Catriona MacPhail, DVM, PhDCatriona.MacPhail@colostate.edu,     Department of Clinical Sciences, Colorado State University, Fort Collins, CO 80523, USA

The most common disease process involving the larynx is laryngeal paralysis, which occurs much more frequently in dogs than in cats. Diagnosis of laryngeal paralysis requires close attention to anesthetic plane and coordination of respiratory effort with laryngeal motion. Surgical arytenoid lateralization improves respiration and quality of life in dogs with laryngeal paralysis; however, aspiration pneumonia is a recognized complication, and generalized neuropathy can progress. Laryngeal collapse can result from any cause of chronic upper airway obstruction, but is most often associated with unaddressed brachycephalic airway syndrome. Laryngeal neoplasia, while generally uncommon, occurs more frequently in cats than in dogs.

Keywords

Upper airway obstruction

Laryngeal paralysis

Aspiration pneumonia

Megaesophagus

Laryngeal collapse

Tracheostomy

Key points

Introduction

Laryngeal disease in dogs and cats results in varying degrees of upper airway obstruction and can be life-threatening. Conditions most commonly affecting the larynx include laryngeal paralysis, laryngeal collapse, and laryngeal masses. Differentials for laryngeal disease include nasal, nasopharyngeal, and tracheal conditions that also result in clinical signs of upper airway obstruction, such as stertor, stridor, wheezing, and gagging. Visual upper airway examination is the fundamental diagnostic tool for localizing the anatomic area involved in airway obstruction.

Anatomy and physiology

The larynx is the collection of cartilages surrounding the rima glottidis. It is responsible for control of airflow during respiration. The four cartilages that constitute the larynx are the paired arytenoids and the unpaired epiglottis, cricoid, and thyroid cartilages. Each of the arytenoid cartilages has a cuneiform process rostrally, a corniculate process dorsally, a muscular process dorsolaterally, and a vocal process ventrally. The vocal processes are the attachment points for the vocal folds. The glottis consists of the vocal folds, the vocal process of the arytenoid cartilages, and the rima glottides. The laryngeal saccules are mucosal diverticula that sit rostral and lateral to the vocal folds. The larynx of the cat differs from that of the dog as the arytenoid cartilage lacks cuneiform and corniculate processes. Also, true aryepiglottic folds are absent and the sides of the epiglottis connect directly to the cricoid lamina by laryngeal mucosa.

The intrinsic muscles of the larynx (cricoarytenoideus dorsalis, cricoarytenoideus lateralis, thyroarytenoideus, vocalis, ventricularis, arytenoideus transversus, hyoepiglotticus, and cricothyroideus) are responsible for all laryngeal functions. These functions include regulation of airflow, protection of the lower airway from aspiration during swallowing, and control of phonation. The cricoarytenoideus dorsalis muscle is solely responsible for enlarging the glottis during inspiration. This muscle originates on the dorsolateral surface of the cricoid and inserts on the muscular process of the arytenoid cartilages. Contraction of this muscle results in external rotation and abduction of the arytenoid cartilages that then pulls the vocal processes laterally. The caudal laryngeal nerve is the terminal segment of the recurrent laryngeal nerve and is responsible for innervation of all intrinsic laryngeal muscles, except the cricothyroid muscle, which is innervated by the cranial laryngeal nerve.

Canine laryngeal paralysis