Nasopharyngeal Disorders

Chapter 157

Nasopharyngeal Disorders

A variety of nasopharyngeal diseases are encountered in small animals. In cats, nasopharyngeal disease is most commonly caused by nasopharyngeal polyps, neoplasia, stenosis, foreign bodies, and cryptococcosis. In dogs, nasopharyngeal diseases include neoplasia, foreign bodies, nasal mites (Pneumonyssoides caninum), and congenital abnormalities. Clinical signs are similar regardless of cause, and a systematic approach to diagnosis is required to ensure that treatable diseases are recognized.

Clinical Signs of Nasopharyngeal Disease

Nasopharyngeal disease usually results in signs of upper airway obstruction, namely, inspiratory respiratory effort and stertor or snoring. In dogs, stertor is usually alleviated by open-mouth breathing. Cats are often unwilling or unable to breathe through the mouth and thus may exhibit severe respiratory distress. Pharyngeal discomfort, repeated attempts at swallowing, coughing, gagging, dysphagia, aerophagia, and changes in phonation also may occur. Animals with acute nasopharyngeal disease may paw at the nose and mouth or have facial discomfort and pruritus. Reverse sneezing is a specific nasopharyngeal sign in dogs. Sneezing is not typical of nasopharyngeal disease but may occur if the caudal nasal turbinates are irritated or if disease also affects the nasal cavity. Unless nasopharyngeal disease is accompanied by significant intranasal pathology, nasal discharge is usually mild or absent, because secretions from the nasopharynx tend to be swallowed. Purulent nasal discharge and fetid breath can be noted in animals with foreign bodies.

Signs of otitis media and vestibular disease can be seen when there is extension of disease from the nasopharynx into the tympanic bulla (or vice versa) or when the opening to the auditory (eustachian) tube is occluded. In one study, bullous effusion, considered most consistent with acute effusive disease, occurred in 34% of all cats with nasopharyngeal disease and 100% of cats with caudal nasopharyngeal disease (Detweiler et al, 2006). Thickening of the soft palate and reduced nasopharyngeal aperture have also been associated with the development of effusive otitis media in cavalier King Charles spaniels (Hayes et al, 2010). Conversely, expansile middle ear disease can cause nasopharyngeal obstruction. Horner’s syndrome is commonly encountered in cats with involvement of the tympanic bullae. Deafness and signs of otic pain may occur, and there also may be signs of facial nerve dysfunction. Occasionally, the main presenting signs are neurologic, resulting from the spread of infection (such as cryptococcosis) or neoplasia, or signs may be related to the gastrointestinal tract (megaesophagus or hiatal hernia).

The speed of onset and severity of signs are variable and depend on the cause. Sudden onset of signs is suggestive of a foreign body, whereas gradual onset of stertor and attempted mouth breathing is more typical of a slow-growing nasopharyngeal mass.

Diagnosis of Nasopharyngeal Disease

Diagnostic Imaging

The normal nasopharynx can be identified on plain lateral radiographs because of the presence of air dorsal to the soft palate. The hyoid apparatus and larynx define its caudal boundary. Space-occupying nasopharyngeal lesions are delineated by surrounding air, and radiopaque objects can be apparent; however, because of the complex anatomy of the region, and secretions within the nasopharynx, radiographic details may be obscured.

Computed tomography (CT) is increasingly used to assess the precise anatomic location of nasopharyngeal lesions and the involvement of other structures such as the middle ear, cribriform plate, brain, and bones of the skull. Use of a restraining device such as the VetMouse Trap allows CT to be performed in the conscious sedated small animal patient; however, assessment of the nasopharyngeal lumen and soft palate dimensions is reportedly more accurate with open-mouth positioning (Laurenson et al, 2011). CT is much quicker to perform than a full series of skull radiographs and is the preferred option if a mass is suspected.

Direct Visualization of the Nasopharynx

The oropharynx, laryngopharynx, and larynx are initially inspected before placement of a cuffed endotracheal tube sufficiently inflated to ensure a leakproof seal. The animal is best positioned in dorsal recumbency, with the maxilla held down firmly by tape applied over the upper canine teeth. Regional anesthesia of the nasopharynx with a topical anesthetic (2% lidocaine gel or lidocaine at 1 mg/kg) can decrease the plane of general anesthesia required to abolish reflexes resulting from mechanical stimulation of nasopharyngeal structures. Maxillary nerve blocks with 0.5% bupivacaine can also provide additional anesthesia. Rostral retraction of the caudal soft palate using a spay hook exposes the caudal nasopharynx. Using this method, the cranial nasopharynx and choanae also can be visualized in cats but not usually in dogs.

The most reliable method for evaluating the nasopharynx is nasopharyngeal endoscopy. A flexible endoscope is introduced into the pharynx and retroflexed above the soft palate or retroflexed before insertion and hooked over the soft palate. Rostral retraction of the retroflexed scope advances the scope (tip) toward the nose to allow visualization of the rostral nasopharynx. Lesions may not be apparent if they are obscured by mucus, blood, or pus. Vigorous saline flushing (via the endoscope or via the nostrils) usually helps with visualization.

Obtaining Diagnostic Samples from the Nasopharynx

Representative specimens for cytologic examination, histologic analysis, and microbial culture are required for definitive diagnosis. Fine-needle aspiration can be performed through the soft palate, and ultrasonographic guidance can aid in obtaining a representative sample. Blind Tru-Cut biopsy of lesions through the soft palate is also feasible, but there is a risk of hemorrhage if large blood vessels lateral to the nasopharynx are perforated. Ideally, biopsy tissue specimens are obtained by direct visualization via soft palate retraction, soft palate incision, or endoscopy. Endoscopic biopsy samples are small and may be superficial, yielding a diagnosis of nonspecific rhinitis rather than the true cause of disease. In some cases, a retroflexed endoscope can be used to visualize the nasopharynx while an independent biopsy forceps is advanced (antegrade) across the nasal cavity to the nasopharyngeal lesion.

When a mass is present, vigorous massage of the lesion through the soft palate often dislodges or fragments the mass, and anterograde flushing via the nares can be successful in dislodging part, or all, of it. The airways must be protected by gently occluding the laryngopharynx with packing material. In dogs, flushing is best achieved via catheters inserted into the ventral nasal meatuses; however, in cats, effective pressure can be generated by inserting the end of a 10-ml syringe directly into the naris and holding both nares closed with the fingers. Material dislodged from the nasal cavity or nasopharynx by flushing then collects on the packing material occluding the laryngopharynx. Anterograde passage of a catheter through the left and right ventral nasal meatuses is also helpful in dislodging foreign material and mucus. The advantages of a vigorous nasal flush technique over endoscopic biopsy are speed, cost, lack of need for any special equipment, immediate relief by debulking, dislodgment of foreign bodies, and usually better-sized biopsy samples; however, histopathologic analysis of nasal flush tissue can lead to inaccurate diagnoses.

Retrieval of canine nasal mites for diagnosis can be achieved with nasal flushing, although endoscopic visualization is preferable. Where permitted, flushing the nasal cavity with halothane can induce mites to migrate caudally into the nasopharynx where they can be easily retrieved and identified. It is conceivable that masking a dog with halothane or another inhalation anesthetic might have the same effect, but this has not been studied.

Adjunctive Tests for Diagnosis of Nasopharyngeal Disease

The results of cytologic analysis of squash-preparation specimens from nasopharyngeal masses in the cat showed good correlation with histologic findings in one study (De Lorenzi et al, 2008), although histopathologic analysis was recommended for differentiating lymphoma from lymphoid reaction. Cytologic examination and culture of nasal swabs may detect organisms such as Cryptococcus spp., but cats and dogs can have asymptomatic carriage of Cryptococcus spp. in the nasal cavity. Serologic testing is useful to differentiate asymptomatic carriage of Cryptococcus spp. from infection because animals with cryptococcosis should have a positive result on the latex cryptococcal antigen agglutination test.

Surgical Access to the Nasopharynx

When extraction of lesions such as inflammatory polyps, cryptococcal granulomas, or foreign bodies is not possible via palatine retraction, or better access is required to obtain diagnostic samples, the nasopharynx can be approached surgically via a longitudinal incision in the soft palate. In most cases, adequate access is obtained by maximally opening the jaws, placing a mouth gag, and having an assistant hold the endotracheal tube out of the way with a malleable retractor. Operating in this area requires some experience, and most cases are best managed by referral to a surgical specialist.

The soft palate is divided longitudinally from the caudal edge of the hard palate to within a centimeter of its caudal free edge. The caudal edge should be left intact to facilitate repair and support the incision during healing. Bleeding from the rich vascular plexuses within the soft palate should be anticipated but usually resolves spontaneously or with digital pressure. When extensive dissection is likely to be undertaken in dogs, blood loss may be ameliorated somewhat by temporary occlusion of the carotid arteries using Rummel tourniquets placed through a ventral midline cervical incision. This technique is not recommended for cats because it can result in permanent neurologic sequelae. In either species, if major blood loss is anticipated, contingency plans for replacement with whole blood or blood components should be made. The surgeon also should have a variety of hemostatic methods available, including sterile gauze for temporary packing of the nasal cavity or nasopharynx, and an implantable product such as Gelfoam. The soft palate incision can be continued rostrally as a mucoperiosteal incision and ventral rhinotomy if indicated, to provide excellent access to the ventral nasal cavity. Two- or three-layer repair of the soft palate with polydioxanone in a continuous suture pattern in the nasal mucosal and muscularis layers and in the oral mucosa provides excellent closure. Postoperative management is usually uncomplicated: animals display little evidence of pain and usually eat and drink within 24 hours of surgery unless systemic illness is present. Healing in this area is rapid and reliable, presumably due to the excellent blood supply. Soft food should be offered for 2 to 3 weeks after surgery and the incision examined at weekly intervals for signs of wound dehiscence.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Nasopharyngeal Disorders

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