Normal trachea with a 4–5:1 cartilage/membranous trachea ratio
Definitions
Congenital Tracheal Stenosis
Proximal (a) and distal (b) views of complete tracheal rings with an “O-shaped” appearance of the cartilage
“Figure-9 trachea” seen in tracheal sleeves with overlap of the posterior cartilaginous portions
Tracheomalacia
(a) Intrinsic posterior tracheomalacia with a “bowed” appearance to the cartilage and a cartilage/membranous trachea ratio of <4–5:1. (b) Severe tracheomalacia seen with absent cartilage rings causing a functional tracheal stenosis. (c) Tracheomalacia in the setting of a tracheoesophageal fistula
A comprehensive discussion of each type of vascular compression is beyond the scope of this chapter; however, several articles and book chapters available provide excellent summaries of this information [8–13]. Briefly, a double aortic arch , the most common vascular ring, is seen when the ascending aorta bifurcates to surround the trachea and esophagus and then rejoins to form the descending aorta. A left-sided aortic arch with aberrant right subclavian artery and right-sided aortic arch with aberrant left subclavian artery occur when there is abnormal involution of the right or left fourth arches, respectively, such that the aberrant subclavian artery takes a retroesophageal course to perfuse the respective side. In a pulmonary artery sling, the left pulmonary artery arises from the right pulmonary artery, travels over the right bronchus, and then passes through the tracheoesophageal groove. Finally, an aberrant innominate artery is seen when the innominate artery takes off from a more distal, leftward position along the aortic arch.
Framework to classify and discuss tracheal anomalies, including stenosis and malacia
Epidemiology
Congenital Tracheal Stenosis
Compared with subglottic stenosis, tracheal stenosis is relatively rare in the pediatric population and is more commonly congenital in origin as opposed to acquired [4]. Congenital tracheal stenosis has been estimated to occur in only 1 in 64,500 births [14] and accounts for only 0.1–0.3% of all laryngotracheal stenosis cases [2]. The most common form of congenital tracheal stenosis is complete tracheal rings; however, these are still extremely rare and account for <1% of all airway stenoses [2]. Complete tracheal rings are associated with other congenital malformations in 60–75% of cases [15–17]. These include cardiovascular anomalies (most commonly a pulmonary artery sling), tracheal bronchus, lung hypoplasia or agenesis, Down syndrome, and variations of the VATER/VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, limb abnormalities) spectrum.
Other causes of congenital tracheal stenosis, including laryngotracheal webs, tracheal sleeves, and trachea agenesis, are even more rare. Tracheal sleeves are universally associated with craniosynostosis syndromes, such as Pfeiffer, Crouzon, or Apert [18]. Tracheal agenesis has a prevalence of less than 1:50,000 births and occurs twice as commonly in males. This is typically associated with premature birth (52%), polyhydramnios, and other congenital malformations (90%) [19]. The incidence of tracheal webs has been reported to be 1/10,000 births [20]. Reports in the literature are sparse, however, and some authors question whether more frequent webs occur and are incidentally treated via intubation [4]. Tracheal agenesis has been reported to occur in 1 in 50,000 to 1 in 100,000 live births [21]. This anomaly is almost universally fatal; however, the presence of a tracheoesophageal fistula or distal trachea may allow for temporary ventilation via esophageal intubation or tracheostomy, respectively, and potential future reconstruction [5, 22, 23].
Tracheomalacia
Primary tracheomalacia is the most common congenital anomaly of the pediatric trachea occurring in approximately 1/2100 children [24]. Congenital tracheomalacia has been associated with other airway anomalies, including laryngomalacia and bronchomalacia [25–27]. Primary tracheomalacia is also seen in the setting of mucopolysaccharidoses [28], connective tissue disorders, and chromosomal abnormalities and may present with more diffuse tracheal involvement [15, 29, 30]. As mentioned previously, congenital tracheomalacia also occurs in patients with tracheoesophageal fistula [31] or large (type 3 or 4) laryngotracheal clefts [25–27]. The prevalence of severe tracheomalacia in patients with esophageal atresia has been reported to range from 11% to 33% [29]. Absent tracheal rings are an extreme form of primary tracheomalacia and are exceedingly rare. Children with this anomaly are typically otherwise normal. Associations with left vocal fold paralysis and esophageal atresia have been reported [4].
Secondary tracheomalacia is not in itself uncommon; however, it is asymptomatic or minimally symptomatic in the majority of cases. As depicted in Fig. 36.5, tracheomalacia can occur secondary to a variety of conditions. Children treated with prolonged mechanical ventilation are one of the most commonly affected patient populations [24, 32]. The prevalence of tracheomalacia in infants with bronchopulmonary dysplasia has been estimated to be at least 16% [33]. However, the true incidence is difficult to determine, as only symptomatic children are typically assessed endoscopically [34]. Patients who have undergone tracheostomy are another population commonly found to have secondary tracheomalacia . Malacia has been reported to occur in at least 10% of patients after tracheostomy due to trauma to the tracheal rings with resultant increased compliance of the suprastomal airway, stoma, site of the tracheostomy cuff, and/or distal end of the tracheostomy tube [15, 34].
Despite vascular rings accounting for <1% of all congenital cardiac defects, they are the most common congenital anomaly resulting in secondary airway compression [10, 35, 36]. The double aortic arch is the most common form of symptomatic vascular ring in the pediatric population, accounting for ~50–60% of vascular rings [8, 9, 11, 12]. Other vascular rings and slings causing airway compression are the left-sided aortic arch with aberrant right subclavian artery, right-sided aortic arch with an aberrant left subclavian artery, pulmonary artery sling, anomalous innominate artery, and cervical aortic arch [8–11]. Innominate artery compression occurs in up to 30% of children [37], but is only symptomatic enough to undergo surgery in 13.7% [38]. Of note, at least 50% of children with a pulmonary artery sling will also have long-segment congenital tracheal stenosis in the form of complete tracheal rings [39]. Additionally, vascular airway compression has been showed to occur in approximately 1–2% of children with congenital heart disease, even in the absence of vascular rings [10].
Pathophysiology
The embryologic development of the aerodigestive tract, particularly in relation to the surrounding vascular structures, is a complex process . An understanding of these mechanisms and the ways they can go wrong, however, can help explain many of the tracheal anomalies encountered by clinicians. In general, developmental lesions occurring by week 4 of gestation result in more severe manifestations of disease (i.e., tracheal agenesis), while those occurring after week 8 may have less drastic effects (i.e., complete tracheal rings) [40].
The laryngotracheal groove appears in the proximal foregut in the third week of development. The trachea and esophagus develop as a single tube from the ventral and dorsal anterior foregut endoderm, respectively, at the fourth week, while the lung buds expand caudally. Complete separation of the trachea and esophagus occurs by the sixth week of gestation as proliferating ridges within the lumen of the foregut unite to form the tracheoesophageal septum [41]. Notably, there is some debate on how this process occurs, but the “septation” model is currently the most widely accepted [42, 43]. The tracheal cartilage, connective tissue, and smooth muscle arise from mesenchyme from the fourth and sixth pharyngeal arches and surround the tracheal tube in weeks 8–10, forming the tracheal rings, the tracheal walls, and the trachealis [41]. The laryngotracheal lumen is occluded by an overproliferation of endoderm that eventually recanalizes by week 10 to create the normal glottic opening. The branching pattern of the lower airway is complete by 16 weeks. With initial development complete, the second half of gestation is characterized by airway maturation and remodeling [44]. During this time, the cartilage strengthens, demonstrating a fivefold decrease in airway compliance [45].
This basic framework provides a primitive schema for how many tracheal anomalies occur. For example, tracheal agenesis results from an early defect in development at the fourth week. Tracheoesophageal fistula form when there is failure of complete separation of the foregut into the tracheal and esophageal lumens. Laryngotracheal clefts arise when there is incomplete fusion of the tracheoesophageal septum. Complete tracheal rings result from a defect in embryogenesis after the eighth week of gestation causing a complete cartilaginous ring with absence of the usual posterior membranous portion of the trachea. Primary tracheomalacia can, in a general sense, be explained by a failure of appropriate development of the tracheal cartilage. While findings may vary based on the etiology of the malacia, the trachea generally appears more “U-shaped” or even “bowed” as compared with normal (Fig. 36.4a). There is also an alteration of the typical 4–5:1 cartilage/membranous trachea ratio. Secondary tracheomalacia, as previously discussed, can result from external compression, as a result of tracheostomy, or following positive pressure ventilation.
While development of individual cardiovascular anomalies with resultant airway compression is beyond the scope of this chapter, the normal embryologic development of the vasculature provides a basis for understanding these complex anomalies. The five paired pharyngeal arches (numbered 1, 2, 3, 4, and 6) each have an associated primitive aortic arch that connect the paired dorsal and ventral aorta. The fifth pharyngeal arch is rudimentary in humans and regresses quickly without any contribution to the ultimate arterial system [1, 46]. Appropriate involution, regression, and persistence of the remaining five primitive arches are required to ultimately have normal anatomy. Typically, the first and second arches regress on leaving the maxillary and stapedial arteries, respectively. The third and fourth arches appear as the first and second regress. The third arch persists as the common carotid and proximal internal carotid arteries, while the fourth arch develops into the proximal subclavian artery on the right side and aortic arch on the left side. Finally, the sixth arch forms and results in the bilateral pulmonary arteries from the ventral portion and the left-sided ductus arteriosus from the left dorsal portion. The right dorsal aorta involutes while the left dorsal aorta becomes the distal aortic arch and descending thoracic aorta. The dorsal intersegmental arteries bilaterally become portions of the subclavian arteries. A double aortic arch is created when both fourth arches persist [12, 46, 47].
Presentation
Clinically, patients with tracheal stenosis and tracheomalacia may have overlapping symptoms. It is important, however, to distinguish between the two, as the management is very different [4, 15].
Congenital Tracheal Stenosis
Children with complete tracheal rings most commonly present in infancy with worsening respiratory function characterized by biphasic “washing-machine” stridor, retractions, apnea, cyanosis, and “dying spells.” Symptoms are typically worse when the child is agitated or feeding. Failure to thrive may also be present. Decompensation is commonly seen around 4 months of age as the child “outgrows” the airway [48]. Respiratory infections may also exacerbate symptoms causing significant respiratory distress requiring intubation [39]. If the tracheal stenosis is undiagnosed, intubation may be described as very difficult, requiring the endotracheal tube to be “screwed in.” A traumatic intubation may further escalate the already tenuous airway into a critical airway, sometimes requiring extracorporeal membrane oxygenation (ECMO) [48]. The severity of the presentation will largely depend on the degree of airway stenosis and the comorbid conditions. While it is the exception, there is a subset of patients that present either incidentally (e.g., when being intubated for another reason) or with mild symptoms (e.g., dyspnea on exertion). Some may even present as young adults with asthma-like symptoms [49]. While tracheal sleeves are not typically stenotic, the posterior tracheal cartilage can sometimes overlap causing airway narrowing. In these cases, symptoms would be similar to other forms of congenital tracheal stenosis; however, tracheal sleeves are universally seen in children with craniosynostosis syndromes [18].
Tracheal agenesis will present with severe respiratory distress at birth and no audible cry, despite obvious effort. Attempts at intubation will be unsuccessful; however, mask ventilation or inadvertent esophageal intubation may temporarily improve symptoms in the setting of a tracheo- or bronchoesophageal fistula. Prenatally, a congenital high airway obstruction syndrome (CHAOS) may develop if there is no tracheoesophageal fistula [50].
Tracheomalacia
The majority of children with tracheomalacia are asymptomatic. When symptomatic, however, these children may not present until weeks to months after birth with insidious onset and worsening of symptoms. There may be significant variation in the severity of presenting symptoms based on both the degree of malacia and if there are associated cardiovascular anomalies. Because of these factors, a high index of suspicion may be required to identify patients with tracheomalacia. Common symptoms include shortness of breath, a “brassy” cough, dyspnea on exertion, noisy breathing (expiratory stridor), and, when more severe, apneic and cyanotic spells (sometimes termed “dying spells”). Poor airway clearance is common; thus, these children are more prone to recurrent respiratory infections [34, 51]. In the intubated patient, tracheomalacia can be a cause of failure to extubate or apparent life-threatening events (ALTEs) despite having a secure airway in place. Additionally, several conditions are often comorbid with tracheomalacia, including cardiovascular abnormalities (20–58% of patients) [52, 53], bronchopulmonary dysplasia (up to 52% of patients) [27, 33, 34], gastroesophageal reflux (50–75% of patients) [15, 27, 54], developmental delay (26%) [52], and/or neurologic impairment [6, 27, 52]. Concomitant airway anomalies, including laryngomalacia, bronchomalacia, vocal cord paralysis, laryngotracheal clefts, tracheoesophageal fistula, and subglottic stenosis, may also be present [6, 24–27].
Similarly, children with vascular compression are often asymptomatic or mildly symptomatic. Symptoms, when present, are typically related to airway compression – including noisy breathing (biphasic stridor) and a “seal-bark” cough. If the compression is more severe, apnea, respiratory distress, cyanosis, and ALTEs or “dying spells” may also be present. Dysphagia is not typically a prominent symptom until the child is old enough to take solid foods. Concomitant cardiovascular anomalies may be present in up to 12% of patients [55]. In general, children with a double aortic arch or pulmonary artery sling tend to have more severe symptoms and present in infancy to the first months of life. Approximately 50% of children with pulmonary artery slings will also have complete tracheal rings contributing to a more severe presentation [56, 57].
Speech-Language Pathologist Approach
Children with congenital or acquired conditions that compress the esophagus and/or trachea are at increased risk for feeding and swallowing issues, depending on the severity and location of the underlying condition [58]. Tracheomalacia, in conjunction with extrinsic defects or anomalies such as vascular rings or congenital or intrinsic tracheal abnormalities, may be associated with respiratory compromise during oral feeding [59]. The extra-respiratory effort expended during oral feeding may exacerbate breathing problems and compromise airway protection during the swallow. Dysphagia associated with an aberrant right subclavian artery (dysphagia lusorum) is characterized by increased intraesophageal pressure and a functional partial obstruction with swallowing [60]. Unrepaired complete tracheal rings result in the potential for respiratory distress, which can be exacerbated by the increased respiratory effort required during feeding, threatening airway integrity with swallowing. The role of the speech-language pathologist in the evaluation of associated dysphagia includes a careful review of the medical history and underlying condition, a clinical dysphagia evaluation, and often an instrumental assessment of swallowing function to rule out swallowing dysfunction and/or airway compromise associated with swallowing. Management of feeding and swallowing issues can be determined following the clinical and instrumental assessments.
History
There is a wide range of patient presentations , from those who have severe respiratory distress and require urgent intervention immediately after birth to those children who present with stridor, dyspnea, cough, wheezing, dysphagia, and recurrent respiratory tract infections during early childhood [10, 15, 61]. Review of the medical history and presenting symptoms is completed prior to the clinical oral motor/feeding assessment. The review includes the following components: prenatal and birth history, confirmed or suspected medical diagnoses, respiratory history, current feeding status (enteral, oral), and social history, including parent/caretaker perception of the feeding difficulty and any barriers to accessing dysphagia treatment. The SLP should be knowledgeable about the underlying condition and the medical plan (including potential or past surgical/medical interventions), confirm physiologic stability prior to the feeding assessment, and collaborate with the medical team during the dysphagia assessment and management process.
Clinical Evaluation
The clinical dysphagia assessment serves as an opportunity to directly assess oral structures and function, to confirm physiologic stability during feeding, and to document clinical signs and symptoms of possible swallowing dysfunction. Nonnutritive assessment of sensorimotor function, ability to integrate sensory input, and the strength and range of oral motor movements is completed prior to the nutritive assessment. Direct observation of a feeding by a familiar feeder when possible is recommended for assessment of a typical feeding.
During the clinical assessment, careful monitoring for clinical signs and symptoms of swallowing dysfunction is essential. Coughing, choking or gagging, noisy wet respirations, and physiologic signs of respiratory compromise such as bradycardia, apnea, increased respiratory rate, or decreased oxygen saturation levels may signal airway protection issues associated with oral feeding. The clinical presentations of symptoms that may be correlated with the type of condition are documented during the clinical assessment [62]. For example, airway symptoms such as stridor, wheezing, and cough that worsen with the respiratory effort of feeding may be associated with an underlying tracheal compression. Reduction of ventilation may lead to declining oxygenation and to periods of apnea and bradycardia during oral feeding attempts. Respiratory and heart rate changes during feeding outside of the normal baseline should be noted and communicated immediately to the medical team.
Compression of the esophagus may be manifested by discomfort during feeding attempts, overt coughing, choking, refusal or vomiting of solid textures, and a preference for intake of liquids, possibly secondary to partial esophageal occlusion. The signs and symptoms of feeding difficulty vary according to the severity of the condition and the age of the child. For example, problems with esophageal clearance of solids secondary to esophageal compression may only become apparent when the child matures to the point that solids are introduced.
A significant and known limitation of the clinical oral motor/feeding assessment is the ability to accurately identify pharyngeal swallowing dysfunction and/or airway protection problems associated with feeding and oral intake [63]. Threats to airway protection such as aspiration may be silent in nature and not detectable during the clinical examination [64]. Instrumental assessments of swallowing are therefore beneficial in providing an objective analysis of swallowing function and informing the goals for dysphagia management.
Instrumental Assessment of Swallowing Function
The examinations that are used most often for objective assessment of swallowing function are the videofluoroscopic swallowing study (VFSS) and fiber-optic endoscopic evaluation of swallowing (FEES). The VFSS provides a comprehensive, dynamic assessment of the oral, oropharyngeal, hypopharyngeal, and cervical esophageal phases of the swallow and helps to identify the type and location of swallowing impairment. For example, diagnosis of an aberrant subclavian artery and the degree of external compression can be made by the VFSS. Compensatory therapeutic strategies such as the use of liquids to clear any persistent residual in the esophagus can be introduced during the examination to directly visualize the effect.
Feeding supersedes the normal ventilator chemoreceptor control mechanism in young infants, and a repetitive swallow pattern without pause intervals may be identified during the VFSS [65]. Feeding under fluoroscopy provides an opportunity to introduce pacing intervals to alter feeding rhythm, increase ventilation time, and determine the effect on maintenance of airway protection. Additional strategies may include slowing the rate of liquid flow to decrease the frequency of swallowing-related apnea, thereby increasing the potential for physiologic stability during feeding.
Fiber-optic endoscopic evaluation of swallowing (FEES) is advantageous for defining airway protection integrity and safety of swallowing in infants or children who have never fed orally or who have suspected secretion management issues. Laryngeal structures and function can be clearly viewed. The integrity of laryngopharyngeal sensation can be assessed, which provides important predictive information about the child’s ability to achieve and sustain airway protection during swallowing [66].
The endoscopic view provides an opportunity to assess the child’s ability to achieve glottic closure and to maintain airway protection during oral feeding. Difficulties with respiratory compromise during feeding and consequential penetration or aspiration can be readily detected during the FEES examination prior to swallow onset. Airway compromise secondary to inadequate respiratory pauses and ventilatory needs can be visualized with the abrupt opening of the airway during feeding. In such circumstances, responses to compensatory strategies to improve the coordination of respiration and swallowing can be determined. As with VFSS, imposed respiratory pauses or pacing intervals to facilitate appropriate respiratory pauses and adequate ventilation can be introduced. The effect of pacing can be assessed by close inspection of the glottic and subglottic areas during the respiratory pause cycles to detect any evidence of aspirated material. It should be noted that the FEES examination is limited to visualization of events before and after the swallow. There is a loss of view during the swallow secondary to the upward excursion of the larynx, contractile force of the hypopharyngeal musculature, and subsequent light deflection from the scope. In addition, the view is frequently obscured during rapid, sequential swallowing sequences, such as during bottle-feeding.
Treatment
Once the interpretation of the instrumental examination is completed, recommendations for dysphagia treatment are formulated, if appropriate. Each set of recommendations is dependent on the individual patient and the particular set of medical circumstances. As above, the patient’s response to compensatory swallowing strategies during the assessment and/or instrumental examination guides recommendations for dysphagia treatment.
Direct dysphagia treatment approaches refer to rehabilitative maneuvers or specific exercises to change the physiology of the swallow and are usually most appropriate for adults and older children who can follow directions. Indirect dysphagia treatment strategies refer to compensatory techniques to eliminate symptoms of dysphagia and improve the safety and efficiency of the feeding/swallowing process. The majority dysphagia treatment strategies in children with a history of tracheal and/or esophageal compression are compensatory and indirect in nature. Modifying position to facilitate increased respiratory support during feeding (side-lying positioning), modifying flow rate (nipple flow rate, altering liquid viscosity) to facilitate organization of airway protection during swallowing, and altering liquid and solid boluses during oral intake to facilitate esophageal clearance are the mainstays of dysphagia treatment. Feeding and swallowing issues may persist even after surgical intervention of the underlying condition; continued follow-up by the SLP to implement compensatory strategies to assist with oral feeding safety and efficiency may be necessary.
Otolaryngologist Approach
History
The history is typically obtained from parental or consulting physician report as this patient population often presents within the first days to months of life. Symptoms may include noisy breathing, increased work of breathing with retractions, respiratory distress, apneic or cyanotic episodes, and recurrent respiratory infections. The time course and evolution of symptoms, description of any noisy breathing, and any alleviating or aggravating factors should be elicited. The otolaryngologist should inquire as to feeding difficulties, reflux symptoms, and if weight gain has been appropriate. Any prior airway surgeries and history of intubation should be discussed. Furthermore, associated syndromes or congenital anomalies may provide clues as to the diagnosis. In older children, it is important to assess for exercise intolerance or dyspnea on exertion.
Of note, patients with congenital tracheal stenosis may present in an emergent fashion and available history may be minimal. In these cases, information regarding noisy breathing, the presence or absence of a cry, history of polyhydramnios, known syndromes or cardiac anomalies, and prior attempts at obtaining or evaluating the airway should be elicited.
Exam
From the otolaryngologist’s perspective, the examination should begin with determining the degree of respiratory distress and if urgent intervention is required. This includes assessment of stridor, retractions, work of breathing, cyanosis, and apnea. Evaluation for other anomalies (i.e., craniofacial anomalies, chest wall deformities, limb abnormalities), listening to the quality of the cry, and assessment of the vital signs and growth chart should be performed.
Differential Diagnosis
The differential diagnosis for a child presenting with noisy breathing or respiratory distress from a congenital tracheal anomaly is outlined in Fig. 36.5. Several other tracheal pathologies that should be considered are acquired stenosis, a tracheal bronchus, and tracheal injury. Acquired tracheal stenosis can occur following intubation or tracheostomy. Congenital or acquired subglottic stenosis may also present very similarly. A tracheal bronchus occurs in 0.1–5% of patients and can be associated with congenital tracheal stenosis, Down syndrome, tracheoesophageal fistula, and rib abnormalities. While it is usually an asymptomatic, incidental finding, in some children, it can be a source of recurrent pneumonia, stridor, and cough [67–69].
Additional levels of airway obstruction should be considered and may be found concomitantly. In addition to affecting the trachea, malacia can also affect the pharynx, larynx, and bronchi. In children with generalized hypotonia , these may all occur to some degree. Choanal atresia and pyriform aperture stenosis can cause significant respiratory distress, particularly in the neonatal period when the child is an obligate nasal breather. Adenotonsillar hypertrophy is typically not seen in the first year of life but is a frequent contributor to upper airway obstruction in older children. Also at the pharyngeal level, micrognathia, glossoptosis, and macroglossia can result in severe airway obstruction. These are more commonly seen in syndromic children or those with Pierre Robin sequence.
Instrumental Assessment
Endoscopic Assessment
Flexible fiber-optic laryngoscopy may be performed in the office setting to evaluate for supraglottic and glottic anomalies, such as laryngomalacia and vocal fold immobility. Information regarding the subglottic and tracheal airway, however, will be limited with this exam.
Site of vascular compression on diagnostic studies
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