Anjop J. Venker-van Haagen, DVM, PhD, ECVS
Glottic stenosis is a rare deformity and not recognized as having a breed predisposition. It occurs in dogs and cats and results from webbing of the vocal folds or deformities of the arytenoid cartilages. Whether treatment is possible or necessary depends entirely on the development and functioning of the larynx as a whole. Given the wide variety of findings, no general recommendations about treatment can be offered. Glottic stenosis in one young dog consisted of the joining of the corniculate process of the left and right arytenoid cartilages. The glottis was obstructed by the deformity and lateral movement of the vocal folds resulted in very little abduction. Electromyography revealed normal periodic activity in the thyroarytenoid muscles and no denervation potentials. Under anesthesia the cartilaginous connection between the left and right arytenoids was found to be thick and lacking an indication of the midline. After step-by-step separation of the corniculate tubercles using a pointed Beaver knife (no. 65), the glottis could be widened only slightly, yet following recovery from anesthesia, respiration was improved. There was partial recurrence of webbing within 6 weeks and it was again necessary to separate the cartilages, but the follow-up revealed progressive improvement in breathing, culminating in a life with almost no restrictions.
Congenital subglottic stenosis occurs in humans, dogs, and cats as a congenital deformity of the cricoid cartilage. There may also be deformities in the glottic part of the larynx, but the name refers to the location of the deformity that obstructs the airway. Depending on the severity of the obstruction it causes, the deformity may come to attention in younger or older animals. Some minor obstructive stenosis may be diagnosed in adult life. Congenital subglottic stenosis must be distinguished from acquired subglottic stenosis by means of the history. It is very important to examine all other structures and functions of the larynx before attempting surgical correction. The overall size of the larynx may be abnormally small. The arytenoid cartilages may be deformed and the vocal folds may not have developed normally. The aryepiglottic folds should be inspected to determine whether they are of sufficient length to permit ventral movement of the epiglottis.
The normal larynx of the cat varies in appearance from one individual to another. A thorough laryngoscopic examination under sedation should furnish a detailed description of the visible laryngeal structures and an impression about their functioning. The corniculate processes normally vary in size and location. Apparent congenital subglottic stenosis in a dyspneic cat should be supported by the history and by complete clinical and specific examinations to exclude other causes of dyspnea, before its relevance can be considered certain. In the cat with congenital subglottic stenosis, the inadequacy of the laryngeal lumen is also indicated by the eversion of the laryngeal ventricles, a rare finding in cats.
Edema of the laryngeal mucosa may cause life-threatening laryngeal obstruction. In dogs the sting of a bee or wasp at or near the laryngeal supraglottic area causes acute laryngeal inflammation and edema. In countries where these insects are common in and around the house, dogs may catch them and the edema immediately following the sting may cause life-threatening obstruction of the airway. Administration of a glucocorticoid will not quickly decrease the edema the edema and a far better approach is immediate sedation (medetomidine and propofol intravenously) and endotracheal intubation, followed by tracheostomy and insertion of a tracheal cannula. The edema disappears in one week, leaving slight laryngeal inflammation, but abduction and adduction of the glottis can then be observed. The tracheal cannula can be removed and after another week of rest, the dog can resume normal activity.
Laryngeal edema in cats is usually based on acute laryngitis. The clinical symptoms of chronic laryngitis in cats are a soft laryngeal stridor and sometimes swallowing during purring. There may be loss of voice or a change in the voice, but coughing is rare. Laryngoscopic examination reveals thickening of the laryngeal mucosa and sometimes an irregular surface. In most cases there have been no distinct signs of acute onset indicating a distinct cause. The medical history reveals that the signs progressed slowly in the beginning and became stationary over a period of a few months. Treatment with a glucocorticoid is not always satisfactory, but the signs are mild and the cat does not change its habits because of the laryngitis. Explaining that no diseases are found other than chronic laryngitis will usually satisfy the owner.
In most dogs and cats the clinical signs of laryngeal tumor that alarm the owner are dyspnea and hoarseness, which usually indicate that the tumor is already large enough to partially obstruct the airway. Hoarseness does not always mean glottic involvement by the tumor, for it may also be caused by secondary edema. Also, hoarseness and loss of voice occur in most of the laryngeal diseases. What strongly arouses suspicion of tumor is a "breaking voice", which describes what happens when vocalization--a bark or mew--begins normally and then suddenly changes to a breathy sound or is lost completely, while the animal continues the barking or mewing behavior. This phenomenon is caused by growths protruding into the glottal space, preventing the glottal borders from touching firmly during the cyclic vibration. Also, a cat may start to purr but suddenly stop, possibly because the sensation of purring is unpleasant, for this is followed by swallowing and movement. Dyspnea and stridor are common signs of an obstruction in the larynx. Laryngeal stridor is usually both inspiratory and expiratory when the obstruction is great enough to cause dyspnea, and the sound is rasping. In cats the stridor is softer but is clearly recognized as a rasping sound. In dogs the dyspnea is accompanied by listlessness and lack of endurance, whereas in cats the behavioral change it causes is slow and interrupted eating.
In cats there is usually enlargement of the larynx, which is not too difficult to detect by palpation, but in dogs this is often not the case. The reason for the difference is partly that laryngeal tumors in cats usually involve multiple laryngeal structures, while in dogs they often involve only the glottis and do not cause overall enlargement of the larynx. In addition, the cat's larynx is a soft and flaccid structure, while many older and larger dogs have a rather rigid larynx. Enlarged lymph nodes are not usually found with laryngeal tumors and hence staging of the tumor should be done on the basis of CT or MRI and thoracic radiographs, when laryngeal surgery is being considered. If treatment of the tumor is being considered, CT and MRI are indispensable. However, the cat's larynx is small and even these techniques may not provide detailed information about it or distinguish small lymph nodes. CT and MRI should be considered complimentary to, and not substitutes for, physical examination and laryngoscopy.
Laryngoscopy is the most important technique for the diagnosis of laryngeal tumor, for it reveals the appearance of the tumor, gives some information about its location and its involvement of visible structures, and facilitates biopsy for histological diagnosis. Fine-needle aspiration biopsy with emergency cytological diagnosis is quite adequate, especially if the owner does not wish treatment for the animal in the event that a malignancy is found or does indeed wish chemotherapy if the diagnosis proves to be malignant lymphoma. While the cytological examination is being carried out, the animal can be kept under anesthesia and provided with an endotracheal tube. If more time is needed, a temporary tracheostomy is preferable. In dogs and cats an obstruction in the larynx that causes serious dyspnea is not accepted as a permissible mode of living by most owners or veterinarians.
Some laryngeal tumors have a very small base of attachment and can be removed surgically. If the attachment is in the glottic or subglottic area it is best to use the ventral midline approach to the larynx. If the tumor has so obviously invaded a large part of the larynx, no treatment may be possible other than the hazardous removal of the larynx and formation of a permanent tracheostoma. Euthanasia may be well advised. When surgery is not an option, costly CT and MRI examinations should be omitted.
1. Venker-van Haagen AJ. The larynx. In: Ear, Nose, Throat, and Tracheobronchial Diseases in Dogs and Cats. Hannover: Schlütersche Verlagsgesellschaft, 2005: 121-161.