By Allyson Berent, DVM, DACVIM and Chick Weisse, VMD, DACVS
- Signalment: 8 year old spayed female domestic shorthair
- Presenting Complaint: 1.5 year history of inspiratory stertor, intermittent dyspnea and weight loss.
- Past Pertinent History: Intermittent nasal discharge started 3 years prior to presentation that progressed to static inspiratory noise requiring the cat to sleep in a separate room from the owner over the past 1.5 years. The cat has a decreased appetite associated with difficulty breathing while eating.
- Previous Diagnostics Performed:
1) Head and Neck radiographs: within normal limits (WNL)
2) Complete blood count/Serum biochemical profile: WNL
3) Antibiotic trials: intermittent improvement in discharge, not breathing
4) Computed Tomography (3 mm slices): Evidence of fluid accumulation in both nasal passages and frontal sinus, thickening of nasal turbinates suggestive of chronic rhinitis
5) Antegrade rhinoscopy and biopsy: thickened nasal turbinates, moderate lymphocystic and plasmacystic rhinitis
- Previous Medications: Clavamox (15 mg/kg PO BID 14 days), Doxycycline (5 mg/kg PO BID for 7 days followed by 10 mL of water PO), Clindamycin (11mg/kg PO BID for 21 days). After biopsy results a tapering course of prednisone was administered per referring internal medicine specialist (1mg/kg/day tapered over 2 months).
- Progression: Each course of antibiotics improved the nasal discharge. The prednisone improved the inspiratory noise slightly but it never fully resolved.
- Physical Examination: Bright, alert, good body condition. Mucopurulent nasal discharge bilaterally. Severe inspiratory stertor with open mouth breathing. Referred upper airway noise over the area of the larynx/pharynx on auscultation. The remainder of the physical examination was within normal limits.
- Problem List:
1) Severe chronic inspiratory stertor and dyspnea
2) Bilateral nasal discharge-chronic
- Differential Diagnoses:
2) Nasal tumor
3) Severe lymphoplasmacystic rhinitis
4) Nasal foreign body
5) Nasopharyngeal Stenosis
- Further Diagnostics:
• Computed tomography with 1mm slices of the entire head and pharynx: Figure 1
• Retroflex and Antegrade Rhinoscopy: Figure 2
1) Severe nasopharyngeal stenosis
2) Moderate chronic lymphoplasmacytic rhinitis
- Treatment Decisions:
The diagnosis was made by a combination of the CT scan using 1mm slices (rather than the previous 3 mm slices in which a narrow lesion was missed) and a retroflexed rhinoscopy. These lesions are often missed on antegrade rhinoscopy alone. During the rhinoscopy interventional endoscopic techniques were used to place a nasopharyngeal stent inside the nasopharynx of the cat through the nostril and permanently open the stenosis non-invasively. The owner was offered serial balloon dilation procedures to try and treat this stenosis but elected immediate stent placement to try and maintain permanent patency. This technique requires a combination of fluoroscopy and endoscopy to appropriately place the nasopharyngeal stent across the stenosis. (Figures 3 and 4)
This patient was discharged the same afternoon and obtained a simultaneous diagnosis and treatment. The recommendation was to continue 2 weeks of Clindamycin (11mg/kg BID PO) and a tapering course of prednisolone (1.5 mg/kg/day tapered over 3 months). This patient was immediately able to breath through her nose upon recovery from anesthesia. She continued to have minor nasal discharge for the following 24 hours at which point it ceased. She had no difficulty eating, drinking or breathing and was able to sleep in bed with the owner permanently. She gained 2 pounds in the first month after stent placement and the owner reported an excellent appetite. The owner reports complete return to “kitten-like” behavior immediately and has remained so over the following 3 years.
The most common cause of nasopharyngeal obstruction in cats is a nasopharyngeal polyp originating from the middle ear. Nasopharyngeal polyps are much less common clinical entities in dogs. The choanae or nasopharynx can also be obstructed by a congenital membrane a condition similar to choanal atresia in humans, called nasopharyngeal stenosis. This is not considered a common etiology of nasopharyngeal stertor but is being diagnosed more commonly, like due to better diagnostic imaging modalities becoming widely available.
Nasopharyngeal stenosis (NPS) is a pathologic condition in which there is a narrowing within the nasopharynx caudal to the choanae, resulting in variable degrees of inspiratory stertor. This can occur as a congenital anomaly similar to choanal atresia, or secondary to an inflammatory condition (chronic rhinitis or aspiration rhinitis from regurgitation), surgery, or secondary to a space-occupying lesion. Nasopharyngeal stenosis has only been described in a small number of cases in the veterinary literature. It is seemingly more common in cats than dogs. In cats this condition is most commonly associated with chronic rhinitis or a congenital deformity, and in dogs it is most commonly associated with aspiration rhinitis.1-4
The diagnosis of NPS is most easily made via the use of retroflex rhinoscopy. The endoscope is passed through the mouth into the caudal oropharynx then retroflexed dorsally over the soft palate to allow visualization of the nasopharynx and choanae. With NPS a narrow opening (or completely closed membrane) is visualized between the end of the soft palate and the choanae (Figure 2). This is typically a nonproliferative membrane that does not produce a mass effect. The membrane can be very short in length (<2-3mm) or very long (over 2 cm). The CT is most helpful to define the length of the stenosis and rostral aspect of the lesion. It also aids in measuring the normal nasopharyngeal lumen diameter to help size for the balloon and stent if needed.
Treatment options for NPS include surgical resection via a transpalatal approach, serial balloon dilation procedures, and nasopharyngeal stenting. Considering a majority of cases develop the stenosis from an inflammatory condition (aspiration rhinitis or chronic rhinitis) surgical fixation is often met with failure due to high recurrence rates.1-4
In the authors’ experience, stenting is ideal to prevent re-stenosis, but will always offer balloon dilation procedures first. If those fail then a stent is more strongly considered. Many clients choose a stent as a first line treatment due to the cost of serial balloon dilation procedures and the low complication rate with stenting. The authors only recommend stenting when the lesion is more than 1 cm rostral to the end of the soft palate to allow for closure of the caudal end of the nasopharynx during eating. When the stent is placed more caudal to this signs of gagging, exaggerated swallowing and palatal irritation can be seen so caution should be exercised. In a small study in 20084 balloon expandable metallic stents (BEMS) were placed in 6 animals (3 dogs and 3 cats) and this procedure was deemed safe, noninvasive and effective for the treatment of NPS in dogs and cats. Since that time the authors’ have successfully placed over 25 stents for NPS in both dogs and cats. The main complications to be aware of are chronic infections (only seen with covered stents which are often needed for more aggressive stenosis with completely closed membranes [rare]), oronasal fistula formation (rare), and stent migration (rare). Overall, for the appropriate case, a BEMS for NPS is highly effective.
Patients with NPS can present at any age, as it can be either congenital or acquired. If an animal presents with chronic inspiratory stertor and rhinoscopy is performed a retroflex examination should always be done to ensure a patent and normal nasopharynx. Finally, when a CT scan is being performed for nasal examination it is recommended to obtain 1 mm slices, as a stenosis can be missed if its length is short (can often be only 1-3 mm in length).
***for more case examples and to see how interventional radiology and interventional endoscopy (IR/IE) can benefit your patients please visit: http://www.amcny.org/interventional-radiology-endoscopy
- Mitten RW. Nasopharyngeal stenosis in four cats. J Small Anim Pract 1988;29:341-345.
- Glaus TM, Gerber M, Tomsa K, et al. Reproducible and long-lasting success of balloon dilation of nasopharyngeal stenosis in cats. Vet Rec 2005;157:257-259.
- Berent AC, Kinns J, Weisse C. Balloon dilation of nasopharyngeal stenosis in a dog. J Am Vet Med Assoc 2006;229:385-388.
- Berent AC, Weisse C, Todd K, et al. The use of a balloon expandable metallic stent for the treatment of nasopharyngeal stenosis in dogs and cats: 6 cases (2005-2007). J Am Vet Med Assoc 2008; 233 (9):
Figure1: This is a CT image of a cat with a nasopharyngeal stenosis. A) Transverse image caudal to the NPS in the nasopharynx. This is the area where measurements are typically taken for stent and balloon sizing. B) This is a transverse image of the NPS. Notice the narrowing. C) This is a transverse image just rostral to the stenosis in the area of the nasopharynx that sits just dorsal to the hard palate. D) This is a saggital image of the nasopharynx (rostral to the right and caudal to the left). Notice the narrowing at the junction of the hard (HP) and soft (SP) palate (NPS=nasopharyngeal stenosis) inside the nasopharynx (NP).
Figure 2: This is a retroflex rhinoscopic view of the nasopharynx showing a narrow opening.
Figure 3: This is a retroflexed endoscopic series of images during the placement of the BEMS for NPS. A) The NPS, B) A guidewire running from the nares and through the small nasopharygeal opening, C) A balloon is passed over the guidewire and the opening is pre-balloon dilated, D) A balloon pre-loaded with a stent is advanced over the guidewire and then the stent is deployed by dilating the balloon. The NPS is now effaced and the airway is open.
Figure 4: These are fluoroscopic images during the placement of the BEMS for NPS in a cat. A) The patient is in lateral recumbency. Cranial is to the left and caudal is to the right. B) The endoscope (yellow arrow) is inserted into the mouth and it is retroflexed over the soft palate to visualize the nasopharynx. A guidewire is placed from the nares and through the NPS (white arrow). C) Over the guidewire a balloon expandable metallic stent (BEMS) (red arrow) is placed across the stenosis. D) The balloon is expanded which deploys the stent (red arrow). E) Contrast is in the balloon as it opens and effaces the stenosis (red arrow). F) The balloon is deflated and removed and the stent remains in place (red arrow).
References: more available upon request