Influence of the location of nasal polyps on olfactory airflow and olfaction

The Effect of the Nasal Structure on the Olfactory Cleft Airflow: A Systematic Review

OBJECTIVE

Conductive olfactory losses mainly involve obstruction of the olfactory cleft (OC) and diminished OC airflow. This study investigated the association between abnormal nasal structure and OC airflow.

METHODS

A systematic search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis to identify studies on the effect of the nasal structure on the OC airflow and olfaction.

RESULTS

A total of 11 studies were included. Nasal vestibule morphological variabilities directly impact the transport of molecules in odorant-laden air to the OC. A greater airflow vortex and a narrower vestibule region intensified the airflow vortex toward the olfactory region. Middle turbinectomy significantly increased the average flux to the OC. The location of the major airflow and airflow velocity maxima shifted towards the OC in patients with septal deviation. The airflow has been redirected into the upper part of the nasal airway in patients with inferior turbinate hypertrophy. For patients with unilateral cleft lip, unilateral nasal airflow on the cleft side has a lower rate and flow. The mean velocity in the posterior OC correlated well with olfaction compared to that in the anterior OC. The nasal polyps (NP) within the middle meatus increased the olfactory airflow but did not enhance the olfaction. NP in the olfactory region or anterior to the olfactory region significantly decreased the olfactory airflow and olfaction. Furthermore, obstruction of the OC did not change the nasal patency. When the OC shape presented with a stenotic slit or lumen structure among patients with conductive olfactory dysfunction without NP, the inspiratory velocity and flow rate within OC were significantly lower than in the healthy control group.

CONCLUSION

Various nasal structural factors affect patterns of OC airflow and olfaction. Identifying the related airflow-limiting structures may promote the comprehensive evaluation of conductive olfactory losses in patients with olfactory dysfunction.

A new surgical technique to increase airflow in the olfactory cleft: superior turbinate lateralization procedure

BACKGROUND

The olfactory cleft (OC) is the most important anatomical site for the maintenance of olfactory function. Obstruction of airflow in the OC by various conditions, such as inflammation, leads to poor olfactory function. Therefore, it is important to increase OC airflow while performing endoscopic sinus surgery (ESS). However, no technique to increase airflow has yet been established.

METHODS

We designed a superior turbinate lateralization (STL) procedure that displaces the entire ST bone laterally by eliminating the connection between the posterior ST and the anterior wall of the sphenoid sinus. The effect of the STL procedure was investigated in terms of anatomy and olfactory function.

RESULTS

ESS with the STL procedure was performed on seven patients with chronic rhinosinusitis and nasal polyps. The cross-sectional area of the OC at 3 months postoperatively was significantly larger than that before ESS. In addition, the Open Essence test and questionnaires revealed significantly improvements in sense of smell. Airflow in the OC was significantly higher in STL procedure group than in the non-STL procedure group.

CONCLUSION

The STL procedure enlarges the bony framework of the OC, and by increasing OC airflow, facilitates the transport of odorants to the olfactory epithelium, thereby improving olfactory perception.

Characterizing Olfactory Dysfunction in Patients with Unilateral Cleft Lip Nasal Deformities

Background: Unilateral cleft lip nasal deformity (uCLND) is associated with olfactory dysfunction, but the underlying etiology remains poorly understood. Objective: To investigate the etiology of uCLND-associated olfactory dysfunction using clinical, computational, and histologic assessments. Methods: Inclusion criteria: uCLND patients >16 years undergoing septorhinoplasty. Exclusion criteria: prior septoplasty or rhinoplasty, pregnancy, sinusitis. Measured outcomes: patient-reported scores, rhinomanometry, smell identification and threshold tests, computational fluid dynamics (CFD) airflow simulations, and histologic analysis of olfactory epithelium. Results: Five uCLND subjects were included: 18-23 years, three male and two female, four left-sided cleft and one right-sided cleft. All subjects reported moderate to severe nasal obstruction. Smell identification and threshold tests showed varying degrees of hyposmia. Nasal resistance was higher on the cleft side versus noncleft side measured by rhinomanometry (median 3.85 Pa-s/mL, interquartile range [IQR] = 21.96, versus 0.90 Pa-s/mL, IQR = 5.17) and CFD (median 1.04 Pa-s/mL, IQR = 0.94 vs. 0.11 Pa-s/mL, IQR = 0.12). Unilateral olfaction varied widely and was dependent on unilateral percentage olfactory airflow. Biopsies revealed intact olfactory neuroepithelium. Conclusions: uCLND-associated olfactory dysfunction appears to be primarily conductive in etiology and highly susceptible to variations in nasal anatomy. Clinical Trial Registration number: NCT04150783.

Olfaction Now and in the Future in CRSwNP

BACKGROUND

Chronic rhinosinusitis (CRS) is the leading cause of olfactory dysfunction in the general population. Olfactory dysfunction is more common in patients with CRS with nasal polyposis (CRSwNP) compared to those without polyps.

PURPOSE

The present review aims to summarize the current literature on the mechanism behind olfactory dysfunction in CRSwNP and the impact of therapy on olfactory outcomes in this patient population.

METHODS

A comprehensive review of the available literature on olfaction in CRSwNP was performed. We evaluated the most recent evidence from studies on the mechanisms behind smell loss in CRSwNP and the impact of medical and surgical therapy for CRS on olfactory outcomes.

RESULTS

The mechanism behind olfactory dysfunction in CRSwNP is not completely understood, but evidence from clinical research and animal models suggests both an obstructive component causing conductive olfactory loss and an inflammatory response in the olfactory cleft leading to sensorineural olfactory loss. Oral steroids and endoscopic sinus surgery have both shown efficacy in improving olfactory outcomes in CRSwNP in the short term; however, the long-term response of these treatments remains uncertain. Newer targeted biologic therapies, such as dupilumab, have also shown remarkable and durable improvement in smell loss for CRSwNP patients.

CONCLUSION

Olfactory dysfunction is highly prevalent in the CRSwNP population. Although significant advances have been made in our understanding of olfactory dysfunction in the setting of CRS, additional studies are needed to elucidate cellular and molecular changes mediated by type 2-mediated inflammation in the olfactory epithelium with potential downstream effects on the central olfactory system. Further identification of these underlying basic mechanisms will be vital for developing future therapies targeted to improve olfactory dysfunction in patients with CRSwNP.

The Impact of Adhesions on Nasal Airflow: A Quantitative Analysis Using Computational Fluid Dynamics

Background

Nasal adhesions (NAs) are a known complication of nasal airway surgery. Even minor NAs can lead to significant postoperative nasal airway obstruction (NAO). Division of such NAs often provides much greater relief than anticipated.

Objective

We examine the impact of NAs at various anatomical sites on nasal airflow and mucosal cooling using computational fluid dynamics (CFD) and multiple test subjects.

Methods

CT scans of healthy adult subjects were used to construct three-dimensional nasal airway computational models. A single virtual 2.5 mm diameter NA was placed at one of five sites commonly seen following NAO surgery within each nasal cavity bilaterally, resulting in 10 NA models and 1 NA-free control for each subject. CFD analysis was performed on each NA model and compared with the subject's NA-free control model.

Results

4 subjects were recruited to create 44 computational models. The NAs caused the airflow streamlines to separate, leading to a statistically significant increase in mucosal temperature immediately downstream to the NAs (wake region). Changes in the mucosal temperature in the wake region of the NAs were most prominent in anteriorly located NAs with a mean increase of 1.62 °C for the anterior inferior turbinate NAs ( P < .001) and 0.63 °C for the internal valve NAs ( P < .001).

Conclusion

NAs result in marked disruption to airflow patterns and reduced mucosal cooling on critical surfaces, particularly in the wake region. Reduced wake region mucosal cooling may be a contributing factor to the exaggerated perception of nasal obstruction experienced by patients with NAs.

Beyond aroma: A scoping review on the impact of chronic rhinosinusitis on retronasal olfaction

Background

Retronasal olfaction (RNO) refers to the perception of odorants inhaled through the mouth and carried through the nasopharynx to olfactory receptors within the olfactory cleft, enabling the perception of flavor. Although orthonasal olfactory dysfunction in chronic rhinosinusitis (CRS) has been widely described, the impact of CRS on RNO is less clear. In this study, we systematically review available literature to provide an update on RNO in the setting of CRS.

Methods

We systematically searched PubMed, Ovid Embase, Web of Science, and the Cochrane Library for studies examining RNO in patients with documented CRS. The primary outcome of interest was objective psychophysical measurement of olfaction, including characterization of RNO.

Results

We identified 404 unique references that underwent title and abstract review by two independent reviewers, with 52 articles undergoing full-text review, where 10 relevant studies underwent data extraction. Although outcome measures varied, all included studies demonstrated diminished RNO in patients with CRS. Of six studies evaluating the relationship between retronasal and orthonasal olfactory test scores in CRS patients two out of six (33%) demonstrated a correlation between both forms of olfaction and CRS, and two out of six studies (33%) found significantly lower orthonasal olfactory test scores compared to retronasal olfactory test scores. Two of three found significant improvement in RNO with treatment of underlying CRS. Of three studies examining patient reported outcome measures (PROMs) in CRS, two found significant associations between retronasal olfactory test scores and PROMs.

Conclusions

Based on the current literature, CRS patients appear to have diminished RNO, which may be associated with orthonasal olfactory dysfunction and decreased quality of life in this population. Higher level of evidence studies are required to further elucidate these relationships and the impact of medical and surgical CRS management on RNO.

Endoscopic modified transseptal bi-nostril approach for pituitary tumors. Efficacy of complex preservation of every turbinate and olfaction: A STROBE analysis

AIMS

Endoscopic modified transseptal bi-nostril approach minimizes turbinate and olfactory mucosal invasion and ensures preservation of the turbinates and bilateral olfaction. The main objective of this study was to investigate the pre- and postoperative variations in olfactory function in patients using this approach, and the secondary objective was to investigate the complications associated with the surgical procedure.

MATERIAL AND METHODS

This study is a single-center prospective cohort study using STROBE analysis. To completely protect the bilateral turbinates and olfactory epithelium, this procedure provided access to the sphenoid sinus by a transseptal approach via the left nasal cavity and by the olfactory cleft approach via the right nasal cavity without any turbinate resection. A T&T olfactometer was used to assess the mean recognition threshold of the left, right, and bilateral nasal passages before and after surgery, and complications associated with the surgical approach were investigated.

OBJECTIVES

We included 27 patients who underwent endoscopic modified transseptal pituitary surgery with an olfactory and turbinate preservation approach at our hospital between April 2018 and December 2019.

RESULTS

The mean postoperative recognition threshold of the right, left, and bilateral nasal cavities did not worsen (P<0.001 for all) relative to the preoperative values, and there was no difference in values between the right and left nasal cavities (P=0.85). The nasal turbinates were preserved in all patients during the study period, and no recurrence was observed.

CONCLUSION

Our modified EETSA could be implemented as an approach for turbinate and olfaction preservation.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

A comparison of central compartment atopic disease and lateral dominant nasal polyps

BACKGROUND

The characteristics and surgical outcomes of central compartment atopic disease (CCAD) vary by region and race. Therefore, we aimed to identify the risk factors, symptom severity, and prognosis of CCAD in the Asian population.

METHODS

This case-control study recruited patients diagnosed with chronic rhinosinusitis with nasal polyps who underwent functional endoscopic sinus surgery (FESS) at a tertiary hospital in Taiwan. Patients were classified into CCAD and lateral-dominant nasal polyp (LDNP) groups based on endoscopic and computed tomography imaging findings. The demographic data, symptom severity scores, and surgical outcomes of the 2 groups were analyzed.

RESULTS

Our study included 442 patients (CCAD group: n = 51; LDNP group: n = 391). We found that CCAD was strongly related to both asthma (9.8% vs 3.5%, p = 0.04) and allergic rhinitis symptoms (43.3% vs 26.6%, p = 0.01). Higher eosinophil counts were detected in blood serum (5.8% vs 2.8%, p < 0.01) and histopathologic profiles (57.0 vs 17.3, p < 0.01) among patients with CCAD. Improvements in 22-item Sino-Nasal Outcome Test (SNOT-22) score and mucociliary clearance time (MCT) after surgical intervention revealed that the CCAD group had a better response to FESS (SNOT-22 score: -31.82 vs -22.66, p < 0.01; MCT: -233.06 vs -191.93 seconds, p = 0.03). The revision FESS rate was not different between the 2 groups.

CONCLUSION

Polyps originating from the central compartment were found to be related to asthma and allergic rhinitis in Taiwanese patients. A higher eosinophil count was suggested in both serum and local nasal tissue from patients with CCAD. FESS serves as an effective treatment for symptom relief in patients with CCAD.

CFD SIMULATIONS AND ANALYSES OF ASYMPTOMATIC AND SYMPTOMATIC NASAL AIRWAY OBSTRUCTIONS

The numerical simulations of the flow in nasal airways were performed for two different clinical cases. The results comprised the distributions of scalars at five different sections and included contours of pressure, velocity magnitude, turbulent kinetic energy and vorticity magnitude. Simulations showed the air branching occurring at the inferior meatus is unaffected by the variations in the volumetric flow rate or the changes in the flow regime through the olfactory cleft. However, the contractions and the following rapid change in the cross-section of the nasopharynx preclude the upward penetration of the vacuum field set by the lungs during the inhalation process. As a result, considerably low velocities and significant cross-sectional nonuniformities are observed, which lead to the appearances of the secondary flow structures and strong unsteadiness. Increased interactions between the airflow and the walls of the nasal cavity resulted in an increase in the vorticity on the right middle meatus and upper inferior meatus. The vorticity was also very high in the nostrils, where the flow was not fully developed.

The impact of nasal adhesions on airflow and mucosal cooling - A computational fluid dynamics analysis

Nasal adhesions are a known postoperative complication following surgical procedures for nasal airway obstruction (NAO); and are a common cause of surgical failure, with patients often reporting significant NAO, despite relatively minor adhesion size. Division of such nasal adhesions often provides much greater relief than anticipated, based on the minimal reduction in cross-sectional area associated with the adhesion. The available literature regarding nasal adhesions provides little evidence examining their quantitative and qualitative effects on nasal airflow using objective measures. This study examined the impact of nasal adhesions at various anatomical sites on nasal airflow and mucosal cooling using computational fluid dynamics (CFD). A high-resolution CT scan of the paranasal sinuses of a 25-year-old, healthy female patient was segmented to create a three-dimensional nasal airway model. Virtual nasal adhesions of 2.5 mm diameter were added to various locations within the nasal cavity, representing common sites seen following NAO surgery. A series of models with single adhesions were created. CFD analysis was performed on each model and compared with a baseline no-adhesion model, comparing airflow and heat and mass transfer. The nasal adhesions resulted in no significant change in bulk airflow patterns through the nasal cavity. However, significant changes were observed in local airflow and mucosal cooling around and immediately downstream to the nasal adhesions. These were most evident with anterior nasal adhesions at the internal valve and anterior inferior turbinate. Postoperative nasal adhesions create local airflow disruption, resulting in reduced local mucosal cooling on critical surfaces, explaining the exaggerated perception of nasal obstruction. In particular, anteriorly located adhesions created greater disruption to local airflow and mucosal cooling, explaining their associated greater subjective sensation of obstruction.

Can computational fluid dynamic models help us in the treatment of chronic rhinosinusitis

PURPOSE OF REVIEW

The aim of this study was to review the recent literature (January 2017-July 2020) on computational fluid dynamics (CFD) studies relating to chronic rhinosinusitis (CRS), including airflow within the pre and postoperative sinonasal cavity, virtual surgery, topical drug and saline delivery (sprays, nebulizers and rinses) and olfaction.

RECENT FINDINGS

Novel CFD-specific parameters (heat flux and wall shear stress) are highly correlated with patient perception of nasal patency. Increased ostial size markedly improves sinus ventilation and drug delivery. New virtual surgery tools allow surgeons to optimize interventions. Sinus deposition of nasal sprays is more effective with smaller, low-inertia particles, outside of the range produced by many commercially available products. Saline irrigation effectiveness is improved using greater volume, with liquid entering sinuses via 'flooding' of ostia rather than direct jet entry.

SUMMARY

CFD has provided new insights into sinonasal airflow, air-conditioning function, the nasal cycle, novel measures of nasal patency and the impact of polyps and sinus surgery on olfaction. The deposition efficiency of topical medications on sinus mucosa can be markedly improved through parametric CFD experiments by optimising nasal spray particle size and velocity, nozzle angle and insertion location, while saline irrigation effectiveness can be optimized by modelling squeeze bottle volume and head position. More sophisticated CFD models (inhalation and exhalation, spray particle and saline irrigation) will increasingly provide translational benefits in the clinical management of CRS.

Correlation of mucus inflammatory proteins and olfaction in chronic rhinosinusitis

BACKGROUND

Chronic rhinosinusitis (CRS) is one of the most common causes of olfactory loss, but the pathophysiology underlying olfactory dysfunction in CRS has not been fully elucidated. Previous studies found correlations between olfactory cleft (OC) inflammatory cytokines/chemokines and olfaction in CRS. The purpose of this study was to evaluate the relationship between OC mucus inflammatory proteins and olfaction in a multi-institutional cohort.

METHODS

Adults with CRS were prospectively recruited. Demographics, comorbidities, olfactory assessment (Sniffin' Sticks), computed tomography (CT), and OC mucus for protein analysis were collected. Statistical analysis was performed to determine associations between olfactory function, OC mucus protein concentrations, and CT opacification.

RESULTS

Sixty-two patients were enrolled in the study, with an average age of 48.2 (standard deviation, 16.2) years, and 56.5% were female and 59.7% were classified as CRS with nasal polyps (CRSwNP). Ten of 26 OC mucus proteins were significantly correlated with threshold, discrimination, and identification (TDI) scores and OC opacification. Subgroup analysis by polyp status revealed that, within the CRSwNP group, C-C motif ligand 2 (CCL2), interleukin-5 (IL-5), IL-6, IL-13, IL-10, IL-9, tumor necrosis factor-α (TNF-α), CCL5, and CCL11 were significantly correlated with olfaction. For CRS without nasal polyps (CRSsNP), only C-X-C ligand 5 (CXCL5) showed a correlation. In CRSwNP, IL-6, IL-10, vascular endothelial growth factor-A, and immunoglobulin E (IgE) correlated with OC opacification, whereas, in CRSsNP, only CXCL5 showed a correlation. OC mucus proteins and Lund-Mackay score correlated only in the CRSsNP group (CXCL5, IL-5, IL-13, IgE).

CONCLUSION

Several OC mucus proteins have been found to correlate with olfactory function and OC opacification. The profile of OC mucus proteins differs between CRSsNP and CRSwNP subgroups, suggesting different mechanisms between groups, but further study is required.

In silico approaches to respiratory nasal flows: A review

The engineering discipline of in silico fluid dynamics delivers quantitative information on airflow behaviour in the nasal regions with unprecedented detail, often beyond the reach of traditional experiments. The ability to provide visualisation and analysis of flow properties such as velocity and pressure fields, as well as wall shear stress, dynamically during the respiratory cycle may give significant insight to clinicians. Yet, there remains ongoing challenges to advance the state-of-the-art further, including for example the lack of comprehensive CFD modelling on varied cohorts of patients. The present article embodies a review of previous and current in silico approaches to simulating nasal airflows. The review discusses specific modelling techniques required to accommodate physiologically- and clinically-relevant findings. It also provides a critical summary of the reported results in the literature followed by an outlook on the challenges and topics anticipated to drive research into the future.

Decreased ciliary beat responsiveness to acetylcholine in the nasal polyp epithelium

OBJECTIVE

We investigated the difference in ciliary beat responsiveness to acetylcholine in ex vivo and the difference in the expressions of associated molecules (M1/M3 muscarinic receptors, pannexin-1 and P2X7 purinergic receptor) between the nasal polyp and turbinate mucosa.

STUDY DESIGN

Laboratorial study.

PARTICIPANTS

Nasal polyp and inferior turbinate were collected from patients with hypertrophic rhinitis and/or nasal polyp during endoscopic sinonasal surgery.

MAIN OUTCOME MEASURES

The mucosa was cut into thin strips, and ciliary movement was observed under a phase-contrast light microscope equipped with a high-speed digital video camera. The samples were also examined by scanning electron microscopy, fluorescence immunohistochemistry, and quantitative reverse transcription-polymerase chain reaction.

RESULTS

Cilia were well preserved in both tissues at the ultrastructural level. The baseline ciliary beat frequency (CBF) was not different between the two tissues. The CBF of the turbinate was significantly increased by stimulation with acetylcholine (P < 0.001), but that of the polyp was not. The ratio of the acetylcholine-stimulated CBF to the baseline CBF was significantly lower in the polyp than in the turbinate (P < 0.001). Immunohistochemical study revealed that immunoreactivities for M3, pannexin-1 and P2X7 were weaker in the polyp than in the turbinate. The mRNA expressions of M1, M3 and P2X7 were significantly lower and that of pannexin-1 tended to be lower in the polyp than in the turbinate.

CONCLUSIONS

These results indicate that ciliary beat responsiveness to acetylcholine is decreased in the nasal polyp. This may be explained by the decreased expressions of M3, P2X7 and probably pannexin-1 in this tissue.

Patterns of olfactory dysfunction in chronic rhinosinusitis identified by hierarchical cluster analysis and machine learning algorithms

BACKGROUND

Olfactory dysfunction is a common symptom of chronic rhinosinusitis (CRS). We previously identified several cytokines potentially linked to smell loss, potentially supporting an inflammatory etiology for CRS-associated olfactory dysfunction. In the current study we sought to validate patterns of olfactory dysfunction in CRS using hierarchical cluster analysis, machine learning algorithms, and multivariate regression.

METHODS

CRS patients undergoing functional endoscopic sinus surgery were administered the Smell Identification Test (SIT) preoperatively. Mucus was collected from the middle meatus using an absorbent polyurethane sponge and 17 inflammatory mediators were assessed using a multiplexed flow-cytometric bead assay. Hierarchical cluster analysis was performed to characterize inflammatory patterns and their association with SIT scores. The random forest approach was used to identify cytokines predictive of olfactory function.

RESULTS

One hundred ten patients were enrolled in the study. Hierarchical cluster analysis identified 5 distinct CRS clusters with statistically significant differences in SIT scores observed between individual clusters (p < 0.001). A majority of anosmic patients were found in a single cluster, which was additionally characterized by nasal polyposis (100%) and a high incidence of allergic fungal rhinosinusitis (50%) and aspirin-exacerbated respiratory disease (AERD) (33%). A random forest approach identified a strong association between olfaction and the cytokines interleukin (IL)-5 and IL-13. Multivariate modeling identified AERD, computed tomography (CT) score, and IL-2 as the variables most predictive of olfactory function.

CONCLUSION

Olfactory dysfunction is associated with specific CRS endotypes characterized by severe nasal polyposis, tissue eosinophilia, and AERD. Mucus IL-2 levels, CT score, and AERD were independently associated with smell loss.