Modified access-establishing technique for balloon dilation in cats with severe nasopharyngeal stenosis

Abstract

Nasopharyngeal stenosis (NPS) is a common upper airway disorder in cats, and balloon dilation (BD) is considered the least invasive treatment. However, advancing a BD catheter can be challenging in cases of severe or imperforate NPS. This technical note describes a simple access-establishing technique that enables BD in such cases. Six cats with NPS in which BD catheter passage was difficult underwent a modified procedure in which a 6-Fr tube was advanced transnasally and connected to an 8-Fr tube, enabling successful BD catheter placement in the nasopharynx. Dilation was confirmed via endoscopy, and all cases showed clinical improvement. No complications were directly attributable to the access technique. This method may facilitate BD in severe feline NPS.

Nasopharyngeal stenosis (NPS), a prevalent upper airway disorder in cats, is characterized by the narrowing of the nasopharyngeal passage. Clinical signs of NPS include inspiratory difficulty, stertor, sneezing, gagging, and open-mouth breathing. Additionally, regurgitation, vomiting, and anorexia may occur, and in severe cases, marked respiratory distress can develop [1,2,3,4, 6,7,8, 10,11,12,13, 15,16,17,18]. NPS can arise as a congenital abnormality [4, 18] or may develop secondarily due to nasopharyngeal inflammation resulting from upper respiratory infections [11,12,13,14], chronic rhinitis, aspiration rhinitis caused by vomitus entering the nasopharynx, trauma, or prior surgery [1, 4].

Treatment options for NPS include forceps dilation, balloon dilation (BD), transpalatal reconstruction with or without mucosal flap rotation, metallic stent placement, and the placement of covered metallic stents [1,2,3,4,5,6,7,10,11,12,13,15,16,17]. Among these methods, BD is considered the least invasive treatment. However, outcomes appear to vary with treatment frequency: cats undergoing multiple planned BDs did not reach a median progression-free interval (PFI), whereas cats treated with a single dilation had a median PFI of 112 days [9]. Nonetheless, BD can pose technical challenges in cases of severe or imperforate NPS, in which passing a BD catheter through the stenotic region proves difficult. In such instances, more invasive surgical methods may be necessary. Therefore, we developed this study to evaluate a less invasive BD technique.

This study involved cats referred by primary care veterinarians to the Veterinary Teaching Hospital at Nippon Veterinary and Life Science University in which NPS was diagnosed based on magnetic resonance imaging and nasopharyngeal endoscopy, and in which passing a BD catheter through the stenotic region was difficult. Among 44 cats that underwent balloon dilation (BD) for nasopharyngeal stenosis (NPS) at our institution, balloon catheter passage across the stenotic region was difficult or not feasible in 9 cats with severe or imperforate stenosis. In 3 of these cats, minimal tissue removal using endoscopic forceps alone was sufficient to enable subsequent passage of the BD catheter. In the remaining 6 cats, additional application of the present access-establishing technique was required to facilitate BD catheter placement. The modified BD access-establishing procedure described below was performed in six cats, encompassing a total of 11 BD procedures that met these criteria.

All procedures were conducted under general anesthesia with endotracheal intubation. After confirming severe or imperforate stenosis via retroflexed nasopharyngeal endoscopy and failing to directly pass a balloon catheter via the external nares (Fig. 1A), the modified technique was employed. A 6-Fr tube was used as a probe to assess luminal patency and establish access. In this study, the term “catheter” refers exclusively to the BD catheter used and failure of balloon catheter passage is the inability to advance the BD catheter across the stenotic segment despite attempted transnasal insertion. The access-establishing procedure is schematically illustrated in Fig. 2. A 6-Fr feeding tube (Atom Medical, Tokyo, Japan) was inserted through the nostril. With the larynx under observation by a laryngoscope, the tube was pulled toward the oral cavity. In cases of imperforate NPS, a small patency of the stenotic area was achieved through tissue curettage using endoscopic forceps or by removing stenotic tissue with argon plasma coagulation (Figs. 1B, 2A, and 3A). For imperforate stenosis, minimal tissue curettage with endoscopic forceps was initially performed to establish luminal patency. If sufficient patency for a 6-Fr tube passage could not be achieved, additional tissue removal using argon plasma coagulation (APC) was applied gradually and incrementally until limited luminal access was established.

Fig. 1.

Nasopharyngeal endoscopic images. (A) Severe or imperforate stenosis prior to balloon dilation. (B) A very small incision was made by forceps, allowing passage of a 6-Fr tube (arrowhead). (C) Improved patency of the nasopharyngeal lumen immediately after dilation.

Fig. 2.

Schematic illustration of the access-establishing technique for balloon dilation (BD) catheter placement in cats with severe nasopharyngeal stenosis. (A) A 6-Fr tube is advanced through the nasal cavity and retrieved from the oral cavity while avoiding injury to the soft palate, after which it is connected to an 8-Fr tube using a nylon suture. (B) The 8-Fr tube is gently withdrawn through the nasal cavity, at which point a BD catheter is connected in place of the 6-Fr tube. (C) The BD catheter is advanced by pulling the 8-Fr tube intraorally with forceps until the connection site becomes visible in the oral cavity.

Fig. 3.

Representative clinical images of the access-establishing procedure for balloon dilation (BD) catheter placement in cats with severe nasopharyngeal stenosis. (A) A 6-Fr tube is advanced from the nasal cavity (arrow) and retrieved from the oral cavity (arrowhead). (B) The 6-Fr tube (arrow) and 8-Fr tube are connected using a nylon suture (arrowhead). (C) The 8-Fr tube (arrow) is gently withdrawn through the nasal cavity while avoiding trauma to the soft palate, after which the BD catheter is connected in place of the 6-Fr tube using a nylon suture (arrowhead). (D) The BD catheter is guided through the 8-Fr tube, traverses the stenotic region, and reaches the oral cavity; the arrow indicates the tip of the reversed BD catheter.

The 6-Fr tube was selected for its balance between flexibility and sufficient stiffness, which allows device exchange. Notably, achieving luminal patency in severe or imperforate cases was technically challenging and often required repeated cycles of tissue removal, bleeding, and restoration of visualization. Coagulation profiles were evaluated preoperatively. When necessary, diluted epinephrine was topically administered through the endoscopic channel to control hemorrhage. To minimize laryngopharyngeal edema and procedural trauma associated with repeated endoscope manipulation, unnecessary endoscope insertion and withdrawal were avoided whenever possible. During prolonged procedures requiring repeated manipulation, medetomidine was administered to facilitate anesthetic management and reduce patient movement.

The 6-Fr and 8-Fr tubes were overlapped, and the tips of the tubes protruding from the oral cavity were securely connected using nylon ligation (Figs. 2A and 3B). To prevent injury to the soft palate, the oral side (6-Fr) of the connected tubes was gently flexed and carefully pulled caudally by mosquito forceps under laryngoscopic observation until it exited the external nostril. Next, the 8-Fr tube was positioned from the external nares through the pharynx to the oral cavity, as shown in Fig. 2B. The exposed tip of the 8-Fr tube was then connected to the BD catheter (Fig. 3C). The BD catheter was advanced by pulling the 8-Fr tube with forceps intraorally under laryngoscopic observation until the connection site was visible in the oral cavity (Figs. 2C and 3D). The nylon sutures were released by pulling the 8-Fr tube, which was then removed. Because the BD catheter was temporarily inverted into the oral cavity, it was redirected toward the esophageal entrance. Once the BD catheter was appropriately positioned at the stenotic site, BD was performed using a standard method. The diameters of the BD catheter ranged from 7 to 8 mm, depending on the degree of stenosis in each case.

The modified technique successfully enabled BD catheter placement in all six cats. Although the procedure time exceeded that required for standard BD catheter insertion, it remained less invasive than previously reported surgical approaches.

No complications were considered directly attributable to the access-establishing technique itself. However, several adverse events occurred during attempts to establish access; these events were likely associated with repeated and prolonged manipulation required in severe cases. One cat developed a hole in the soft palate due to argon plasma coagulation and developed mediastinal emphysema after the first BD procedure, which resulted from pharyngeal wall damage caused by endoscopic manipulation. In another case, a cleft palate was identified following multiple BD procedures; however, this complication was considered attributable to the repeated BDs. Endoscopic confirmation of improved stenosis following BD was achieved in all cases (Fig. 1C), with each cat exhibiting some degree of clinical improvement.

In this technical note, we presented a straightforward access-establishing technique that facilitates BD in cats with severe or imperforate NPS, in which standard catheter passage is challenging or impossible. Utilizing a transnasal tube-guided approach, BD catheter placement was successfully achieved in all cases.

In the present study, all cases exhibited short-term clinical improvement and improved nasopharyngeal patency. This observation is consistent with previous reports on the efficacy of balloon dilation for feline nasopharyngeal stenosis [9,10,11, 17]. However, recurrence was suspected in two cats during follow-up. As this technique is intended to facilitate catheter access rather than modify the underlying disease process, long-term outcomes may be more strongly influenced by factors such as chronic inflammation and disease duration.

Establishing luminal patency in severe or imperforate cases was technically demanding and required careful manipulation. Although this approach is less invasive than surgical intervention in selected cases, it is complex and technically demanding, requires a prolonged period of anesthesia, and is associated with procedural risks related to repeated instrumentation. Further, even though only a small number of cases have been reported, surgical approaches such as transpalatal excision, mucosal flap reconstruction, and extended palatoplasty have historically been used for the treatment of feline nasopharyngeal stenosis [1, 5, 12, 16]. While these procedures have produced favorable outcomes, they are inherently invasive because they require tissue incision and reconstruction. In addition, surgical wound healing and subsequent scar formation may contribute to restenosis in some cases, and repeated surgical intervention may be required in cases of recurrent stenosis. Notably, one cat died during a third surgical treatment attempt for recurrent disease [5]. More recently, endoscopic balloon dilation has become the preferred first-line treatment because of its minimally invasive nature and favorable outcomes reported in larger case series [5, 9,10,11, 17]. However, severe or imperforate stenosis may preclude passage of a balloon catheter, limiting the applicability of conventional balloon dilation. Therefore, the present method was developed as an adjunctive access-establishing technique to facilitate balloon catheter placement when standard catheter passage was unsuccessful, rather than as a replacement for surgical intervention.

Although catheters with a smaller diameter, such as 4-Fr catheters, may theoretically facilitate passage through extremely narrow stenotic regions, we have previously experienced difficulty advancing and exchanging these smaller tubes owing to insufficient rigidity.

This study is limited by its retrospective design, small sample size, and lack of direct comparison with other access-establishing techniques. In addition, because endoscopic follow-up data were not available, the influence of subsequent scar formation could not be fully evaluated. Nevertheless, clinical follow-up data were available for all six cats treated with the technique. Three cats developed restenosis within 6 months, which was considered to be related more to the severity of the original stenosis than to the procedure itself. Of these, one cat underwent temporary silicone stent placement followed by stent removal, and has remained free of recurrence during the more than 2-year follow-up period. One cat did not undergo further treatment at the owner’s request, and one died from an unrelated cause. The remaining three cats have been followed for more than 1 year without clinical evidence of restenosis suggestive of postoperative scar formation. Prospective studies with larger case numbers and standardized long-term follow-up are warranted to further evaluate the safety, durability, and long-term outcomes of the technique.

Conflicts of Interest

The authors declare that they have no conflicts of interest.