Introduction

The larynx is a cartilaginous structure consisting of the cricoid, thyroid and paired arytenoid cartilages, and the epiglottis. These cartilages interact under the control of the neuromuscular system of the larynx to protect the lower airways (coughing), to regulate the respiratory airflow, and to vocalize.¹

In this lecture, laryngeal paralysis will be discussed in detail, including indications and technique of temporary tracheotomy and thyroid-arytenoid lateralization for permanent stabilization.

Laryngeal Paralysis

Laryngeal paralysis is a complete or partial failure of the arytenoid cartilages and vocal folds to abduct during inspiration, causing upper airway obstruction and predisposing the patient to aspiration pneumonia.^1,2,5-9 Congenital hereditary laryngeal paralysis is seen in the Bouvier des Flandres, Bullterriers, Siberian Husky and Dalmatian breeds. Acquired laryngeal paralysis is usually idiopathic but may occur secondary to trauma or disease or it may be iatrogenic after surgery.^1,2,5

Clinical signs are more common in large-breed dogs than in small-breed dogs with males being affected 2–4 times more often than females.^5-7 Middle-aged to older Labrador Retrievers, Afghans and Irish Setters are often affected with acquired idiopathic laryngeal paralysis. A progressive inspiratory stridor and decreased exercise intolerance are noted. Usually, voice changes (dysphonia), coughing, gagging, and restlessness are noted as well. Excitement, stress, obesity, and high ambient temperatures exacerbate clinical signs.^1,5

Physical examination is usually unremarkable with the exception of tachypnea with a laryngeal stridor, panting, and sometimes hyperthermia. Radiographs of the neck and thorax or CT-scans are made to exclude other causes of the dyspnea. Blood examination is usually unremarkable. The diagnosis can be made on visual evaluation of laryngeal function during a superficial plane of general anesthesia. The arytenoids are in a paramedian position in affected animals and show no active abduction during inspiration. Denervation of the laryngeal muscles can be diagnosed during electromyography.¹

With acute dyspnea, an emergency medical treatment should be started with sedation, corticosteroids, supplemental oxygen, and cooling when necessary. If the obstruction is severe, a temporary tracheostomy should be performed. Surgical treatment is recommended, however, for animals with moderate to severe dyspnea.^5,6 Many surgical techniques have been described, ranging from muscle-nerve pedicle transposition for reinnervation of the larynx to castellated laryngofissures and partial laryngectomy. Arytenoid lateralization procedures are recommended, however, because of the consistently good results with minimal complications. Both unilateral cricoid-arytenoid and unilateral thyroid-arytenoid lateralisation procedures give reliable and comparable results and are equally effective in decreasing from a clinical point of view.^5,7,8

Tracheostomy

A tracheostomy for temporary use is indicated in patients with obstruction of the upper airway in the nose, larynx, or cranial part of the trachea. It is also used as an alternative route for endotracheal intubation in laryngeal surgery and as an ancillary procedure to prevent postoperative dyspnea after extensive surgical procedures on the pharynx or larynx.⁹ Temporary tracheostomy includes the introduction of a tracheal cannula that will be left in place until the airways are patent. Silastic tracheal cannulas or stainless steel cannulas with an inner cannula that can be removed and cleaned are preferred. Temporary tracheostomies require inhalation anaesthesia in all patients, including emergency cases.

The patient is placed in dorsal recumbency with a pillow under the neck.⁹ A transverse skin incision of approximately two centimetres is made over the trachea at the midpoint between the larynx and the thoracic inlet. The subcutaneous fat and the left and right sternothyroid and sternohyoid muscles are divided in the midline by blunt dissection. Care should be taken not to damage the tracheal veins, which lie immediately lateral to the trachea on both sides. A small self-retaining wound retractor is inserted into the wound to expose the trachea. The ligament between two adjacent rings is incised with a No. 11 scalpel. A small forceps is placed on one of the tracheal rings beside the incision. The forceps is locked tight to provide a firm hold on the tracheal ring. This is done to prevent the piece that will be removed from slipping into the trachea. The scalpel is then used to make a circular incision around the forceps. A round piece of tracheal cartilage and intercartilage ligament is removed to produce an opening of the same size and shape as the tracheal tube or cannula. If the window is made too large, air may leak around the cannula and subcutaneous emphysema will form. The oropharyngeal endotracheal tube is removed and replaced by a Silastic® endotracheal cannula that is inserted through the tracheal window. The cannula is sutured to the skin with four sutures. In addition, two cotton ribbons are attached to the wings of the tracheal cannula and then tied around the neck. The cannula is left in place until the upper airway is patent. Silastic cannulas have an inner cannula that should be cleaned every two hours. After removing the cannula, the tracheostomy wound is not sutured, but left open to heal spontaneously. Healing is usually rapid because the incision was made parallel to the natural skin folds, which will result in good apposition of the wound margins.

Thyroid-Arytenoid Lateralisation for Laryngeal Paralysis

Corticosteroids can be given during the induction of anesthesia to diminish postoperative mucosal swelling.⁵ The entire neck should be aseptically prepared for surgery. The animal is placed in dorsal recumbency with a towel under the neck to elevate the laryngeal area. A temporary tracheostomy can be performed as an alternative route for endotracheal intubation and to prevent postoperative dyspnea, but this prolongs postoperative hospitalisation. A paramedian skin incision is made on the left side from 2 cm caudal to the larynx extending to the caudal angle of the mandible.¹ The subcutaneous tissues and platysma are then incised and blunt dissection is performed along the sternohyoid and sternocephalic muscles until the dorsal edge of the thyroid can be palpated and lifted. An incision is made in the thyropharyngeal muscle along the dorsolateral edge of the thyroid. Stay sutures can be placed in the thyroid cartilage lamina to retract and rotate the larynx laterally. The cricothyroid articulation is disarticulated with scissors after which the dorsal cricoarytenoid muscle and muscular process of the arytenoid can be identified. The cricoarytenoid articulation is now disarticulated and the arytenoid is dissected free from its attachments without entering the laryngeal lumen and the interarytenoid ligament is dissected last. Two synthetic nonabsorbable sutures are placed through the muscular process of the arytenoid to the most caudodorsal part of the thyroid to lateralize the arytenoid. The abduction is now verified with the help of the anesthesiologist by intraoral visualisation of via intraoperative endoscopy. The thyropharyngeal muscle can be apposed with a simple continuous pattern with absorbable material. The subcutaneous tissues and the skin are closed routinely. Postoperative care consists of close monitoring of the patient, regular cleaning of the tracheal inner canula, and providing broad-spectrum antibiotics and analgesics.¹

Complications of lateralization procedures are hematoma formation, suture avulsion, discomfort during swallowing, temporary glottic dysfunction, and coughing after eating or drinking, sometimes resulting in aspiration pneumonia.^3,5,6 The prognosis is good, however, after lateralization with over 90% of the patients having less dyspnea and increased exercise tolerance.

References

1.  Venker-van Haagen AJ. The larynx. In: Venker-van Haagen AJ, ed. Ear, Nose, Throat, and Tracheobronchial Diseases in Dogs and Cats. Hannover, Germany: Schlütersche Verlagsgesellschaft mBH & Co.; 2005: 121–165.

2.  Venker-van Haagen AJ. Laryngeal paralysis in Bouviers Belge des Flandres and breeding advice to prevent this condition. Tijdschrift voor diergeneeskunde. 1982;(107):21–22.

3.  MacPhail CM, Monnet E. Outcome of and postoperative complications in dogs undergoing surgical treatment of laryngeal paralysis: 140 cases (1985–1998). Journal of the American Veterinary Medical Association. 2001;218(12):1949–1956.

4.  White R. Unilateral arytenoid lateralisation: an assessment of technique and long-term results in 62 dogs with laryngeal paralysis. The Journal of Small Animal Practice. 2011;30(10):543–549.

5.  Monnet E, Tobias KM. Larynx. In: Tobias KM, Johnston SA, eds. Veterinary Surgery Small Animal. St. Louis, MO, USA: Elsevier Saunders; 2012: 1718–1733.

6.  Hammel SP, Hottinger HA, Novo RE. Postoperative results of unilateral arytenoid lateralization for treatment of idiopathic laryngeal paralysis in dogs: 39 cases (1996–2002). Journal of the American Veterinary Medical Association. 2006;228(8):1215–1220.

7.  Griffiths LG, Sullivan M, Reid SWJ. A comparison of the effects of unilateral thyroarytenoid lateralization versus cricoarytenoid laryngoplasty on the area of the rima glottidis and clinical outcome in dogs with laryngeal paralysis. Veterinary Surgery. 2001;30(4):359–365.

8.  Demetriou JL, Kirby BM. The effect of two modifications of unilateral arytenoid lateralization on rima glottidis area in dogs. Veterinary Surgery. 2002;32(1):62–68.

9.  Venker-van Haagen AJ. The trachea and bronchi. In: Venker-van Haagen AJ, ed. Ear, Nose, Throat, and Tracheobronchial Diseases in Dogs and Cats. Hannover, Germany: Schlütersche Verlagsgesellschaft mBH & Co.; 2005: 167–208.