Etiology and Pathogenesis

Laryngomalacia is the most common congenital abnormality of the extrathoracic airway. Structural abnormalities that occur in some cases include shortened aryepiglottic folds; a flaccid, omega-shaped epiglottis; and prolapsing arytenoid cartilages. Poor tone and coordination of the laryngeal muscles caused by neuromuscular immaturity contributes to inspiratory collapse of laryngeal structures.

Laryngeal atresia is a life-threatening condition that occurs when the occluded laryngeal lumen fails to recanalize at 10 weeks of gestation. Incomplete recanalization can result in laryngeal webs, which are often associated with DiGeorge or velocardiofacial syndromes. Congenital subglottic stenosis is similar in pathogenesis; however, the defect occurs below the glottis at the level of the cricoid cartilage. Laryngeal clefts develop between 25 and 35 days in utero because of abnormal separation of the trachea from the foregut.

Tracheomalacia may be either primary or secondary, the latter being more common. In primary tracheomalacia, there is an intrinsic weakness of the tracheal cartilage and sometimes shortening of the cartilage rings so that the posterior membrane comprises a greater proportion of the tracheal circumference. Secondary tracheomalacia results from extrinsic compression of the airway in association with cardiovascular abnormalities such as double aortic arch, or it may be a complication of prolonged intubation, tracheostomy placement, or severe tracheobronchitis.

Tracheoesophageal fistula (TEF) occurs when there is incomplete mesodermal septation of the primitive foregut. The trachea is anatomically abnormal, causing primary malacia. In 85% of cases, there is a proximal blind-ending pouch with a distal fistula (Figure 39-1). The pouch expands and compresses the trachea, thus also causing secondary malacia. Less common types include the H-type fistula and upper esophageal fistula with distal atresia. The fistulae are often small and found between the larynx and the thoracic inlet.

Figure 39-1 Tracheoesophageal fistula.

Tracheal stenosis refers to a fixed narrowing of the trachea either from extrinsic compression or from an intrinsic abnormality. Intrinsic tracheal stenosis is usually associated with complete cartilaginous tracheal rings. The rings completely encircle the trachea, and there is absence of the posterior membranous portion. Complete rings are commonly seen in association with a left pulmonary artery sling. The left pulmonary artery arises from the right pulmonary artery and then passes around the right side and behind the carina and then between the trachea and esophagus. Tracheal atresia is rare and usually caused by a malformation of the laryngotracheal groove.

Bronchial abnormalities include bronchomalacia, which may be diffuse from intrinsic airway properties, or isolated because of local compression or damage (e.g., after prolonged mechanical ventilation). Williams-Campbell syndrome is a severe form with marked deficiency of airway cartilage. Mounier-Kuhn syndrome is congenital tracheobronchomegaly associated with tracheomalacia and bronchiectasis. Anatomic abnormalities of the bronchi include a tracheal bronchus or “pig bronchus” in which an abnormal bronchus arises from the trachea proximal to the carina rather than from the right main bronchus; it usually supplies a segment of the right upper lobe. An aberrant “bridging bronchus” occurs when the right lower lobe bronchus arises from the left bronchial tree.

Clinical Presentation

Airway abnormalities can present with immediate respiratory distress after birth or their presentation may be subtle (e.g., an abnormal cry or difficulty feeding). Inspiratory stridor is often a key feature in laryngeal abnormalities. Increased inspiratory airflow or effort accentuates the stridor (e.g., during crying, feeding or upper respiratory tract infections). Laryngomalacia is associated with other congenital anomalies in 20% of cases. Episodes of recurrent croup in the first 18 months of life or episodes of croup that continue past 5 or 6 years of age should always raise the possibility of a fixed upper airway narrowing such as laryngeal web or subglottic stenosis. Laryngeal clefts can present with the triad of stridor, excessive salivation, and a muted cry. They, similar to the H-type TEF, are also associated with coughing during feedings. Other diagnostic considerations for stridor to consider include congenital hemangiomas and laryngeal cysts.

Patients with tracheomalacia and bronchomalacia may present with a harsh “barking” cough and homophonous wheeze, representing intrathoracic obstruction. Some cases are misdiagnosed as difficult-to-treat asthma. Symptoms of TEF can be varied and include recurrent coughing with feeds, choking or cyanotic spells, and frothing. If symptoms are mild, the diagnosis can be delayed beyond infancy. Recurrent infection in the same location of the lung can point to a structural bronchial anomaly, including stenosis or malacia.

Evaluation and Management

In most cases of laryngomalacia, a careful history and physical examination are sufficient to make a diagnosis. However, when symptoms are associated with failure to thrive or other laryngeal malformations are being considered, a flexible endoscopy should be performed. Anteroposterior and lateral airway radiographs may also help to localize a fixed anatomic narrowing. If a laryngeal cleft is suspected, a contrast swallow can demonstrate the defect, but a rigid bronchoscopy is also usually necessary. Laryngomalacia is usually a benign entity that resolves without intervention within the first 2 years of life, but aryepiglottoplasty has been used to treat cases associated with severe airway obstruction. Surgical excision or laser ablation is used to treat many laryngeal anomalies, including webs and cysts. Surgery for subglottic stenosis, if warranted, may involve a cricoid split or laryngotracheoplasty. Rarely in these cases or with laryngeal clefts, a tracheostomy is needed to allow for staged repair.

Tracheobronchial abnormalities usually require rigid or flexible bronchoscopy for diagnosis. Areas of extrinsic airway compression should prompt imaging by computed tomography (CT) or magnetic resonance imaging (MRI) to define the offending lesion. Patients with significant obstructive symptoms from tracheomalacia may benefit from an aortopexy, tracheostomy with or without continuous positive airway pressure (CPAP), or use of bronchoconstrictor drugs. Bronchomalacia, if severe, may also require use of CPAP; complications relating to impaired airway clearance often require chest physiotherapy and antibiotic administration.

In suspected cases of TEF, the diagnosis is made by injecting contrast via a nasogastric tube in the prone position and monitoring by fluoroscopy as the tube is withdrawn up from the midesophagus. Surgical repair involves a cervical approach in most cases with ligation of the fistula and either primary or subsequent repair of the atresia. Recurrent laryngeal nerve injury is a risk of the procedure.

Etiology and Pathogenesis

These lesions occur early in lung development, and the degree to which they affect the rest of the lung depends on their size and position. Classification of parenchymal lesions is a controversial topic, but most authors agree that descriptive terms based on imaging (e.g., presence or absence of cysts) are preferable to the assignment of histologic terms until a tissue diagnosis is made.

Congenital lobar emphysema (CLE) describes cases of an overdistended, hyperlucent lobe (Figure 39-2). The most commonly affected region is the left upper lobe (42% of cases). CLE may be caused by partial bronchial obstruction producing a ball-valve effect or a deficiency of bronchial cartilage. Less commonly, alveolar hyperplasia produces a polyalveolar lobe.

Figure 39-2 Congenital lobar emphysema.