Tracheal Collapse: A Look Beyond Stenting
Arathi Vinayak, DVM, DACVS
Tracheal collapse is flaccidity of the cartilage and subsequent collapse causing airway obstruction. Normal hyaline cartilage that makes up the trachea becomes replaced with fibrocartilage and collagen fibers with loss of the matrix that holds the cartilage together. This leads to loss of tracheal conformation and inability to maintain shape during normal respiration. The collapse is usually dorso-ventral. This disease is often confused with tracheal stenosis (narrowing of the trachea) that is congenital or due to trauma/scarring and hypoplastic trachea (smaller than normal tracheas) typical of brachycephalic breeds.
Figure 1 Lateral thoracic radiograph taken during inspiration demonstrating severe collapse of the trachea cervically and at the thoracic inlet.
Tracheal collapse typically occurs in miniature and toy breeds with Yorkshire terriers, Chihuahuas, Pomeranians, Toy Poodles, Maltese, and Bichons being overrepresented. There is no sex predilection. The clinical signs become severe most commonly in middle aged to older dogs (6-10 years of age) with most dogs having respiratory signs as early as 1-5 years old. Clinical signs often progress with age and include noisy panting, goose honking cough, hacking, wheezing, cyanosis, and syncopal episodes (losing consciousness due to lack of oxygen). Not all of the signs are present in every dog and some have as little as one of the above clinical signs.
Figure 2 Tracheoscopy image showing a grade 4 cervical tracheal collapse with 100% narrowing of the tracheal lumen.
Physical examination reveals flattened lateral borders on palpation of the cervical trachea and at the inlet with a cough easily elicited on palpation. Radiographs are diagnostic only in 50-60% of the cases. Films taken during inspiration and expiration are useful as the cervical trachea tends to collapse during inspiration and the intrathoracic trachea collapses on expiration (Figure 1). It is possible to not diagnose tracheal collapse on x-rays alone as they are an image of the trachea at only one point in time and collapse can be dynamic. Fluoroscopy (real time x-rays) can be more diagnostic as it captures tracheal motion during the respiratory cycle and help evaluate the mainstem bronchus for collapse. Tracheoscopy is the definitive test prior to surgery under the same anesthetic or for diagnosis to determine options for treatment. This allows for evaluation of the cervical, thoracic inlet, intrathoracic tracheal collapse as well as mainstem bronchus collapse. It allows for accurate grade of collapse, location, and whether the collapse is static or dynamic. An evaluation of the laryngeal function is also recommended at the same time as 30% of dogs with tracheal collapse have concurrent laryngeal collapse.
Figure 3 Image of an unconstrained nickel-titanium (Nitinol) stent.
Tracheal collapse is classified on a grade-wise on a scale of 1 through 4, based on location, and whether the collapse is static vs. dynamic. A grade 1 collapse is a 25% narrowing of the trachea; grade 2 is a 50% narrowing of the trachea, grade 3 is a 75% narrowing of the trachea, and a grade 4 is a 100% collapse of the trachea with no appreciable airway (Figure 2). In addition, tracheal collapse can be cervical, thoracic inlet, intrathoracic, or a combination of the three in location. The collapse can also be static (present all the time in all phases of respiration), or dynamic where the collapse occurs during the respiratory phase or while coughing. Accurate assessment of the collapse allows for appropriate treatment recommendations to be made. Treatment options are medical management, tracheal stents, and extraluminal tracheal rings with extraluminal tracheal rings being the preferred option.
Medical management is reserved for patients with grade 2 (50% collapse) or less. This generally involves treatment with an anti-cough medication, antibiotics, bronchodilators, sedatives, and steroidal anti-inflammatories. Stenting or rings are considered in patient s where clinical signs do not resolve despite medical management or if progression occurs as the patient ages. Medical management is often continued in patients after stent or ring placement as 50% of dogs have concurrent mainstem bronchus collapse. Mainstem bronchus collapse is a medically managed condition as it is not feasible or recommended to stent or ring this area.
Figure 4 A lateral thoracic radiograph showing stenting of the trachea from caudal to the larynx to just cranial to the carina.
Intraluminal tracheal stenting is an option for tracheal collapse when the severity is greater than a 50% collapse. These are nickel-titanium stents deployed inside the trachea and open out the trachea collapse from within (Figure 3). The entire affected trachea segment can be stented starting from about 1cm caudal to the larynx all the way to 1cm cranial to the carina (Figure 4). The advantages are that it is done with either endoscopic or fluoroscopic guidance without incisions made, and that the entire trachea can be stented. Disadvantages are continued coughing from the stent placement being too close to the larynx, asphyxiation because of stent migration to the carina, granuloma formation (scar tissue) causing airway obstruction, breakage of the metal stent, pneumonia/tracheal infection, collapse of the trachea in front of or behind the stent, tracheal hemorrhage, continued coughing, tracheal rupture, implant collapse or deformation, inability to remove the stent after the first few weeks of placement (Figure 5).
Figure 5 A lateral thoracic radiograph with stent fracture noted just caudal to the thoracic inlet.
In a review of 12 dogs with tracheal stents in the Journal of the American Veterinary medical Association, 7 of 12 dogs died within 2 years of stent placement (60% mortality rate) with a stent fracture rate of 42%. Fracture of the stent generally requires a second stent to be deployed within the first. Another study in the Veterinary Surgery Journal showed that 9/18 dogs with severe tracheal collapse had major complications with a mortality rate of 11% within the first 60 days.
Figure 6 Extraluminal polypropylene tracheal ring. The first ring has been placed but not sutured. Collapse of the trachea is noted caudal to this ring.
Extraluminal tracheal rings is the preferred surgical option when the grade of collapse is a 2 or greater and ideally when the majority of the collapse is cervical, thoracic inlet, and up to the 2nd rib. This is still the preferred method even if there is a <grade 2 collapse caudal to the 2nd ICS as resolution of negative airway pressure cranial to the intrathoracic collapse can yield significant improvement in the intrathoracic collapse as well as the patient’s quality of life. Collapse of the intrathoracic trachea past the 2nd rib without concurrent cervical and thoracic inlet tracheal collapse (uncommon scenario) cannot be managed with extraluminal rings as it is not possible to surgically access this area of the trachea. With extraluminal tracheal ring procedure, an incision is made in the neck to gain access to the trachea. Rings are made of polypropylene and are placed on the outside of the trachea (Figure 6). The trachea is then sutured to the rings to maintain its normal shape (Figure 7). The advantage of this procedure is a low major complication rate of <10%, minimal risk of fracture of the rings, low infection risk, and normal life span with the procedure. The major complication can occur in <10% of the cases because of the need to dissect the recurrent laryngeal nerves on either side of the trachea away to facilitate ring placement. Inadvertent damage to both of these nerves can lead to laryngeal paralysis creating the need for either a permanent tracheostomy or a tie-back procedure during the same anesthesia. Damage to one nerve will still allow for partial function of the larynx and does not warrant any further surgery. Reports of laryngeal paralysis following extraluminal tracheal rings is reportedly as high as 40%, however, I believe this is surgeon dependent with surgeons trained heavily and specializing in this procedure having rates <10%. Disadvantages are that the procedure can only be performed up to the 2nd rib space, requires an incision, risk of damage to laryngeal function, possibility of progression of tracheal collapse within the intrathoracic portion with time requiring a stent placement.
Figure 7 Note that the tracheal diameter has been restored after placement of several extraluminal rings around the trachea.
In conclusion, surgical correction of tracheal collapse is recommended when the grade of collapse is greater than 50% and when medical management fails to fully control symptoms. Most tracheal collapses start in the cervical trachea and thus early correction of collapse involving the cervical, thoracic inlet, and intrathoracic trachea up to the 2nd ICS can help reduce severity of tracheal collapse caudal to the 2nd ICS by eliminating negative airway resistance and may help prevent progression of the collapse past the 2nd ICS. If the collapse is amenable to extraluminal rings placement (i.e., tracheal collapse extending from caudal to the larynx to the 2nd ICS), this is the preferred method due to the lower major complication rate and mortality. If the collapse extends the entire length of the trachea to the mainstem bronchi, and is severe in grade for the entire length of collapse, either a long intraluminal stent or extraluminal rings for the cervical region in conjunction with an intraluminal intrathoracic tracheal stent should be considered. Medical management of the mainstem bronchus collapse is recommended as this area cannot be stented and is not surgically accessible for extraluminal ring placement.
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