Tracheomalacia 

Tracheomalacia is a process characterized by flaccidity of the supporting tracheal cartilage, widening of the posterior membranous wall, and reduced anterior-posterior airway caliber. These factors cause tracheal collapse, especially during times of increased airflow, such as coughing, crying, or feeding.^{[1, 2, 3]} Tracheomalacia most commonly affects the distal third of the trachea and can be associated with various congenital anomalies, including cardiovascular defects, developmental delay, gastroesophageal reflux, and tracheoesophageal fistula.

Tracheomalacia can be categorized into 3 groups based on histological, endoscopic, and clinical presentation.

• Type I presents as congenital or intrinsic tracheal abnormalities that can be associated with a tracheoesophageal fistula or esophageal atresia.
• Type II presents as extrinsic defects or anomalies, such as a vascular ring causing undue pressure on the trachea.
• Type III presents as acquired tracheomalacia that occurs with prolonged intubation, chronic tracheal infections, or inflammatory conditions like relapsing polychondritis.

Tracheomalacia is a structural abnormality of the tracheal cartilage allowing collapse of its walls and airway obstruction. A deficiency and/or malformation of the supporting cartilage exists, with a decrease in the cartilage-to-muscle ratio.

Immaturity of the tracheobronchial cartilage is thought to be the cause in type I, whereas degeneration of previously healthy cartilage is thought to produce other types. Inflammatory processes, extrinsic compression from vascular anomalies, or neoplasms may produce degeneration.

Diffuse malacia of the airway of the congenital origin improves by age 6-12 months as the structural integrity of the trachea is restored gradually with resolution of the process. See the images below.

Frequency

All types of tracheomalacia are extremely rare; no definite incidence rates are available.^[4]

In a total of 512 bronchoscopies, airway malacia was diagnosed in 160 children (94 males) at a median age of 4.0 years (range, 0-17 y). Airway malacia was classified as primary in 136 children and as secondary in 24 children. The incidence of primary airway malacia was estimated to be at least 1 in 2,100.^[5]

Tracheomalacia can be associated with a variety of congenital anomalies, including cardiovascular defects, developmental delay, esophageal anomalies, and gastroesophageal reflux. Tracheomalacia can be caused by a diffuse process of congenital origin or by a localized abnormality such as a vascular ring, anomalous innominate artery, esophageal atresia,^[1] and tracheoesophageal fistula. Internal compression by an endobronchial or tracheostomy tube also may be the culprit. Tracheal cartilage deficiency may be present in 75% of the patients with tracheoesophageal fistula. Tracheomalacia rarely is found in combination with laryngomalacia.

The entire cartilaginous structure of the upper airway is diffusely involved in congenital abnormality, or a localized area of decreased rigidity may be observed secondary to abnormal development of foregut and vasculature in embryonic life. A vascular ring around the trachea does not allow normal development in that area of trachea, and tracheomalacia is observed in the area of impingement.

The cases of acquired tracheomalacia occur with increasing frequency both in children and in adults, and the tracheomalacia often is not recognized clearly. These lesions usually cause focal tracheomalacia and may result from indwelling tracheostomy^[6] and endobronchial tube, chest trauma, chronic tracheobronchitis, and inflammation (relapsing polychondritis). They may be secondary to pulmonary resection and tracheal malignancy (cylindroma), and they may be idiopathic.

Classification of adult tracheomalacia ^[2]

• Primary (congenital)

  • Polychondritis
  • Idiopathic (Mounier-Kuhn syndrome)
• Secondary (acquired)

  • Posttraumatic (postintubation, posttracheotomy, external chest trauma, post-lung transplantation)
  • Emphysema
  • Chronic bronchitis
  • Chronic inflammation (relapsing polychondritis)^[7]
  • Chronic external compression of trachea (malignancy, benign tumors, cysts, abscesses, aortic aneurysm)
  • Vascular rings (undiagnosed in childhood)

Tracheomalacia most commonly affects the distal third of the trachea. By virtue of its intrinsic flexibility, or compliance, the trachea changes caliber during the respiratory cycle. Tracheal dilatation and lengthening occurs during inspiration; narrowing and shortening occurs during expiration. Accentuation of this cyclic process may cause excessive narrowing of tracheal lumen, thus deforming the entire length or a localized segment. However, it is rarely found in combination with laryngomalacia because of the separate developmental pathways for the trachea and the larynx.

In general, abnormal collapsibility denotes a loss of structural rigidity, such as softening, better expressed as abnormally increased compliance. Any disease process affecting the integrity of the tracheal wall is apt to cause a change in tracheal compliance. The anatomic defect may be trivial or even may escape detection. The functional interference with ventilation may cause expiratory flow obstruction and interfere with clearance of secretions.

Functional impairment is proportional to the length of the involved segment and the degree of stenosis. Furthermore, kinking may occur at the transition between healthy tracheal wall and the indurated segment, as well as in the malacic segment. In diffuse tracheal disease or extensive peritracheal adhesions, the trachea usually distends unevenly during inspiration and collapses during expiration, thus interfering with the tracheal function.

History

• Infants present after a few weeks of life with expiratory stridor (also called laryngeal crow).
• Expiratory stridor may worsen with supine position, crying, and respiratory infections.
• Feeding difficulties are reported sometimes.
• Hoarseness, aphonia, and breathing also may be reported.
• Obtain history of an acquired etiology such as prolonged intubation, tracheostomy, chest trauma, recurrent tracheobronchitis, cartilage disorder (relapsing polychondritis), and lung resection.

Physical

• Inspiratory retractions of supraclavicular and intercostal spaces may occur.
• Thoracic deformity may be present in cases of chronic tracheomalacia, especially in younger patients.
• Auscultation reveals normal inspiration but abnormal expiratory noises.
• Not uncommonly, infants may demonstrate signs of growth failure.

Differential Diagnosis

The differential diagnosis of tracheomalacia includes laryngomalacia, subglottic stenosis, congenital cysts, vocal cord paralysis, and hypocalcemic tetany. Complications include problems with acute airway obstruction and perioperative morbidity and mortality.

According to a recent study by Boogaard in 2005, when pediatric pulmonologists diagnosed airway malacia (based on symptoms, history, and lung function) prior to bronchoscopy, a correct diagnosis was made in 74% of the cases. However, in 52% of the diagnoses of airway malacia, the diagnosis was not suspected prior to bronchoscopy. The children with tracheomalacia present with atypical and variable clinical features; considerable overlap occurs with features of allergic asthma.^{[5, 8]}

Surgical therapy is indicated when conservative measures fail. The indications for tracheostomy are severe symptoms, failure of conservative therapy, and proximal or diffuse tracheomalacia. The indications for aortopexy are dying spells or reflex apnea, recurrent pneumonia, intermittent respiratory obstruction, and inability to extubate airway in an infant who is intubated.

• The trachea commences at the cricoid cartilage and terminates at the fifth thoracic vertebra. It lengthens and dilates during inspiration and narrows and shortens during expiration. Fifteen to 20 incomplete rings of cartilage prevent it from collapsing.
• The trachea is separated from the vertebral column by the esophagus posteriorly.
• In the thorax, the jugular venous arch lies anteriorly at the sternum; the brachiocephalic trunk and left common carotid artery lie at the level of the third thoracic vertebra.
• The arch of the aorta is to the left and front of the distal trachea just before it bifurcates. On the right of the trachea are pleura, on the left is the aortic arch, and posterolaterally is the left subclavian artery.
• The relation of the trachea to the aortic arch makes it liable to compress from aneurysm or from vascular rings, which occur with abnormal arterial development. Therefore, for distal tracheomalacia, whether associated with tracheoesophageal fistula or with vascular anomalies, aortopexy is the procedure of choice.

Most infants who have mild-to-moderate symptoms should be offered conservative therapy because these patients improve by age 18-24 months.^{[6, 9]}