Diagnostic Investigation of Feline Nasopharyngeal Disease
World Small Animal Veterinary Association World Congress Proceedings, 2007
Vanessa Barrs

Presentation for upper respiratory signs is common in feline practice. From the findings of a thorough history and physical examination including careful observation of the respiratory pattern, it is usually possible to localise upper respiratory disorders to the sinonasal cavity, larynx or caudal nasal cavity/nasopharynx (Table 1).

The nasopharynx is dorsal to the soft palate and extends from the choanae to the larynx. Nasopharyngeal diseases arise from tissues within, bordering or contiguous with the nasopharynx, including the base of the skull, caudal nasal ethmoturbinates, auditory tubes, middle-ears, palate and pharyngeal mucosa.

Table 1. Localisation of feline upper respiratory disorders.

For each category, some or all of clinical signs listed may be present. Localising signs are asterisked.

 Sinonasal cavity disease:

 Nasal discharge

 Epistaxis

 Sneezing*

 Facial distortion

 Caudal nasal cavity/nasopharyngeal disease:

 Inspiratory dyspnoea

 Stertor (inspiratory)*

 Excessive swallowing

 Gagging

 Paroxysmal reverse sneezing*

 Coughing

 Sneezing

 Nasal discharge

 Epistaxis

 Halitosis

 Dysphonia

 Concurrent otitis externa/head shaking

 Concurrent media/interna (OMI)

 Laryngeal disease:

 Stridor (inspiratory)*

 Cough

 Dysphonia

 Gagging

 Retching

 Dysphagia

Clinical Signs of Caudal Nasal Cavity/Nasopharyngeal Disease

An obstructive respiratory pattern characterised by a normal or mildly increased respiratory rate and inspiratory dyspnoea, together with stertor, localises disease to the caudal nasal cavity or nasopharynx. A stertor is a snoring or snorting sound that results from turbulent air-flow caused by airway obstruction rostral to the larynx. This sonorous respiration is characteristic of caudal nasal cavity/nasopharyngeal disease. Other signs that may be present are listed in Table 1. Nasal discharge is present in some cats due to obstruction of nasopharyngeal drainage by a mass lesion or because of concurrent sinonasal cavity disease.

Cats with nasopharyngeal disease may develop otitis media/interna (OMI) from occlusion of the pharyngeal openings of the auditory tube by a mass lesion (e.g., cryptococcal granuloma). A mucoid effusion develops in the tympanic bullae. This is often complicated by secondary ascending bacterial infection with oropharyngeal flora. OMI may also develop because of direct involvement of the tympanic bullae in the disease process (e.g., nasopharyngeal polyp).1,2 Rupture of the tympanic membrane from polyp growth or infection can cause otitis externa and clinical signs of head-shaking, or ear-scratching/grooming.

In cats with nasopharyngeal disease and OMI, head-shaking, signs of peripheral vestibular disease, Horner's syndrome and/or facial nerve palsy may occur, ipsilateral to the affected bulla. Rarely, in cats with nasopharyngeal disease and OMI there may be intracranial extension of infection through the internal acoustic meatus, resulting in signs of central nervous system dysfunction.3

Aetiologies

Once disease has been localised to the caudal nasal cavity/nasopharynx, the following differential diagnoses should be considered:

Table 2. Differential diagnoses of caudal nasal cavity/nasopharyngeal disease.

 Neoplasia

 Lymphoma

 Carcinoma

 Other

 Inflammatory

 Nasopharyngeal polyp

 Nasopharyngeal stenosis

 Infectious

 Mycotic nasopharyngeal diseases

 Cryptococcosis

 Aspergillosis

 Atypical bacterial infections

 Mycobacteria

 Accumulation of excessive nasal secretions

 Infectious/inflammatory rhinosinusitis

 Sinonasal cavity disease

 Foreign body

 Congenital

 Choanal atresia

 Palatine defects

The most frequent causes of nasopharyngeal disease in cats are neoplasia, non-infectious inflammatory disease, and in certain geographical regions such as Australia, mycotic granulomatous infections, especially cryptococcosis.2,4-5

Neoplasia

Of neoplastic diseases lymphoma is by far the most common, followed by carcinomas.

Inflammatory

Nasopharyngeal polyps are the most common inflammatory cause and are thought to occur in response to ascending oropharyngeal viral infection. These pedunculated growths arise from the mucosa of the tympanic bullae or auditory tube and protrude into the nasopharynx. Polyps may also extend through the tympanic membrane into the horizontal ear canal, or rarely, through the internal acoustic meatus of the tympanic bulla into the cranial vault.3

Acquired nasopharyngeal stenosis (NPS) is characterised by the presence of a web of fibrous scar tissue (cicatrix) that spans the nasopharynx caudal to the choanae and has a small central aperture. It occurs as an inflammatory response to mucosal ulceration of the nasopharynx. In cats this is thought to occur secondary to viral or bacterial upper respiratory infections.6-7 Acquired NPS has also been described in other species secondary to caustic burns, oropharyngeal surgery or reflux of gastric contents through the nares during general anaesthesia.

Infectious

Infectious agents that cause granulomatous disease are a differential diagnosis for feline nasopharyngeal disease, including fungi and bacteria. Cryptococcal infections that originate in the caudal nasal cavity can develop into mass lesions that obstruct one or both choanae.5

Nasopharyngeal involvement is common in sino-orbital aspergillosis infections of cats.8 This newly recognised clinical syndrome in cats is characterised by a retrobulbar mass (exophthalmos, prolapse of the nictitating membrane, ocular discharge and exposure keratitis), stertor and oral cavity lesions including palatine ulceration and/or mass lesions in the pterygopalatine fossa. This distinctive constellation of clinical signs reflects the propensity of sinonasal cavity aspergillosis in cats to invade contiguous tissues including the orbit, nasopharynx, palate and cribriform plate. Importantly, signs of rostral nasal cavity or sinus infection may be subtle or absent.

Preliminary investigations by the author's group have shown that in contrast to canine sinonasal aspergillosis which is typically caused by Aspergillus fumigatus, infections in cats involve other species of Aspergillus including Neosartorya sp. Identification of nasopharyngeal involvement is important clinically, since biopsy of nasopharyngeal lesions is a reliable method of obtaining tissues for definitive diagnosis through fungal culture and histopathology.

Excessive Nasal Secretions

Any cause of sinonasal cavity disease, including infectious and inflammatory rhinosinusitis can cause accumulation of nasal secretions in the caudal nasal cavity/ nasopharynx, resulting in presentation for stertor. Infection with Feline Herpesvirus causes epithelial necrosis and osteolysis of nasal turbinates. In severe infections turbinate destruction may be permanent, resulting in chronic rhinosinusitis, often with secondary bacterial infection.

Foreign Bodies

Nasopharyngeal foreign bodies, such as plant or food material, may enter the nasopharynx during incomplete vomition, during attempts to swallow or during regurgitation in oesophageal motility disorders.

Congenital

Choanal atresia is a congenital anomaly characterised by developmental failure of the caudal nasal cavity to communicate with the nasopharynx. Unilateral, membranous choanal atresia has recently been described in a Himalayan cat, and should be considered as a differential diagnosis for chronic unilateral nasal discharge.9 In other species the choanal obstruction may be unilateral or bilateral, partial or complete, and membranous or bony.

Diagnostic Investigation

Diagnostic investigation of cats with nasopharyngeal disease is relatively straightforward and should be conducted in two stages. The first stage includes non-invasive investigations. Sedation may be required for some procedures. The second stage includes imaging and biopsy collection, performed with the patient under general anaesthesia.

Stage 1

1.  Otoscopy: Thorough otoscopic examination should be performed to visualise the integrity of both tympanic membranes. In cats with nasopharyngeal polyps, there may be extension of growth through the tympanic membrane into the horizontal ear canal. Pink, fleshy masses and otitis externa may be observed. In cats with OMI the tympanic membrane may be discoloured or bulging.

2.  Neurological Examination: A neurological examination should be performed in any cat with nasopharyngeal disease and suspected middle-ear involvement. Signs of peripheral vestibular disease in cats with OMI include vomiting, head tilt, circling, ataxia and spontaneous nystagmus in the absence of postural reaction deficits. Facial nerve palsy and components of Horner's syndrome (ptosis, miosis, enophthalmos, prolapse of the nictitating membrane) ipsilateral to the affected bulla may be seen concurrently. It is important to distinguish between peripheral vestibular disease and central vestibular disease in all patients since intracranial extension of infection from the middle-ear can occur.

3.  Serology: A latex cryptococcal antigen agglutination test (LCAT) detects the presence of cryptococcal antigen in serum. A positive titre is indicative of active infection.

4.  Aspiration Cytology & Microbial Culture: Where present, enlarged local lymph nodes (mandibular or retropharyngeal) or facial soft-tissue masses should be aspirated. Bacterial culture of superficial nasal swabs is usually unrewarding since normal flora is present and bacterial infections are usually secondary to underlying disease. Exceptions include infection with Bordetella bronchiseptica or Actinomyces sp, which may be primary pathogens. Cytology and fungal culture of nasal swabs is useful for the detection of Cryptococcus sp, and to perform in vitro susceptibility testing of the fungal pathogen. Since the nasal cavity of healthy cats can be colonised with Cryptococcus sp, diagnosis also requires cytological evidence of inflammation or the presence of abundant organisms. Step 3 (LCAT) should always be performed since fungal infection may not be detectable on swabs of the rostral nasal cavity.

5.  Thoracic Radiography: Thoracic radiography is useful to screen for lower respiratory tract involvement in the primary disease process, e.g., metastatic pulmonary neoplasia, pulmonary cryptococcosis.

Stage 2

If definitive diagnosis is not obtained using these non-invasive procedures, the following diagnostic investigations should be performed, sequentially, under general anaesthesia:

1.  Soft Palate Inspection: The soft-palate should be inspected during induction of general anaesthesia and intubation. A large nasopharyngeal mass will cause ventral deviation of the soft-palate and can be palpated dorsal to the soft-palate. After intubation, some large nasopharyngeal masses can be digitally massaged into the oropharynx for biopsy or removal. Nasopharyngeal polyps can be removed with firm traction, using curved extraction forceps by grasping the rostral stalk of the polyp. Haemorrhage is usually minimal. Recurrence is common and ventral bulla osteotomy is often required.

2.  Diagnostic Imaging: The nasal cavity, nasopharynx, frontal sinuses and tympanic bullae should be assessed in patients with caudal nasal cavity/nasopharyngeal disease. The diagnostic imaging modality used will depend on availability. If radiography is used views should include lateral skull, ventrodorsal skull, dorsoventral occlusal view or open-mouth ventrodorsal view and rostrocaudal open-mouth or rostro 10° ventro-caudodorsal oblique view. Nasopharyngeal masses are most easily identified as soft-tissue opacities dorsal to the soft-palate on a lateral skull radiograph. The sensitivity of radiography for the detection of acute otitis media, as identified by loss of aeration of the bullae, is low. Chronic otitis media is more readily detected as mild bony reaction and thickening of the tympanic bulla wall. Computed tomography (CT) is more sensitive than radiography. Furthermore, middle-ear involvement in cats with caudal nasal cavity/nasopharyngeal disease is more common than previously thought. Recently, a third of cats with nasopharyngeal disease were found to have effusive bulla disease on CT. The most common neoplasm implicated was nasopharyngeal lymphoma.10 On CT, destruction of maxillary turbinates is commonly seen in cats with inflammatory or neoplastic sinonasal disease.11 However, severe destruction of both maxillary turbinates and ethmoturbinates, particularly where unilateral, and/or lysis of paranasal bones is more predictive of sinonasal neoplasia than inflammatory disease. CT is also useful to document involvement of extrasinonasal structures including facial soft-tissues, the orbit and calvarium in cats with neoplasia or filamentous fungal infections. CT is generally superior to magnetic resonance imaging (MRI) for evaluation of destructive lesions in bony structures contiguous with the nasopharynx. In patients with suspected otogenic intracranial infection, MRI after intravascular contrast administration is superior for evaluation of intracranial soft-tissues.3

3.  Visualisation of the Nasopharynx: The patient is placed in dorsal recumbency with an intra-oral gag in place. Large nasopharyngeal mass lesions may be visualised by retraction of the soft palate with a spay hook. Visualisation of the choanae requires retroflexed nasopharyngeal endoscopy. Regional anaesthesia of the pharynx with 2% topical lignocaine gel and maxillary nerve blocks using 0.5% bupivacaine facilitate a decreased plane of general anaesthesia in some, but not all cats, during nasopharyngeal endoscopy. When the choanae are clearly visualised endoscopically, a size 5 or 6 Fr urinary catheter is inserted via each ventral nasal meatus into the nasopharynx, to check patency and dislodge foreign material or masses. Mass lesions in the choanae/nasopharynx can be biopsied using endoscopic biopsy forceps. In cats with suspected sinonasal cavity disease rhinoscopy should be performed after nasopharyngeal endoscopy. Haemorrhage, although mild, is common during rhinoscopy and can impair visualisation of the nasopharynx. Cup biopsy forceps are useful to obtain 'blind' tissue biopsies from the nasal cavity. Care should be taken not to advance biopsy forceps caudal to the medial canthus of the eye, to prevent inadvertent penetration of the cribriform plate.

4.  Nasal Cavity Lavage: Flushing saline from the nasal cavities into the nasopharynx is useful to dislodge foreign bodies and diagnostic fragments of friable tumours or granulomas. A cuffed endo-tracheal tube, with adequate insufflation to seal the trachea and protect from aspiration of lavage solution, should be used. The pharynx is packed with sterile swabs to prevent aspiration and to trap flushed material. A 10 ml aliquot of sterile saline is flushed vigorously through one naris into the ventral nasal meatus, whilst occluding the other naris, and then repeated on the other side. Diagnostic tissue specimens dislodged during this procedure can be retrieved from the packing material in the pharynx for cytology, culture and histopathology. Harvesting of biopsy samples utilising this flushing technique obviates the need for endoscopic biopsy and often yields larger biopsy specimens than can be obtained using endoscopy alone.

5.  Other Procedures: Where endoscopic visualisation of the nasopharynx is hampered by excessive secretions or haemorrhage, fine-needle aspirates of mass lesions through the soft-palate can be obtained for cytological analysis. Alternatively, though rarely necessary for diagnostic purposes, the soft-palate can be incised longitudinally, leaving the caudal edge intact, to facilitate superior access to the rostral nasopharynx.2

References

1.  Beatty JA, Barrs VR, Swinney GR, Martin PA, Malik R. (2000) Peripheral Vestibular Disease Associated With Cryptococcosis in Three Cats. Journal of Feline Medicine and Surgery 2, 29-34.

2.  Hunt GB, Perkins MC, Foster SF, Barrs VR, Swinney GR, Malik R. (2002) Nasopharyngeal Disorders of Dogs and Cats: A Review and Retrospective Study. Compendium of Continuing Education for the Practising Veterinarian 24, 184-200.

3.  Sturges BK, Dickinson PJ, Kortz GD, Berry WL, Vernau KM, Wisner ER, LeCouter RA. (2006) Clinical Signs, Magnetic Resonance Imaging Features, and Outcome after Surgical and Medical Treatment of Otogenic Intracranial Infection in 11 Cats and 4 Dogs. Journal of Veterinary Internal Medicine 20, 648-656.

4.  Allen HS, Broussard J, Noone K. (1999) Nasopharyngeal Diseases in Cats: A Retrospective Study of 53 Cases (1991-1998). Journal of the American Animal Hospital Association 35, 457-461.

5.  Malik R, Martin P, Wigney DI, Church DB, Bradley W, Bellinger CR, Lamb WA, Barrs VR, Foster SF, Hemsley S, Canfield PJ, Love DN. (1997) Nasopharyngeal cryptococcosis. Australian Veterinary Journal. 75, 9-14.

6.  Mitten RW. (1988) Nasopharyngeal Stenosis in Four Cats. Journal of Small Animal Practice 29, 341-345.

7.  Glaus TM, Gerber B, Tomsa K, Keiser M, Unterer S. (2006) Reproducible and long-lasting success of balloon dilation of nasopharyngeal stenosis in cats. The Veterinary Record 157, 157-259.

8.  Barrs VR, Beatty JA, Lingard AE, Malik R, Krockenberger MB, Martin P, O'Brien C, Angles J, Dowden M, Halliday C. Feline Sino-Orbital Aspergillosis: An Emerging Clinical Syndrome. (2007) Australian Veterinary Journal 85, N23.

9.  Khoo AML, Marchevsky AM, Barrs VR, Beatty JA. (2007) Choanal atresia in a Himalayan cat-first reported case and successful treatment Journal of Feline Medicine and Surgery Mar 23 (epub ahead of print)

10. Detweiler SA, Johnson LR, Kass PH, Wisner ER. (2006) Computed Tomographic Evidence of Bulla Effusion in Cats with Sinonasal Disease: 2001-2004. Journal of Veterinary Internal Medicine 20, 1080-1084.

11. Tromblee TC, Jones JC, Etue AE, Forrester D. (2006) Association Between Clinical Characteristics, Computed Tomography Characteristics, and Histologic Diagnosis for Cats with Sinonasal Disease. Veterinary Radiology & Ultrasound 2006 47, 241-248.

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Vanessa Barrs
Valentine Charlton Cat Centre, Faculty of Veterinary Science, The University of Sydney
NSW, Australia


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