This condition is due to a narrowing or occlusion of the nasal passage in the caudal aspect of the nasal cavity (nasopharynx). This leas to an obstruction of air flow through the nasal passages.
Causes for nasopharyngeal stenosis (NPS) includes congenital or acquired causes. Acquired causes includes an infectious, inflammatory, caustic (e.g. aspiration rhinitis), traumatic, or cancerous process. Symptoms of NPS includes stertorous nasal breathing, dyspnea, open-mouth breathing, gagging, repeated swallowing, sneezing, chronic nasal discharge, among others.
Evaluation of the nasopharynx is necessary to diagnose NPS. Evaluation can be done via retropharyngoscopy, CT of the nasopharynx, or both.
Treatment options for NPS include surgical resection, laser ablation, mechanical dilation, and stenting. Balloon dilation is considered minimally invasive leading to immediate resolution of clinical signs. However, it is associated with a high recurrence rate. Placement of an uncovered metallic stent and covered metallic stents has been described. Typically, there are no immediate complications associated with stent placement in these patients and immediate relief of clinical signs is achieved. Long term complications included tissue ingrowth, oronasal fistula development, granulation tissue development, hair ball entrapment (cats), stent compression, dysphagia, and chronic infections. Most complications can be relieved with additional interventions.
A recent study showed that no dogs and only 50% of cats had successful treatment with sole balloon dilation. In this study, success was determined by the lack of tissue regrowth and absence of clinical signs after 1 or more balloon dilation procedures. Balloon diameter ranged from 6-18 mm (median 9mm) in dogs and from 10-12 mm (median 11mm) in cats. In unsuccessful cases median time for tissue regrowth was 4 weeks. Caudal lesions tend to be associated with higher success rate.
Given the low success rate of sole balloon dilation, balloon dilation followed by stent placement has been recommended. Uncovered stent placement has been shown to have a 67% success rate. However, covered stents were associated with a 100% success rate in a small number of patients. For cats, the diameter of the stent was 8 mm (7-10 m) and length 20 mm (16-34 mm). For dogs, the median stent diameter was 10 (7-16mm) and length 30 mm (20-40mm). Mitomycin C and triamcinolone are occasionally used with the hope of preventing tissue ingrowth. However, the use of either medication has not proven to increase the success rate. Approximately 68% of patients that underwent stent placement developed complications. Uncovered stents were associated with a 70% complication rate, which included tissue ingrowth (33%), chronic infection (23%), stent fracture (17%), oronasal fistula (13%), stent removal (13%), exaggerated swallowing (10%), stent bending (10%), and stent migration (7%). Sixty four percent of patients that underwent covered stent placement developed complications. These complications includes chronic infection (63%), oronasal fistula (27%), stent removal (18%), and stent migration (9%). The main advantage of a covered stent is that tissue regrowth does not typically occur. However, this type of stent is more likely associated with oronasal fistula development (13 vs. 27%) and chronic infections (63% vs. 23%). Overall, both uncovered and covered stents have similar complication rate.
Nasopharyngeal stenosis occurring in the caudal aspect of the nasal cavity are more likely to be associated with an exaggerated swallowing post-stent placement. Nonetheless, it is possible that rostral nasopharyngeal stenosis (33%) is more likely to be associated with complications than patients with caudal nasopharyngeal stenosis (27%). Stent removal is typically done because of an exaggerated swallowing and gagging, oronasal fistula development, chronic infection, or stent migration.
Overall success rate for nasopharyngeal stenosis treatment via stent placement is 60% in dogs and 78% in cats as determined by maintenance of nasopharyngeal patency, complications encountered and overall satisfaction. Success is also associated with lesion location. Successful outcome was achieved in 91% of patients with caudal nasopharyngeal stenosis vs. 67% in cases with rostral nasopharyngeal stenosis or 60% in the middle aspect of the nasal cavity.
Unfortunately, nasopharyngeal stenosis does not have a simple and effective treatment option. These cases can be frustrating due to the lack of great treatment options. Nonetheless, stenting has offered a possible solution for a problem that did not have a viable treatment option previously.
Sole balloon dilation is not recommended. Uncovered stent placement is recommended if there is the option of considering placement of a covered stent if tissue regrowth occurs. Otherwise, covered stent placement should be considered. The main concerns with covered stent placement is the rate of chronic infections and oronasal fistula development in these cases.