Nasopharyngeal Disorders of Dogs and Cats
Geraldine B Hunt, BVSc MVetClinStud PhD FACVSc
Associate Professor in Small Animal Surgery, University of Sydney
The nasopharynx is situated between the choanae, the soft palate, the base of the skull and the larynx. Animals with nasopharyngeal disease present mainly with stertor (snoring). Cats may be dyspnoeic due to unwillingness or inability to breath through their mouth. Some animals show pharyngeal discomfort and make repeated attempts at swallowing or pawing at the mouth. The duration and severity of signs is dependent on the disease process. Rapid onset of stertor, purulent nasal discharge or fetid breath, can suggest a foreign body, whereas slow onset may be more compatible with a tumour or polyp. Likewise, young cats are more likely to have polyps, whereas old cats are more likely to have neoplasia. Nasal discharge is often mild or absent, however sneezing may occur if the disease also affects the nasal cavity. Otitis media and vestibular disease result from disease extending into the tympanic bulla or if the opening to the Eustachian tube is occluded. Regional lymphadenomegaly may indicate neoplasia. Lymphosarcoma, various forms of carcinoma, mast cell tumour, fibrosarcoma and osteosarcoma have all been encountered in dogs and cats. Other clinical signs may result from systemic spread of diseases like lymphosarcoma or cryptococcosis.
In tractable animals, palpation through the soft palate may reveal masses in the nasopharynx. Regional lymph nodes sometimes provide a more convenient source of diagnostic material. Assessment prior to anaesthesia should include evaluation of mucous membrane colour, cardiopulmonary function, and thoracic radiography. Likewise, an attempt should be made to differentiate stertor from stridor (a high-pitched noise arising from disturbance of air flow through the larynx or trachea). If possible, the effect of opening the mouth should be determined. The animal is then examined under general anaesthesia using IV propofol (5 mg/kg) and subsequent inhalation of halothane or isoflurane. Laryngeal paralysis should be ruled out prior to endotracheal intubation. The cuff should be inflated and the laryngopharynx packed with gauze. The animal is positioned in dorsal recumbency, with the maxilla held firmly with tape applied over the upper canine teeth. Topical lignocaine (1 mg/kg) is instilled to attenuate responses to mechanical stimulation of sensitive nasopharyngeal structures. The nasopharynx is examined by palpation through the soft palate, followed by rostral retraction of the soft palate using a spay hook. Use of a heated dental mirror can improve visualization of the choanae.
Routine hematology and biochemistry are rarely diagnostic. Cytology may detect cryptococcosis, however diagnosis should be supported by using the latex cryptococcal antigen test (LCAT). Cryptococcosis is diagnosed frequently in our hospital, but not in North America. Aspergillosis and pythiosis have also been reported.
The next step is flexible retrograde endoscopy. Masses may be immediately apparent or obscured by secretions. Antegrade passage of a catheter up the left and right ventral nasal meati is helpful in dislodging foreign material and mucus. Flushing with saline through the nares and nasopharyngeal suction can enhance visualization. However, this is likely to interfere with interpretation of nasal and nasopharyngeal radiographs or CT, so these should be performed prior to other manipulations if deemed necessary.
Tissue specimens for cytology, histology and microbial culture may be obtained by biopsying through the endoscope. Alternatively, massage of the lesions through the soft palate may dislodge or fragment the mass and antegrade flushing via the nares may then dislodge part or all of it. Fine needle aspiration biopsy may also be performed through the soft palate. Biopsy forceps may either be inserted through the nostril or through the soft palate. Large masses, or those in the caudal nasopharynx, may be visualised and biopsied by cranial retraction of the soft palate.
The nasopharynx is identified on plain radiographs due to air dorsal to the soft palate. The hyoid apparatus and larynx define its caudal boundary. Some space occupying lesions of the nasopharynx may be delineated by surrounding air. Objects with abnormal radiodensity may also be apparent. Unfortunately, due to the complex anatomy of the region, the presence of endotracheal tubes and oesophageal stethoscopes and secretions can obscure radiographic details. Positive-contrast studies of the nasal cavity and nasopharynx have been described, but are not often used. In our experience, radiography provides little more information than thorough examination under anaesthesia. Ultrasonography can be useful in animals with soft tissue or fluid-filled masses in the nasopharynx and assist the acquisition of diagnostic samples using ultrasound guided needle aspiration or biopsy. Incisional or Tru-Cut® biopsies should be taken with care due to the vascularity of the area. Advanced imaging such as CT and MRI probably unnecessary for diagnosis in the majority of cases, however it may provide more detailed information about the pathogenesis and extent of disease into surrounding structures, as well as the need for follow up radiotherapy or chemotherapy following cytoreductive surgery.
Nasopharyngeal masses and foreign bodies may be dislodged by passing a urinary catheter caudally from the nares, with or without vigorous flushing. Small balloon catheters may be positioned via the nares, then the balloon inflated to push foreign bodies towards the caudal edge of the soft palate. Manipulation of a foreign body or a mass through the soft palate may assist removal by dislodging or fragmenting it.
The nasopharynx may 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. Although intubation via a pharyngostomy incision improves the working area, we believe it takes longer and results in more postoperative morbidity. The palate is divided longitudinally from the caudal edge of the hard palate. The caudal edge of the soft palate is left intact to facilitate repair and support the incision during healing. Bleeding usually resolves spontaneously or with digital pressure. Surgical suction, good lighting and an assistant are mandatory. Blood loss may be ameliorated by temporary occlusion of the carotid arteries in dogs but not in cats. If major blood loss is anticipated, contingencies for replacement with whole blood or a blood replacement product should be made. The soft palate incision may be continued rostrally as a mucoperiosteal incision and ventral rhinotomy if indicated, providing excellent access to the ventral nasal cavity. The soft palate is repaired in two or three layers using continuous polydioxanone suture. Animals will usually eat and drink within 24 hours unless systemic illness is present. Healing is usually uneventful. Soft food should be offered for two to three weeks after surgery, and the incision examined weekly for evidence of wound dehiscence.
In conclusion, despite the reputation of the nasopharynx for being difficult to access and visualize, endoscopy and surgical exposure via the soft palate have made it possible to diagnose and successfully treat a large proportion of cases with nasopharyngeal disease.
Geraldine B Hunt, BVSc MVetClinStud PhD FACVSc