Abstract
Background:
Topical sinus irrigation plays a critical role in the management of sinonasal diseases. Yet, the penetration of irrigant to targeted sinuses may be highly variable and difficult to predict. Here, we investigate the use of 3D printing as a planning tool to optimize outcomes.
Methods:
Eight post-operative models were 3D printed with a FormLabs Form3 printer based on individual CT scans. Irrigations were performed and video recorded with a squeeze bottle attached via silicon water-tight seal, in 4 head positions: 45° to-the-side, 90° to-the-side, 45° forward and 45° to-the-side, and 90° forward, with irrigation fluid entering the upper (conventional) or lower (backfill) nostrils.
Results:
Significant individual variations were observed in sinus penetration as a function of head position. In general, the maxillary sinus was the easiest to irrigate in most head positions (P < .05), followed by frontal and ethmoid, with sphenoid being the most difficult. Both the 90°-to-the-side and the 90°-forward positions were significantly more effective than the others (P < .05), with 90°-forward better for frontal sinuses and 90°-to-the-side superior for all other sinuses. The backfill was significantly superior to conventional technique in head positions involving a side tilt (P < .05).
Conclusion:
Variations in technique and position significantly impacted irrigation outcome. Backfill irrigation that pushes fluid against gravity to pool around the ostium, seems to provide overall better outcomes. This study demonstrates the advantage of 3D printing as a rapid planning tool to guide irrigation strategies.
Keywords: rhinosinusitis, 3D modeling, irrigation
Introduction
Chronic Rhinosinusitis (CRS) is a common condition affecting millions of patients worldwide. Unfortunately, there are no definitive treatment options for the condition; rather, a combination of medical and surgical options are used to suppress chronic inflammation within the sinuses.1 While not curative, treatments can often help to ease symptom burden.1
Standard of care often begins with saline nasal irrigation or topical nasal steroids, with or without antibiotics depending on the presence of acute infection.2 While less convenient for patients, nasal steroid irrigation has been shown to be a superior treatment option in comparison to the more user-friendly nasal sprays.3,4 Perhaps unsurprisingly, significant variations in nasal anatomy,5 in addition to significant patient variability in performing the irrigation,6 often leads to the irrigation only minimally penetrating the affected sinuses, or not at all.7 Studies have sought to better understand how medical or surgical interventions impact the efficacy of nasal irrigations using cadaver modes, for example: comparing in-office balloon sinuplasty versus FESS,9 different irrigation devices,10 and different types of Draf frontal sinusotomy.11,12 Despite these efforts, we lack a validated technique to predict and improve patient-specific irrigation outcomes in live patients.
Conventional nasal irrigations are performed with the head tilted to one side, with fluid pushed into the superior nostril, filling the paranasal cavity according to gravity, and exiting via the inferior nostril. We have previously implemented a backfill method of nasal irrigation, a permutation of the conventional irrigation, with the fluid pushed into the inferior nostril.8 While counterintuitive, this method may improve the delivery of irrigating agent to some sinuses.8 This method may provide a potential option for patients whose symptoms are resistant to conventional irrigation, although further evidence is needed.
In recent years, 3D printing has been used to replicate patients’ nasal cavities using low-dose head CT scans.13 These models can be generated from a patient’s clinical CT scan and are anatomically identical to the patient’s nasal airway and paranasal sinuses at that point in time, which can then be used to directly visualize dyed fluids as they are pushed into the nostril to determine how effective irrigations would be in that patient, and to compare effectiveness of irrigation using different settings. 3D printing to create a personalized model may present a promising technique to improve irrigation treatment outcomes for patients suffering from CRS. Currently, the major drawback is the lack of a study to demonstrate its effectiveness in optimizing sinus irrigations outcome.
Thus, the objective of our study is to expand upon our previous case reports8,13 and to conduct a retrospective study to demonstrate the use of personalized 3D printed models to determine the effects of head positioning and irrigation method on sinus penetration. Given the significant global cost of ineffectively treating the condition and increasing availability of 3D printing technology, it could be an important tool to improve patients-specific treatment outcomes.
Methods
Patients
Pre-existing CT scans from 8 CRS patients were retrospectively selected for this study, including 3 male and 5 female, with ages ranging from 39 to 67 years (mean: 53.75). Each of the subjects had some history of endoscopic sinus surgery, usually involving all sinuses. Several of the subjects also had a history of turbinate reduction. Table 1 describes the nasal surgical histories of the 8 subjects included in the study.
Table 1.
Sinonasal Surgical Histories for Each Subject.
| Maxillary antrostomy |
Frontal sinusostomy |
Total ethmoidectomy |
Total sphenoidotomy |
|||||
|---|---|---|---|---|---|---|---|---|
| Subject | L | R | L | R | L | R | L | R |
| 1 | + | + | + | + | + | + | ||
| 2 | + | + | ||||||
| 3 | *No sinus surgery, patient had history of complete bilateral inferior turbinate resection | |||||||
| 4 | + | + | + | + | ||||
| 5 | + | + | + | + | + | + | + | + |
| 6 | + | + | + | + | + | + | ||
| 7 | + | + | + | + | + | + | + | + |
| 8 | + | + | + | + | + | + | + | + |
The time between surgery and post-operative CT scan for 5 of the subjects (1, 2, 4, 7, and 8) ranged from 52 to 68 days (average 60 days). Subjects, 3, 5, and 6 had gaps of 9 years, 310 days, and 3 years from surgery to CT, respectively. Post-operative SNOT-22 scores at the time of CT for subjects 1 and 4 were 5 and 8, respectively, indicating symptom resolution, while the other subjects reported SNOT-22 scores ranging from 43 to 82 (mean of 51.7), indicating the persistence of CRS symptoms.
Institutional review board (IRB) approval was obtained for this study.
3D Printing
Anatomically correct post-operative models were constructed based on CT scan by tracing the nasal airway on each CT slice and creating a boundary between the nasal mucosa and airway through specialized software (AMIRA®, Thermo Fisher Scientific, Waltham, MA). Each of these traces are then combined into a “stack” to create the 3D geometric model, and additional post-processing was done through Autodesk Meshmixer (Autodesk, Inc, San Rafael, CA), such as adding vent holes and cleaning up artifacts. The nasopharyngeal opening was blocked off and impenetrable to liquid or air, representing the closure of the soft palate. These models were then 3D printed with a FormLabs Form3 SLA printer using a clear resin (Figure 1A).
Figure 1.
(A) FormLabs form3 SLA printer. (B) Clamp setup used for irrigation simulations. (C and D) Irrigation squeeze bottle attached to silicon water-tight seal.
Irrigation Procedure
Using a clamp stand with a digital protractor, the models were locked into pre-determined head positions (Figure 1B). Irrigation of 120 mL of dyed water were performed with a squeeze bottle via silicon water-tight seal (Figure 1C and D) and video recorded from frontal and lateral views (See Supplemental Video).
Conventional irrigation involves a head tilt to one side with fluid entering the upper nostril and exiting the lower nostril along the direction of gravity. Here, we also investigate the permutation of fluid entering through the lower nostril and exiting the upper nostril (Backfill Technique) in conjunction with conventional irrigation at 4 head positions: 45° to-the-side, 90° to-the-side, 45° to-the-side and 45° forward, and 90° forward (Figure 2).
Figure 2.
Examples of nasal irrigations in different head positions using backfill method (A-C) and conventional method (D-F). Author’s consent was obtained to appear in the image.
For all models, the effectiveness of irrigation was determined by scoring the greatest filling percentage during the full course of the procedure of each sinus, qualitatively into 4 categories: none (0), less than 50% filled (1), greater than 50% filled (2), and completely filled (3). Since in nearly all circumstances, sinuses were filled based on gravity, with the most inferiorly located sinuses filling first; therefore, a completely filled sinus in the tables below refers to only the inferior sinus, unless otherwise indicated. The scores were first rated by 2 of the co-authors blindly. For sinuses with a rating discrepancy, all authors re-watched the irrigation video together and reached a joint conclusion.
Results
Figures 3 and 4 display example irrigation outcomes of two subjects (1 and 5). For subject 1 (Figure 3), the backfill method was either slightly or moderately better in every head position. The 90°-to-the-side head positioning was able to effectively reach the ethmoidal sinuses using either nostril. This was noteworthy since irrigations in a majority of head positions struggled to reach these sinuses. Interestingly, the more natural head position, 45°-to-the-side and 45° forward tilt, provided the most dichotomy of outcomes with almost no maxillary penetration for conventional irrigation versus 100% for backfill technique.
Figure 3.
Nasal irrigation for subject 1 using conventional (D-F) and backfill (A-C) methods in 45°-to-the-side tilt, 90°-to-the-side tilt, and 45°-to-the-side/45° forward tilt head positions. The backfill method was either slightly or moderately better in every head position. The 45°-to-the-side and 45° forward provided the most dichotomy of outcomes, with almost no maxillary penetration for conventional irrigation versus 100% for backfill technique. This finding was mirrored in 4 of the 8 patients examined, including Subject 5, shown in Figure 4.
Figure 4.
Nasal irrigation for subject 5 using conventional (D-F) and backfill (A-C) methods in 90° forward, 90°-to-the-side tilt, and 45°-to-the-side/45° forward tilt head positions. Irrigation was very effective overall at reaching most sinuses. In particular, the 90° forward positioning filled the frontal and ethmoid sinuses completely while also filling the maxillary sinus more than halfway.
Figure 4 shows that for subject 5, irrigation was very effective overall at reaching most sinuses. In particular, the 90° forward positioning filled the frontal and ethmoid sinuses completely while also filling the maxillary sinus more than halfway. This was one of the most effective individual head positions, and an example of what an individualized irrigation method could look like in an optimized treatment plan. In comparison, the efficacy in sinus filling among other head positions varied. Again, the more natural head position, 45°-to-the-side and 45° forward tilt, provided the greatest dichotomy of outcomes with almost no penetration to the inferior maxillary for conventional irrigation versus 100% for backfill technique, which occurred in 4 of the 8 patients examined.
Table 2 summarizes the irrigation filling grade for every sinus using both the backfill and conventional irrigation methods at different head positions for all 8 subjects. First, there was significant variation in sinus penetration among the 8 subjects (Figure 5A), with subjects 1, 5, and 8 having significantly better irrigation outcomes in general than the rest of the subjects (P < .05), despite having similar surgeries to the other subjects (with the exception of subjects 2 and 3). We also showed that the backfill technique was superior to the conventional technique in the 2 head positions involving a side tilt (the 90°-to-the-side, P < 0.05, and 45°-to-the-side, 45° forward head positions, P < .01, as well as all head positions combined, P < .05, (Figure 5B)). Of note, the 90° forward position is a poor example of backfill/conventional irrigation since gravity is level between the 2 sides (no upper vs lower side). In this position, there was no significant difference between the conventional and the backfill method.
Table 2.
Sinus Penetration of Nasal Irrigation at 4 Different Head Positions Using Backfill and Conventional Irrigation Methods (0: no irrigant reached sinus, 1: sinus ≤50% filled, 2: sinus >50% filled, 3: sinus completely filled).
| Subject 1 | Subject 2 | Subject 3 | Subject 4 | Subject 5 | Subject 6 | Subject 7 | Subject 8 | Averages | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SNOT-22 | 8 | 49 | 43 | 5 | 48 | 45 | 82 | 43 | 40.375 | |||||||||||
| Lund-Mackay | 13 | 5 | 3 | 5 | 10 | 12 | 19 | 6 | 9.125 | |||||||||||
| Head Position | Sinus | B | C | B | C | B | C | B | C | B | C | B | C | B | C | B | C | B | C | Overall |
| 90° to the right | Frontal | 3 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 3 | 0.75 | 0.625 | 0.688 |
| Maxillary | 2 | 1 | 0 | 0 | 0 | 0 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 2.125 | 2 | 2.063 | |
| Ethmoid | 3 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 2 | 0 | 0 | 3 | 3 | 3 | 3 | 1.5 | 1.375 | 1.438 | |
| Sphenoid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 3 | 0 | 0 | 0 | 0 | 3 | 2 | 0.75 | 0.625 | 0.688 | |
| 45° to the right | Frontal | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Maxillary | 3 | 1 | 0 | 0 | 0 | 0 | 3 | 3 | 2 | 3 | 3 | 3 | 2 | 0 | 3 | 3 | 2 | 1.625 | 1.813 | |
| Ethmoid | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 0 | 0.375 | 0 | 0.188 | |
| Sphenoid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 0 | 0.375 | 0 | 0.188 | |
| 45° forward, 45° right | Frontal | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0.25 | 0.25 | 0.25 |
| Maxillary | 2 | 0 | 0 | 0 | 1 | 0 | 3 | 2* | 3 | 2* | 3 | 2** | 3 | 2* | 3 | 2* | 2.25 | 1.25 | 1.75 | |
| Ethmoid | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0.375 | 0 | 0.188 | |
| Sphenoid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 90° forward | Frontal | 3 | 3 | 0 | 3 | 0 | 0 | 0 | 0 | 2 | 2 | 0 | 0 | 0 | 0 | 3 | 3 | 1 | 1.375 | 1.188 |
| Maxillary | 1 | 0 | 0 | 3 | 1 | 0 | 0 | 0 | 2 | 2 | 0 | 0 | 0 | 0 | 2 | 2 | 0.75 | 0.875 | 0.813 | |
| Ethmoid | 1 | 1 | 0 | 3 | 0 | 0 | 0 | 0 | 3 | 3 | 0 | 0 | 0 | 0 | 2 | 2 | 0.75 | 1.125 | 0.938 | |
| Sphenoid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| Averages | 1.375 | 0.733 | 0.067 | 0.6 | 0.133 | 0 | 0.6 | 0.533 | 1.4 | 1.4 | 0.6 | 0.533 | 0.733 | 0.533 | 2.067 | 1.6 | 0.828 | 0.695 | 0.762 | |
Note. Gray boxes correspond to completely obstructed sinuses; therefore, irrigation could not feasibly reach these specific sinuses.
Irrigation filled superior maxillary sinus only,
irrigation filled both superior and inferior maxillary sinuses.
Figure 5.
(A) Average and standard error of overall sinus filling among 8 subjects included in this study. (B) Average and standard error of sinus filling of all sinuses comparing backfill irrigation method to conventional method. (C) Effect of head positioning on the filling of each sinus by nasal irrigation. (D) Extent to which each sinus is filled by irrigation based on head positioning.
Looking at different head positions, both the 90°-to-the-side and the 90° forward positions were more effective than the others in terms of general sinus penetration (Figure 5C, P < .05). Of the 2, the 90°-to-the-side position appeared slightly better, but the difference was not statistically significant. While the 90° forward was the best option for filling the frontal sinuses, the 90°-to-the-side position was superior in filling all other sinuses.
Looking at different sinuses, the maxillary sinus was the easiest to irrigate in most head positions, followed by frontal and ethmoid sinuses. The sphenoid sinus was the most difficult to irrigate, with the 90°-to-the-side being most effective at filling the sinus, and the 45°-to-the-side being slightly less effective. The ethmoid sinuses were most effectively penetrated at the 90°-to-the-side and 90° forward head positions (Figure 5D). Sinuses that had been operated on had significantly better irrigation outcomes than those that had not in for both backfill and conventional irrigation methods (Operated: backfill = 1.465, conventional = 1.21; Non-operated: backfill = 0.071, conventional = 0.107, both P < .05). The averaged irrigation scores correlated significantly to the Lund-Mackay scores (Spearman r = .778, P < .05), however there was no correlation between Lund-Mackay and SNOT-22 score.
Discussion
Significant variations exist between different subjects in the effectiveness of sinus penetration by nasal irrigation. In this study, despite each model being tested in identical head positions, no 2 models had the same irrigation outcome, aside from those that were completely ineffective. There were significant differences in sinus anatomy for each subject, resulting in differences in sinus penetration during the irrigation.10 This presents an obvious clinical challenge when patients are typically instructed to irrigate their nasal cavity using a standardized technique. Irrigations were more effective in some subjects (ie, subjects 1, 5, and 8) than others (ie, 2, 3, 4, 6, 7), with head positioning, backfill/conventional method, and history of sinus surgery being important parameters affecting irrigation outcome. The success rate of the irrigations significantly correlated to Lund Mackay scores (Spearman r = .778, P < .05), but not to patients’ SNOT-22 score.
There are several important observations in this study that can potentially improve future clinical outcomes. First, we can recommend 90° forward head positioning for frontal sinus-specific disease. For disease involving any of the other sinuses, 90° head tilt to the side would be preferable. While the 90° side tilt was the best option for sphenoid sinus penetration in this study, irrigation was still less effective at penetrating the sphenoid sinuses compared to the other sinuses, even in patients with a history of surgery involving the sphenoid sinuses. Sphenoid sinus-specific disease may require further studies examining more drastic head positions, for example, nose to ceiling.5
Surprisingly, the most natural head positions for typical irrigations (45°-to-the-side or combined with 45° forward tilt) generally produced the worst outcomes using the conventional method. To mitigate this, we recommend using the backfill method when the head is tilted to the side. Both the 90°-to-the-side and the 45° forward/45°-to-the-side head positions were significantly superior using the backfill method compared to the conventional, while the 45°-to-the-side follows the same trend and may become significantly if given a greater sample size. Using backfill instead of conventional irrigation can be a simple recommendation to improve sinus penetration for most patients.
Finally, hospitals and clinics with 3D printing capabilities can produce effective, personalized irrigation techniques for patients with CRS, beyond the general guidelines that we observed. Given the large nasal anatomic variabilities14, creating a technique that maximizes sinus penetration for each individual patient would be the best possible treatment option. The cost of 3D printing has decreased over time. For example, our printers cost about $3000, and each model costs $300. However, 3D printing may still not be widely available in many disadvantaged regions. Because of this, it is practical to identify generalizations that can be made from this and future studies to help optimize treatment with nasal sinus irrigation.
A reasonable follow-up to this study could examine clinical outcomes using personalized irrigation methods to confirm the clinical impact of improved sinus penetration with increased sample size. Collecting prospective clinical outcomes of the intervention as well as additional patient education values could provide definitive support to our findings. Additionally, the examination of further head positions and/or motorized irrigation to optimize sphenoid sinus penetration would be of clinical value. Chronic sphenoid sinusitis is historically unresponsive to medical management, and usually requires surgery,15 so finding an optimal medication delivery method to the sphenoid sinus could benefit these patients.
Limitations of this study include: the retrospective nature and heterogonous patient cohort, although the expectation was to present pilot data of which we can use our preliminary findings to guide more in-depth and homogeneous studies the future. Second, the nasal mucosa is a dynamic structure, while a CT scan is just a snapshot at one point in time. Therefore, the 3D printed models are not always a perfect representation of a subject’s nasal anatomy. Third, the contact surface properties between the fluid and the 3D printed acrylic surface is different than with true nasal mucosal tissue, which may further impact nasal irrigation outcomes. We plan on conducting future studies to address these limitations by using a 3D printer with greater precision which is capable of printing different hydrophilic material as well as coating the interior model wall with artificial mucous.
Conclusions
3D modeling may be used to personalize nasal irrigation to improve the topical steroid delivery to the diseased sinuses. Of the head positions tested, the 90° forward was the best option for treating frontal sinus disease, while the 90°-to-the-side position was optimal for all other sinuses. If a patient is tilting their head to the side while irrigating, the backfill method is a superior option to the conventional method.
Supplementary Material
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: NIH NIDCD R01 DC020302 to KZ.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Supplemental Material
Supplemental material for this article is available online.
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