Anjop J. Venker-van Haagen, DVM, PhD, DECVS
The medical history in diseases of the pharynx usually reveals specific problems caused either by dysfunction of the airway through the oropharynx or nasopharynx or by difficulty in swallowing (dysphagia). In some cases the appearance of the pharyngeal mucosa may suggest a systemic disorder, but in all cases additional questions are asked about any changes in the animal's general condition, appetite, eating, drinking, physical activity, and habits. The answers to these questions together with a general physical examination will provide an impression of the patient's condition.
Dyspnea in pharyngeal disease. Signs of dyspnea in pharyngeal disease are caused by obstruction of the nasopharynx or the oropharynx. Obstruction of the laryngopharynx primarily hinders the passage of air through the nasopharynx and hence it also results in signs of nasopharyngeal obstruction. Severe obstruction of the oropharynx or laryngopharynx hinders the passage of food as well as air and thus causes dysphagia as well as dyspnea. Large masses in the nasopharynx can also obstruct the oropharynx and thus also result in dysphagia.
When dyspnea is caused by pharyngeal obstruction the signs are those of more forceful inspiration, which usually produces a snoring stridor. In cats the sounds may be soft and sometimes difficult to distinguish from the wheezing stridor caused by nasal obstruction.
Dysphagia in pharyngeal disease. The signs of dysphagia involving the pharyngeal phase are gagging, choking, and repeated swallowing of one bolus. The food may be regurgitated and will be seen to be covered with thick mucus, and the dog may eat it again. When there is severe dysphagia and part of the food or liquid passes into the larynx and trachea, there is immediate coughing and, after successful ejection of the misdirected particles of food into the pharynx and after signs of choking, swallowing is repeated. If the food or liquid is ejected into the nasopharynx, snoring and sneezing may follow. When given solid food, a dog with severe dysphagia may stop eating and walk away from the pan. When this dog drinks it drools much of the water and mucoid saliva into and around the water pan. Knowledge of these signs can be helpful in composing meaningful questions for the history and in recognizing dysphagia.
Special Diagnostic Techniques
Pharyngoscopy. Direct inspection of the pharynx with a laryngoscope is the most important diagnostic procedure in disorders of the oropharynx and laryngopharynx. Under anesthesia it is possible to inspect the soft palate, the base of the tongue, the palatine tonsils, and the hypopharynx including the laryngopharynx, with a minimum of instruments. The animal is intubated and placed in lateral recumbency with the mouth open and fixed in that position. The soft palate can be retracted with a forceps to facilitate inspection of the nasopharynx, in which any large masses can be recognized and biopsies can be taken. Complete inspection, including the rostral part of the nasopharynx, the caudal part of the choanae, and the openings of the auditory tubes, can be performed with a flexible endoscope capable of 180° retroflexion and having a working channel for the passage of biopsy forceps.
Radiographic examination. Plain radiographs of the pharyngeal area are especially useful for recognition of structures obstructing the airway and the passage of food; for locating radiopaque foreign bodies such as stones, needles, and bones; and for inspection of the hyoid bone for fracture and for arthritis of its joints, either of which can cause dysphagia. Laterolateral radiographs usually provide sufficient information.
Computed tomography and MRI are indispensable in determining the location and extent of neoplasms in the pharyngeal area.
Contrast videofluorography is almost indispensable for imaging the dynamics of the swallowing process in dogs. Recordings are made while the animal eats food (ground meat) mixed with barium. The procedure needs the cooperation of the patient and is extremely time consuming, even in a routine set-up.
Electromyography (EMG) of the pharyngeal muscles is useful in dogs with signs of dysphagia when no abnormalities are found by pharyngoscopy. Further information may be found in the abstract "Electromyography for diagnosing pharyngeal and laryngeal diseases".
Nasopharyngeal polyps. The most common polyp in the nasopharynx of the cat originates in the middle ear and descends to the nasopharynx via the auditory tube. These polyps develop on a stalk and reach the nasopharynx, where they may grow substantially--a diameter of 3 cm is not uncommon--and thus form a nasopharyngeal polyp.
The clinical signs of a nasopharyngeal polypare due to obstruction of the nasopharynx, inspiratory dyspnea being the principal effect. Food intake is interrupted because of blockage of the passage of air through the nose, but there is no nasal discharge initially.
Treatmentconsists of removal of the polyp under anesthesia. The soft palate is retracted rostrally or incised so that a curved mosquito forceps can be inserted between the dorsal wall of the nasopharynx and the polyp in order to clamp the polyp stalk. After rotating the forceps and polyp, to be certain that no nasopharyngeal mucosa is included, the polyp is removed by a sharp tug. Bleeding is controlled by pressing a gauze sponge into the nasopharynx at the location of the openings of the auditory tubes.
A foreign body in the nasopharynx is accompanied by secondary bacterial infection. The usual route of entry is via the intrapharyngeal isthmus. When a cat chews on grass, a ball of grass and mucus may become lodged in the hypopharynx and a blade of grass may enter the nasopharynx during attempts to swallow the grass ball. The blade may remain behind when the grass ball finally passes the upper esophageal sphincter. Sometimes the blade of grass enters one of the nasal cavities and causes unilateral rhinitis, and sometimes snoring and repeated swallowing indicate that the blade of grass is also located in the nasopharynx and sometimes the laryngopharynx.
Hyperplasia of the soft palate is associated with brachycephaly and a relatively narrow pharynx. It is thought that the genetic defect responsible for shortening the nose does not affect the soft tissue, the result being too much tongue and soft palate in a narrow pharynx. The clinical signs of an overlong soft palate are snoring, regurgitation, and dyspnea, usually increasing in severity during the second and third years of the dog's life. The pharyngeal disproportions are not the same in all brachycephalic dogs. In some the pharyngeal mucosa and soft palate are very thick and the musculature is insufficient, which results in snoring during closed-mouth breathing. Little can be done for these dogs when dyspnea eventually develops. This is in contrast to those with an overlong soft palate, which can be reduced in length so that it no longer covers the laryngeal inlet. The surgical technique to shorten an overlong soft palate is simple but the patient's recovery following surgery may be complicated by obstruction of the airway due to swelling of the mucosa of the remainder of the soft palate.
The medical history in laryngeal disease often includes clear statements of specific problems caused by laryngeal dysfunction. The most specific of these are a dry cough and dyspnea with remarkable respiratory sounds. Additional questions are then asked about the animal's general condition, appetite, drinking, physical activity, and endurance, and about changes in its habits. The answers to these questions and a general physical examination may lead to an overall impression of the condition of the patient.
Coughing in laryngeal disease. When coughing is the prominent sign, the time and specific circumstances of onset, the frequency, the sound, the productivity, and changes in severity since the cough began will provide information about the nature of the disease. An acute onset may indicate a foreign body in the trachea or bronchi. The onset of coughing shortly after a stay in a kennel or cattery may indicate infectious disease, while the frequency of coughing indicates the severity and persistence of the stimulus. The cough may be sharp and short and be followed by gagging, as in laryngitis, or deep and soft, as in chronic bronchitis.
Dyspnea in laryngeal disease. When dyspnea is the leading sign in the medical history, it is usually described as labored breathing in cats and as diminished endurance in dogs. When the dyspnea is caused by laryngeal dysfunction, a laryngeal stridor is to be expected as an additional sign. Especially in dyspneic dogs with laryngeal obstruction or hypoplasia of the larynx or laryngeal paralysis, the forced panting respiration may cause hyperthermia. Body temperature may rise above 40°C, even within a matter of minutes, at which point, while the mucosa is still red, cooling is more important than oxygen. Spraying or sponging cool water over the entire surface of the dog will lower the body temperature to normal in about 20 minutes.
When laryngoscopy is performed for diagnosis of laryngeal disease, the dog or cat is usually in a certain state of dyspnea. The laryngoscope is fitted with a blade suitable for the size of the animal and lubricated endotracheal tubes of several sizes are prepared. The anesthetic is then administered to effect, preferably by intravenous injection. Propofol is satisfactory and may be used after premedication with medetomidine. Medetomidine premedication is given to cats intramuscularly and to dogs intravenously. When the laryngeal movements are absent and the depth of anesthesia may be the cause, the short half-life of propofol is advantageous because after a short pause there is sufficient recovery for the inspection to proceed.
Radiographs, CT, and MRI. Radiographs of laryngeal structures are not easy to interpret. In the lateral projection the overlapping of structures and the presence of "air pockets" are unpredictable, particularly in the dyspneic patient. The extension of neoplastic or cystic masses and the presence of calcification of the laryngeal cartilages can be recognized. When surgery is being considered for removal of a laryngeal tumor, CT or MRI will be found indispensable for estimating the involvement of laryngeal and surrounding structures by the tumor. CT is less expensive than MRI and almost always answers the question. MRI is added in only a few cases. In human patients these techniques do not always require anesthesia and endotracheal tubes are avoided. In dogs and cats the use of anesthesia and endotracheal intubation cannot be avoided and this will influence the aspect of processes in the lumen of the larynx.
Laryngeal dysfunction is often an indication for electromyography (EMG) of the intrinsic laryngeal muscles. EMG can be performed routinely in the dog but the cat is not a good candidate because it has a small larynx and is too prone to develop laryngeal edema after the larynx is touched. . Further information may be found in the abstract "Electromyography for diagnosing pharyngeal and laryngeal diseases".
Laryngeal Paralysis and Functional Disorders of the Larynx
Paralysis is the loss or impairment of motor function in a part due to lesion of the neural or muscular mechanism; also, by analogy, impairment of sensory function (sensory paralysis). Fine-tuned vocalization is of minor social importance in dogs and cats and partly because dogs can produce a bark without very highly specialized vibrations of the vocal folds. Dogs use the loudness of the voice more than its tone. Some cats use their voice to produce a variety of tones in communication and thus loss of the voice is recognized by the owner and is part of the clinical history. In dogs and cats respiratory dysfunction is the primary cause of signs and symptoms of laryngeal paralysis. In most cases it is insufficient abduction of the glottis that causes the clinical signs of laryngeal stridor and sometimes dyspnea.
Tumor in the Larynx
Primary laryngeal tumors occur occasionally in dogs and cats. In a review of 36 reported primary laryngeal tumors in dogs, 8 were oncocytomas, 6 were rhabdomyomas, and 4 were rhabdomyosarcomas.
Ventral midline approach to the larynx.The procedure is essentially for the dog, in which it is safe, while all approaches to the larynx of the cat can be complicated by laryngeal edema. The aim of approaching through the ventral midline of the thyroid cartilage is to obtain satisfactory visibility of the glottis and supraglottic area. In this way biopsy material can be taken or proliferations can be removed. The laryngeal lumen should not be obstructed by an endotracheal tube passing through the larynx and hence the procedure begins with a tracheostomy for insertion of a tube into the trachea caudal to the larynx.
1. Venker-van Haagen AJ. The Pharynx. In: Ear, Nose, Throat, and Tracheobronchial Diseases in Dogs and Cats. Hannover: Schlütersche Verlagsgesellschaft, 2005: 83-116.
2. Venker-van Haagen AJ. The Larynx. In: Ear, Nose, Throat, and Tracheobronchial Diseases in Dogs and Cats. Hannover: Schlütersche Verlagsgesellschaft, 2005: 121-161.