Tracheobronchomalacia

Mair and Parsons [1] provide a comprehensive review of the historical aspects of tracheobrochomalacia (TBM), with a description of pediatric TBM in 1948 by Gross and Neuman and the endoscopic appearances by Holinger et al in 1952. Of note was the expiratory nature of the collapse and the fact that it could be eliminated by the passage of a bronchoscope. The various treatments developed during the middle of this century from extended tracheotomy tubes through aortopexy to the more recent use of endobronchial stents are dealt with separately later in this chapter.

Introduction

Definition

Tracheomalacia[2] is an abnormal collapse of the trachea which when severe can produce symptoms of airway obstruction. Brochomalacia is the equivalent in the bronchi. The trachea and bronchi of children and particularly of neonates are more compliant than in the adult. This compliance can produce a degree of collapse even in normals particularly for instance if a child coughs during endoscopy because of insufficient topical and general anesthesia. This normal collapse needs to be excluded from any definition of tracheobronchomalacia as does the minor degree of anterior displacement of the trachealis which unless severe is more often a sign of light anesthesia than of significant malacia.

In general, collapse has to be greater than 10-20% to be readily appreciated at endoscopy and if the child is well anesthetized at the time this degree of collapse is usually abnormal though not necessarily clinically symptomatic. To be clinically significant 50% obstruction is probably required, less for neonates and more for older children. Different values for collapse are appropriate for other forms of investigation such as radiological screening [3].

Filler [4] describes tracheomalacia as a generalized or localized weakness of the trachea that results in excessive narrowing of the tracheal lumen during expiration or whenever intra-thoracic pressure increases.

Classification

The classical categorization of tracheomalacia is into primary or intrinsic malacia in which the collapse is due to an abnormality in the wall of the airway or secondary malacia which is due to extrinsic compression or other insult causing weakness and collapse.

Primary Tracheomalacia is seen relatively rarely[5,6], while Secondary Tracheobronchomalacia occurs in association with a number of conditions:

Tracheoesophageal fistula (TEF)

Although a flattened trachea is seen commonly in TEF, significant complications from TBM following fistula repair are relatively rare (1:54 in the series from Spitz)[7]. Spitz also provides a general review of TEF[8]. The suggestion that TBM in TEF could arise from pressure of the dilated proximal esophageal remnant is not borne out by the infrequent association of TBM with primary esophageal atresia without TEF.[9]

Cardiac abnormalities and vascular anomalies[10],[11]

The anatomical variants of cardiopulmonary circulation that result in extrinsic compression of the trachea and bronchi are illustrated (Fig 2.a.-d.). An aberrant innominate artery compresses the right anterior trachea just above the carina. A double aortic arch surrounds the trachea and main bronchi producing concentric or triangular shaped compression at endoscopy. A pulmonary artery sling compresses the right main bronchus often to the extent that the lumen of the right main bronchus is a thin slit.

Localized tracheomalacia associated with a tracheotomy

Prescott[12] feels that the localized collapse above most long standing tracheotomies is inevitable and is due to damage to the cartilage. Though he feels some of this may be prevented by careful design of the incision, most is probably secondary to the presence of the tracheotomy tube. Improvements in tube design may offer some hope.

Localized tracheomalacia associated with mediastinal masses.

Even benign masses such as a large cystic hygroma or bronchogenic cyst can produce localized tracheomalacia, perhaps by a pressure effect or perhaps through localized vascular insufficiency.

Laryngeal cleft

The association between tracheomalacia and laryngeal cleft[13] presumably stems from the combined embryological origin with separation of the trachea from the esophagus.

Larsens syndrome [14], Hunters syndrome [15]

Both Larsens syndrome and Hunters syndrome are associated with TBM though the embryological cause is unclear.

Major Airways Collapse (A further recent classification)

Based on histopathologic, endoscopic, and clinical findings of the flaccid airway Mair and Parsons [1] further subdivide secondary tracheomalacia into 2 types depending on the anatomical ratio of cartilage to muscle and whether external compression is noted. This gives 3 types of Major Airways Collapse (M.A.C.), a new descriptive term, which they propose to try to define tracheobronchomalacia more clearly. Type I (see Fig 3.b.) is equivalent to primary tracheomalacia and is usually seen with syndromic associations (see below). Type II (see Figs 3.c. and 3.d.) is classical secondary malacia occurring from external compression. Mair and Parsons suggest that this can either occur congenitally, such as with abnormal cardiovascular anatomy or be acquired. Type III (see Fig 3.e.) is acquired TBM either locally as a result of a tracheotomy tube or throughout the tracheobronchial tree as a result of prolonged high pressure ventilation. Types I, III and most type II have widened posterior walls with a cartilage to muscle ratio closer to 2:1 than the usual 4:1 or 5:1. So far this new classification does not seem to have been generally accepted.

Mair and Parsons also suggest a staging system analogous to that used for subglottic stenosis [16] with “mild” describing less than 70% obstruction, “moderate” 70-90% obstruction and “severe” greater than 90% obstruction at the end of expiration.

Pathophysiology

Hollinger[17]gives a careful description of the findings of six pathological specimens of neonatal larynges prepared as whole organ macrosections. The increased muscle to cartilage ratio is seen pathologically as it is endoscopically. Interestingly, one specimen shows thickening of the anterior tracheal ring i.e. a strengthening rather than a weakening of the cartilaginous part of the trachea.

Patient Assessment

History and exam

Often the diag is susp from exam/hist but usually ….spec invesdt

Investigations ---derek

Barium swallow

This is a useful investigation not only to identify vascular anomalies such as a double aortic arch but also during screening to observe the change in antero-posterior tracheal dimension seen in TBM.

Ultra Fast CT or cine CT if available.

These newer modalities[21,22] offer a noninvasive method of determining the site, extent, severity, and dynamics of airway collapse in the trachea and bronchus though occasionally without the addition of high definition CT as well they can misdiagnose tracheal stenosis as tracheomalacia[23]. TBM is defined radiologically as greater than 50% collapse.

Magnetic resonance imaging [24,25]

This is particularly appropriate for the assessment of vascular anomalies and mediastinal masses but is less sensitive at differentiating a static tracheal narrowing such as a stenosis from TBM.

Echocardiography

While this has become an invaluable tool for cardiologists it is not always accurate in excluding or defining vascular anomalies.

pH probe study

This is important if TBM is associated with a TEF as there is often associated gastro-esophageal reflux [6,26].

Endoscopy ben

Even if TBM has been demonstrated radiologically it is important to undertake a full endoscopy to examine the TBM at first hand and to exclude other abnormalities such as a cleft larynx which may be associated.

Laryngoscopy

Laryngomalacia may be seen as it is common but there does not seem to be any association with TBM. Posterior laryngeal cleft needs to be positively excluded by passing a probe between the arytenoids. If the patient has undergone repair of TEF or cardiovascular anomaly it is important during laryngoscopy to check vocal cord function.

Bronchoscopy

Bronchoscopy has been considered the gold standard for assessing TBM but there are many traps for the inexperienced that can result both in over and underdiagnosis.

Overdiagnosis can occur with poor anesthesia resulting in a child coughing as the bronchoscope touches the carina. In infants this can produce collapse in their normally compliant tracheas mimicking true TBM. This can be avoided by a level of anesthesia which is sufficiently deep to reduce coughing but still allowing spontaneous respiration.

Underdiagnosis occurs with splinting of the airway. Physical splinting from the bronchoscope can be avoided by using a small bronchoscope or advancing a small telescope beyond the tip of the bronchoscope (see Fig 4.a.-c.) Airway splinting due to an increased airway pressure can be avoided again by using a small bronchoscope that has a lower airways resistance and by avoiding the use of positive end expiratory pressure (P.E.E.P.) Techniques of anesthesia that rely on paralysis and venturi ventilation will also underdiagnose dynamic conditions such TBM.

Tracheobronchomalacia should be carefully recorded as a description for the operative report supplemented by still and video images for later consultation with for instance the cardiothoracic surgeons or general pediatric surgeons. The level and vertical extent as well as the % occlusion of the airway are all recorded along with the ratio of muscle to cartilage to help classify the TBM. [1]

The common vascular anomalies have sufficiently characteristic findings to aid diagnosis. With an aberrant innominate artery the artery arises from the aorta more posteriorly than normal compressing the right anterior wall of the trachea as it crosses in front of the trachea from left to right. Endoscopically this oblique flattening of the right anterior wall occurs 1 to 2 cm above the carina. Raising the tip of the bronchoscope can occlude the right radial pulse, best appreciated using pulse oximetry. With a double aortic arch the trachea is encircled by the normal anterior and the aberrant posterior arch, either of which may predominate. The endoscopic finding is of a triangular compression again just above the carina. In the rare anomaly of pulmonary artery sling the left pulmonary artery arises from the right pulmonary artery instead of the auricles. It crosses the right main bronchus and then passes behind the trachea to reach the left lung. The endoscopic findings are of a flat lower trachea with a very collapsed right main bronchus. TBM may also be a part of other complex congenital heart defects[27]

Treatment ben

Wait-no rx

cpap

trach tubes

vasc surgery

aortopexy

relocation/resectn of 2^nd arch

?endoscopic-stents with derek

tracheal surgery

ext stents

resection

cartilage

tent

- mild

Mild tracheobronchomalacia

Usually no treatment is required for mild TBM as the disease is self-limiting over 1-2 years and usually resolves without surgery[28]. However parents need a lot of support and information as well as being taught CPR if the child has a history of apneas or dying spells. All that may be required with resuscitation is a little positive airways pressure delivered mouth to mouth or with a resuscitation mask and bag. Parents are often told to avoid getting the child upset to prevent attacks relating to crying though how practical this is with a young child is open to doubt.

Vascular surgery for compressing abnormal vasculature

An aberrant innominate artery if causing significant apneas and cyanotic episodes can be suspended forwards in innominate arteriopexy. The non dominant (usually anterior) arch in a double aortic arch [29] can be resected combined if necessary with a vascular suspension procedure. Long term intubation as a conservative approach has also proved successful[30]. With a pulmonary artery sling the left pulmonary artery can be reimplanted anterior to the trachea but again this may need to be combined with tracheopexy[31].

Aortopexy

Aortopexy was initially used in TBM associated with TEF[32,33] but has also been used in TBM without an associated TEF.[5,6] Putting a suture through the outer wall of the aorta through a relatively small incision is a significant procedure and should not be undertaken unless there is severe collapse (>50%) and symptoms warrant major surgery. The results of lifting the aorta forwards are however encouraging [22]. Pericardial flap aortopexy may prove to be a safer technique[34].

Bronchopexy

Occasionally bronchomalacia can be improved with a suspension procedure[35] though this is less established than aortopexy.

Custom made tracheostomy tubes

An extended tracheotomy tube[36,37] will effectively support midtracheal tracheomalacia but is less effective for low tracheal and bronchial collapse. A tracheotomy tube reduces airways resistance making TBM distal to the tube tip worse. The tracheotomy tube is however easy to connect a ventilating bag to for resuscitation and increased airways pressure. Longer tubes with a straight cut rather than beveled end can be made to sit just above the carina but at the risk creating a tube tip stenosis at a very difficult site. Recently tubes have been developed to support the carinal area with a bifurcation into two flexible tubes to enter and support the main stem bronchi.

Nasal or tracheostomy CPAP

Carinal tracheomalacia and severe bronchomalacia can be supported with Continuous Positive Airways Pressure (CPAP)[38,39] from a standard home CPAP machine as used in obstructive sleep apnoea. The device can be used nasally with a close fitting mask (with some difficulties of acceptance) or via a tracheotomy tube.

Tracheostomy related collapse

Supra stomal collapse related to tracheotomy can be corrected by a surgical decannulation procedure in which the tracheocutaneous fistula is excised and the stoma formally closed. Sutures are brought laterally to the sternomastoids to support the area of collapse and the patient intubated for 24 to 48 hours.[40] If the collapse is particularly severe a cartilage graft may be required sometimes placed horizontally between the strap muscles for extra support.

Surgical alternatives for severe disease

External stents

As open thoracic operations for TBM are traditionally in the domain of cardiothoracic surgeons early attempts to stiffen the collapsing trachea externally used pericardial patches. Some fibrosed and were successful while others were as malacic as the original trachea. Marlex and a number of other synthetics have also been tried with sporadically good results.

Internal stents

Internal stents support the area of collapse well but suffer from migration, extrusion and localized reactions including granulations and frank infections. Both siliconized plastic and expandable metal stents have been used with success. The expandable metal stents[41-44] are difficult to insert even using an introducer and need to expand at just the right point in the lumen once released. Balloon dilatation can be used to further increase the lumen to accommodate future growth[43]. The plastic stents are inserted folded or on an introducer and have a variety of external pegs and lips to try to prevent migration.

Segmental resection

If the TBM is confined to a short segment this can be resected and a primary anastamosis performed[45]. Anastamotic stenosis occurs as it does when segmental resection is employed in short segment stenosis.

Cartilage grafting

Rib cartilage grafts can be used to stiffen long segment tracheal or bronchial malacia with good re-epithelialization if the cartilage amounts to 25% or less of the circumference of the airway, but when 30% or more of the circumference is rib graft, epithelialization may be impaired[45].

Perils and pitfalls

Tracheotomy can make unsupported areas worse such as the carina and bronchi by reducing the natural airways pressure.

Aortopexy carries a risk of aortic perforation and phrenic nerve palsy but seem to be successful in patients both with and without TEF.

Heroic measures such as stenting or resection should be reserved for very severe cases.

Severe bronchomalacia can be very difficult to treat even with intubation and/or tracheostomy and CPAP and may therefore be life threatening[46]

Management of complications

Sudden deterioration

The most feared complication of TBM is the child whose airway is so collapsed by his effort to exhale that the more he panics the more obstructed he becomes. These children can change suddenly from being quite well to being obstructed very quickly, progressing to apnoea. Sometimes this is in response to crying or coughing and sometimes to feeding. The respiratory arrest may be self-limiting though dramatic but usually if witnessed some form of resuscitation will have been commenced before recovery occurs spontaneously. Some children in hospital have required full CPR but at home a face mask and CPAP can buy time. Many of the procedures to combat TBM have complications as significant as the disease itself.

Gradual worsening of symptoms

Progression of the disease is not uncommon in the first (and second) year of life before the disease improves. Again the parents will have to deal emergently with collapse at home but once in hospital intubation with CPAP may be necessary. In the older child surgical alternatives should be avoided if possible as the disease my be about to “turn the corner”. This scenario is particularly depressing for parents if they have been told that their child will grow out of the disease by 18 months.

Summary

Tracheobronchomalacia when mild is common and self limiting. When severe the child’s life is at risk and heroic measures need to be considered but only used if the risk of complication is less than that of the disease itself.

References

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Figure	Diagram	Type	Cartilage to posterior Membrane ratio	Etiology
3.a.		Normal	4.5 : 1
3.b.		I	2 : 1	Congenital
3.c.		II	2 : 1	Acquired: Secondary to external compression
3.d.		II	4.5 : 1 (less commonly)	Acquired: Secondary to external compression
3.e.		III	2 : 1	Acquired: Localized reaction to tracheotomy