Primary Tracheal Collapse in a Cat

Case Report

A 7-year-old, neutered male, domestic shorthair cat was presented for persistent dyspnea of 2 to 3 days’ duration. Abnormalities on physical examination at presentation included increased inspiratory effort and tachypnea. A cough was easily elicited on palpation of the extrathoracic trachea. No abnormalities were noted on auscultation of the heart and lungs. Thoracic radiographs indicated narrowing of the tracheal lumen at the junction of the thoracic inlet on inspiration, with no evidence of extraluminal compression [Figure 1]. The cat was placed in a 40% oxygen cage and given dexamethasone (0.2 mg/kg intravenously [IV]).

Hematological and serum biochemical analyses performed the next day revealed a mature neutrophilia (15.326 × 10³/μL, reference range 1.1 to 10.4 × 10³/μL), lymphopenia (0.316 × 10³/μL, reference range 1.5 to 7 × 10³/μL), eosinopenia (0 × 10³/μL, reference range 0.037 to 0.914 × 10³/μL), hyperglycemia (223 mg/dL, reference range 59 to 124 mg/dL), hyperproteinemia (8.3 g/dL, reference range 6.5 to 7.7 g/dL), hyperglobulinemia (4.9 g/dL, reference range 2.5 to 4.7 g/dL), and hypocholesterolemia (76 mg/dL, reference range 101 to 409 mg/dL). The hematological changes and hyperglycemia were attributed to stress. The mild elevation in globulins and the hypocholesterolemia were considered incidental findings. Results of feline immunodeficiency virus and feline leukemia virus tests were negative.

Anesthesia was induced with propofol (6 mg/kg IV) and maintained with isoflurane. Laryngeal examination performed before intubation revealed no evidence of pharyngeal or laryngeal masses. Arytenoid abduction was within normal limits. The nasopharynx was normal on retroflex examination. An endotracheal tube was then placed to maintain general anesthesia. Tracheobronchoscopy revealed a normal tracheal lumen for the first 20 cm of the trachea (measured from the upper canine teeth), with collapse along the dorsal membrane thereafter [Figure 2]. The distal luminal diameter was decreased by approximately 75% and was classified as a grade III collapse.¹ Beyond the thoracic inlet, the diameter of the trachea appeared within normal limits, and the main-stem bronchi were identified. Esophagoscopy revealed no evidence of extraluminal compression, suggesting a diagnosis of tracheal collapse.

Over the following 2 days, the cat remained in an oxygen (40%) cage, and dexamethasone treatment was continued. Diazepam (0.37 mg/kg IV) and butorphanol (0.2 mg/kg IV) were administered as needed for increased respiratory difficulty or increased anxiety.An oral suspension of terbutaline (0.03 mg/kg per os [PO] q 8 hours) was started on day 3 of hospitalization in an attempt to induce bronchodilation. The cat’s clinical signs continued to worsen despite medical management, and the owners elected surgery on day 4.

The cat was anesthetized using the previously described protocol and was prepared for surgery. The skin and subcutaneous tissues along the ventral cervical midline were incised from the larynx to the manubrium. The sternohyoid and sternocephalicus muscles were separated along their midline to expose the cervical trachea. The recurrent laryngeal nerves were identified, protected, and retracted away from the trachea. The peritracheal tissues were dissected, creating a tunnel immediately around the specific areas of the trachea that were to be fitted with prosthetic rings. Nine prosthetic rings (each 1 cm wide) were placed around the trachea about 5 to 8 mm apart. The rings had been constructed from 3-mL syringe cases and fenestrated in four places to allow suture placement. The first tracheal prosthesis was placed 1 cm distal to the larynx, and the last was placed at the thoracic inlet. A curved hemostat was used to guide and position each ring around the trachea. The open end in each ring was positioned on the ventral aspect of the trachea, and the rings were then secured ventrally, laterally, and dorsally with 4-0 polypropylene sutures. Sutures were directed around rather than through the cartilages, with at least one of the sutures for each ring engaging the trachealis muscle. Cranial traction on the prosthesis allowed one ring to be placed at the thoracic inlet.After each ring was placed, the endotracheal tube was manipulated to ensure it had not been sutured to the trachea. Specimens for bacterial culture were obtained from several of the prosthetic rings before closure.

The sternohyoid and sternocephalicus muscles were apposed with simple continuous sutures of 3-0 polydioxanone (PDS), and the subcutaneous tissues were closed in the same fashion. The dermis was closed with a continuous intradermal pattern using 4-0 PDS. Cruciate sutures were then placed using 3-0 nylon.

Tracheobronchoscopy was performed immediately after surgery. The trachea was erythematous, with a small amount of blood visible within the lumen. The scope was advanced 13 to 15 cm caudal to the nares. Narrowing of the tracheal lumen was minimal as far distally as could be visualized. The suture material used to secure the prosthetic rings could be seen within the lumen. The bronchi appeared normal, with no evidence of collapse. A 25-μg fentanyl patch was placed postoperatively for analgesia.

The cat recovered well from anesthesia and surgery. Oral amoxicillin-clavulanate (12 mg/kg q 12 hours) was administered for 2 weeks after surgery. Bacterial cultures of tracheal specimens taken at surgery were negative. Thoracic radiographs taken before discharge showed a 100% increase in the diameter of the tracheal lumen compared with the size of the lumen on radiographs taken at initial presentation [Figure 3]. By the time of discharge 7 days after surgery, the clinical signs of tracheal collapse had markedly improved. Two months later, the owners reported the cat was doing well with minimal coughing.

The cat returned 1 month after surgery for reevaluation. The owners reported no respiratory difficulty, coughing, heat intolerance, or exercise intolerance since the surgery, but they had noticed a change in voice. A laryngeal examination performed under light sedation revealed right-sided laryngeal paralysis. This complication was attributed to damage to the recurrent laryngeal nerve that was likely secondary to retraction during surgery, despite the authors’ attempts to protect the nerve. During tracheobronchoscopy, suture material could be seen intermittently in the tracheal lumen from 9.5 cm caudal to the upper canines to the thoracic inlet [Figure 4]. Redundant dorsal membrane was evidenced in the distal trachea, but overall, the tracheal diameter appeared normal.

Discussion

Tracheal collapse is described as a dorsoventral flattening of the tracheal rings with concurrent laxity of the dorsal tracheal membrane.^1–5 It is diagnosed most commonly in middle- aged toy and small-breed dogs, but it has also been reported rarely in cats, calves, pigs, horses, and goats.⁶ Clinical signs are often exacerbated by heat, excitement, and eating or drinking. A history of chronic coughing, exercise intolerance, and dyspnea is common in canine patients; coughing is less common in feline patients. Feline cases are typically secondary to intra- or extraluminal obstruction caused by tumors, trauma, or congenital abnormalities.^7,8

Definitive diagnosis of tracheal collapse requires imaging studies and/or tracheobronchoscopy. Plain radiographs have been shown to be diagnostic in 59% of canine cases.^2,8 Lateral views of the thorax should be obtained during both inspiration and expiration. Inspiratory films best demonstrate collapse of the cervical trachea, while expiratory films demonstrate collapse of the main-stem bronchi or intrathoracic trachea.^1,2 Other noninvasive techniques, such as fluoroscopy and ultrasonography, can provide diagnostic support when thoracic radiographs alone are insufficient.³ Fluoroscopy can be beneficial in identifying collapse of the main-stem bronchi, which is not often evident on thoracic radiographs.¹ Fluoroscopy is also a dynamic study that is performed in a conscious animal and allows identification of tracheal collapse during active coughing.⁸ Regardless, tracheobronchoscopy remains the most sensitive and specific diagnostic method, and it is the method of choice for visualizing the dorsal tracheal ligament and tracheal mucosa.^2,3 In addition, the tracheal mucosa and secretions can be evaluated, and samples for cytology and bacteriology can be collected. The animal should be lightly anesthetized before tracheoscopy to allow evaluation of swallowing reflexes and laryngeal function.¹

Although the inciting cause of tracheal collapse has not yet been determined, it is known that this condition is associated with a defect in the tracheal cartilage that results in loss of rigidity.² In some dogs with tracheal collapse, the tracheal cartilage is hypocellular with less chondroitin sulfate and calcium than normal tracheal cartilage.¹ It has been postulated that both the abnormal cartilage and the aging process play a role.⁹

Tracheal collapse can be managed medically or surgically, but neither treatment is curative. Medical management most often includes some combination of weight loss, antibiotics, antitussives, bronchodilators, antiinflammatories, and treatment of the underlying cause (if identified).¹ Medical treatment of an animal with acute tracheal collapse and dyspnea should include oxygen.

Specimens collected from the trachea for cytology and culture can be used to guide antibiotic therapy and to diagnose bacterial infection or allergic tracheitis that could be the initiating cause of tracheal collapse. Positive tracheal cultures have not been associated with cytological evidence of infection or inflammation, which suggests that antimicrobial therapy is not necessarily indicated in the treatment of tracheal collapse.¹⁰ Organisms other than Bordetella bronchiseptica may be normal tracheal flora.

Antitussives are commonly recommended in dogs to reduce irritation and epithelial damage caused by chronic coughing. Coughing perpetuates collapse by initiating inflammation, which increases mucous production and decreases mucociliary clearance.¹ Bronchodilator treatment is controversial and appears to improve large-airway collapse by minimizing small-airway obstruction and thereby reducing intrathoracic pressure.⁸ Terbutaline was added to the treatment regimen of this cat to reduce intrathoracic pressure and potentially prevent large-airway collapse despite absence of small-airway disease.

Surgical treatment is recommended when the animal is not responding to medical therapy or when the quality of life has diminished.¹ Many surgical options for tracheal collapse have been described, including tracheal ring chondrotomy, plication of the dorsal tracheal membrane, tracheal resection and anastomosis, and intra- or extraluminal tracheal prostheses.^5,11–13 Most of these techniques have not been successful, but extraluminal prostheses (spiral or total ring) have had the most success.¹¹ Some surgeons prefer spiral prostheses over complete-ring prosthetics because of reports of improved flexibility and support of the trachea, as well as uniform contact of the spiral prostheses and the trachea. ^1,13 Also, in a ventral approach through the cervical midline, the spiral prosthesis can be placed further into the thorax than the complete-ring prosthesis.¹⁴ Spiral prostheses have been associated with tracheal necrosis due to extensive soft-tissue dissection, but newer surgical approaches have been described to help avoid this complication.^1,13

Placement of prosthetic rings generally reduces clinical signs by 75% to 85%, with the most common postoperative complications being laryngeal paralysis, coughing, and dyspnea. ¹ Laryngeal paralysis is most often caused by trauma to the recurrent laryngeal nerve during surgery.¹⁵ Tracheal necrosis can occur in the days after surgery if the tracheal blood supply is damaged during the procedure.¹

Since 1974, six cases of intratracheal obstruction or neoplasia have been reported in cats, but only two of these cases had evidence of secondary tracheal collapse.^16–20 In these two cases, tracheal collapse was cranial to the thoracic inlet and caudal to an intraluminal obstructing lesion. Squamous metaplasia was the primary cause of collapse in one of these cats, and a congenital abnormality with granulomatous changes was the primary cause of collapse in the other.²⁰ In 1991, a case of tracheal collapse in a cat was reported secondary to suspected trauma, and surgical correction using a spiral-cut prosthesis was successful.⁷ The authors are unaware of any previous reports of successful surgical correction of primary tracheal collapse in a cat.

The signalment in this case was atypical, because primary tracheal collapse is not common in cats, and this cat had no history of prior or progressive clinical signs. No signs of an inciting cause were identified on radiography, laryngeal examination, tracheobronchoscopy, or esophagoscopy. No gallop rhythm or heart murmur was auscultated in this cat, although echocardiography would be required to exclude concurrent heart disease. The acute onset of signs after being outdoors is more consistent with trauma, allergies, or toxins, although none could be identified. It is plausible that heat stress could have contributed to the acute onset and exacerbated the weakened dorsal tracheal membrane. Multiple radiographic images of the thorax were obtained to exclude other disease processes. Ideally, both inspiratory and expiratory thoracic radiographs should have been obtained, but they were not in this case because of the cat’s respiratory distress upon initial presentation. The diagnosis in this case was based on tracheobronchoscopy, which revealed the redundant dorsal tracheal membrane that is consistent with tracheal collapse in small-breed dogs.

The cat’s condition continued to worsen in the hospital with medical management alone, and increasingly frequent sedation was required to decrease anxiety and ease respiratory effort. Medical management with corticosteroids was ultimately insufficient, and the decision for surgery was a final attempt at treatment. The surgical approach and procedure were identical to those reported for repair of collapsing trachea in dogs, and they effectively reduced clinical signs in this cat. The surgeon chose individual, polypropylene rings as prostheses. Intraluminal stents were not used, because the surgeons were not experienced using this new modality at the time. In addition, intraluminal stenting was associated with many complications and was not a widely accepted procedure at the time.

Conclusion

Primary tracheal collapse is diagnosed most commonly in toy and small-breed dogs, but cats can also be affected. A history of exercise intolerance and dyspnea in feline patients should prompt airway evaluation via radiography, fluoroscopy, or tracheobronchoscopy. Although most reported cases of tracheal collapse in cats have been secondary to other disease processes such as neoplasia, primary tracheal collapse should also be considered. Surgery using extraluminal prostheses seems to be a viable option for correction of primary tracheal collapse in cats.

Acknowledgments

The authors thank TC Coffman and Drs. Michelle Fabiani and Derek Burney for their contributions.