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Treating nasopharyngeal stenosis: A case study


DVM360 MAGAZINE


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 http://www.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.


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