Successful Surgical Treatment of a Suspected Iatrogenic Arytenoid Cartilage Fracture in a Dog

Case Report

A 3-year-old, intact female golden retriever was presented for evaluation of dyspnea. The animal had undergone a left caudal mastectomy 4 days previously for treatment of a necrotic mammary gland that had developed after whelping. The dog was reported to have had a difficult and aggressive recovery following endotracheal extubation after the mastectomy; later in the same day of the procedure, the dog began exhibiting episodes of inspiratory stridor and dyspnea. These episodes worsened in severity over the following day. The dog displayed cyanosis, stridor, and hyperpnea during these periods, but a normal respiratory rate and pattern were noted between these episodes.

The surgeon who had performed the mastectomy performed survey radiography of the neck and chest (right lateral views). The radiographic findings were judged as normal. On the basis of clinical examination findings and radiographic findings, this surgeon made a presumptive diagnosis of laryngeal paralysis. Theophylline,^a furosemide,^b and diazepam^c were administered; however, the dyspneic episodes continued with the same severity.

The dog was referred to another veterinarian 48 hours postoperatively. Survey orthogonal cervical and thoracic radiographs were obtained, and laryngoscopic and bronchoscopic examinations were performed. A tentative diagnosis of left-sided laryngeal paralysis was made, based on the clinical signs of inspiratory stridor and dyspnea and a laryngoscopic finding of a slight asymmetry between the two cuneiform processes. It was noted, however, that a unilateral laryngeal paralysis would be unlikely to account for the dyspneic episodes. Enrofloxacin^d and meloxicam^e were added to the dog’s treatments. The dog was discharged with the hope that spontaneous improvement might occur.

The dyspneic episodes continued, and the dog was referred to the University of Bristol Small Animal Hospital. On clinical examination, no stridor or dyspnea was noted. The dog was eupneic with a respiratory rate of 30 breaths per minute. Thoracic auscultation was unremarkable. The dog was normothermic (rectal temperature 38.2°C). The authors witnessed the dog experiencing several dyspneic episodes following admission. These episodes occurred spontaneously, lasted for a few minutes, and stopped abruptly. They were not preceded by activity or excitement and were not associated with hyperthermia.

Laryngeal examination, under a light plane of general anesthesia, revealed both arytenoid cartilages to abduct briskly during inspiration. No mucosal lesions or vocal cord edema were evident. A subtle asymmetry was noted between left and right arytenoid cartilages, and a slight overlap of the cuneiform processes was seen to occur on adduction. The arytenoid cartilages were probed with a plastic endotracheal tube obturator. The right arytenoid cartilage was considered normal. The cuneiform process of the left arytenoid cartilage was markedly mobile and, with gentle pressure, could readily be deviated medially approximately 130° from its resting position to point caudally. Both corniculate processes were probed and found to be unremarkable. Thoracic radiographs were suggestive of a mild bilateral aspiration pneumonia. Cervical radiographs were within normal limits. A fracture of the cuneiform process of the left arytenoid cartilage was suspected.

A combined cricoarytenoid and thyroarytenoid caudolateralization procedure was performed on the left side in a manner similar to that described previously.^1,2 The dog was positioned in right lateral recumbency, and a left lateral approach to the extrinsic muscles of the larynx was used.¹ The left thyropharyngeus muscle was incised along the left dorsal border of the thyroid cartilage. Care was taken to preserve the left cranial laryngeal nerve. The thyroid cartilage was disarticulated from the cricoid cartilage at its caudal cornu attachment.

Following the lateral retraction of the left thyroid lamina, examination of the intrinsic muscles of the left larynx revealed a subjectively normal-sized left cricoarytenoideus dorsalis (CAD) muscle with no evidence of muscle fiber atrophy. The insertion of the muscle onto the muscular process of the left arytenoid cartilage was transected. The left arytenoid cartilage was completely disarticulated from its articular facet on the rostral border of the left cricoid lamina, and the interarytenoid band was transected. Manipulation of the left arytenoid cartilage confirmed its complete release from the cricoid and contralateral arytenoid cartilages, allowing the structure to be freely moveable in a caudal direction.

Lateralization and caudal fixation of the arytenoid cartilage were accomplished by the use of two sutures. The first was a 2-0 polypropylene^f mattress suture placed through the left caudal cornu of the thyroid cartilage, then through the articular facet and muscular process of the left arytenoid cartilage. The second was a simple interrupted suture of 2-0 polypropylene placed through the caudolateral border of the cricoid cartilage, then through the articular facet and muscular process of the arytenoid cartilage. The second suture is sometimes referred to as a prosthetic CAD muscle suture, because when the suture is tied, its line of tension is in the same direction as the muscle fibers of the left CAD muscle.

The procedure was performed without complication, and the dog did not have any more episodes of dyspnea after recovery from anesthesia. Amoxicillin clavulanate^g was administered intravenously at 20 mg/kg three times daily to treat the suspected aspiration pneumonia. Nebulization and coupage were also performed three times daily during this period. The dog’s moist cough resolved after 5 days of this protocol, and treatment was discontinued. The owners were contacted by telephone 3 and 7 months after surgery, and they reported the dog had no episodes of dyspnea and normal exercise tolerance.

Discussion

This is the first report, to the authors’ knowledge, of a suspected arytenoid fracture in a dog. In dogs, respiratory obstruction resulting from laryngeal dysfunction can occur secondary to conditions including laryngeal paralysis, laryngeal collapse, and laryngeal neoplasia. Iatrogenic glottic obstruction is usually caused by laryngeal edema following tracheal intubation. The authors hypothesize that the left arytenoid cartilage fractured as a result of traumatic endotracheal intubation for general anesthesia for the mastectomy. The dog had no history of dyspnea prior to this procedure. The most likely site of fracture is the narrow isthmus of cartilage that connects the cuneiform process to the rest of the arytenoid cartilage [Figure 1]. This is a site of weakness of the arytenoid cartilage, and medial deviation of the cuneiform process is a component of laryngeal collapse syndrome.³

Interestingly, the cuneiform process is derived from elastic cartilage while the remainder of the arytenoid cartilage is composed of hyaline cartilage; the two cartilages are embryologically distinct.⁴ Instability at this site would permit medial folding of the cuneiform process during inspiration, when air pressure within the upper respiratory tract lumen is at its lowest [Figure 2]. The resultant partial glottic occlusion and consequent increased respiratory effort would act to increase airflow speed at the rima glottidis, further reducing air pressure at this location and exacerbating any medial displacement of the cuneiform process. Not known was whether significant medial excursion of the cuneiform process would still occur in its more caudal location, following arytenoid caudolateralization and stabilization.

Careful attention was given to ensure substantial caudal translocation of the left arytenoid cartilage following tying of the arytenoid caudolateralization sutures. This was achieved by completely disarticulating the left arytenoid cartilage from the cricoid cartilage and by transecting the interarytenoid sesamoid band to gain maximum mobilization of the arytenoid cartilage. The thyroarytenoid suture was placed using the most caudal portion of the cornu of the thyroid wing. Although an arytenoid caudolateralization procedure may be performed without disarticulating the cricoid and thyroid cartilages, achieving better surgical exposure and allowing a more thorough inspection of the region were considered necessary in this case. A goal of the surgery was also to produce enough caudal translocation of the arytenoid cartilage to but-tress it between the thyroid wing and the cricoid cartilage.

Two factors likely contributed to the success of the procedure. First, the lateralization of the left arytenoid cartilage widened the rima glottidis; second, the arytenoid was but-tressed between the cricoid and thyroid cartilages as the arytenoid cartilage was drawn caudally. The excessively mobile cuneiform process was, thus, wedged between the cricoid and thyroid cartilages, preventing the medial folding that had occurred during inspiration. Two sutures were used to provide two-point fixation; this minimized the risk of cranial displacement of the arytenoid cartilage if one suture were to break or be pulled out.

Laryngeal fractures occur in humans most commonly during car accidents because of poorly positioned seatbelts or from blunt trauma from airbags.⁵ Fractures also occur during strangulation or attempted hanging.^6,7 Laryngeal fractures have not been reported in humans following endotracheal intubation for anesthesia. This may be because the pyramidal shape of the human arytenoid cartilage does not have the same isthmus as the dog; the isthmus in the dog can act as a potential “point of weakness.”

A presumptive diagnosis was made in this dog based on the history and laryngeal examination. While laryngeal paralysis was tentatively diagnosed by another veterinarian, the arytenoids abducted appropriately during inspiration when examined under light anesthesia; this finding ruled out a diagnosis of laryngeal paralysis. The cricoarytenoid articulation was not subluxated or luxated as assessed during the surgical procedure, and no atrophy of the CAD muscle was apparent. Fracture of the left arytenoid cartilage between the cuneiform process and the remainder of the arytenoid appeared to be the most plausible explanation for the dog’s clinical signs of intermittent obstructive inspiratory dyspnea and the profound mobility of the left cuneiform process. The cartilaginous isthmus of the left arytenoid cartilage was not visualized during the surgical procedure, because additional dissection to prove the presence of a fracture was considered unnecessary and potentially detrimental to the outcome. The caudal positioning and fixation of the damaged arytenoid cartilage depended on the presence of intact pericartilaginous structures to ensure that moving the body of the cartilage would result in similar movement of the cuneiform process.

A definitive diagnosis of arytenoid fracture may have been possible using advanced imaging, such as magnetic resonance imaging. High-resolution spiral computed tomography is the method of choice for imaging traumatized larynges in humans.⁸ Standard computed tomography incorporating the window technique can be used, although some laryngeal fractures can be overlooked with this approach.⁸

The authors are optimistic regarding the long-term prognosis for the dog reported, particularly because the arytenoid cartilage contralateral to the one operated on has normal function. This is in contrast to most dogs undergoing laryngoplasty for idiopathic laryngeal paralysis.

Conclusion

This report suggests that combined cricoarytenoid and thyroarytenoid caudolateralization may be a useful procedure for treatment of cuneiform process instability resulting from arytenoid cartilage fracture in dogs.