Tracheomalacia

Definition:

Tracheomalacia is defined as abnormal collapse of tracheal walls during inspiration.

In these patients there is widening of the posterior tracheal wall with reduction of antero posterior diameter of trachea causing obstruction during inspiration or expiration depending on the site of lesion. There is also associated flaccidity of tracheal cartilages.

Pathophysiology:

Tracheomalacia can be classified as primary and secondary.

Primary tracheomalacia occurs as a primary lesion due to abnormal development of tracheal cartilage. If the lesion involves the extrathoracic portion of trachea then obstruction occurs during inspiration, and if it is intrathoracic then the obstruction occurs during expiration. Since majority of trachea lies intrathoracic obstruction occurs during expiration.

Secondary tracheomalacia occurs always in conjunction with conditions that compress the airway. It could be mediastinal mass, vascular arches and malformations compressing trachea. Rarely thyroid malignancies may cause secondary tracheomalacia. In children chronic aspiration can cause secondary tracheomalacia.

Tracheomalacia commonly affects the distal 1/3 of trachea. Due to its intrinsic flexibility, trachea is capable of changing its caliber during the respiratory cycle. Dilatation and lengthening occurs during inspiration, narrowing and shortening occurs during expiration. Accentuation of this process may cause excessive narrowing of the tracheal lumen causing tracheomalacia. Tracheomalacia can not only cause respiratory embarrassment, it could also interfere with clearence of secretions.

Age of occurrence:

Since tracheomalacia commonly encountered is of primary variety, it is seen in infants and young children. In majority of cases the tracheal lumen increases in size, and the tracheal cartilages firm up causing resolution of symptoms by the time child reaches the age of 3.

Complaints:

The patient has wheeze which manifests in affected child between 4-8 weeks. These children are also known as "Happy Wheezers" because despite their airway problems they maintain good oxygen saturation and grow normally. This is in contrast to patients suffering from cystic fibrosis or bronchial asthma.

Physical findings:

1. The baby appears to be clinically well despite the wheeze

2. Patients respitaratory rate and oxygen saturation are mostly normal except in extreme cases when the respiratory rate may increase.

3. Feeding difficulties have also been reported

4. Inspiratory retraction of supraclavicular and intercostal spaces occur

5. Thoracic deformity is also seen in some patient with tracheomalacia

Causes of tracheomalacia: Most common cause of tracheomalacia is idiopathic, and hence primary tracheomalacia. Transient defects in tracheal cartilage development may cause primary tracheomalacia.

Secondary causes of tracheomalacia include compression of trachea due to vascular rings, or due to a malignant mass. It is also commonly found in patients with gastro oesophageal reflux. It is also known to coexist in children with cystic fibrosis and bronchopulmonary dysplasia. Prolonged intubation and tracheitis can cause secondary tracheomalacia.

Tracheomalacia is classified in to three groups depending on histologic, endoscopic and clinical correlation.

Type I tracheomalacia: Congenital or intrinsic tracheal anamolies associated with tracheo oesophageal fistula

Type II tracheomalacia: Extrinsic defects / anamolies that could cause undue pressure on the trachea i.e. abnormal vascular rings / tumors etc.

Type III tracheomalacia: Acquired tracheomalacia due to prolonged intubation, tracheitis etc.

Differential diagnosis:

Laryngomalacia, subglottic stenosis, bilateral abductor palsy, congenital cysts of trachea etc.

Investigations:

X-ray chest may reveal hyperinflation and tracheal lumen narrowing during expiration. Vascular anamolies like double aortic arch may also be revealed in the chest radiograph.

Dynamic expiratory CT scans may be useful in clinching the diagnosis

Cineflouroscopy with contrast in the oesophagus may also demonstrate tracheomalacia

Bronchoscopy:

Is diagnostic. The cardinal features seen in bronchoscopy are:

1. Loss of normal semicircular shape of tracheal lumen

2. Forward ballooning of posterior tracheal wall

3. Antero posterior narrowing of tracheal lumen

Management:

Primary tracheomalacia of milder variety can be managed by conservative means. This condition is commonly benign and most of the infants manage to out grow this problem by the time they reach 3 years.

Bronchodilators are not of help in this condition, and may sometimes worsen tracheomalacia. It is only the tone of the tracheal smooth muscles that maintain the tracheal lumen. When the tracheal muscles relax due to the effects of bronchodilators the situation is likely to worsen. If the patient has retained secretions, chest physiotherapy may be of help.

Reflux oesophagitis if present should be treated aggressively. Systemic steroids may be of some help in some patients with associated tracheitis.

Continuous postitive pressure ventilation may be adminsitered via nasal mask to tide over acute crisis.

If tracheomalacia involves proximal segment of trachea then tracheostomy or stenting can be resorted to in extreme cases.

Surgery is indicated only if the patient:

1. Has difficulty in gaining weight

2. Recurrent episodes of pneumonia / apnoea

3. Air way obstruction necessitating long term airway support

If the tracheomalacia occurs in the proximal segment tracheostomy may act as a stenting device. If the presence of aortic arch is the cause for compression then aortopexy should be resorted to. In this procedure the arch of the aorta is lifted out of the trachea. This procedure is successful in 75% of the cases. If vascular rings are present then repair of these rings should be performed.

When tracheomalacia involves intrathoracic segment of trachea then stenting can be resorted to. Metalic stents or silicone stents could be used. Stents can be placed during bronchoscopy. Silicone stents are easy to insert and remove. Metallic stents can cause tracheal granulations.