The term tracheomalacia indicates a condition characterized by a structural abnormality of the tracheal cartilage inducing excessive collapsibility of the trachea. It constitutes about half of the congenital pathologies of the trachea and is distinguished in diffuse and localized varieties depending on the extent of the disease. The distinction also concerns the primary forms due to an alteration of the development of the trachea and the secondary conditions, produced by causes that act after the normal development of the organ. The primary forms can be diffuse or localized; the secondary ones are generally localized.
Primary diffuse tracheomalacia is a rare congenital defect, characterized by the immaturity of the cartilaginous rings (usually at the distal third of the trachea), which leads to a weakness of the entire tracheal structure. It is more frequent in the premature baby and can be associated with laryngomalacia or can involve trachea along with other respiratory tracts. When the main bronchi are also affected, this condition is termed as tracheobronchomalacia. Congenital tracheomalacia can combine with other congenital defects (e.g., cardiac defects), tracheoesophageal fistula, developmental delay, and gastroesophageal reflux (GER). Some conditions, such as vascular rings, can produce a localized primary defect in the development of the trachea.
The secondary forms concern acquired conditions which induce a weakening of the tracheal wall. These conditions can be ascribable to inflammatory processes that produce a diffuse tracheomalacia, although these secondary forms are also the result of external compressions due to cardiovascular structures or other masses which produce localized area of weakness of the tracheal wall.
In pathophysiological terms, the structural alterations of the trachea alter its mechanics. As by Poiseuille’s Law, even a small amount of narrowing in the lumen of the trachea can cause a significant decrease in airflow. Depending on the causative pathology (primary or secondary tracheomalacia and underlying diseases), patients’ symptoms may spontaneously resolve over the natural history of the disease or can cause persistent respiratory distress.
Although there is no internationally agreed classification system, the etiology of the disease can divide into three main categories: congenital defects in tracheal integrity, acquired conditions weakening the whole or partial tracheal structure, and conditions causing extrinsic compression of the airway. The first group refers to conditions that cause immaturity of the trachea; the other two groups refer to conditions in which a normally developed trachea undergoes a degeneration process.
Congenital defects in tracheal integrity
Numerous diseases may cause immaturity of the tracheobronchial cartilage and, in turn, congenital tracheomalacia. Systemic conditions like Ehlers Danlos and bronchopulmonary dysplasia can result in an innately weakened trachea. There are many childhood syndromes associated with tracheomalacia. There is a significant incidence of coexisting congenital heart diseases, and tracheoesophageal fistula (a tracheal defect may be present in up to 75% of the patients with tracheoesophageal fistula) or esophageal atresia. Some conditions may compromise the normal development of the trachea in the area where they exert compression. Among these conditions that compromise the tracheal integrity, there are vascular rings; they primarily result from the persistence of the double aortic arch after the second month of fetal life and determine a localized alteration of the development of the trachea (and esophagus). Apart from the double aortic arch which accounts for approximately 40% of the congenital vascular compressions, other conditions including a right aortic arch, a left-sided origin of the (right) innominate artery, a right-sided origin of the left common carotid artery, or an anomalous origin of the left pulmonary artery from the right pulmonary artery can provoke tracheal compression.
In adults, congenital tracheomalacia can be due to Mounier-Kuhn syndrome. It is a rare disease produced by atrophy of elastic fibers in the trachea and main bronchi, which induces tracheobronchial flaccidity, dilatation, and collapse. The syndrome is often associated with Ehlers-Danlos syndrome, Marfan syndrome, and cutis laxa. The disorder, also referred to as tracheobronchomegaly, can occur at various ages but is usually diagnosed in young adults with recurrent bronchopulmonary infections with chronic non-productive or productive cough, dyspnoea, and hemoptysis, and wheezing. However, clinical manifestations vary from paucisymptomatic cases (chronic cough) to severe cases with bronchiectasis or bullous emphysema, which can lead to severe impairment of respiratory function. Although Mounier-Kuhn syndrome may hank a link to a genetic defect, research has yet to identify any gene alteration.
Acquired conditions weakening the tracheal structure
There are multiple potential causes for acquired tracheomalacia. Inflammatory processes such as tracheobronchitis, recurrent polychondritis, as well as chronic lung conditions such as bronchiectasis, can weaken the structure of the airway, predisposing it to collapse. Recurrent polychondritis is a rare autoimmune rheumatic disease characterized by episodes of painful and destructive inflammation of the cartilage and other connective tissues in various organs. Acquired diffuse tracheobronchial collapse is often a finding in chronic obstructive pulmonary disease (COPD). Other conditions such as prolonged intubation, surgery (e.g., pulmonary resection), chest trauma, or foreign bodies can cause segmental disease. Neoplastic pathologies in the respiratory tract (e.g., cylindroma) may also affect the structure of the airway leading to tracheomalacia.
Disease processes that are extrinsic to the respiratory system such as cardiovascular masses (e.g., vascular aneurysms, and dilated cardiomyopathy), and non-pulsatile fixed compressions including large thyroid goiters, and intrathoracic neoplastic diseases may externally compress on the airway leading to tracheomalacia.
Primary congenital tracheomalacia is a rare condition, and the exact disease incidence and prevalence are uncertain. A proportion of the disease likely goes undiagnosed as often it may resolve spontaneously. A single-center retrospective study where 512 bronchoscopies were analyzed found the estimated incidence of disease to be at least 1 in 2100 children.. The secondary forms have a variable incidence according to the underlying pathology. Of note, recurrent intubation, and duration of intubation represent the most common cause of adult acquired tracheomalacia. The overall reported incidence of tracheobronchomalacia in COPD individuals is 7 to 15%. Mounier-Kuhn syndrome is a rare disorder, as there are only approximately 300 cases reported to date.
The trachea connects the larynx to the distal airways, and its structural support derives from 16 to 20 rings of hyaline cartilage. The rings form a "U" shape as they are incomplete at the posterior aspect, which is covered by a posterior membrane. A variety of different disease processes can disrupt this support structure, causing narrowing of the lumen of the trachea (reduced anterior-posterior airway caliber) with associated loss of the semicircular shape and bulging of the posterior membranous wall. This narrowing of the trachea causes the symptoms experienced by patients. Under normal conditions, a modest expiratory collapse of the trachea constitutes a condition of frequent occurrence; in the infant, during forced expiration, a reduction of the tracheal lumen can be achieved up to 30% of its diameter. A tracheal collapse capable of producing an obstacle to lung ventilation must be greater than 50% of the tracheal diameter. In these cases, clinically evident expression of tracheomalacia occurs.
Symptoms may be persistent or intermittent, depending on the severity and extent of disease. Due to expiratory flow obstruction, patients can present with expiratory stridor. Moreover, alteration of the clearance of secretions can be expressed as productive cough and increased susceptibility to upper airway infections. Furthermore, while intrathoracic collapse occurs during expiration, extrathoracic malacia (upper malacia) results in inspiratory collapse. Infants may be asymptomatic; however, the trachea may be easily compressed during the swallowing of a food bolus, leading to failure to thrive . In congenital forms, the expiratory stridor begins after 4-6 weeks and increases during times of increased airflow, such as activity, coughing, crying or feeding, and in the supine position, while it decreases at rest. A worsening after meals indicates a possible association with GER (a potential cause). Again, crying is normal, as is the children's weight growth. Children affected by compression du to vascular rings lie with the head and neck hyperextended to stretch the trachea and reduce its compression.
Apart from stridor, the clinical picture of tracheomalacia can encompass different symptoms and signs, including inspiratory retractions of supraclavicular and intercostal spaces, hoarseness, aphonia, breathing difficulties, and feeding problems. Furthermore, recurrent respiratory infections can exacerbate these symptoms, and, if severe, can lead to respiratory distress, apnea, cyanosis, and airway obstruction, which may require intubation. However, congenital tracheomalacia, if not associated with other pathologies, and is not extended to other respiratory tracts, generally resolves in 12 to 24 months. Abnormal expiratory noises usually characterize auscultation despite a normal inspiration.
The clinician needs to take a thorough history, focusing primarily on any respiratory symptoms, as well as information regarding the perinatal period, prematurity, any surgical procedures or intubations performed, and feeding and growth in young children. Subglottic airway pathology should be considered in children presenting with recurrent episodes of croup and atypical wheeze.
Patients with other causes of subglottic airway narrowing may present similarly. Therefore, a thorough physical examination should include a full assessment of the head and neck, as well as the cardio-respiratory systems. Syndromic features may indicate potential concurrent disease. A small proportion of patients with cutaneous haemangiomas (especially facial) may have subglottic hemangiomas.
Although the diagnosis is by endoscopy, diagnostic imaging has an important role in the etiological definition and especially in the identification of external compressions, in secondary tracheomalacia. For instance, cine fluoroscopy combined with contrast swallow may give information regarding the degree of tracheal collapse, as well as delineating esophageal abnormalities and external tracheal compression. It is of high specificity and low sensitivity; however, the exam is a useful adjunct to endoscopy, mainly when other imaging modalities are not available. Many centers also use tracheobronchography as an alternative method alongside bronchoscopy for diagnosis.
Multidetector or ultrafast computed tomography (CT) imaging allows a quick assessment of the airway. Other mediastinal structures can also be studied if using contrast. When paired with bronchoscopy, it demonstrates good diagnostic accuracy. Nevertheless, CT is associated with radiation exposure, and in young children, this may require sedation, which can change airway dynamics. These issues are potentially solvable by using lower doses of radiation in expiratory phase scans and free-breathing cine-multidetector CT imaging, respectively.
The gold standard investigation is direct visualization of the airway during spontaneous respiration via bronchoscopy; this is often undertaken alongside other imaging methods, as previously described. Bronchoscopy can demonstrate the narrowing of the lumen of the trachea with associated loss of the semicircular shape and bulging of the posterior membranous wall. There are currently no studies comparing rigid bronchoscopy to flexible bronchoscopy, and it is accepted that each has its benefits and drawbacks.
A variety of imaging techniques may give further information about the disease. Plain radiographs might not show tracheal abnormalities; however, other abnormalities such as vascular anomalies and respiratory pathologies may be visible. Although the literature around the use of dynamic magnetic resonance imaging (MRI) in the assessment of tracheomalacia is limited, it provides excellent delineation of the anatomy along with no radiation. Thanks to advances in technology, cine-MRI may enable a dynamic assessment of the airway. The technique is, however, time-consuming and, therefore, may require intubation or sedation in younger children. Novel imaging approaches such as ultrashort echo-time magnetic resonance imaging (UTE MRI) can represent an interesting solution for assessing tracheomalacia dynamically in neonates without sedation and ionizing radiation.
Pulmonary function tests may show an obstructive pattern and can provide supportive evidence; however, they should not be used in isolation to diagnose tracheomalacia.
Depending on the extent of disease and other associated conditions, tracheomalacia can be treated conservatively or with medical management and surgery. The management of these patients is best by an interprofessional team with input from a variety of specialists.
Congenital and mild acquired disease may resolve spontaneously; therefore, these patients should be treated conservatively with adequate monitoring. Healthcare team members should dispense advice to parents regarding appropriate immunizations, vaccinations, and passive smoking avoidance. Although clinicians use bronchodilators, anti-muscarinic agents, mucolytics, and antibiotics, there is currently little evidence for their benefit.
Chest physiotherapy may be required to help the management of secretions and to prevent airways infections. Prevention and management of GER are mandatory, and specific feeding regimes are necessary to avoid aspiration and to ensure adequate growth and development.
In adults, tracheomalacia may be an incidental finding, and if they do not suffer from any symptoms, then a conservative approach should be adopted. Often there is a concurrent disease such as COPD that requires simultaneous management. Continuous positive pressure ventilation (CPAP) is an option in those who fail conservative management. Surgery is the last resort.
The literature around the efficacy of medical treatment options is limited, and the majority of the evidence has its basis in small retrospective studies. There is anecdotal evidence that supports the use of nebulized hypertonic saline in aiding clearing of mucus, and prophylactic antibiotics. Co-existing disease requires appropriate management. In the acute setting, CPAP may be used to provide ventilatory pressure support, although there are no available prospective or randomized trials to guide treatment algorithms.
Patients with severe symptoms and acquired disease are more likely to require surgical intervention; this is particularly true of patients who experience apneic spells, failure to thrive, recurrent pneumonia, and cyanotic episodes. It is essential to look for the presence of a tracheoesophageal fistula during surgery and correct it if required.
Stenting is an option in severe disease. There are a variety of different options for intraluminal stenting; however, each poses its own potential issues. Granulation tissue, vascular erosion, and mucosal hyperplasia can occur in all variety of stents. Although silicone stents may be easier to remove, they require a general anesthetic and insertion via rigid bronchoscopy. Although often patients experience short term improvement of symptoms from stenting, the longevity of resolution of symptoms is unpredictable. Thus, stenting is not appropriate for diffuse disease. If the patient can tolerate stenting, definitive surgical treatment (for example, with tracheobronchoplasty) is an option. In patients with short segmental disease, tracheal resection and anastomosis may also be a consideration in centers with the appropriate expertise.
Historically, surgery involved tracheostomy, which allows long term mechanical ventilation if required and a degree of airway stenting. Clinicians can perform tracheostomy either surgically or percutaneously. However, the relative morbidity can be high, and therefore, clinicians should reserve this option for end-stage disease or disease, which is either proximal or diffuse.
Aortopexy is a surgical approach to tracheomalacia and a favored option in many centers. The approach provides an anterior lifting of the aorta that is sutured to the posterior surface of the sternum. Nevertheless, there are different surgical approaches and different techniques. Aortopexy is most commonly performed in the anterior direction. It involves the anterior fixation of the ascending aorta and may be performed via a left anterior thoracotomy, partial sternotomy, or thoracoscopically. Key procedural steps may include the movement of overlying vessels to the back of the sternum, elevation of the pulmonary arteries, and occasionally direct suturing to the trachea if required. These techniques aim to increase the space within the mediastinum and therefore relieve potential external compressive forces on the trachea. If the clinician places sutures in the vessel, a balance between suture strength and the risk of hemorrhage is a consideration. Recently, there have been encouraging results from a single-center study looking at posterior aortopexy, which may address the inwards collapse of the membranous posterior wall of the trachea during inspiration.
Clinicians must consider different clinical conditions that manifest themselves with the typical symptoms of tracheomalacia (e.g., stridor) in the differential diagnosis:
Laryngomalacia is a condition characterized by tight aryepiglottic folds with weakness in the supraglottic structures resulting in inwards collapse during inspiration. Patients can present with feeding difficulties and inspiratory stridor, which is worse on lying flat. The stridor is usually not present at birth but appears in the first 4 to 6 weeks of life and then increases in the following months. Nevertheless, laryngomalacia often resolves by the age of 2. It is diagnosable using flexible nasendoscopy.
Subglottic stenosis commonly results from repeated trauma from either intubations or high sited tracheostomies. Patients often have biphasic stridor, which does not typically change with position. These patients may be mistaken for children who are getting recurrent episodes of croup. Diagnosis is via endoscopic examination, either flexible nasendoscopy or bronchoscopy.
Vocal cord paralysis can either be congenital or acquired. If unilateral, patients may have weak phonation or hoarseness with potential issues with swallowing and aspiration. If bilateral, this is a potential airway emergency, and the patient will present with stridor and severe dyspnea. The unilateral form is due to a direct lesion of the vocal cords, but above all to damage to the recurrent laryngeal nerve (compression, surgical trauma, neoplastic invasion). The bilateral acquired vocal cord paralysis with adduction is a serious iatrogenic condition whereas the bilateral congenital form is usually associated with CNS problems such as perinatal asphyxia or hemorrhagic stroke, hydrocephalus, Arnold Chiari malformation. Diagnosis is via laryngoscopy, flexible nasendoscopy, or bronchoscopy.
Epiglottitis and other infections of the airway may cause stridor and dysphagia. The clinical picture develops acutely and requires rapid treatment.
Patients with foreign body aspiration usually have a history of choking after swallowing an object. Plain radiographs will show the foreign body if it is radio-opaque. Ventilating bronchoscopy may be both diagnostic and therapeutic for these patients. It is particularly important to determine if the foreign body is of organic material or a button battery, as both can lead to significant damage to the respiratory epithelial lining.
Recurrent respiratory papillomatosis in children is an uncommon but potentially life-threatening benign tumor of the respiratory tract. This condition is characterized by recurrent growth of polyps due to the human papillomavirus, especially in the larynx but also in the tracheal and distally. Patients may have symptoms of upper airway obstruction and have a hoarse cry and phonation. The diagnosis is with flexible nasendoscopy or bronchoscopy.
For patients with the congenital disease and mild symptoms, the prognosis is generally favorable, and symptoms tend to resolve by around the age of 2 years. Patients with other co-existing comorbidities tend to have symptoms that are persistent until later in childhood. For those whose symptoms persist until adulthood, they may have a degree of exercise intolerance. The prognosis of the secondary conditions depends on the pathology that produced the alteration and on the degree of the lesion.
Complications of untreated tracheomalacia involve potential airway obstruction, recurrent respiratory infections, and failure to thrive. The main objective of treatment is to reduce the likelihood of developing these complications; however, the treatment options are not without their risks. Early complications from tracheostomy include bleeding, infection, recurrent laryngeal nerve damage, and false passage. Later issues include trachea-esophageal fistula, a fistula between the trachea and innominate artery, subglottic stenosis. Aortopexy poses potential risks of pneumothorax, pleural effusion, atelectasis, phrenic nerve palsy, and bleeding.
It is of paramount importance that patients, parents of children, and primary care providers are familiar with the symptoms of the disease and potential complications to enable optimum secondary disease prevention.
Depending on disease severity and pathology, patients with tracheomalacia may need input from a variety of interprofessional team members. Primary care and emergency medicine triage nurses and physicians should be aware of the variety of ways that patients with tracheomalacia may present. They should be mindful of the potential of acute airway obstruction and apneic attacks and suspicious of subglottic pathology in those children presenting with recurrent croup or atypical wheeze. Acutely unwell patients will require nursing staff to obtain vitals, attach appropriate monitoring, and aid with resuscitative measures. If the patient is particularly ill, anesthesiologists may be needed to secure the airway. All of the above will facilitate diagnosis and enable appropriate referrals to reduce delays in treatment.
After the diagnosis of tracheomalacia is made by respiratory pediatric physicians and radiologists, interprofessional input is often required to optimize the management of the disease. Physiotherapists may be necessary to provide chest physiotherapy to aid with secretions and reduce respiratory infections. Speech and language therapists, along with dieticians, can provide an assessment of feeding and nutrition to ensure adequate growth and development is made in children. If conservative management fails, then cardiothoracic and otorhinolaryngology surgeons may be needed to guide further surgical intervention. Communication between the interprofessional team must be maintained at all stages of the patient journey to ensure the best possible care. [Level 5]
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