Case Report Rapport de cas Bilateral laryngeal paralysis in a dog secondary to laryngeal osseous metaplasia Alicia Marie Skelding, Agatha Kisiel, Stephanie Essman, Bronwyn E. Rutland Abstract — A 7-year-old spayed female Lurcher was evaluated for a chronic history of increased upper respiratory noise. Advanced imaging including digital radiography and pre- and post-contrast computed tomography (CT) scan confirmed the presence of an ill-defined soft tissue mineralized mass of the ventral larynx. Histopathology demonstrated pleocellular myositis and fasciitis with osseous metaplasia. Résumé — Paralysie laryngée bilatérale chez un chien secondaire à la métaplasie osseuse. Une chienne Lurcher stérilisée âgée de 7 ans a été évaluée pour une anamnèse chronique de bruit des voies respiratoires supérieures. Une imagerie avancée, dont une radiographie numérique et une image par tomodensitométrie avant et après contraste a confirmé la présence d’une masse minéralisée floue de tissus mous dans le larynx ventral. Unexamen histopathologique a démontré une myosite pléocellulaire et une fasciite avec une métaplasie osseuse. (Traduit par Isabelle Vallières) Can Vet J 2016;57:157–159
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n October 2013, a 7-year-old 17-kg spayed female Lurcher was presented to the 404 Veterinary Emergency and Referral Hospital in Newmarket, Ontario for evaluation of increased upper respiratory noise. Veterinary consultation was sought 2 to 3 mo earlier when the owners noticed a change in the patient’s bark (deeper than usual). The increase in upper respiratory noise was most noticeable after strenuous activity and when the dog was sleeping, although the dog was not noted to have any respiratory distress or exercise intolerance. The dog also had more difficulty swallowing kibble but had no problems eating wet food. No changes in drinking, urination, or defecation were seen by the owner. To the owner’s knowledge, the dog had no history of neck or laryngeal trauma.
Case description Physical examination revealed normal vital parameters. Inspiratory stridor was present, most audible when the dog was panting. The dog’s larynx was prominent and firm on palpation but was smooth, symmetrical and non-painful. A complete blood cell count and biochemistry performed by the 404 Veterinary Emergency and Referral Hospital, Newmarket, Ontario (Skelding, Kisiel, Rutland); Veterinary Imaging Consultations — Diagnostic Imaging, Del Mar, California, USA (Essman). Address all correspondence to Dr. Alicia Skelding; e-mail: [email protected] Use of this article is limited to a single copy for personal study. Anyone interested in obtaining reprints should contact the CVMA office ([email protected]) for additional copies or permission to use this material elsewhere. CVJ / VOL 57 / FEBRUARY 2016
referring veterinarian prior to referral revealed no abnormalities. Three-view thoracic radiographs were within normal limits. A right lateral cervical radiograph revealed an increased amount of mineralization over the larynx and an ill-defined soft tissue opacity. (Figure 1). A computed topography (CT) scan of the laryngeal region was acquired using a 64-slice helical scanner (Aquilion 64; Toshiba America Medical Systems, Tustin, California, USA). The patient was sedated with butorphanol (Torbugesic; Fort Dodge Animal Health, Fort Dodge, Iowa, USA), 0.2 mg/kg body weight (BW) and physically restrained with the use of sandbags and padded straps. The patient was positioned in sternal recumbency and scanning parameters were: 3-mm section collimation thickness, PF 0.828/HP 53.0, 120 kVp, 125 mAs. Pre- and post-contrast images were acquired. Iohexol (Omnipaque 350 mg/mL; GE Healthcare, Mississauga, Ontario) was administered as a bolus injection into a cephalic vein via catheter at a rate of 2 mL/min without a pressure injector at a dose of 600 mg of iodine per kg BW. Post contrast images were obtained 60 s after completion. There was an ill-defined, contrast enhancing soft tissue mass or thickening of the ventral aspect of the larynx at the region of the basihyoid bone and cricoid cartilage. Irregular bony proliferation and lysis associated with the hyoid apparatus was also noted. There was no evidence of lymphadenopathy (Figures 2A, 2B). On subsequent examination later that week, the dog was sedated with butorphanol (Torbugesic; Fort Dodge Animal Health), 0.2 mg/kg BW and dexmedetomidine (Dexdomitor; Zoetis, Florham Park, New Jersey), 5 mg/kg BW, intravenously. General anesthesia was induced with propofol (Diprivan; AstraZeneca, Mississauga, Ontario), 4 mg/kg BW, IV, and maintained with 2% isoflurane (Isoflurane USP; Pharmaceutical 157
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Figure 1. Right lateral cervical radiograph with mineral opacity at the level of the larynx (arrow). Projection: right lateral cervical radiograph
Partners of Canada, Richmond Hill, Ontario) and 100% oxygen. Endoscopy of the larynx did not reveal any evidence of masses or abnormalities within the lumen of the larynx or upper trachea. Multiple incisional biopsies of the ventral laryngeal mass were taken immediately following endoscopic examination of the larynx. The procedure was routine and the dog recovered from anesthesia uneventfully. Histopathology of the biopsies demonstrated pleocellular myositis and fasciitis with osseous metaplasia. A separate laryngeal examination using propofol without premedication, to eliminate any potential influence of sedation on laryngeal function, was performed by 2 of the authors (BR and AK) at a follow-up appointment 2 wk later and bilateral laryngeal paralysis was confirmed. The dog was treated with prednisone (Novo-Prednisone; Novopharm, Toronto, Ontario), 1 mg/kg BW, PO, q24h for 2 wk and tapered to a maintenance dose of 0.5 mg/kg BW, PO, q24h. At the recheck appointment, 11 wk following the biopsies, the mass was still palpable and similar to that observed at the previous examination. Repeat CT showed improvement in the soft tissue thickening and less prominent lysis. Clinically, the dog had not improved. Surgical intervention to address the laryngeal paralysis was discussed but not recommended at this time because of the lack of significant clinical abnormalities affecting the patient’s quality of life.
Figure 2A. Pre-contrast CT at the level of the hyoid. Irregular bony proliferation lysis is associated with the hyoid apparatus and cricoid cartilage (arrow).
Discussion The patient in this case presented with unusual laryngeal disease, characterized by bilateral laryngeal paralysis presumed to be secondary to chronic mineralization of the laryngeal cartilages and surrounding soft tissue. The results of the biopsy of the laryngeal mass indicated that the lesion found in this dog was consistent with osseous metaplasia. To the authors’ knowledge, this is the first report of laryngeal osseous metaplasia resulting in secondary laryngeal paralysis in a canine patient. Myositis ossificans (MO) is a condition in humans that is characterized by abnormal bone formation, usually involving skeletal muscle (1). Several subtypes of MO exist. Post-traumatic myositis ossificans (PTMO) occurs as benign, solitary reactive bone formation following a traumatic event (1). In humans, PTMO is usually self-limiting and advanced imaging is used 158
Figure 2B. Post-contrast CT at the level of the hyoid. Ill-defined contrast-enhancing mass is present along the left medial aspect of the larynx and measures approximately 1.3 cm in thickness (arrow).
to confirm the diagnosis. A similar condition, inflammatory myofibroblastic pseudotumor, occurs in humans following an initiating trauma (2). A single case report describes an incident in which trauma resulting from a vehicular air bag resulted in a subglottis lesion of MO (2). The human patient in this case exhibited similar clinical signs of dyspnea and stridor and complete surgical excision was reportedly curative (2). While there is no history of observed trauma in the dog presented herein, an unseen trauma may have occurred at some point when the CVJ / VOL 57 / FEBRUARY 2016
CVJ / VOL 57 / FEBRUARY 2016
of innervation of the recurrent laryngeal nerve it is reasonable to speculate that the laryngeal paralysis was secondary to the inflammation and mineralization of the surrounding muscles and less likely primary neurologic dysfunction. Advanced diagnostic imaging was valuable for the diagnosis and monitoring of this case. It showed the origin and characteristics of the palpable mass in more depth than was appreciated on external visualization, radiographs, or laryngeal examination. It remains unclear why the dog herein developed an osteoproductive and lytic lesion of its larynx. The histopathology results suggest that the lesion itself was a result of a chronic inflammatory process in the extraluminal tissues of the larynx. This chronic inflammation was most likely the stimulus for the development of osseous metaplasia in the surrounding soft tissues with resultant secondary laryngeal paralysis. This case is an example of laryngeal paralysis secondary to local soft tissue inflammation.
Acknowledgments The authors thank Dr. Kevin Isakow for his generous support and financial contribution that made this case report possible. We also thank the referring veterinarian and the technical staff at 404 Veterinary Emergency and Referral Hospital. CVJ
References 1. Tyler P, Saifuddin A. The imaging of myositis ossificans. Semin Musculoskeletal Radiol 2010;14:201–216. 2. Alaani A, Hogg R, Warfield AT, Olliff J, Jennings C. Air bag injury as a cause of inflammatory myofibroblastic pseudotumour of the subglottic larynx progressing to myositis ossificans. Acta Otolaryngol 2005;125: 674–677. 3. Haynes DR. Bone lysis and inflammation. Inflamm Res 2004;53: 96–600. 4. Park JK, Han JY, Hong IH, et al. Salivary mucocele with osseous metaplasia in a dog. J Vet Med Sci 2009;71:975–977. 5. Prassinos NN, Tontis DK, Adamama-Moraitou K, Galatos AD, Siochu A. Metaplastic ossification of a cervical sialocoele in a dog. Aust Vet J 2005;83:421–423. 6. Fernandes TR, Grandi F, Lidianne NM, Salgado BE, Rocha RM, Rocha NS. Ectopic ossification presenting as osteoid metaplasia in a salivary mucocele in a Shih Tzu dog. BMC Vet Res 2010;8:13–17. 7. Lynch GL, Scagliotti RH. Osseous metaplasia in the eye of a dog. Vet Pathol 2007;4:222–224. 8. Park JK, Lee SK, Park SJ, Hwa I, Jeong KS. Fibroma with osseous metaplasia of external auditory canal in a dog. J Vet Diagn Invest 2010; 22:635–638. 9. Pieczarka EM, Russell DS, Santangelo KS, Aeffner F, Burkhard MJ. Osseous metaplasia within a canine insulinoma. Vet Clin Pathol 2014; 43:89–93. 10. MacPhail C. Laryngeal disease in dogs and cats. Vet Clin Small Anim 2013;44:19–31. 11. Kitshoff AM, Goethem BV, Stegen L, Vandekerckhove P, de Rooster H. Laryngeal paralysis in dogs: An update on recent knowledge. J S Afr Vet Assoc 2013;84:1–9. 12. Millard RP, Tobias KM. Laryngeal paralysis in dogs. Compendium 2009;31:212–219. 13. Gross ME, Dodam JR, Pope ER, Jones BD. A comparison of thiopental, propofol and diazepam-ketamine anesthesia for evaluation of laryngeal function in dogs premedicated with butorphanol-glycopyrrolate. J Anim Hosp Assoc 2002;38:503–506. 14. Tasker S, Foster DJ, Corcoran BM, Whitbread TJ, Kirby BM. Obstruc tive inflammatory laryngeal disease in three cats. J Feline Med Surg 1999;1:53–59.
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dog was unsupervised. Also, the lesion of this dog’s larynx had a component of bony lysis that appeared to improve following prednisone therapy. The authors hypothesized that the bone lysis was a result of the inflammatory infiltrates as no neoplastic or other lytic processes were identified. A relationship between bone loss and an inflammatory process has been previously documented (3). Osseous metaplasia is a type of heterotrophic bone formation, in which metaplastic bone is formed directly from connective tissue as a result of alternative differentiation of fibroblastic cells. It has been reported infrequently in veterinary patients and typically the pathogenesis is unclear, but trauma and chronic inflammation are consistently implicated. Three cases of salivary mucocele with osseous metaplasia have been reported in dogs (4–6). These reports comment on the presence of ossifying components within the wall of the salivary mucocele and implicate chronic inflammation and irritation as a likely cause. A case of osseous metaplasia in the iris of a dog, in which no underlying etiology could be identified, has also been reported, but the authors comment on the possibility of an unobserved trauma (7). Cases of osseous metaplasia have also been associated with a fibroma of the external auditory canal in a dog (8) and within a canine insulinoma (9). The larynx is composed of hyaline cartilages and muscles (10,11). The cartilages of the larynx include the paired arytenoids and unpaired epiglottis, cricoid, and thyroid cartilages (10,12). Contraction of the cricoarytenoideus dorsalis muscle occurs during inspiration, resulting in abduction of the arytenoid cartilages (10,11). This allows air to pass freely through the glottis. The cricoarytenoideus dorsalis muscle is innervated by the caudal laryngeal nerve, which is the terminal segment of the recurrent laryngeal nerve (10). The recurrent laryngeal nerve leaves the vagus nerve as left and right branches and courses cranially to the larynx. Each recurrent laryngeal nerve sends branches to the heart, trachea, and esophagus before terminating in the laryngeal muscles. Laryngeal paralysis is one of the most common diseases of the larynx. Diagnosis of laryngeal paralysis is made by evaluation of laryngeal cartilage function under light anesthesia (11,13). Laryngeal paralysis results from lack of function of the caudal laryngeal nerve. The acquired form of laryngeal paralysis may be caused by trauma (iatrogenic and accidental), cervical/intrathoracic masses or neuromuscular diseases, with idiopathic disease being the most common (10). The initial primary differential diagnoses for the cause of the laryngeal mass in the dog herein were foreign body, trauma, or a concurrent cervical neoplasia. Inflammatory laryngeal disease is a rare condition of the arytenoid cartilages and surrounding tissues that has been described in dogs and cats (10,14). The disease tends to be multifactorial and the inflammatory process can be granulomatous, lymphocytic-plasmacytic, or eosinophilic (10). The patient in this case report had a degree of myositis in addition to ossification of the laryngeal cartilages. The cellular infiltrates were mixed, being composed of neutrophils, eosinophils, plasma cells, and lymphocytes. Considering the anatomy of the larynx and the pathway
I
n October 2013, a 7-year-old 17-kg spayed female Lurcher was presented to the 404 Veterinary Emergency and Referral Hospital in Newmarket, Ontario for evaluation of increased upper respiratory noise. Veterinary consultation was sought 2 to 3 mo earlier when the owners noticed a change in the patient’s bark (deeper than usual). The increase in upper respiratory noise was most noticeable after strenuous activity and when the dog was sleeping, although the dog was not noted to have any respiratory distress or exercise intolerance. The dog also had more difficulty swallowing kibble but had no problems eating wet food. No changes in drinking, urination, or defecation were seen by the owner. To the owner’s knowledge, the dog had no history of neck or laryngeal trauma.
Case description Physical examination revealed normal vital parameters. Inspiratory stridor was present, most audible when the dog was panting. The dog’s larynx was prominent and firm on palpation but was smooth, symmetrical and non-painful. A complete blood cell count and biochemistry performed by the 404 Veterinary Emergency and Referral Hospital, Newmarket, Ontario (Skelding, Kisiel, Rutland); Veterinary Imaging Consultations — Diagnostic Imaging, Del Mar, California, USA (Essman). Address all correspondence to Dr. Alicia Skelding; e-mail: [email protected] Use of this article is limited to a single copy for personal study. Anyone interested in obtaining reprints should contact the CVMA office ([email protected]) for additional copies or permission to use this material elsewhere. CVJ / VOL 57 / FEBRUARY 2016
referring veterinarian prior to referral revealed no abnormalities. Three-view thoracic radiographs were within normal limits. A right lateral cervical radiograph revealed an increased amount of mineralization over the larynx and an ill-defined soft tissue opacity. (Figure 1). A computed topography (CT) scan of the laryngeal region was acquired using a 64-slice helical scanner (Aquilion 64; Toshiba America Medical Systems, Tustin, California, USA). The patient was sedated with butorphanol (Torbugesic; Fort Dodge Animal Health, Fort Dodge, Iowa, USA), 0.2 mg/kg body weight (BW) and physically restrained with the use of sandbags and padded straps. The patient was positioned in sternal recumbency and scanning parameters were: 3-mm section collimation thickness, PF 0.828/HP 53.0, 120 kVp, 125 mAs. Pre- and post-contrast images were acquired. Iohexol (Omnipaque 350 mg/mL; GE Healthcare, Mississauga, Ontario) was administered as a bolus injection into a cephalic vein via catheter at a rate of 2 mL/min without a pressure injector at a dose of 600 mg of iodine per kg BW. Post contrast images were obtained 60 s after completion. There was an ill-defined, contrast enhancing soft tissue mass or thickening of the ventral aspect of the larynx at the region of the basihyoid bone and cricoid cartilage. Irregular bony proliferation and lysis associated with the hyoid apparatus was also noted. There was no evidence of lymphadenopathy (Figures 2A, 2B). On subsequent examination later that week, the dog was sedated with butorphanol (Torbugesic; Fort Dodge Animal Health), 0.2 mg/kg BW and dexmedetomidine (Dexdomitor; Zoetis, Florham Park, New Jersey), 5 mg/kg BW, intravenously. General anesthesia was induced with propofol (Diprivan; AstraZeneca, Mississauga, Ontario), 4 mg/kg BW, IV, and maintained with 2% isoflurane (Isoflurane USP; Pharmaceutical 157
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Figure 1. Right lateral cervical radiograph with mineral opacity at the level of the larynx (arrow). Projection: right lateral cervical radiograph
Partners of Canada, Richmond Hill, Ontario) and 100% oxygen. Endoscopy of the larynx did not reveal any evidence of masses or abnormalities within the lumen of the larynx or upper trachea. Multiple incisional biopsies of the ventral laryngeal mass were taken immediately following endoscopic examination of the larynx. The procedure was routine and the dog recovered from anesthesia uneventfully. Histopathology of the biopsies demonstrated pleocellular myositis and fasciitis with osseous metaplasia. A separate laryngeal examination using propofol without premedication, to eliminate any potential influence of sedation on laryngeal function, was performed by 2 of the authors (BR and AK) at a follow-up appointment 2 wk later and bilateral laryngeal paralysis was confirmed. The dog was treated with prednisone (Novo-Prednisone; Novopharm, Toronto, Ontario), 1 mg/kg BW, PO, q24h for 2 wk and tapered to a maintenance dose of 0.5 mg/kg BW, PO, q24h. At the recheck appointment, 11 wk following the biopsies, the mass was still palpable and similar to that observed at the previous examination. Repeat CT showed improvement in the soft tissue thickening and less prominent lysis. Clinically, the dog had not improved. Surgical intervention to address the laryngeal paralysis was discussed but not recommended at this time because of the lack of significant clinical abnormalities affecting the patient’s quality of life.
Figure 2A. Pre-contrast CT at the level of the hyoid. Irregular bony proliferation lysis is associated with the hyoid apparatus and cricoid cartilage (arrow).
Discussion The patient in this case presented with unusual laryngeal disease, characterized by bilateral laryngeal paralysis presumed to be secondary to chronic mineralization of the laryngeal cartilages and surrounding soft tissue. The results of the biopsy of the laryngeal mass indicated that the lesion found in this dog was consistent with osseous metaplasia. To the authors’ knowledge, this is the first report of laryngeal osseous metaplasia resulting in secondary laryngeal paralysis in a canine patient. Myositis ossificans (MO) is a condition in humans that is characterized by abnormal bone formation, usually involving skeletal muscle (1). Several subtypes of MO exist. Post-traumatic myositis ossificans (PTMO) occurs as benign, solitary reactive bone formation following a traumatic event (1). In humans, PTMO is usually self-limiting and advanced imaging is used 158
Figure 2B. Post-contrast CT at the level of the hyoid. Ill-defined contrast-enhancing mass is present along the left medial aspect of the larynx and measures approximately 1.3 cm in thickness (arrow).
to confirm the diagnosis. A similar condition, inflammatory myofibroblastic pseudotumor, occurs in humans following an initiating trauma (2). A single case report describes an incident in which trauma resulting from a vehicular air bag resulted in a subglottis lesion of MO (2). The human patient in this case exhibited similar clinical signs of dyspnea and stridor and complete surgical excision was reportedly curative (2). While there is no history of observed trauma in the dog presented herein, an unseen trauma may have occurred at some point when the CVJ / VOL 57 / FEBRUARY 2016
CVJ / VOL 57 / FEBRUARY 2016
of innervation of the recurrent laryngeal nerve it is reasonable to speculate that the laryngeal paralysis was secondary to the inflammation and mineralization of the surrounding muscles and less likely primary neurologic dysfunction. Advanced diagnostic imaging was valuable for the diagnosis and monitoring of this case. It showed the origin and characteristics of the palpable mass in more depth than was appreciated on external visualization, radiographs, or laryngeal examination. It remains unclear why the dog herein developed an osteoproductive and lytic lesion of its larynx. The histopathology results suggest that the lesion itself was a result of a chronic inflammatory process in the extraluminal tissues of the larynx. This chronic inflammation was most likely the stimulus for the development of osseous metaplasia in the surrounding soft tissues with resultant secondary laryngeal paralysis. This case is an example of laryngeal paralysis secondary to local soft tissue inflammation.
Acknowledgments The authors thank Dr. Kevin Isakow for his generous support and financial contribution that made this case report possible. We also thank the referring veterinarian and the technical staff at 404 Veterinary Emergency and Referral Hospital. CVJ
References 1. Tyler P, Saifuddin A. The imaging of myositis ossificans. Semin Musculoskeletal Radiol 2010;14:201–216. 2. Alaani A, Hogg R, Warfield AT, Olliff J, Jennings C. Air bag injury as a cause of inflammatory myofibroblastic pseudotumour of the subglottic larynx progressing to myositis ossificans. Acta Otolaryngol 2005;125: 674–677. 3. Haynes DR. Bone lysis and inflammation. Inflamm Res 2004;53: 96–600. 4. Park JK, Han JY, Hong IH, et al. Salivary mucocele with osseous metaplasia in a dog. J Vet Med Sci 2009;71:975–977. 5. Prassinos NN, Tontis DK, Adamama-Moraitou K, Galatos AD, Siochu A. Metaplastic ossification of a cervical sialocoele in a dog. Aust Vet J 2005;83:421–423. 6. Fernandes TR, Grandi F, Lidianne NM, Salgado BE, Rocha RM, Rocha NS. Ectopic ossification presenting as osteoid metaplasia in a salivary mucocele in a Shih Tzu dog. BMC Vet Res 2010;8:13–17. 7. Lynch GL, Scagliotti RH. Osseous metaplasia in the eye of a dog. Vet Pathol 2007;4:222–224. 8. Park JK, Lee SK, Park SJ, Hwa I, Jeong KS. Fibroma with osseous metaplasia of external auditory canal in a dog. J Vet Diagn Invest 2010; 22:635–638. 9. Pieczarka EM, Russell DS, Santangelo KS, Aeffner F, Burkhard MJ. Osseous metaplasia within a canine insulinoma. Vet Clin Pathol 2014; 43:89–93. 10. MacPhail C. Laryngeal disease in dogs and cats. Vet Clin Small Anim 2013;44:19–31. 11. Kitshoff AM, Goethem BV, Stegen L, Vandekerckhove P, de Rooster H. Laryngeal paralysis in dogs: An update on recent knowledge. J S Afr Vet Assoc 2013;84:1–9. 12. Millard RP, Tobias KM. Laryngeal paralysis in dogs. Compendium 2009;31:212–219. 13. Gross ME, Dodam JR, Pope ER, Jones BD. A comparison of thiopental, propofol and diazepam-ketamine anesthesia for evaluation of laryngeal function in dogs premedicated with butorphanol-glycopyrrolate. J Anim Hosp Assoc 2002;38:503–506. 14. Tasker S, Foster DJ, Corcoran BM, Whitbread TJ, Kirby BM. Obstruc tive inflammatory laryngeal disease in three cats. J Feline Med Surg 1999;1:53–59.
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dog was unsupervised. Also, the lesion of this dog’s larynx had a component of bony lysis that appeared to improve following prednisone therapy. The authors hypothesized that the bone lysis was a result of the inflammatory infiltrates as no neoplastic or other lytic processes were identified. A relationship between bone loss and an inflammatory process has been previously documented (3). Osseous metaplasia is a type of heterotrophic bone formation, in which metaplastic bone is formed directly from connective tissue as a result of alternative differentiation of fibroblastic cells. It has been reported infrequently in veterinary patients and typically the pathogenesis is unclear, but trauma and chronic inflammation are consistently implicated. Three cases of salivary mucocele with osseous metaplasia have been reported in dogs (4–6). These reports comment on the presence of ossifying components within the wall of the salivary mucocele and implicate chronic inflammation and irritation as a likely cause. A case of osseous metaplasia in the iris of a dog, in which no underlying etiology could be identified, has also been reported, but the authors comment on the possibility of an unobserved trauma (7). Cases of osseous metaplasia have also been associated with a fibroma of the external auditory canal in a dog (8) and within a canine insulinoma (9). The larynx is composed of hyaline cartilages and muscles (10,11). The cartilages of the larynx include the paired arytenoids and unpaired epiglottis, cricoid, and thyroid cartilages (10,12). Contraction of the cricoarytenoideus dorsalis muscle occurs during inspiration, resulting in abduction of the arytenoid cartilages (10,11). This allows air to pass freely through the glottis. The cricoarytenoideus dorsalis muscle is innervated by the caudal laryngeal nerve, which is the terminal segment of the recurrent laryngeal nerve (10). The recurrent laryngeal nerve leaves the vagus nerve as left and right branches and courses cranially to the larynx. Each recurrent laryngeal nerve sends branches to the heart, trachea, and esophagus before terminating in the laryngeal muscles. Laryngeal paralysis is one of the most common diseases of the larynx. Diagnosis of laryngeal paralysis is made by evaluation of laryngeal cartilage function under light anesthesia (11,13). Laryngeal paralysis results from lack of function of the caudal laryngeal nerve. The acquired form of laryngeal paralysis may be caused by trauma (iatrogenic and accidental), cervical/intrathoracic masses or neuromuscular diseases, with idiopathic disease being the most common (10). The initial primary differential diagnoses for the cause of the laryngeal mass in the dog herein were foreign body, trauma, or a concurrent cervical neoplasia. Inflammatory laryngeal disease is a rare condition of the arytenoid cartilages and surrounding tissues that has been described in dogs and cats (10,14). The disease tends to be multifactorial and the inflammatory process can be granulomatous, lymphocytic-plasmacytic, or eosinophilic (10). The patient in this case report had a degree of myositis in addition to ossification of the laryngeal cartilages. The cellular infiltrates were mixed, being composed of neutrophils, eosinophils, plasma cells, and lymphocytes. Considering the anatomy of the larynx and the pathway
