Abstract
Objective
To develop and evaluate the use of 3-D–printed instrument guides for nasopharyngoscopy, focusing on maneuverability, the ability to biopsy the nasal choanae, and foreign body retrieval.
Methods
Various sizes of 3-D–printed guides (small, medium, large) and angles (160°, 170°, 175°, and 180°) were tested alongside retroflex nasopharyngoscopy in cadavers. Four cadavers representing different sizes and species (3 canines and 1 feline) were utilized to evaluate the success of the 3-D–printed instrument guides. The study evaluated the maneuverability of each guide within the nasopharynx, along with their effectiveness in facilitating choanal biopsies and retrieving a simulated grass foreign body. Performance was compared across guides to determine the most effective design.
Results
The 180° guide had limited maneuverability and was unable to facilitate biopsies or foreign body retrieval. The 175° guide showed moderate maneuverability and successfully performed biopsies and foreign body removal, although with mild resistance to movement. The 170° guide demonstrated high maneuverability, enabling smooth access in all directions and consistent procedural success. The 160° guide exhibited the greatest flexibility and procedural success, providing superior maneuverability and ease of use.
Conclusions
Three-dimensional–printed instrument guides with more acute angles improve nasopharyngeal access and procedural efficiency. The 160° guide showed the greatest potential for clinical application in facilitating biopsies and foreign body removal.
Clinical Relevance
Three-dimensional–printed nasopharyngoscopy guides enhance diagnostic and therapeutic procedures by improving access, biopsy collection, and foreign body retrieval. More acute angles offer greater maneuverability, supporting their clinical use for minimally invasive nasopharyngeal interventions in veterinary medicine.
Common disorders affecting the nasopharynx of dogs and cats include foreign bodies, neoplastic masses, nasopharyngeal polyps, fungal granulomas, and nasopharyngeal stenosis, among others.1 Endoscopy is a widely used tool, along with cross-sectional imaging (CT and MRI) for diagnosis and treatment of the various conditions affecting this area. The nasopharynx is positioned dorsal to the soft palate, with the nasal choanae located rostrally and the larynx caudally, thereby posing significant challenges for endoscopic access.
Multiple techniques have been utilized to visualize the nasopharynx including an anterograde approach (rigid endoscope passed through the nasal cavity) and a retrograde approach (flexible endoscope is inserted orally and retroflexed into the nasopharynx). Studies2 have indicated that the anterograde approach provides limited visualization of the entire nasopharynx in animals weighing less than 10 kg, particularly in accessing the ventral meatus due to restricted mobility. Conversely, retrograde endoscopic techniques using a flexible endoscope often provide superior visualization of the nasopharynx, especially in smaller patients. In 1 study1 investigating nasopharyngeal diseases in 38 dogs and 24 cats, a combination of retrograde endoscopy and soft palate retraction during surgery/necropsy achieved definitive diagnoses in 37 of the 38 dogs and 23 of the 24 cats.
While retrograde endoscopy may provide improved visualization, the insertion of instruments through a flexed endoscope is not possible to facilitate biopsy collection or foreign body removal. This limitation necessitates removing the scope before instrument passage, a process that can be both challenging and time consuming.2 One study3 conducted in feline cadavers found that when a retroflexed endoscopic approach was utilized to biopsy the soft palate and choanae, only 58% of endoscopists were able to visualize both landmarks and 53% successfully biopsied them. In addition, treating nasopharyngeal foreign bodies remains difficult. Techniques such as passing urinary catheters caudally through the nose or positioning small balloon catheters in the nares to dislodge foreign bodies have been used with varying success.1 Literature in veterinary medicine regarding proper techniques and instrumentation to access and diagnose diseases of the nasopharynx is limited. A recent study3 explored a novel retroesophagoscopic method for biopsying the soft palate and choanae in feline cadavers, reporting that 97% of veterinarians successfully identified and biopsied both landmarks. However, this method is more invasive than traditional retroflex nasopharyngoscopy, necessitating an esophagotomy incision. As such, the development of instrumentation to more easily access the nasopharynx in a less invasive way is desirable.
Three-dimensional–printing technology offers a promising avenue for developing instrument guides to better facilitate nasopharyngeal access in veterinary medicine. While extensively utilized in human medicine to create surgical models and prototypes across various specialties, 3-D printing is gaining traction in veterinary applications as well. Reports4 highlight its use in designing surgical implants for correcting angular limb deformities and fabricating prosthetics for animals. This technology relies on computer-aided design (CAD) to create structures through a layer-by-layer additive manufacturing process. Key advantages of 3-D printing are rapid prototyping of new designs, and material efficiency, as only the exact amount required for the model is used, minimizing waste.5
The aim of the present study is to introduce and evaluate a novel approach to nasopharyngeal access facilitated by 3-D–printed instrument guides. Specifically, this study assesses the maneuverability of guides with varying angles, as well as their ability to facilitate biopsies of the nasal choanae and removal of a simulated foreign body. As a proof-of-concept study, it highlights the potential for advancing veterinary tools and techniques, setting the stage for further refinement and broader clinical applications.
Methods
Cadavers
The present study was conducted at Oregon State University and involved the use of 4 cadavers (3 canines and 1 feline). Cadavers were chosen based on differing sizes, weights, and species (Table 1). The cadavers used in this study had been euthanized for purposes unrelated to the research conducted and were donated for academic and scientific use. The cadavers were stored at −20 °C and thawed at 5 °C for a period of 4 to 5 days. Following thawing, they were transferred to a room maintained at 20 to 22 °C, where they were kept for 24 to 48 hours before use. Cadavers were excluded from the study if significant autolysis or lesions in the nasopharynx were noted.
Summary of cadavers and equipment involved in scoping the nasopharynx.
| Breed | Weight (kg) | Endotracheal tube size (mm) | Scope size (mm) | Scope type | Guide size | Biopsy tool size (mm) |
|---|---|---|---|---|---|---|
| Doberman Pinscher | 40 | 14 | 5.0 | Olympus GIF-XP190N | Large guide | 2.3 |
| Labrador Retriever | 33 | 14 | 5.8 | Verathon GlideScope | Large guide | 2.3 |
| Miniature Poodle | 12 | 9 | 5.0 | Verathon GlideScope | Medium guide | 2.3 |
| Domestic shorthair feline | 6 | 5 | 3.8 | Verathon GlideScope | Small guide | 1.8 |
Three-dimensional printing of instrument guides
Instrument guides were designed in the CAD software program Fusion, version 2.0.20460 (Autodesk Inc). The initial prototype featured a 180° bend to mimic the endoscope in the fully retroflexed position. Analysis of a sagittal reconstruction of a CT scan of a canine skull showed that the maximum angle to access the choana without interference from the maxilla was approximately 170° (Figure 1). Therefore, additional instrument guides were designed at various angles (160°, 170°, and 175°) with 3 sizes to accommodate a range of animals. A representative example of the design process of the guides is shown in Figure 2. All guides were constructed with a wall thickness of 0.8 mm; the large and medium guides were 5 mm in outer diameter (3.4-mm working channel) with a 20- and 18-mm bend diameter, respectively. The small guide had a 4.2-mm outer diameter (2.6-mm working channel) and a 12.5-mm bend diameter. These dimensions were chosen to allow for the passage of 2.3-mm flexible biopsy forceps through the large and medium guides and 1.8-mm forceps for the small guide.
Sagittal CT of a canine skull showing approximately 170° minimal approach angle to the nasopharynx, avoiding maxillary interference.
Citation: American Journal of Veterinary Research 2025; 10.2460/ajvr.25.01.0005
Detailed view of development of instrument guide with 170° angle (A); representative images of computer-aided design modeling showing initial sketch, extrusion of sketch, and hollowing, rounding, and smoothing of edges to final shape (B); examples of 3-D–printed guides with varied angles (C); and examples of guides of different sizes (D).
Citation: American Journal of Veterinary Research 2025; 10.2460/ajvr.25.01.0005
Final designs were exported as .3mf files and imported into GrabCAD Print, version 1.94.18.46867 (Stratasys Inc). Files were prepared for printing at standard resolution. Instrument guides were printed on a J5 MediJet printer using UltraClearS material (Stratasys Inc). This material is rigid and clear and mimics the properties of polymehtylmethacrolate (acrylic). Support material was removed to leave the final instrument guide (Figure 2). No additional postprocessing of the prints was performed.
Experimental procedure
Each cadaver was positioned in sternal recumbency and intubated with an appropriately sized endotracheal tube to mimic the procedure in a live patient. A mouth gag was placed to provide improved visibility during the procedure. A flexible video endoscope was passed through the oral cavity and retroflexed into the nasopharynx of the cadavers. Scopes used varied in size from 3.8 to 5.6 mm in diameter and were selected based on patient size (GIF-XP190N, Olympus Inc; GlideScope BFlex 3.8, 5.0, and 5.8, Verathon Inc).
Three-dimensional–printed guides of small, medium, or large size were selected for each cadaver according to the animal's size. Guides with 180° and 175° angles were tested in 3 cadavers, while guides with a 170° angle were tested in all 4 cadavers. In addition, a guide with a 160° angle was tested in 1 cadaver. The use of the 3-D–printed guides allowed for the introduction of biopsy forceps alongside the scope, facilitating tissue sample collection from the nasal choanae and foreign body retrieval. The size of the biopsy tool used was dependent on the size of the guide (Table 1).
The 3-D–printed guide was placed in the nasopharynx, with the scope used for visualization, and a biopsy instrument was inserted through the guide. A biopsy sample was taken from the nasal choanae, and a blade of grass was placed into the nasopharynx to simulate the removal of a foreign body. The scoping and guide manipulation were performed by 2 veterinarians: the first veterinarian was responsible for positioning the endoscope, while the second manipulated the 3-D–printed guide, passed the instruments, and performed the biopsies or foreign body retrieval.
Outcomes assessment
The outcomes of interest included the ability to maneuver the guide, successfully biopsy the nasal choanae, and remove a grass foreign body from the nasopharynx.
Maneuverability—The ability to maneuver the guide and instruments in multiple directions (dorsal, ventral, left, and right lateral) to access different regions of the nasopharynx was evaluated. Successful mobility was defined as the ability to move the instruments freely within the nasopharynx without obstruction, ensuring complete access to the entire nasopharyngeal region. Maneuverability was classified as low, moderate, high, or very high. This was based on the ability to move the guide in 4 directions (dorsal, ventral, left, and right lateral) and the overall flexibility of motion. Low maneuverability was defined as movement restricted to 1 or 2 directions with limited flexibility in instrument manipulation. Moderate maneuverability was characterized by movement in 3 directions with some flexibility in instrument manipulation. High maneuverability was defined as the ability to move the guide in all directions with good flexibility. Very high maneuverability was assigned to guides that allowed movement in all directions with excellent flexibility, enabling effortless instrument manipulation.
Biopsy of the nasal choanae—The effectiveness of the 3-D–printed guides in facilitating biopsy of the nasal choanae was evaluated. Successful biopsies were defined as the ability to obtain tissue samples from the choanal region using the biopsy forceps introduced through the guide. The success of biopsying the nasal choanae was categorized as either “Yes” or “No” depending on whether a tissue sample was successfully obtained. To ensure consistency across cadavers and guide angles, the same technique was applied for each trial. The biopsy forceps were introduced through the guide in the nasopharynx with the scope used for visualization. The guides were maneuvered in all directions to assess whether any portion of the nasal choanae could be accessed for biopsy.
Foreign body removal—The ability to remove a grass foreign body from the nasopharynx was assessed. Foreign body retrieval was considered successful if the guide facilitated the removal of the foreign body using forceps without causing damage to the surrounding tissue. The success of foreign body retrieval was categorized as Yes or No depending on whether the grass blade could be successfully removed from the nasopharynx. To ensure consistency, the procedure was performed in the same manner across all cadavers and guide angles. The scope was used for visualization, while the guide was maneuvered in all directions to aid in foreign body retrieval.
These outcomes were used to determine the effectiveness of the different guide angles in improving access, maneuverability, and procedural success within the nasopharynx.
Data analysis
This study is a proof-of-concept investigation and was not intended to generate statistically generalizable findings. As a result, no formal statistical analysis was performed. The primary focus was on evaluating feasibility and functionality.
Results
A total of 4 cadavers, representing varying sizes and species were included in the study: 1 Doberman Pinscher (40 kg), 1 Labrador Retriever (33 kg), 1 Miniature Poodle (12 kg), and 1 domestic shorthair feline (6 kg). The nasopharynx of all cadavers was explored with a retroflexed endoscope, and a 3-D–printed guide was inserted to allow for instrument guidance. The Doberman Pinscher was used to evaluate the 160° guide. The Labrador Retriever, Miniature Poodle, and domestic shorthair feline were used to evaluate the 170°, 175°, and 180° guides.
Four 3-D–printed guide angles were evaluated for maneuverability and procedural success. The 180° guide demonstrated limited mobility within the nasopharynx, permitting lateral movement but presenting challenges with ventral and dorsal navigation. When a biopsy instrument was inserted, a biopsy of the nasal choanae and retrieval of a grass foreign body was not achievable. Consequently, the maneuverability of this guide was classified as “low,” indicating an inability to access all regions of the nasopharynx (Table 2). These findings were consistent across all 3 cadavers tested.
Comparison of guide angles for maneuverability and procedural success rates based on cadaver testing.
| Guide angle/cadavers tested | Maneuverability | Biopsy success | Removal of foreign body success |
|---|---|---|---|
| 180° | |||
| Labrador Retriever | Low | No | No |
| Miniature Poodle | |||
| Domestic shorthair feline | |||
| 175° | |||
| Labrador Retriever | Moderate | Yes | Yes |
| Miniature Poodle | |||
| Domestic shorthair feline | |||
| 170° | |||
| Labrador Retriever | High | Yes | Yes |
| Miniature Poodle | |||
| Domestic shorthair feline | |||
| 160° | |||
| Doberman Pinscher | Very high | Yes | Yes |
In contrast, the 175° 3-D–printed guide, tested in the same 3 cadavers, offered improved maneuverability. This guide allowed full access to the nasopharynx, with movement achievable laterally, ventrally, and dorsally. However, mobility was somewhat restricted, with mild resistance noted in all directions. As such, the maneuverability of this guide was classified as “moderate.” Notably, the insertion of an instrument through the 175° guide enabled a successful biopsy of the nasal choanae and retrieval of a grass foreign body (Table 2).
The 170° guide, also tested in the same 3 cadavers, demonstrated excellent maneuverability within the nasopharynx. This guide allowed smooth and unrestricted movement in all directions, lateral, ventral, and dorsal, facilitating full access to the nasopharynx. Its performance was classified as “high” for maneuverability. With this guide, a biopsy of the nasal choanae and retrieval of a grass foreign body was consistently successful, highlighting its superior functionality compared to the 180° and 175° guides (Table 2).
The final guide tested, the 160° angle, was evaluated in a single cadaver (a 40-kg Doberman Pinscher) due to the limited availability of cadavers at the time of the experiment. This guide demonstrated the highest level of maneuverability among all tested angles, offering even greater flexibility than the 170° guide. Movement in all directions (lateral, ventral, and dorsal) was smooth and unrestricted, providing exceptional access to the nasopharynx (Figure 3). The guide facilitated both successful biopsy of the nasal choanae and retrieval of a grass foreign body with ease (Figure 4), earning it the highest rating for maneuverability and procedural success (Table 2). However, since the guide was only tested in 1 larger cadaver, it is difficult to say if the same results would be applicable to small animals. Despite variations in angles, all guides were successfully placed within the nasopharynx alongside the scope and endotracheal tube in all cadavers.
Endoscopic images of the nasopharynx in a Doberman Pinscher cadaver. A large 160° instrument guide is utilized with a 2.3-mm biopsy tool. Maneuverability is demonstrated with ventral (A), dorsal (B), and bilateral access (C and D).
Citation: American Journal of Veterinary Research 2025; 10.2460/ajvr.25.01.0005
Endoscopic images of procedures performed in the nasopharynx of a Doberman Pinscher cadaver using a large 160° instrument guide and a 2.3-mm biopsy tool. Successful biopsy of the nasopharynx is shown (A), along with retrieval and removal of a grass foreign body (B to D).
Citation: American Journal of Veterinary Research 2025; 10.2460/ajvr.25.01.0005
Discussion
In this study, 3-D–printed instrument guides with varying angles were evaluated for use alongside retroflex nasopharyngoscopy in 4 cadavers of different sizes and species. The 3-D–printing technology utilized throughout this study allowed for rapid creation of prototypes as well as modification to the design as needed for various cadaver sizes. Performance metrics included maneuverability, nasal choanae biopsy capability, and successful foreign body retrieval. Guides with more acute angles demonstrated superior maneuverability, particularly the 160° guide, which enabled efficient access to all nasopharyngeal regions. While all tested angles (180°, 175°, 170°, and 160°) except the 180° guide facilitated biopsies and foreign body retrieval, the 160° guide was subjectively the most effective, enabling smoother and more efficient procedures. Despite the presence of an endotracheal tube, endoscope, and instrument guide, adequate space remained to perform all procedures, even in smaller cadavers. The use of 3 instrument guide sizes ensured compatibility with varying patient dimensions, and appropriately sized biopsy forceps complemented the guides to optimize procedural success.
Traditional retrograde nasopharyngoscopy is limited by the inability to pass instruments through the retroflexed endoscope, restricting biopsy collection and foreign body removal.2 In humans, nasopharyngeal endoscopy is typically conducted through a transnasal approach, and biopsies can be obtained by inserting the biopsy forceps through the endoscope itself.6 However, anatomical differences in veterinary patients make this method less applicable as it requires a much smaller scope. More invasive techniques, such as the retroesophagoscopic approach, can overcome some limitations but are associated with greater complexity.3 The development of 3-D–printed instrument guides for nasopharyngeal endoscopy addresses these key challenges. The guides enable precise biopsies and efficient foreign body removal, even in anatomically challenging regions or smaller patients. The ability to navigate through tight spaces while accommodating an endotracheal tube and endoscope highlights their practicality for clinical use. Moreover, the customizable design of the 3-D–printed guides allows for adjustments to be made based on patient size and procedural requirements. In addition, passing instruments through these guides adjacent to the scope (rather than through the working channel of the scope itself) permits more effective use of suction to improve visualization. As such, this leads to potentially reduced procedural time and improved diagnostic accuracy. This advancement could expand the diagnostic and therapeutic capabilities of nasopharyngoscopy.
This study had several limitations. First, the use of cadavers did not account for physiological factors such as increased secretions or hemorrhage as well as potential procedure-related complications that may arise in live patients. Second, the small sample size was not representative of diverse anatomical variations across all dog and cat breeds. This limitation is particularly relevant for brachycephalic breeds, where anatomical features such as elongated soft palates or everted tonsils could hinder the insertion of instrument guides alongside the endoscope and endotracheal tube. The CT findings revealed that brachycephalic dogs exhibit increased nasal mucosal contact and caudal aberrant nasal turbinates compared to normocephalic breeds.7 However, a study8 demonstrated the successful use of retroflexed endoscopy for diagnosing and surgically deroofing nasopharyngeal sialoceles using endoscopic-guided biopsy forceps in brachycephalic dogs. That study8 suggested that a flexible endoscope with a retrograde technique is essential for the adequate investigation of the nasopharyngeal area. In addition, significant structural differences in the nasopharynx exist even among dogs classified as “small breeds.” For example, 1 study9 found that Chihuahuas have a significantly smaller rostral nasopharynx compared to Pomeranians and Dachshunds, highlighting the variability in anatomy within similar-sized breeds. Furthermore, the only instrument type assessed with the use of the 3-D–printed guides were biopsy forceps. While we would expect the guides to work for other instruments as well, ideal angles were not evaluated. Finally, the 160° guide was tested in only 1 cadaver due to limited cadaver availability, which restricts the broader applicability of this instrument guide.
Future directions for this research include testing the instrument guides in live animals to assess safety, usability, and real-world functionality. For instance, under conditions that involve physiological challenges like increased secretions or airway sensitivity, refinements to the guide design, such as exploring adjustable or patient-specific angles, could improve versatility and adaptability for diverse patient anatomies, including brachycephalic breeds and smaller dogs/cats. In addition, the potential applications of 3-D–printed tools in veterinary medicine should be further investigated, with opportunities to develop similar innovations for other minimally invasive diagnostic or therapeutic procedures. This would involve incorporating additional endoscopic tools and adjusting the instrument guides accordingly.
In conclusion, this study demonstrates the feasibility of using 3-D–printed instrument guides to improve nasopharyngeal access, facilitating precise biopsies and efficient foreign body retrieval in veterinary patients. By addressing the challenges of traditional nasopharyngeal endoscopy, these guides provide a promising solution for enhancing diagnostic and therapeutic procedures in anatomically complex or smaller animals. Looking ahead, the integration of 3-D printing into veterinary practice holds significant potential to revolutionize patient-specific care, streamline procedures, and expand the applications of minimally invasive techniques. More research needs to be conducted to determine optimal instrument guides for brachycephalic breeds.
Acknowledgments
We extend our sincere gratitude to Tammy Gigoux for her assistance in providing cadavers. In addition, we thank Dr. Susanne Stieger-Vanegas for granting us access to her 3-D printer, which was instrumental to this study.
Disclosures
The authors have nothing to disclose.
AI-assisted technologies (ChatGPT) were used in the composition of this manuscript for grammar and flow.
Funding
The authors have nothing to disclose.
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