tracheal Malformations

Vascular Compression

Compression and partial obstruction of the trachea may be caused by abnormalities of the aortic arch that impinge on, or encircle, the trachea or esophagus, or both.5,6 When both the trachea and esophagus are compressed, swallowing frequently produces airway compression and respiratory distress. Vascular rings are often asymptomatic in neonates and infants, yet can lead to significant airway obstruction in a child.⁷

The physiologic impingement on the trachea by a vascular ring is similar to that seen in patients after repair of esophageal atresia. The persistently distended upper esophageal pouch can displace the trachea anteriorly, producing tracheomalacia (Fig. 21-5). Particularly with swallowing, the distended esophageal pouch may compress the trachea against the innominate artery (Figs 21-6 and 21-7). Correction of this problem centers on anterior mobilization and suspension of the innominate artery (Fig. 21-8).^8–12 The treatment of a pulmonary vascular sling may require not only relocation and reimplantation of the pulmonary artery, but also repair of the stenotic distal trachea.^7,12,13

Stridor and dyspnea are symptoms that can be produced by vascular impingement on the trachea. Patients with severe compromise from a double aortic arch are usually symptomatic, but their manifestations are variable (Fig. 21-9). Some patients are seen with frequent coughing episodes and stridor accompanied by dyspnea and cyanosis, whereas small infants may have apneic episodes. The symptoms of vascular impingement on the trachea are usually more dramatic than those from compression of the esophagus.

Classically, vascular ring anomalies are diagnosed on a barium esophagogram with indentations on the esophageal column of barium and a decrease in the tracheal air column. Offset of the axis of the barium column above and below the indentation is diagnostic of a double aortic arch (Fig. 21-10A). More recently, rapid computed tomographic (CT) scans allow a graphic reconstruction of the trachea and adjacent vessels (Fig. 21-10B). Magnetic resonance imaging (MRI) enhanced with intravenous administration of a contrast agent allows excellent visualization of the trachea and vessels as well.

Occasionally, a child will appear with acute airway obstruction or other medical problems requiring intensive care, during which endotracheal intubation and a concomitant nasogastric tube are inserted. The presence of tubes in both airway and esophagus makes detection of a vascular ring difficult and can generate complications. In a child who is already intubated, performance of contrast radiographic procedures may not be possible. Ultrasonography (US), or CT, or contrast-enhanced MRI may delineate the vascular abnormality. When both tracheal and esophageal intubations are necessary in a patient with a double aortic arch, the encircling vessels may sustain pressure necrosis. Erosion into the aortic arch can produce an aortoesophageal fistula that may not be manifest until either the endotracheal or the esophageal tube is removed. A sentinel hemorrhage may occur before a massive, and often fatal, hemorrhage occurs into the esophagus. The passage of a Sengstaken–Blakemore tube with inflation of the esophageal balloon can be life-saving by tamponading the fistula.¹⁴ Because no reliable diagnostic study is available to demonstrate an aortoesophageal fistula, the observation of a sentinel hemorrhage in such a patient with ultrasound confirmation of a double aortic arch is a clear indication for urgent cardiopulmonary bypass and repair.¹⁴

Vascular rings cause airway constriction and not vascular problems. Thus, simple division of the vascular ring is often not enough to relieve tracheal compression. Following division of a vascular ring, if part of the ring continues to compress the airway, it should not be dissected away from the trachea but suspended anteriorly, often to the back of the sternum. The vascular-tracheal attachments will lift the anterior tracheal wall and enlarge the lumen (see Fig. 21-8). Traditionally, an open operation has been used for vascular ring repair. Significant numbers of patients are now being treated by the thoracoscopic approach.¹⁵ Regardless of the approach, whether from the right or from the left,¹⁶ or other technical variations,¹⁷ the recurrent laryngeal and phrenic nerves need to be identified and protected. Flexible endoscopic observation of the trachea during these maneuvers can corroborate relief of the compression.⁶

Tracheomalacia

Often, tracheomalacia is produced by constant pressure from a cardiovascular structure. Thus it is almost always necessary to suspend the offending vessel and utilize its attachments to the trachea to expand the tracheal lumen. Tracheomalacia can be primary in nature without evidence of compression. In these cases, suspension of the large mediastinal vessels may enlarge the tracheal lumen, or the peritracheal fascia can be suspended to the sternum to overcome collapse of the airway.18–21 In the UK (Scotland), guidelines have been promulgated for the use of thoracoscopic aortopexy to treat severe primary tracheomalacia. Interestingly, the National Health Service believed that these guidelines were necessary because individual surgeons would operate infrequently on infants and children who are good candidates for operative correction.

Inflammatory Obstructions

Viral laryngotracheitis (croup), bacterial or membranous tracheitis, and epiglottitis are inflammatory conditions that occasionally require operative intervention. In cases of inflammatory obstruction, endotracheal intubation is preferred instead of tracheostomy if possible. It is important to distinguish croup and bacterial tracheitis from epiglottitis because the treatments are quite different (Table 21-1).