Lower Large Airway Disease

Overview

Disorders of the lower large airways occur frequently in the pediatric population and have the potential to be life threatening. Because these disorders are often associated with nonspecific clinical symptoms, the diagnosis frequently is missed or delayed, particularly in infants and young children. After careful investigation of the clinical history and physical examination, imaging evaluation is the next management step. Imaging plays an important role in the diagnosis of congenital and acquired lower large airway disorders. By becoming familiar with the characteristic imaging findings of lower large airway disorders, radiologists can play an important role in ensuring prompt diagnosis, guiding appropriate management, and providing follow-up evaluation of these often acute and complex conditions in pediatric patients.

This chapter reviews the etiology, imaging findings, and management of the frequently encountered congenital and acquired lower large airway disorders in the pediatric population. Large airway disorders due to primary benign neoplasms and extrinsic compression due to mediastinal vascular anomalies are not included in this chapter because they are discussed in other chapters (see Chapters 51 and 76 , respectively) in this book.

Spectrum of Lower Large Airway Disease

Congenital Anomalies

Tracheobronchial Branching Anomalies

Tracheal Agenesis

Etiology.

Tracheal agenesis is characterized by either partial or complete tracheal underdevelopment. Three main types of tracheal agenesis exist. Type 1 consists of absent upper trachea and connection of the lower trachea to the esophagus; type 2 consists of a common bronchus connecting bilateral main bronchi to the esophagus; and type 3 consists of independent bilateral main bronchi arising from the esophagus ( Fig. 52.1A ). Of these three types, type 2 is the most common. Affected pediatric patients typically present with severe respiratory distress and absence of an audible cry, and the airway cannot be intubated below the larynx immediately after birth. The diagnosis of tracheal agenesis should be considered in any infant who demonstrates improved lung ventilation after placement of the endotracheal tube in the esophagus after an initial unsuccessful intubation attempt. Once tracheal agenesis is diagnosed, radiologists should carefully investigate for other congenital anomalies that frequently are associated with this condition, such as congenital heart disease, duodenal atresia, and radial ray anomalies.

Imaging.

Chest radiographic imaging findings of tracheal agenesis often are nonspecific, such as unaerated lungs or decreased lung volume. However, the diagnosis of tracheal agenesis should be considered when absence of the normal tracheal air lucency, abnormal carinal position, and placement of the endotracheal tube in the esophagus are seen on chest radiographs immediately after birth ( Fig. 52.1B and C ). Computed tomography (CT) and/or bronchoesophagoscopy confirm the diagnosis, which can show both the partial or complete tracheal underdevelopment and anomalous bronchi connected to the esophagus ( Fig. 52.1D ).

Treatment and Follow-up.

Because of difficulties related to both early diagnosis and treatment, tracheal agenesis usually is a fatal condition. The initial management of tracheal agenesis is aimed at early diagnosis at birth and immediate maintenance of airway patency, usually via the esophagus in the presence of a bronchoesophageal fistula. Patients with short-segment tracheal agenesis may be amenable to direct tracheal anastomosis.

Tracheal Bronchus

Etiology.

Tracheal bronchus is a congenital bronchial branching anomaly in which an ectopic (more frequently) or supernumerary bronchial branch arises from the lateral tracheal wall just above the carina. This condition also is known as bronchus suis because it is a normal finding in pigs. The incidence of tracheal bronchus in the pediatric population is between 0.1% and 5%. Tracheal bronchus most frequently occurs on the right side. Most pediatric patients with tracheal bronchus are asymptomatic, and it is usually an incidental finding detected on imaging studies obtained for the workup of other medical conditions. However, patients with tracheal bronchus also may present with symptoms of persistent or recurrent upper lobe pneumonia, atelectasis, or air trapping. Additionally, tracheal bronchus may unexpectedly be discovered after intubation as a result of upper lobe atelectasis related to inadvertent occlusion of the ectopic upper lobe bronchial orifice by a low-lying endotracheal tube.

Imaging.

On chest radiographs, secondary imaging findings of tracheal bronchus such as upper lobe atelectasis or pneumonia can be detected, but the anomalous upper lobe bronchus cannot be reliably visualized. In the past, tracheal bronchus was evaluated with tracheobronchography. However, CT with two-dimensional (2D) and three-dimensional (3D) reconstructions is the imaging technique of choice for evaluating anomalous tracheal bronchus and associated lung abnormalities ( Fig. 52.2 ). Bronchoscopy can confirm the diagnosis of tracheal bronchus when necessary.

Treatment and Follow-up.

Patients with incidentally detected tracheal bronchus generally do not require treatment. However, symptomatic children with recurrent upper lobe infection due to tracheal bronchus may require surgical resection, especially if permanent lung damage has developed or they are considered at risk for the development of permanent lung damage.

Esophageal Bronchus or Lung

Etiology.

Esophageal bronchus or lung is a rare congenital anomaly. The term esophageal bronchus refers to the condition in which a lobar bronchus, typically the medial basal segment of the right lower lobe, arises directly from the esophagus. The term esophageal lung is used when the main bronchus arises directly from the esophagus. It is associated with a wide spectrum of clinical presentations ranging from asymptomatic to recurrent severe pulmonary infections or even death depending on the size and location of the anomaly. In general, symptomatic pediatric patients with esophageal bronchus or lung typically present with feeding difficulties and recurrent respiratory tract infections. Other associated congenital anomalies include congenital heart disease, duodenal atresia, duodenal stenosis, distal tracheoesophageal fistula, and esophageal atresia.

Imaging.

Affected pediatric patients typically present as a result of aspiration during feeding, with radiographic findings of air space opacification in the medial lower lobe in the case of esophageal bronchus and air space opacification that involves the entire lung in the case of esophageal lung. An esophagram can provide a definitive diagnosis by allowing visualization of a direct communication between a bronchus and the esophagus ( Fig. 52.3 ). CT may be helpful for evaluating associated lung parenchymal abnormalities and guiding surgery.

Treatment and Follow-up.

Surgical lobectomy or pneumonectomy is the current management of choice for symptomatic patients with esophageal bronchus or lung, respectively.

Congenital Tracheal Stenosis

Etiology.

Congenital tracheal stenosis is a rare condition characterized by intrinsic narrowing of the tracheal lumen, usually as a result of underlying complete cartilaginous rings. Such cartilaginous rings with an absent or deficient posterior membranous portion render the tracheal lumen smaller and less pliable. Affected pediatric patients typically present in the first year of life with expiratory stridor, wheezing, and respiratory distress. Congenital tracheal stenosis traditionally is classified into three types: (1) focal (50%), (2) generalized (30%), and (3) funnel shaped (20%). Other congenital anomalies often associated with congenital tracheal stenosis are tracheoesophageal fistula, pulmonary agenesis or hypoplasia, pulmonary artery sling type 2, and bronchial stenosis.

Imaging.

Although neck and chest radiographs or fluoroscopy may lead to the suspicion of congenital tracheal stenosis when a narrowed trachea is encountered in pediatric patients with respiratory symptoms, CT is the current imaging modality of choice for diagnosis and characterization. With CT, the diagnosis of congenital tracheal stenosis is based on the identification of decreased caliber with a rounded configuration of the trachea without evidence of tracheal wall thickening. The size of the subglottic region (which does not contain tracheal cartilage) can serve as an internal reference standard. The use of 2D/3D reconstructed CT imaging is particularly helpful for increasing detection of subtle stenoses, improving measurement of craniocaudal extent of disease, and enhancing evaluation of its anatomic relationship with other mediastinal structures for preoperative assessment ( Fig. 52.4 ). This appearance contrasts with the normal appearance in which the C -shaped rings do not extend to the posterior membranous wall. In addition, virtual bronchoscopy can evaluate the airways distal to high-grade tracheal stenoses, beyond which a conventional bronchoscope cannot pass. CT also may aid in the detection of other associated anomalies that often have an abnormal lung component.

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