- Email: [email protected]
Tracheomalacia
PAEDIATRIC RESPIRATORY REVIEWS (2004) 5, 147–154 doi:10.1016/j.prrv.2004.01.010
SERIES: THORACIC SURGERY
Tracheomalacia V. M. McNamara and D. C. G. Crabbe* Department of Paediatric Surgery, Clarendon Wing, Leeds General Infirmary, Leeds LS2 9NS, UK KEYWORDS tracheomalacia; stridor; tracheo-oesophageal fistula (TOF); oesophageal atresia (OA); aortopexy; endoluminal stent
Summary Tracheomalacia is a rare condition characterised by collapse of the trachea during respiration. The condition is seen most often in infants and young children. Mild cases can be managed expectantly; however, severe cases can be associated with lifethreatening cyanotic attacks and intervention to stabilise the airway is invariably necessary. Most commonly this involves an aortopexy to suspend the anterior wall of the trachea but other options include endoluminal or extraluminal stenting, long-term positive pressure ventilation and tracheostomy. Although tracheomalacia resolves spontaneously in most infants within the first few years of life, severe tracheomalacia is associated with significant morbidity and mortality that should not be underestimated. ß 2004 Elsevier Ltd. All rights reserved.
Tracheomalacia is a condition characterised by a deficiency of the supporting cartilages of the trachea. The distal third of the trachea is most commonly affected. The normal trachea has 16–20 horseshoe-shaped cartilages that support the airway and a narrow posterior wall that is membranous. In tracheomalacia, these supporting cartilages may be small, fragmented or even absent. As a result, the trachea tends to assume a comma-shaped cross-section in the affected area (Fig. 1). The anterior–posterior (AP) diameter of the trachea is reduced and the membranous posterior wall forms a substantially larger part of the circumference. As a consequence, there is substantial dynamic variation in the internal diameter of the airway during breathing with collapse of the malacic segment. This is most pronounced during times of increased air flow, for example during crying, feeding or coughing. In severe cases, this will produce a life-threatening degree of airway obstruction. In rare instances, the abnormal cartilage pathology extends into the main bronchi (tracheobronchomalacia) or is restricted to the bronchi alone (bronchomalacia). Bronchomalacia can be associated with major cardiac malformation and may be fatal.
INCIDENCE AND AETIOLOGY The true incidence of tracheomalacia is unknown. Although a rare condition, tracheomalacia is the most common cause *
Correspondence to: D.C.G. Crabbe. Tel.: þ44 (0)113 392 5077; Fax: þ44 (0)113 392 6609; E-mail: [email protected] 1526–0542/$ – see front matter
of stridor in infants and children. The majority have mild/ moderate symptoms which resolve spontaneously. Tracheomalacia may be primary or secondary (Table 1). Severe primary tracheomalacia is rare, although there are case reports of infants with complete absence of tracheal cartilage. Tracheomalacia can be often secondary to oesophageal atresia/tracheo-oesophageal fistula (OA/ TOF). Less commonly, tracheomalacia is secondary to a vascular ring or a mediastinal mass. Tracheomalacia is also seen occasionally in infants following long-term endotracheal intubation or tracheostomy. Diffuse tracheomalacia has been reported in children with connective tissue disorders, e.g. Larsen’s syndrome. Cartilage first appears in the fetal trachea at about 7 weeks of gestation. This coincides with the start of the pseudoglandular phase of fetal lung development, during which serial branching of the tracheobronchial tree occurs. When tracheomalacia occurs in association with OA/TOF, the tracheal cartilages are frequently malformed and fragmented in the lower trachea.1 This has been attributed to pressure from the dilated, obstructed, proximal oesophageal pouch compressing the posterior wall of the trachea and preventing normal cartilage development. Recent experimental work with a rat–adriamycin model that accurately reproduces the pathology seen in humans with OA/TOF suggested that the explanation is more fundamental; it seems likely that the teratogenic process that disrupts tracheo-oesophageal septation also perturbs tracheal cartilage specification.2 Vascular rings3 are a group of conditions that arise from anomalous development of the fetal branchial arch vessels. ß 2004 Elsevier Ltd. All rights reserved.
148
V.M. MCNAMARA AND D.C.G. CRABBE
Figure 1 Diagrammatic cross-section of the normal (left) and malacic (right) trachea.
By the end of Week 4 post conception, the pharyngeal foregut is surrounded by paired aortic arches and paired dorsal aortae. By the end of Week 8, regression of the right dorsal aorta, persistence of the left dorsal aorta and remodelling of the aortic arches results in the definitive arrangement of the great vessels. The most common vascular ring is a double aortic arch that occurs as a result of persistence of both left and right dorsal aortic segments. The trachea and oesophagus lie surrounded by this vascular ring and are compressed to a variable degree. This compression disturbs formation of normal tracheal cartilage and results in a local malacic segment. Although not a vascular ring by definition, innominate artery compression of the trachea is conveniently included in this group of conditions. The innominate artery arises from an abnormally distal origin on the aortic arch and pursues an ascending course over the front of the trachea. Either by being especially taut or due to the overlying tracheal cartilages being abnormally compliant, localised tracheomalacia may develop. Tracheomalacia associated with prolonged intubation or following a tracheostomy is occasionally seen in infants and children.4 This is probably the result of chronic tracheal inflammation. Mucosal ischaemia due to pressure from a tightly fitting endotracheal tube and mechanical leverage from a tracheostomy tube will result in a chronic perichondritis and may cause tracheomalacia or even stricture formation. Although minor in most cases, this tracheomalacia may be severe enough to prevent successful decannulation during infancy. Table 1
Classification of tracheomalacia.
Primary tracheomalacia Congenital absence of tracheal-supporting cartilages Secondary tracheomalacia Oesophageal atresia/tracheo-oesophageal fistula Vascular rings (e.g. double aortic arch) Tracheal compression from an aberrant innominate artery Tracheal compression from mediastinal masses Abnormally soft tracheal cartilages associated with connective tissue disorders Prolonged mechanical ventilation/chronic lung disease
CLINICAL FEATURES Children with mild tracheomalacia may have no symptoms apart from a characteristic barking or seal-like cough. In children with OA/TOF, this accounts for the characteristic ‘TOF cough’. In more severe cases, stridor is the striking clinical feature. Stridor is often the first physical sign and may appear within a few days of birth. Recurrent respiratory infection is common. In more severe tracheomalacia, the stridor becomes biphasic and signs of respiratory distress will develop. All the signs of tracheomalacia become more marked when the child is upset. Severe episodes of airway obstruction may occur during feeding, especially with solids. This is frequently, although not exclusively, a problem seen in infants post-OA repair. The likely mechanism is compression of the posterior trachea by the passing food bolus in the oesophagus; the problem is exacerbated by an anastomotic stricture, oesophageal dysmotility and gastro-oesophageal reflux (GOR). Hypoxia and cyanosis are characteristic of the aptly named ‘dying spells’ seen in children with severe tracheomalacia. Collapse of the tracheal lumen results in complete airway obstruction. The infant loses consciousness, collapses and the airway re-opens. Bradycardia leading to cardiac arrest may occur if prompt resuscitation is not commenced. These are life-threatening events and indicate the need for surgical intervention.
NATURAL HISTORY The natural history of tracheomalacia is one of gradual improvement as the tracheal lumen increases in diameter with growth and the supporting cartilages become more rigid. Symptoms and signs will resolve in most children by 2 years of age and the majority of children demonstrate clinical improvement by 6–12 months. The ‘TOF cough’ may take years to disappear or may never fully do so. Recurrent respiratory infection is common in early life but persisting problems are uncommon.
INVESTIGATIONS Initial assessment depends on the frequency and severity of symptoms. Investigations are aimed at establishing the
TRACHEOMALACIA
Table 2
149
Investigation of tracheomalacia.
Chest x ray: anteroposterior þ/ lateral view Barium swallow with fluoroscopic assessment of airway calibre Bronchoscopy Compued tomography/magnetic resonance imaging 24-h oesophageal pH study [Pulmonary function tests – flow/volume loops] [Bronchography] [Angiography]
diagnosis and determining the extent and severity of tracheomalacia (Table 2). The diagnosis of OA will already be known. If children presenting with stridor are found to have tracheomalacia, a vascular ring must be considered and excluded. The presence and severity of GOR should be determined in infants with severe tracheomalacia. A plain chest radiograph is of limited value and will usually fail to show any abnormality in the airway. It may, however, document a mediastinal mass. A lateral neck x ray may show narrowing of the intrathoracic trachea but this is somewhat dependent on the phase of respiration when the film is exposed. The barium swallow is a very important investigation. Changes in airway calibre can often be seen on fluoroscopy. An upper gastrointestinal contrast study will identify a vascular ring and may demonstrate GOR. On the AP view, the normal aortic arch produces an indentation on the left side of the column of contrast in the oesophagus. A double aortic arch will produce indentations on both sides of the oesophagus on the AP projection (Fig. 2) and also an impression on the posterior wall of the oesophagus, best seen on a lateral projection. Pulmonary function tests are classically abnormal with truncation of the expiratory limb of the flow volume loop. Given the technical difficulties with lung function testing in young unco-operative patients, this is not often used in clinical practice for diagnosis. Bronchoscopy is the investigation of choice to confirm the diagnosis and assess the severity of the airway collapse. Bronchoscopy should be performed under light general anaesthesia with spontaneous respiration. The examination can be performed with either a rigid or a fibre-optic bronchoscope and should include a careful inspection of the entire airway. A fine fibre-optic bronchoscope inserted through a laryngeal mask airway causes very little airway obstruction and allows a clear assessment of the degree of airway collapse to be made. We consider this to be more accurate than assessment with a rigid bronchoscope because a degree of airway obstruction inevitably occurs when an anaesthetised child breathes through a ventilating bronchoscope without assistance and this may exaggerate the severity of the tracheomalacia. The malacic airway assumes a comma-like configuration (Figs 3 and 4). The anterior and posterior walls will approximate in severe
Figure 2 Barium swallow demonstrating a vascular impression on both the right (normal) and left (abnormal) side of the oesophagus, indicative of a double aortic arch.
cases, particularly as the depth of anaesthesia is reduced. This finding may be missed if the child is paralysed and ventilated with positive pressure. An estimate of the percentage airway collapse should be made. Computerised tomography (CT) and magnetic resonance imaging (MRI) are valuable investigations in children with tracheomalacia to detect extrinsic airway compression. Changes in airway calibre during respiration can be observed with cine-CT imaging. However, it may be difficult to differentiate tracheomalacia from tracheal stenosis without endoscopy. More complex analysis of helical CT images, with multi-planar reconstruction, allows milder degrees of airway narrowing to be identified. Both CT and MRI will identify a mediastinal mass compressing the airway. MRI is the investigation of choice to demonstrate a
150
V.M. MCNAMARA AND D.C.G. CRABBE
Figure 3 Bronchoscopic view of the trachea of a child with tracheomalacia associated with oesophageal atresia/tracheo-oesophageal fistula (TOF). The opening of the TOF stump is visible on the posterior wall of the trachea.
Figure 4 Bronchoscopic view of the trachea of a child with tracheomalacia associated with a double aortic arch (same case as Fig. 2).
TRACHEOMALACIA
vascular ring although angiography may be necessary prior to surgery to confirm the dominant side of the ring, so that non-dominant side can be divided. Bronchography is a sensitive method to detect tracheomalacia, although the invasive nature of this investigation precludes widespread use. In practice, bronchography is used mainly as an adjunct to endobronchial stent placement or segmental tracheal resection when it is crucial to define the limits of the malacic segment accurately.
MANAGEMENT It is self evident that when tracheomalacia is secondary to a remediable cause, the primary pathology should be corrected; for example, a mediastinal tumour that is compressing the airway should be excised which should lead to improvement in the tracheomalacia. The situation is not so clear cut with vascular rings. The decision to operate is determined by the severity of the symptoms; nowadays, if feeding and growth are adequate, there is less urgency to operate. Even after surgery, significant residual tracheomalacia has been found; this may continue to produce symptoms.5 Tracheomalacia associated with OA/TOF invariably develops in the months following repair of the atresia. Children with mild tracheomalacia do not require any specific treatment. Intercurrent respiratory infections should be treated promptly with antibiotics and early admission to hospital may be necessary, particularly in young children. Inhaled bronchodilators may aggravate rather than improve the airway by reducing the tracheal muscle tone. If feeding is a problem, adjusting the feeding regimens of infants and prescribing anti-reflux medication may help. Feeding problems are particularly common in infants with tracheomalacia secondary to OA/TOF. This is
151
often multi-factorial with tracheomalacia, GOR, anastomotic stricture and oesophageal dysmotility all contributing to varying degrees. In moderate-to-severe tracheomalacia, conservative measures and reassurance will not be sufficient. Parents should be taught basic life-support skills and provided with an oxygen cylinder for emergency use at home. When the child becomes distressed, for example after feeding or bathing, supplemental oxygen may be required. Aggressive treatment of GOR is necessary and anti-reflux surgery is often required. The management of severe tracheomalacia is controversial. This is because tracheomalacia improves with growth and also because surgery may not completely abolish the cyanotic spells. Continuous positive airway pressure can be used to maintain a patent airway. Although helpful in the short term, this is not a good long-term solution although it may be the only option for children with bronchomalacia. Tracheostomy is occasionally used for long-term airway support, particularly if other measures have failed; however, the risk of iatrogenic problems is high. A tracheostomy may exacerbate tracheomalacia because it bypasses the physiological function of the glottis to maintain positive airway pressure. Surgical options for severe tracheomalacia include aortopexy, segmental tracheal resection and external splintage of the trachea. Aortopexy aims to treat the airway collapse by ventral suspension of the trachea. The aortic arch is exposed through a sternotomy or an anterior thoracotomy and the thymus is excised. Sutures are placed in the pericardial reflection over the aortic root and in the adventitia of the aortic arch and then tied to the underside of the sternum. As the aorta is pulled forwards, fibrous attachments between the aorta and the trachea ensure that the front wall of the trachea is pulled forwards, opening the lumen (Fig. 5). Best results are
Figure 5 Diagram showing the mediastinal anatomy before (left) and after (right) aortopexy. The aortic arch is suspended from the back of the sternum and this pulls the front wall of the trachea forwards.
152
V.M. MCNAMARA AND D.C.G. CRABBE
Figure 6 Palmaz stent in place in the lower trachea.
obtained when intra-operative bronchoscopy is used to confirm that adequate suspension has been achieved. Resection of the malacic segment may be curative if satisfactory improvement in the lumen cannot be achieved by aortopexy. Procedures to increase the intrinsic rigidity of the tracheal wall by fashioning rings out of costal cartilage or wrapping the malacic segment in synthetic mesh to provide external splintage have been tried but the results are generally unsatisfactory. Over recent years, interest has focused on the use of indwelling endotracheal or endobronchial stents to stabilise the malacic airway. Expandable metallic stents have been used successfully to palliate malignant airway strictures in adults since the mid 1980s. Use in children with benign disease is limited and the only significant experience has been with expandable metallic coronary artery stents (e.g. the Palmaz–Schatz stent).6 Biodegradable stents are being developed but these are still at an experimental stage. The stent is inserted using a balloon catheter which is inflated in the airway. The expanded stent is lodged inside the airway (Fig. 6). Stents can be used in the trachea and main bronchi. The lattice of the stent can be placed over a lobar bronchial orifice without compromising ventilation of the lung. From a purely mechanical perspective, stents provide very effective treatment for tracheomalacia and bronchomalacia; symptom relief can be expected. However, indwelling airway stents do not become epithelia-
lised in the same way that endovascular stents do; as a consequence, they always excite the formation of granulation tissue in the airway and this can cause recurrent problems with obstruction and bleeding. There are risks of erosion of the stent through the wall of the airway into adjacent blood vessels with predictable consequences. Although stents are comparatively easy to insert into the airway, they are most definitely not easy to remove. In the context of tracheomalacia, this is important because it is likely that the stent will become redundant as the child grows. Removal is a hazardous undertaking that involves grasping the stent and twisting to disimpact the lattice from the wall of the airway and then retrieving the crumpled stent through a rigid bronchoscope (Fig. 7). This manoeuvre is invariably associated with brisk bleeding from the trachea and risks loss of control of the airway. No data are available on the long-term consequences of stenting of the paediatric airway.
COMPLICATIONS AND OUTCOME Information on the long-term consequences of tracheomalacia in children is largely derived from studies of children with OA. Distinguishing the extent to which symptoms are related to tracheomalacia per se from symptoms that are related to residual oesophageal pathology is difficult. What is clear from these studies is that respiratory morbidity is
TRACHEOMALACIA
153
Figure 7 Appearance of the stent as removed from the airway.
greatest in infancy and improves progressively during childhood. The best long-term follow-up study of children after OA/TOF repair is from Melbourne, Australia.7 Chetcuti and Phelan interviewed over 300 children and adults who had had OA/TOF repair and discovered that 44% had subsequently been admitted to hospital with respiratory symptoms; the majority of these admissions were in the first 5 years of life. Admission after 10 years of age was unusual.8 Infants and children with symptomatic tracheomalacia often spend prolonged periods of time in hospital because of feeding problems and respiratory infections. This poses practical and emotional problems for the family. Parents may need to learn advanced resuscitation skills, which adds to the stress. The cyanotic ‘dying spells’ associated with severe tracheomalacia require prompt recognition and resuscitation. Although uncommon, permanent neurological damage is well recognised in children with tracheomalacia of this severity. The results of surgery for severe tracheomalacia have been reported by several groups.9,10 In general, the results of aortopexy are encouraging with significant improvement or cessation of symptoms reported in over 95% of cases.10 This procedure is not without complications, the most significant being major vascular injury and phrenic nerve damage with resultant paralysis of the ipsilateral diaphragm. Aortopexy is most likely to be successful in children with tracheomalacia secondary to OA/TOF or a vascular ring. Data on the long-term outcome of children with indwelling airway stents are not yet available. The main areas of concern relating to long-term usage are the risks of stent erosion and disturbance of tracheal growth. In animal experiments, squamous metaplasia of the airway mucosa
has been observed following stent placement, although this phenomenon has not been observed in humans.
CONCLUSIONS Tracheomalacia is an uncommon condition of variable severity. It is often associated with OA/TOF. In the absence of OA/TOF, a diligent search should be made for a vascular ring or a mediastinal mass. The natural history of tracheomalacia is one of progressive improvement during early childhood and this mitigates against surgical intervention. However, severe tracheomalacia is a life-threatening condition and intervention is invariably required.
PRACTICE POINTS Tracheomalacia is mainly a disease of infancy. It is associated with OA and vascular rings. Severe tracheomalacia with ‘dying spells’ indicates the need for surgery. Treatment options include aortopexy, airway stenting, long-term continuous positive airway pressure and tracheostomy. Most infants with tracheomalacia spontaneously improve given time.
REFERENCES 1. Wailoo MP, Emery JL. The trachea in children with tracheoesophageal fistula. Histopathology 1979; 3: 329–338. 2. Pole RJ, Qi BQ, Beasley SW. Abnormalities of the tracheal cartilages in the rat fetus with tracheo-oesophageal fistula or tracheal agenesis. Pediatr Surg Int 2001; 17: 25–28.
154
3. Backer CL, Ilbawi MN, Idriss FS, DeLeon SY. Vascular anomalies causing tracheoesophageal compression. Review of experience in children. J Thorac Cardiovasc Surg 1989; 97: 725–731. 4. Doull IJM, Mok Q, Tasker RC. Tracheobronchomalacia in preterm infants with chronic lung disease. Arch Dis Child 1997; 76: F203–F205. 5. Marmon LM, Bye MR, Haas JM et al. Vascular rings and slings: longterm follow-up of pulmonary function. J Pediatr Surg 1984; 19: 683– 690. 6. Filler RM, Forte V, Fraga JC, Matute J. The use of expandable metalic stents for tracheobronchial obstruction in children. J Pediatr Surg 1995; 30: 1050–1056.
V.M. MCNAMARA AND D.C.G. CRABBE
7. Beasley SW, Myers NA, Auldist AW (eds). Oesophageal Atresia. London: Chapman & Hall Medical, 1991. 8. Chetcuti P, Phelan P. Respiratory morbidity after repair of oesophageal atresia and tracheo-oesophageal fistula. Arch Dis Child 1993; 68: 167–170. 9. Corbally MT, Spitz L, Kiely E, Brereton RJ, Drake DP. Aortopexy for tracheomalacia in oesophageal anomalies. Eur J Pediatr Surg 1993; 3: 264–266. 10. Weber TR, Keller MS, Fiore A. Aortic suspension (aortopexy) for severe tracheomalacia in infants and children. Am J Surg 2002; 184: 573–577.
SERIES: THORACIC SURGERY
Tracheomalacia V. M. McNamara and D. C. G. Crabbe* Department of Paediatric Surgery, Clarendon Wing, Leeds General Infirmary, Leeds LS2 9NS, UK KEYWORDS tracheomalacia; stridor; tracheo-oesophageal fistula (TOF); oesophageal atresia (OA); aortopexy; endoluminal stent
Summary Tracheomalacia is a rare condition characterised by collapse of the trachea during respiration. The condition is seen most often in infants and young children. Mild cases can be managed expectantly; however, severe cases can be associated with lifethreatening cyanotic attacks and intervention to stabilise the airway is invariably necessary. Most commonly this involves an aortopexy to suspend the anterior wall of the trachea but other options include endoluminal or extraluminal stenting, long-term positive pressure ventilation and tracheostomy. Although tracheomalacia resolves spontaneously in most infants within the first few years of life, severe tracheomalacia is associated with significant morbidity and mortality that should not be underestimated. ß 2004 Elsevier Ltd. All rights reserved.
Tracheomalacia is a condition characterised by a deficiency of the supporting cartilages of the trachea. The distal third of the trachea is most commonly affected. The normal trachea has 16–20 horseshoe-shaped cartilages that support the airway and a narrow posterior wall that is membranous. In tracheomalacia, these supporting cartilages may be small, fragmented or even absent. As a result, the trachea tends to assume a comma-shaped cross-section in the affected area (Fig. 1). The anterior–posterior (AP) diameter of the trachea is reduced and the membranous posterior wall forms a substantially larger part of the circumference. As a consequence, there is substantial dynamic variation in the internal diameter of the airway during breathing with collapse of the malacic segment. This is most pronounced during times of increased air flow, for example during crying, feeding or coughing. In severe cases, this will produce a life-threatening degree of airway obstruction. In rare instances, the abnormal cartilage pathology extends into the main bronchi (tracheobronchomalacia) or is restricted to the bronchi alone (bronchomalacia). Bronchomalacia can be associated with major cardiac malformation and may be fatal.
INCIDENCE AND AETIOLOGY The true incidence of tracheomalacia is unknown. Although a rare condition, tracheomalacia is the most common cause *
Correspondence to: D.C.G. Crabbe. Tel.: þ44 (0)113 392 5077; Fax: þ44 (0)113 392 6609; E-mail: [email protected] 1526–0542/$ – see front matter
of stridor in infants and children. The majority have mild/ moderate symptoms which resolve spontaneously. Tracheomalacia may be primary or secondary (Table 1). Severe primary tracheomalacia is rare, although there are case reports of infants with complete absence of tracheal cartilage. Tracheomalacia can be often secondary to oesophageal atresia/tracheo-oesophageal fistula (OA/ TOF). Less commonly, tracheomalacia is secondary to a vascular ring or a mediastinal mass. Tracheomalacia is also seen occasionally in infants following long-term endotracheal intubation or tracheostomy. Diffuse tracheomalacia has been reported in children with connective tissue disorders, e.g. Larsen’s syndrome. Cartilage first appears in the fetal trachea at about 7 weeks of gestation. This coincides with the start of the pseudoglandular phase of fetal lung development, during which serial branching of the tracheobronchial tree occurs. When tracheomalacia occurs in association with OA/TOF, the tracheal cartilages are frequently malformed and fragmented in the lower trachea.1 This has been attributed to pressure from the dilated, obstructed, proximal oesophageal pouch compressing the posterior wall of the trachea and preventing normal cartilage development. Recent experimental work with a rat–adriamycin model that accurately reproduces the pathology seen in humans with OA/TOF suggested that the explanation is more fundamental; it seems likely that the teratogenic process that disrupts tracheo-oesophageal septation also perturbs tracheal cartilage specification.2 Vascular rings3 are a group of conditions that arise from anomalous development of the fetal branchial arch vessels. ß 2004 Elsevier Ltd. All rights reserved.
148
V.M. MCNAMARA AND D.C.G. CRABBE
Figure 1 Diagrammatic cross-section of the normal (left) and malacic (right) trachea.
By the end of Week 4 post conception, the pharyngeal foregut is surrounded by paired aortic arches and paired dorsal aortae. By the end of Week 8, regression of the right dorsal aorta, persistence of the left dorsal aorta and remodelling of the aortic arches results in the definitive arrangement of the great vessels. The most common vascular ring is a double aortic arch that occurs as a result of persistence of both left and right dorsal aortic segments. The trachea and oesophagus lie surrounded by this vascular ring and are compressed to a variable degree. This compression disturbs formation of normal tracheal cartilage and results in a local malacic segment. Although not a vascular ring by definition, innominate artery compression of the trachea is conveniently included in this group of conditions. The innominate artery arises from an abnormally distal origin on the aortic arch and pursues an ascending course over the front of the trachea. Either by being especially taut or due to the overlying tracheal cartilages being abnormally compliant, localised tracheomalacia may develop. Tracheomalacia associated with prolonged intubation or following a tracheostomy is occasionally seen in infants and children.4 This is probably the result of chronic tracheal inflammation. Mucosal ischaemia due to pressure from a tightly fitting endotracheal tube and mechanical leverage from a tracheostomy tube will result in a chronic perichondritis and may cause tracheomalacia or even stricture formation. Although minor in most cases, this tracheomalacia may be severe enough to prevent successful decannulation during infancy. Table 1
Classification of tracheomalacia.
Primary tracheomalacia Congenital absence of tracheal-supporting cartilages Secondary tracheomalacia Oesophageal atresia/tracheo-oesophageal fistula Vascular rings (e.g. double aortic arch) Tracheal compression from an aberrant innominate artery Tracheal compression from mediastinal masses Abnormally soft tracheal cartilages associated with connective tissue disorders Prolonged mechanical ventilation/chronic lung disease
CLINICAL FEATURES Children with mild tracheomalacia may have no symptoms apart from a characteristic barking or seal-like cough. In children with OA/TOF, this accounts for the characteristic ‘TOF cough’. In more severe cases, stridor is the striking clinical feature. Stridor is often the first physical sign and may appear within a few days of birth. Recurrent respiratory infection is common. In more severe tracheomalacia, the stridor becomes biphasic and signs of respiratory distress will develop. All the signs of tracheomalacia become more marked when the child is upset. Severe episodes of airway obstruction may occur during feeding, especially with solids. This is frequently, although not exclusively, a problem seen in infants post-OA repair. The likely mechanism is compression of the posterior trachea by the passing food bolus in the oesophagus; the problem is exacerbated by an anastomotic stricture, oesophageal dysmotility and gastro-oesophageal reflux (GOR). Hypoxia and cyanosis are characteristic of the aptly named ‘dying spells’ seen in children with severe tracheomalacia. Collapse of the tracheal lumen results in complete airway obstruction. The infant loses consciousness, collapses and the airway re-opens. Bradycardia leading to cardiac arrest may occur if prompt resuscitation is not commenced. These are life-threatening events and indicate the need for surgical intervention.
NATURAL HISTORY The natural history of tracheomalacia is one of gradual improvement as the tracheal lumen increases in diameter with growth and the supporting cartilages become more rigid. Symptoms and signs will resolve in most children by 2 years of age and the majority of children demonstrate clinical improvement by 6–12 months. The ‘TOF cough’ may take years to disappear or may never fully do so. Recurrent respiratory infection is common in early life but persisting problems are uncommon.
INVESTIGATIONS Initial assessment depends on the frequency and severity of symptoms. Investigations are aimed at establishing the
TRACHEOMALACIA
Table 2
149
Investigation of tracheomalacia.
Chest x ray: anteroposterior þ/ lateral view Barium swallow with fluoroscopic assessment of airway calibre Bronchoscopy Compued tomography/magnetic resonance imaging 24-h oesophageal pH study [Pulmonary function tests – flow/volume loops] [Bronchography] [Angiography]
diagnosis and determining the extent and severity of tracheomalacia (Table 2). The diagnosis of OA will already be known. If children presenting with stridor are found to have tracheomalacia, a vascular ring must be considered and excluded. The presence and severity of GOR should be determined in infants with severe tracheomalacia. A plain chest radiograph is of limited value and will usually fail to show any abnormality in the airway. It may, however, document a mediastinal mass. A lateral neck x ray may show narrowing of the intrathoracic trachea but this is somewhat dependent on the phase of respiration when the film is exposed. The barium swallow is a very important investigation. Changes in airway calibre can often be seen on fluoroscopy. An upper gastrointestinal contrast study will identify a vascular ring and may demonstrate GOR. On the AP view, the normal aortic arch produces an indentation on the left side of the column of contrast in the oesophagus. A double aortic arch will produce indentations on both sides of the oesophagus on the AP projection (Fig. 2) and also an impression on the posterior wall of the oesophagus, best seen on a lateral projection. Pulmonary function tests are classically abnormal with truncation of the expiratory limb of the flow volume loop. Given the technical difficulties with lung function testing in young unco-operative patients, this is not often used in clinical practice for diagnosis. Bronchoscopy is the investigation of choice to confirm the diagnosis and assess the severity of the airway collapse. Bronchoscopy should be performed under light general anaesthesia with spontaneous respiration. The examination can be performed with either a rigid or a fibre-optic bronchoscope and should include a careful inspection of the entire airway. A fine fibre-optic bronchoscope inserted through a laryngeal mask airway causes very little airway obstruction and allows a clear assessment of the degree of airway collapse to be made. We consider this to be more accurate than assessment with a rigid bronchoscope because a degree of airway obstruction inevitably occurs when an anaesthetised child breathes through a ventilating bronchoscope without assistance and this may exaggerate the severity of the tracheomalacia. The malacic airway assumes a comma-like configuration (Figs 3 and 4). The anterior and posterior walls will approximate in severe
Figure 2 Barium swallow demonstrating a vascular impression on both the right (normal) and left (abnormal) side of the oesophagus, indicative of a double aortic arch.
cases, particularly as the depth of anaesthesia is reduced. This finding may be missed if the child is paralysed and ventilated with positive pressure. An estimate of the percentage airway collapse should be made. Computerised tomography (CT) and magnetic resonance imaging (MRI) are valuable investigations in children with tracheomalacia to detect extrinsic airway compression. Changes in airway calibre during respiration can be observed with cine-CT imaging. However, it may be difficult to differentiate tracheomalacia from tracheal stenosis without endoscopy. More complex analysis of helical CT images, with multi-planar reconstruction, allows milder degrees of airway narrowing to be identified. Both CT and MRI will identify a mediastinal mass compressing the airway. MRI is the investigation of choice to demonstrate a
150
V.M. MCNAMARA AND D.C.G. CRABBE
Figure 3 Bronchoscopic view of the trachea of a child with tracheomalacia associated with oesophageal atresia/tracheo-oesophageal fistula (TOF). The opening of the TOF stump is visible on the posterior wall of the trachea.
Figure 4 Bronchoscopic view of the trachea of a child with tracheomalacia associated with a double aortic arch (same case as Fig. 2).
TRACHEOMALACIA
vascular ring although angiography may be necessary prior to surgery to confirm the dominant side of the ring, so that non-dominant side can be divided. Bronchography is a sensitive method to detect tracheomalacia, although the invasive nature of this investigation precludes widespread use. In practice, bronchography is used mainly as an adjunct to endobronchial stent placement or segmental tracheal resection when it is crucial to define the limits of the malacic segment accurately.
MANAGEMENT It is self evident that when tracheomalacia is secondary to a remediable cause, the primary pathology should be corrected; for example, a mediastinal tumour that is compressing the airway should be excised which should lead to improvement in the tracheomalacia. The situation is not so clear cut with vascular rings. The decision to operate is determined by the severity of the symptoms; nowadays, if feeding and growth are adequate, there is less urgency to operate. Even after surgery, significant residual tracheomalacia has been found; this may continue to produce symptoms.5 Tracheomalacia associated with OA/TOF invariably develops in the months following repair of the atresia. Children with mild tracheomalacia do not require any specific treatment. Intercurrent respiratory infections should be treated promptly with antibiotics and early admission to hospital may be necessary, particularly in young children. Inhaled bronchodilators may aggravate rather than improve the airway by reducing the tracheal muscle tone. If feeding is a problem, adjusting the feeding regimens of infants and prescribing anti-reflux medication may help. Feeding problems are particularly common in infants with tracheomalacia secondary to OA/TOF. This is
151
often multi-factorial with tracheomalacia, GOR, anastomotic stricture and oesophageal dysmotility all contributing to varying degrees. In moderate-to-severe tracheomalacia, conservative measures and reassurance will not be sufficient. Parents should be taught basic life-support skills and provided with an oxygen cylinder for emergency use at home. When the child becomes distressed, for example after feeding or bathing, supplemental oxygen may be required. Aggressive treatment of GOR is necessary and anti-reflux surgery is often required. The management of severe tracheomalacia is controversial. This is because tracheomalacia improves with growth and also because surgery may not completely abolish the cyanotic spells. Continuous positive airway pressure can be used to maintain a patent airway. Although helpful in the short term, this is not a good long-term solution although it may be the only option for children with bronchomalacia. Tracheostomy is occasionally used for long-term airway support, particularly if other measures have failed; however, the risk of iatrogenic problems is high. A tracheostomy may exacerbate tracheomalacia because it bypasses the physiological function of the glottis to maintain positive airway pressure. Surgical options for severe tracheomalacia include aortopexy, segmental tracheal resection and external splintage of the trachea. Aortopexy aims to treat the airway collapse by ventral suspension of the trachea. The aortic arch is exposed through a sternotomy or an anterior thoracotomy and the thymus is excised. Sutures are placed in the pericardial reflection over the aortic root and in the adventitia of the aortic arch and then tied to the underside of the sternum. As the aorta is pulled forwards, fibrous attachments between the aorta and the trachea ensure that the front wall of the trachea is pulled forwards, opening the lumen (Fig. 5). Best results are
Figure 5 Diagram showing the mediastinal anatomy before (left) and after (right) aortopexy. The aortic arch is suspended from the back of the sternum and this pulls the front wall of the trachea forwards.
152
V.M. MCNAMARA AND D.C.G. CRABBE
Figure 6 Palmaz stent in place in the lower trachea.
obtained when intra-operative bronchoscopy is used to confirm that adequate suspension has been achieved. Resection of the malacic segment may be curative if satisfactory improvement in the lumen cannot be achieved by aortopexy. Procedures to increase the intrinsic rigidity of the tracheal wall by fashioning rings out of costal cartilage or wrapping the malacic segment in synthetic mesh to provide external splintage have been tried but the results are generally unsatisfactory. Over recent years, interest has focused on the use of indwelling endotracheal or endobronchial stents to stabilise the malacic airway. Expandable metallic stents have been used successfully to palliate malignant airway strictures in adults since the mid 1980s. Use in children with benign disease is limited and the only significant experience has been with expandable metallic coronary artery stents (e.g. the Palmaz–Schatz stent).6 Biodegradable stents are being developed but these are still at an experimental stage. The stent is inserted using a balloon catheter which is inflated in the airway. The expanded stent is lodged inside the airway (Fig. 6). Stents can be used in the trachea and main bronchi. The lattice of the stent can be placed over a lobar bronchial orifice without compromising ventilation of the lung. From a purely mechanical perspective, stents provide very effective treatment for tracheomalacia and bronchomalacia; symptom relief can be expected. However, indwelling airway stents do not become epithelia-
lised in the same way that endovascular stents do; as a consequence, they always excite the formation of granulation tissue in the airway and this can cause recurrent problems with obstruction and bleeding. There are risks of erosion of the stent through the wall of the airway into adjacent blood vessels with predictable consequences. Although stents are comparatively easy to insert into the airway, they are most definitely not easy to remove. In the context of tracheomalacia, this is important because it is likely that the stent will become redundant as the child grows. Removal is a hazardous undertaking that involves grasping the stent and twisting to disimpact the lattice from the wall of the airway and then retrieving the crumpled stent through a rigid bronchoscope (Fig. 7). This manoeuvre is invariably associated with brisk bleeding from the trachea and risks loss of control of the airway. No data are available on the long-term consequences of stenting of the paediatric airway.
COMPLICATIONS AND OUTCOME Information on the long-term consequences of tracheomalacia in children is largely derived from studies of children with OA. Distinguishing the extent to which symptoms are related to tracheomalacia per se from symptoms that are related to residual oesophageal pathology is difficult. What is clear from these studies is that respiratory morbidity is
TRACHEOMALACIA
153
Figure 7 Appearance of the stent as removed from the airway.
greatest in infancy and improves progressively during childhood. The best long-term follow-up study of children after OA/TOF repair is from Melbourne, Australia.7 Chetcuti and Phelan interviewed over 300 children and adults who had had OA/TOF repair and discovered that 44% had subsequently been admitted to hospital with respiratory symptoms; the majority of these admissions were in the first 5 years of life. Admission after 10 years of age was unusual.8 Infants and children with symptomatic tracheomalacia often spend prolonged periods of time in hospital because of feeding problems and respiratory infections. This poses practical and emotional problems for the family. Parents may need to learn advanced resuscitation skills, which adds to the stress. The cyanotic ‘dying spells’ associated with severe tracheomalacia require prompt recognition and resuscitation. Although uncommon, permanent neurological damage is well recognised in children with tracheomalacia of this severity. The results of surgery for severe tracheomalacia have been reported by several groups.9,10 In general, the results of aortopexy are encouraging with significant improvement or cessation of symptoms reported in over 95% of cases.10 This procedure is not without complications, the most significant being major vascular injury and phrenic nerve damage with resultant paralysis of the ipsilateral diaphragm. Aortopexy is most likely to be successful in children with tracheomalacia secondary to OA/TOF or a vascular ring. Data on the long-term outcome of children with indwelling airway stents are not yet available. The main areas of concern relating to long-term usage are the risks of stent erosion and disturbance of tracheal growth. In animal experiments, squamous metaplasia of the airway mucosa
has been observed following stent placement, although this phenomenon has not been observed in humans.
CONCLUSIONS Tracheomalacia is an uncommon condition of variable severity. It is often associated with OA/TOF. In the absence of OA/TOF, a diligent search should be made for a vascular ring or a mediastinal mass. The natural history of tracheomalacia is one of progressive improvement during early childhood and this mitigates against surgical intervention. However, severe tracheomalacia is a life-threatening condition and intervention is invariably required.
PRACTICE POINTS Tracheomalacia is mainly a disease of infancy. It is associated with OA and vascular rings. Severe tracheomalacia with ‘dying spells’ indicates the need for surgery. Treatment options include aortopexy, airway stenting, long-term continuous positive airway pressure and tracheostomy. Most infants with tracheomalacia spontaneously improve given time.
REFERENCES 1. Wailoo MP, Emery JL. The trachea in children with tracheoesophageal fistula. Histopathology 1979; 3: 329–338. 2. Pole RJ, Qi BQ, Beasley SW. Abnormalities of the tracheal cartilages in the rat fetus with tracheo-oesophageal fistula or tracheal agenesis. Pediatr Surg Int 2001; 17: 25–28.
154
3. Backer CL, Ilbawi MN, Idriss FS, DeLeon SY. Vascular anomalies causing tracheoesophageal compression. Review of experience in children. J Thorac Cardiovasc Surg 1989; 97: 725–731. 4. Doull IJM, Mok Q, Tasker RC. Tracheobronchomalacia in preterm infants with chronic lung disease. Arch Dis Child 1997; 76: F203–F205. 5. Marmon LM, Bye MR, Haas JM et al. Vascular rings and slings: longterm follow-up of pulmonary function. J Pediatr Surg 1984; 19: 683– 690. 6. Filler RM, Forte V, Fraga JC, Matute J. The use of expandable metalic stents for tracheobronchial obstruction in children. J Pediatr Surg 1995; 30: 1050–1056.
V.M. MCNAMARA AND D.C.G. CRABBE
7. Beasley SW, Myers NA, Auldist AW (eds). Oesophageal Atresia. London: Chapman & Hall Medical, 1991. 8. Chetcuti P, Phelan P. Respiratory morbidity after repair of oesophageal atresia and tracheo-oesophageal fistula. Arch Dis Child 1993; 68: 167–170. 9. Corbally MT, Spitz L, Kiely E, Brereton RJ, Drake DP. Aortopexy for tracheomalacia in oesophageal anomalies. Eur J Pediatr Surg 1993; 3: 264–266. 10. Weber TR, Keller MS, Fiore A. Aortic suspension (aortopexy) for severe tracheomalacia in infants and children. Am J Surg 2002; 184: 573–577.