Treating nasopharyngeal stenosis: A case study

Nasopharyngeal stenosis is a pathologic condition in which there is a narrowing within the nasopharynx caudal to the choanae, resulting in variable degrees of inspiratory stertor. See how interventional radiography and endoscopy can help you identify and treat this abnormality in this case study.

Initial findings

• Signalment: 8-year-old spayed female domestic shorthaired cat

• Presenting complaint: 1.5-year history of inspiratory stertor, intermittent dyspnea and weight loss

• Pertinent history: Intermittent nasal discharge started three years before 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

—Head and neck radiographs: results normal

—Complete blood count and serum chemistry profile: results normal

—Antibiotic trials: intermittent improvement in discharge, no improvement in breathing

—Computed tomography (CT) (3-mm slices): Evidence of fluid accumulation in both nasal passages and frontal sinus; thickening of nasal turbinates suggestive of chronic rhinitis

—Antegrade rhinoscopy and biopsy: thickened nasal turbinates, moderate lymphoplasmacytic rhinitis

• Previous medications: Amoxicillin-clavulanic acid (15 mg/kg orally b.i.d. for 14 days) doxycycline (5 mg/kg orally b.i.d for seven days followed by 10 ml of water orally), and clindamycin (11 mg/kg orally b.i.d. for 21 days). After biopsy results, a tapering course of prednisone was administered per the referring internal medicine specialist (1 mg/kg/day tapered over two months).

• Progression: Each course of antibiotics improved the nasal discharge. The prednisone improved the inspiratory noise slightly, but it never fully resolved.

Initial diagnostic evaluation

• 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

• Problem list

—Severe chronic inspiratory stertor and dyspnea

—Chronic bilateral nasal discharge

• Differential diagnoses

—Nasopharyngeal polyp

—Nasal tumor

—Severe lymphoplasmacytic rhinitis

—Nasal foreign body

—Nasopharyngeal stenosis

Further diagnostics

• CT with 1-mm slices of the entire head and pharynx (Figure 1)

• Retroflex and antegrade rhinoscopy (Figure 2,)

Diagnosis

• Severe nasopharyngeal stenosis

• Moderate chronic lymphoplasmacytic rhinitis

Figure 1: A CT image of the cat in this case with a nasopharyngeal stenosis. A) A transverse image caudal to the nasopharyngeal stenosis (NPS) in the nasopharynx. This is the area where measurements are typically taken for stent and balloon sizing. B) A transverse image of the stenosis. Note the narrowing. C) A transverse image just rostral to the stenosis in the area of the nasopharynx that sits just dorsal to the hard palate. D) A sagittal image of the nasopharynx (rostral to the right and caudal to the left). Note the narrowing at the junction of the hard (HP) and soft (SP) palate inside the nasopharynx (NP).

Figure 2: A retroflex rhinoscopic view of the nasopharynx showing a narrow opening.

Treatment decisions

This cat's condition was diagnosed with a combination of the CT scan using 1-mm slices (rather than the previous 3-mm slices in which a narrow lesion was missed) and 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 cat's nasopharynx through the nostril and permanently open the stenosis noninvasively. 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).

Figure 3: A retroflexed endoscopic series of images during the placement of a balloon-expandable metallic stent (BEMS) for nasopharyngeal stenosis. A) The nasopharyngeal stenosis. B) A guidewire running from the nares and through the small nasopharyngeal opening. C) A balloon is passed over the guidewire; the opening is pre-balloon dilated. D) A balloon preloaded with a stent is advanced over the guidewire and then the stent is deployed by dilating the balloon. The nasopharyngeal stenosis is now effaced and the airway is open.

Outcome

This patient was discharged the same afternoon as the simultaneous diagnosis and treatment. The recommendation was to continue two weeks of clindamycin (11 mg/kg orally b.i.d.) and a tapering course of prednisolone (1.5 mg/kg/day tapered over three months). The cat was immediately able to breath through its nose upon recovery from anesthesia. It continued to have minor nasal discharge for the next 24 hours, at which point it ceased. It had no difficulty eating, drinking or breathing and was able to sleep in bed with the owner permanently. The cat gained 2 lb in the first month after stent placement, and the owner reported an excellent appetite. The owner reported complete return to kittenlike behavior, which the cat has maintained over the following three years.

Figure 4

Discussion

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 people called nasopharyngeal stenosis. This is not considered a common etiology of nasopharyngeal stertor but is being diagnosed more commonly, likely because of better diagnostic imaging modalities becoming widely available.

Nasopharyngeal stenosis 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 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 in dogs. In cats, this condition is most frequently associated with chronic rhinitis or a congenital deformity, and in dogs it is most frequently associated with aspiration rhinitis.1-4

Nasopharyngeal stenosis is most easily diagnosed with 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 nasopharyngeal stenosis, 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 short (< 2 to 3 mm) or long (> 2 cm). 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 the balloon and stent if needed.

Treatment options for nasopharyngeal stenosis include surgical resection via a transpalatal approach, serial balloon dilation procedures and nasopharyngeal stenting. Considering that most cases develop the stenosis from an inflammatory condition (aspiration rhinitis or chronic rhinitis), surgical fixation is often met with failure because of high recurrence rates.1-4

In our experience, stenting is ideal to prevent restenosis, but 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 because of the cost of serial balloon dilation procedures and the low complication rate with stenting. We 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 2008, balloon-expandable metallic stents (BEMS) were placed in six animals (three dogs and three cats), and this procedure was deemed safe, noninvasive and effective for treating nasopharyngeal stenosis in dogs and cats.4 Since that time, we have successfully placed over 25 stents to treat nasopharyngeal stenosis in both dogs and cats. The main complications are chronic infections (only seen with covered stents, which are often needed for more aggressive stenosis with completely closed membranes), oronasal fistula formation and stent migration—all of which are rare. Overall, for the appropriate case, a BEMS for nasopharyngeal stenosis is highly effective.

Interventional radiology and endoscopy tip

Patients with nasopharyngeal stenosis can present at any age, as it can be either congenital or acquired. If an animal is presented 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 to 3 mm in length).

For more case examples and to see how interventional radiology and interventional endoscopy can benefit your patients, visit amcny.org/interventional-radiology-endoscopy.

Dr. Berent is the director of Interventional Endoscopy Services in the Department of Diagnostic Imaging at The Animal Medical Center in New York City. Dr. Weisse is the director of Interventional Radiology Services in the Department of Diagnostic Imaging at The Animal Medical Center in New York City.

References

1. Mitten RW. Nasopharyngeal stenosis in four cats. J Small Anim Pract 1988;29:341-345.

2. 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(9):257-259.

3. Berent AC, Kinns J, Weisse C. Balloon dilation of nasopharyngeal stenosis in a dog. J Am Vet Med Assoc 2006;229(3):385-388.

4. Berent AC, Weisse C, Todd K, et al. Use of a balloon-expandable metallic stent for treatment of nasopharyngeal stenosis in dogs and cats: six cases (2005-2007). J Am Vet Med Assoc 2008;233(9):1432-1440.