Stenting the Eustachian tube to treat chronic otitis media - a feasibility study in sheep

First Investigation of a Eustachian Tube Stent in Experimentally Induced Eustachian Tube Dysfunction

Unmet needs in the treatment of chronic otitis media and Eustachian tube dysfunction (ETD) triggered the development of stents for the Eustachian tube (ET). In this study, for the first time, stents were placed in an artificially blocked ET to evaluate stent function. Eight adult female sheep were injected with stabilized hyaluronic acid (HA) on both sides to induce ETD. Subsequently, a tapered nitinol ET stent was inserted on one side, and animals were examined bilaterally by endoscopy, tympanometry, cone beam computed tomography, and final histology. Seven of the stents were placed in the desired cartilaginous portion of the ET. At the end of the study, one stented side appeared slightly open; all other ET orifices were closed. Tympanometry revealed re-ventilation of the middle ear in four out of seven correctly stented animals within 3 to 6 weeks after stent insertion. The major amount of HA was found at the pharyngeal orifice of the ET anterior to the stent. Thus, the stent position did not completely align with the HA position. While a functional analysis will require refinement of the experimental setup, this study provides first promising results for stent insertion in a sheep model of ETD.

Long-Term Preclinical Evaluation of a Permanent Stent Developed for the Human Eustachian Tube

The Eustachian tube (ET) is a bottleneck when it comes to middle ear (ME) health. If its function is impaired, this can lead to serious consequences for the patient, such as hearing problems or deafness. Therefore, this study investigated a tapered nitinol stent (3-5 mm × 14 mm) for the human ET as a potential new permanent treatment for chronic Eustachian tube dysfunction (ETD) and thus ME ventilation disorders. The self-expanding stent was inserted unilaterally into the ET of 24 sheep with observation periods of 3, 6, and 12 months. Local tissue effects and the safety of the stent insertion were analyzed based on regular endoscopic checks, weekly tympanometry measurements, final imaging, and histological examinations. The animals showed no stent-related health restrictions. However, the individual anatomy and stenting procedure had an influence on the results. The tissue reaction in the endoscopic examinations was mild even though no concomitant antibiotics were administered. After all three monitoring periods, stented ETs had a significantly larger ET lumen than the non-stented contralateral ETs. However, tissue growth was detected in the stent. Overall, the first long-term study on an ET stent showed that the tapered ET stent could be a promising treatment option for ETD.

Investigation of Stent Prototypes for the Eustachian Tube in Human Donor Bodies

Chronic otitis media is often connected to Eustachian tube dysfunction. As successful treatment cannot be guaranteed with the currently available options, the aim is to develop a stent for the Eustachian tube (ET). Over the course of this development, different prototypes were generated and tested in ex vivo experiments. Four different prototypes of an ET stent and one commercially available coronary stent were implanted in the ET of seven human donor bodies. The position of the stents was verified by cone beam CT. The implanted ETs were harvested, embedded in resin and ground at 200 µm steps. Resulting images of the single steps were used to generate 3D models. The 3D models were then evaluated regarding position of the stent in the ET, its diameters, amount of squeezing, orientation of the axes and other parameters. Virtual reconstruction of the implanted ET was successful in all cases and revealed one incorrect stent placement. The cross-section increased for all metal stents in direction from the isthmus towards the pharyngeal orifice of the ET. Depending on the individual design of the metal stents (open or closed design), the shape varied also between different positions along a single stent. In contrast, the cross-section area and shape remained constant along the polymeric prototype. With the current investigation, insight into the behavior of different prototypes of ET stents was gained, which can help in defining the specifications for the intended ET stent.

Comparative study of optical coherence tomograph and histological images of eustachian tube nasopharyngeal region and adjacent structures in vivo and ex-vivo miniature pigs

OBJECTIVES

Optical Coherence Tomograph (OCT) imaging technology can be used to examine, in vivo, the human ET. At present, it is impossible to achieve the OCT scanning vivo and ex vivo in the same individual human body, or study the consistency between OCT images and histological images of the eustachian tube nasopharyngeal region and adjacent structures. The aim of this study was to determine the consistency between OCT images and histological sections in vivo and ex vivo in miniature pigs.

METHODS

OCT imaging was performed on five adult miniature pigs in vivo and ex vivo. The images of the eustachian tube OCT (ET-OCT), nasopharynx OCT (NP-OCT) and histological cross sections were further studied.

RESULTS

All five miniature pigs achieved the OCT scan successfully, acquiring ET-OCT and NP-OCT images in vivo and ex vivo on both sides. The acquired ET OCT images closely matched the histological images, revealing details of the cartilage, submucosa, glands, and mucosa. The lower segment of the ET wall mucosa had an abundance of glands and submucosal tissues, with more low-signal areas appearing in the ex vivo images. The NP-OCT images of the nasopharynx matched the details of the mucosa and submucosal tissues. The ex-vivo OCT images showed thicker mucosa and more scattered slightly lower signal areas compared to the vivo OCT images.

CONCLUSIONS

ET-OCT images and NP-OCT images matched the histological structure of eustachian tube nasopharyngeal region structures in miniature pigs both in vivo and ex vivo. OCT images may be sensitive to changes in edema and ischemia status. There is a great potential for morphological assessment of inflammation, edema, injure, mucus gland status.

Preliminary results of absorbable magnesium stent for treating eustachian tube dysfunction in a porcine model

Absorbable magnesium (Mg) stents have an attractive biocompatibility and rapid degradation rate, but their degradable behavior and efficacy in the Eustachian tube (ET) have not yet been investigated. In this study, the degradable behavior of the Mg stent in artificial nasal mucus was evaluated. The Mg stents in the porcine ET model were also investigated to evaluate their safety and efficacy. Four Mg stents were placed into the four ETs of two pigs. The mass loss rate of the Mg stents gradually decreased over time. The decrease rates were 30.96% at one week, 49.00% at two weeks, and 71.80% at four weeks. On the basis of histological findings, the thickness of submucosal tissue hyperplasia and the degree of inflammatory cell infiltration significantly decreased at four weeks compared with two weeks. Biodegradation of the Mg stent occurred before tissue proliferative reactions, and the ET patency was successfully maintained without stent-induced tissue hyperplasia at four weeks. The Mg stent that biodegrades rapidly seems to be effective and safe in porcine ET. Further investigation is required to verify the optimal stent shape and indwell period in the ET.

Intravascular Ultrasonography (IVUS)-A Tool for Imaging the Eustachian Tube?

The Eustachian tube (ET) has a key role in the pathogenesis of otitis media. Until now, there has been a lack of meaningful imaging methods to investigate the ET and its surrounding tissue. The aim of the current study was to investigate the possibilities of imaging the ET using Intravascular Ultrasonography (IVUS). ETs from sheep were scanned ex vivo and in vivo with different IVUS probes. In addition to native ETs, water was also used to improve coupling. Scans were subsequently compared with histological sections and a 3D model of the ET. In addition, ETs with a stenosis induced by a hyaluronic acid depot, after stent insertion, and during lower jaw movement were examined. The IVUS catheter was inserted into the ET lumen without any problems or injuries in all cases. The surrounding structures of the ET were identified in the ultrasound image. In addition, a change in size of the ET lumen due to movement was observed, and the position of the stent and the depot of hyaluronic acid could be examined. With the use of IVUS, a non-invasive possibility to examine the ET over its course with the adjacent structures as well as after different treatments is presented.

Tapered self-expandable metallic stent optimized for Eustachian tube morphology in a porcine ET model

Several investigations on the feasibility of stent placement into the Eustachian tube (ET) are being conducted. However, stents optimized for the anatomical structure of the ET have not yet been developed. In this study, the efficacy and safety of a self-expandable metallic stent (SEMS) optimized for porcine ET morphology was investigated. Silicone was injected into a cadaveric porcine ET to analyze the ET morphology. The three-dimensional-reconstructed porcine ET phantom images obtained after a computed tomography scan were measured to determine the dimensions of the porcine ET. The SEMS was designed as a tapered structure on the basis of the morphological findings of the porcine ET. The tapered SEMS (T-SEMS) and conventional SEMS (C-SEMS) were placed into the porcine ET to compare the safety and efficacy of the two types of SEMSs. Stent-induced tissue hyperplasia in the T-SEMS group was significantly lower than that in the C-SEMS group (p < 0.001). The T-SEMS optimized for the porcine ET was effective in maintaining stent patency. T-SEMS seems to be better than C-SEMS in suppressing stent-induced tissue hyperplasia, owing to the reduced stent-mediated mechanical injuries and maintaining ET patency.

Development of an In Vivo Model for Eustachian Tube Dysfunction

Otitis media is often connected to Eustachian tube dysfunction (ETD). Until now, there was no large animal model available for the examination of new treatment methods such as stents for the Eustachian tube (ET). Thus, the aim of the study was to develop a method to reproducibly induce ETD by injection of fillers and without permanent closure of the ET. Tools for safe injection of hyaluronic acid (HA) in the surrounding of the ET were developed. In ex vivo experiments, HA mixed with Imeron® was injected close to the nasopharyngeal orifice of the ET of blackface sheep. The established depot was visualized using cone beam computer tomography and magnetic resonance imaging, and stents could be placed into the ET. A reliable position of the HA depot was achieved. This method was transferred to in vivo, and middle ear ventilation was investigated by tympanometry. ETD was achieved with amounts of 2.5 mL HA or higher. None of the animals showed any sign of discomfort or complications. The induced ETD lasted for 3 to 13 (maximum observation period) weeks and was also combined with middle ear effusion. A model of ETD based on injection of HA next to the ET was successfully established and is now available to test novel treatment options for ET functionality.

Sirolimus-eluting cobalt-chrome alloy stent suppresses stent-induced tissue hyperplasia in a porcine Eustachian tube model

Various preclinical studies with developed Eustachian tube (ET) stents are in progress but have not yet been clinically applied. ET stent is limited by stent-induced tissue hyperplasia in preclinical studies. The effectiveness of sirolimus-eluting cobalt–chrome alloy stent (SES) in suppressing stent-induced tissue hyperplasia after stent placement in the porcine ET model was investigated. Six pigs were divided into two groups (i.e., the control and the SES groups) with three pigs for each group. The control group received an uncoated cobalt–chrome alloy stent (n = 6), and the SES group received a sirolimus-eluting cobalt–chrome alloy stent (n = 6). All groups were sacrificed 4 weeks after stent placement. Stent placement was successful in all ETs without procedure-related complications. None of the stents was able to keep its round shape as original, and mucus accumulation was observed inside and around the stent in both groups. On histologic analysis, the tissue hyperplasia area and the thickness of submucosal fibrosis were significantly lower in the SES group than in the control group. SES seems to be effective in suppressing stent-induced tissue hyperplasia in porcine ET. However, further investigation was required to verify the optimal stent materials and antiproliferative drugs.

Application of New Materials in Auditory Disease Treatment

Auditory diseases are disabling public health problems that afflict a significant number of people worldwide, and they remain largely incurable until now. Driven by continuous innovation in the fields of chemistry, physics, and materials science, novel materials that can be applied to hearing diseases are constantly emerging. In contrast to conventional materials, new materials are easily accessible, inexpensive, non-invasive, with better acoustic therapy effects and weaker immune rejection after implantation. When new materials are used to treat auditory diseases, the wound healing, infection prevention, disease recurrence, hair cell regeneration, functional recovery, and other aspects have been significantly improved. Despite these advances, clinical success has been limited, largely due to issues regarding a lack of effectiveness and safety. With ever-developing scientific research, more novel materials will be facilitated into clinical use in the future.

Functional aspects of the Eustachian tube by means of 3D-modeling

The extent of dysfunction of the Eustachian tube (ET) is relevant in understanding the pathogenesis of secondary otological diseases such as acute or chronic otitis media. The underlying mechanism of ET dysfunction remains poorly understood except for an apparent genesis such as a nasopharyngeal tumor or cleft palate. To better describe the ET, its functional anatomy, and the biomechanical valve mechanism and subsequent development of diagnostic and interventional tools, a three-dimensional model based on thin-layer histology was created from an ET in this study. Blackface sheep was chosen as a donor. The 3-D model was generated by the coherent alignment of the sections. It was then compared with the cone-beam computed tomography dataset of the complete embedded specimen taken before slicing. The model shows the topographic relation of the individual components, such as the bone and cartilage, the muscles and connective tissue, as well as the lining epithelium with the lumen. It indicates a limited spiraling rotation of the cartilaginous tube over its length and relevant positional relationships of the tensor and levator veli palatine muscles.

Morphological Analysis of the Adult Eustachian Tube: A Fresh-Frozen Human Cadaver Study

OBJECTIVES

To evaluate the dilated Eustachian tube (ET) anatomy configuration using fresh human cadavers.

METHODS

Fourteen ears from human cadavers were used to identify the ET configuration. The cadaver head was cut in the sagittal plane parallel to the nasal septum, dividing it into right and left sides. Silicone was then inserted into the ET through the nasopharyngeal orifice (NO). The volume and length of the impression were measured using 3D computed tomography imaging.

RESULTS

The ET lumen was found to narrow from the NO to the isthmus, and the ET surface was concave anteriorly and convex posteriorly. The lower portion of the ET lumen was the most dilated and displayed a narrow top. The average volume of the ET impression was 1.4 ± 0.5 ml. The total length of the posterior side was 30.5 ± 3.6 mm, and that of the anterior side was 26.3 ± 3.4 mm. The widest ET area of the NO was 10.1 ± 0.9 mm in height and 8.0 ± 1.5 mm in width. The preisthmus was 2.4 ± 0.4 mm in height and 1.3 ± 0.5 mm in width. The height and width were 8.37 and 5.33 mm at the 5 mm point from the NO, and 5.51 and 1.94 mm at the 20 mm point from the NO, respectively.

CONCLUSION

We evaluated the configuration of the cartilaginous ET lumen, which is the main target of balloon dilation, and our findings may give insights into this dilation process and assist with the further development of ET balloons and stents.

The expression of VEGF and VEGFR in endotoxin induced otitis media with effusion in rats

OBJECTIVE

To investigate the expression and correlation of vascular endothelial growth factor (VEGF) and its receptor with hypoxia-inducible factor-1 α (HIF-1 α) in otitis media with effusion (OME).

METHODS

A rat model of OME was induced by injection of lipopolysaccharide (LPS) into the middle ear. Hematoxylin and eosin (HE) staining was used to observe the pathomorphological changes of the tympanic cavity in the middle ear of rats. Immunohistochemistry (IHC), western blotting and RT-qPCR were used to determine the mRNA and protein expression of VEGF, VEGFR-1, VEGFR-2 and HIF-1α in mucosa of tympanic cavity mucosa, respectively.

RESULTS

In the OME group, the epithelial space of the middle ear mucosa was significantly thickened and infiltration of a large number of inflammatory cells was found on postoperative day (POD), and the otitis media basically subsided 2 weeks after operation. VEGF mRNA expression was significantly increased on POD 1, and its protein expression peaked on POD 3. HIF-1α mRNA expression was significantly increased and peaked on POD 1, while its protein expression began to increase on POD 3 and was significantly expressed in the middle ear mucosal epithelium. HIF-1α mRNA showed a positive correlation with VEGF mRNA and VEGFR-1 mRNA expression.

CONCLUSION

VEGF mainly plays a role in the acute phase of OME, and it is abundantly expressed mediated by HIF-1α. And then it play a role in vasodilatation and increase of vascular permeability, thus promoting the generation of middle ear effusion.

Dimensions and position of the Eustachian tube in Humans

Eustachian tube (ET) dysfunction is one of the causes for chronic otitis media. To develop new therapies such as stents to facilitate middle ear ventilation, a better knowledge on dimensions and positions of the ET in individual patients is necessary. Cone beam CT scans of 143 patients were retrospectively investigated. Parameters such as lengths of the ET and its cartilaginous and bony parts, diameters, angles as well as distance of the ostium from the nasal conchae were determined and evaluated for side, gender and age specific differences. The average length of the cartilaginous and bony tubes was smaller in women than men. The average deviation from the horizontal plane was 1.7° larger on the left side (35.4°) compared to the right side (33.7°). Tools to manipulate the ET or to insert stents into the ET should cover angles from at least 42° to 64°. The distance of the pharyngeal orifices from the conchae nasalis inferior increased with age, becoming most prominent above 70 years of age. This investigation provides necessary information to develop stents for human application and tools for safe positioning of the stents.

Panel 7 - Pathogenesis of otitis media - a review of the literature between 2015 and 2019

OBJECTIVE

To perform a comprehensive review of the literature from July 2015 to June 2019 on the pathogenesis of otitis media. Bacteria, viruses and the role of the microbiome as well as the host response are discussed. Directions for future research are also suggested.

DATA SOURCES

PubMed database of the National Library of Medicine.

REVIEW METHODS

PubMed was searched for any papers pertaining to OM pathogenesis between July 2015 and June 2019. If in English, abstracts were assessed individually for their relevance and included in the report. Members of the panel drafted the report based on these searches and on new data presented at the 20th International Symposium on Recent Advances in Otitis Media.

CONCLUSIONS

The main themes that arose in OM pathogenesis were around the need for symptomatic viral infections to develop disease. Different populations potentially having different mechanisms of pathogenesis. Novel bacterial otopathogens are emerging and need to be monitored. Animal models need to continue to be developed and used to understand disease pathogenesis.

IMPLICATIONS FOR PRACTICE

The findings in the pathogenesis panel have several implications for both research and clinical practice. The most urgent areas appear to be to continue monitoring the emergence of novel otopathogens, and the need to develop prevention and preventative therapies that do not rely on antibiotics and protect against the development of the initial OM episode.

Panel 1: Biotechnology, biomedical engineering and new models of otitis media

OBJECTIVE

To summarize recently published key articles on the topics of biomedical engineering, biotechnology and new models in relation to otitis media (OM).

DATA SOURCES

Electronic databases: PubMed, Ovid Medline, Cochrane Library and Clinical Evidence (BMJ Publishing).

REVIEW METHODS

Articles on biomedical engineering, biotechnology, material science, mechanical and animal models in OM published between May 2015 and May 2019 were identified and subjected to review. A total of 132 articles were ultimately included.

RESULTS

New imaging technologies for the tympanic membrane (TM) and the middle ear cavity are being developed to assess TM thickness, identify biofilms and differentiate types of middle ear effusions. Artificial intelligence (AI) has been applied to train software programs to diagnose OM with a high degree of certainty. Genetically modified mice models for OM have further investigated what predisposes some individuals to OM and consequent hearing loss. New vaccine candidates protecting against major otopathogens are being explored and developed, especially combined vaccines, targeting more than one pathogen. Transcutaneous vaccination against non-typeable Haemophilus influenzae has been successfully tried in a chinchilla model. In terms of treatment, novel technologies for trans-tympanic drug delivery are entering the clinical domain. Various growth factors and grafting materials aimed at improving healing of TM perforations show promising results in animal models.

CONCLUSION

New technologies and AI applications to improve the diagnosis of OM have shown promise in pre-clinical models and are gradually entering the clinical domain. So are novel vaccines and drug delivery approaches that may allow local treatment of OM.

IMPLICATIONS FOR PRACTICE

New diagnostic methods, potential vaccine candidates and the novel trans-tympanic drug delivery show promising results, but are not yet adapted to clinical use.

Intraluminal three-dimensional optical coherence tomography - a tool for imaging of the Eustachian tube?

OBJECTIVES

The cause of Eustachian tube dysfunction often remains unclear. Therefore, this study aimed to examine the feasibility and possible diagnostic use of optical coherence tomography in the Eustachian tube ex vivo.

METHODS

Two female blackface sheep cadaver heads were examined bilaterally. Three conditions of the Eustachian tube were investigated: closed (resting position), actively opened and stented. The findings were compared (and correlated) with segmented histological cross-sections.

RESULTS

Intraluminal placement of the Eustachian tube with the optical coherence tomography catheter was performed without difficulty. Regarding the limited infiltration depth of optical coherence tomography, tissues can be differentiated. The localisation of the stent was accurate as was the lumen.

CONCLUSION

The application of optical coherence tomography in the Eustachian tube under these experimental conditions is considered to be a feasible, rapid and non-invasive diagnostic method, with possible diagnostic value for determining the luminal shape and superficial lining tissue of the Eustachian tube.