Mastoid cavity dimensions and shape: method of measurement and virtual fitting of implantable devices

Status and Depth of Mastoid Antrum and the Pattern of Mastoid Pneumatization in Cases of Large, Subtotal Perforations and Posterosuperior Retraction Pockets (PSRP)

The present study aimed to evaluate the pneumatization status of the mastoid air cells in general with the depth and status of mastoid antrum in particular, in patients of chronic otitis media (COM). This is an observational cross-sectional study in sample size of 60 participants with large, subtotal perforation and posterosuperior retraction pocket (PSRP). Mean age with large central and subtotal perforation combined was 35.78 years, compared to 32.13 years in PSRP. Granulations seen in antrum in 71.6% and cholesteatoma observed in 15%. Mean depth of the mastoid antrum was 17.27 mm. A well pneumatized mastoid in 21.6%, diploic 28.3% and sclerotic in 50% was noted in this study. Chronic otitis media affects temporal bone pneumatization, particularly the mastoid antrum. Our findings indicate that the depth of the mastoid antrum is slightly greater in cholesteatoma cases due to bone erosion. As early intervention enhances postoperative quality of life by preserving or restoring auditory function, understanding the mastoid pneumatization and antrum depth is crucial for managing chronic otitis media effectively.

Anatomical Variations of the Epitympanum and the Usable Space for Middle Ear Implants Analyzed With CT-assisted Imaging Using a Tablet-based Software

OBJECTIVE

To evaluate interindividual anatomical variations of the epitympanum and the usable space for implantation of active middle ear implants (AMEI) as well as the usefulness of a tablet-based software to assess individual anatomy on computed tomography (CT) scans.

PATIENTS

CT scans of 126 patients, scheduled for cochlea implantation (50.8% men; 0.6-90.0 yr) without middle ear malformations or previous middle ear surgery and with slice thickness ≤0.7 mm were analyzed.

MAIN OUTCOME MEASURES

Since no standardized measurements to assess the size of the epitympanum are available, relevant distances were defined according to anatomical landmarks. Three independent raters measured these distances using a tablet-based software. Interrater correlation was computed to evaluate the quality of the measurement process. Descriptive data were analyzed for validation and for evaluation of interindividual anatomical variations. Influence of age and sex on the taken measurements was assessed.

RESULTS

No relevant correlation between age or sex and the anatomy of the epitympanum was found. Interrater correlation ranged from Spearman's ρ = 0.3-0.9 and there were significant differences between individual rater results for various combinations. Descriptive data revealed high interindividual anatomical variance of the epitympanum, especially regarding the distance between incus and skull base.

CONCLUSION

The reported descriptive data regarding the anatomy of the epitympanum emphasizes the importance of preoperative planning, especially since the height of the epitympanum showed great interindividual variance potentially limiting implantation of AMEIs. The herein used tablet-based software seems to be convenient for preoperative assessment of individual anatomy in the hand of otosurgeons.

Pediatric morphometric study to guide the optimized implantation of the Osia® 2 implant system

PURPOSE

Continuous technological advances result in the availability of new bone conduction hearing implants, of which their suitability for pediatric patients is of major concern. The Cochlear^TMOsia^® 2 is a new active osseointegrated steady-state implant system that uses digital piezoelectric stimulation to treat hearing loss. The implant in the United States was approved for patients aged 12 years and above, whereas the CE mark is independent of age, the only requirement is body weight of at least 7 kg. Therefore, further clinical studies are required to assess device characteristics in younger patients. The aim of our study was to perform a morphometric study among 5-12-year-old children, and to develop a surgical protocol for Osia 2 system implantation based on these findings.

METHODS

We examined retrospectively cranial CT scans of 5-12-year-old patients from our clinical database. We measured the bone and soft-tissue thickness in the region of interest, and the position of the sigmoid sinus. 3D printed temporal bones were also used for planning.

RESULTS

Soft-tissue thickness varied between 3.2 ± 0.5 mm and 3.6 ± 0.6 mm and bone thickness varied between 3.5 ± 1.1 mm and 4.7 ± 0.3 mm. The sigmoid sinus was located 1.3 ± 0.2 cm posterior to the ear canal, and the anterior distance was 4.8 ± 0.9 to 7.1 ± 1.1 mm.

CONCLUSIONS

Our morphometric studies showed that patients aged 5-12 have different anatomical dimensions compared to adults, but that implantation of the Osia 2 system is feasible in these patients using an altered implant positioning recommended by our data. The Cochlear™ Osia^® 2 is, therefore, an option for hearing rehabilitation in younger pediatrics.

Microfabricated reciprocating micropump for intracochlear drug delivery with integrated drug/fluid storage and electronically controlled dosing

The anatomical and pharmacological inaccessibility of the inner ear is a major challenge in drug-based treatment of auditory disorders. This also makes pharmacokinetic characterization of new drugs with systemic delivery challenging, because efficacy is coupled with how efficiently a drug can reach its target. Direct delivery of drugs to cochlear fluids bypasses pharmacokinetic barriers and helps to minimize systemic toxicity, but anatomical barriers make administration of multiple doses difficult without an automated delivery system. Such a system may be required for hair-cell regeneration treatments, which will likely require timed delivery of several drugs. To address these challenges, we have developed a micropump for controlled, automated inner-ear drug delivery with the ultimate goal of producing a long-term implantable/wearable delivery system. The current pump is designed to be used with a head mount for guinea pigs in preclinical drug characterization experiments. In this system, we have addressed several microfluidic challenges, including maintaining controlled delivery at safe, low flow rates and delivering drug without increasing the volume of fluid in the cochlea. By integrating a drug reservoir and all fluidic components into the microfluidic structure of the pump, we have made the drug delivery system robust compared to previous systems that utilized separate, tubing-connected components. In this study, we characterized the pump's unique infuse-withdraw and on-demand dosing capabilities on the bench and in guinea pig animal models. For the animal experiments, we used DNQX, a glutamate receptor antagonist, as a physiological indicator of drug delivery. DNQX suppresses compound action potentials (CAPs), so we were able to infer the distribution and spreading of the DNQX over time by measuring the changes in CAPs in response to stimuli at several characteristic frequencies.

Recent advances in local drug delivery to the inner ear

Inner ear diseases are not adequately treated by systemic drug administration mainly because of the blood-perilymph barrier that reduces exchanges between plasma and inner ear fluids. Local drug delivery methods including intratympanic and intracochlear administrations are currently developed to treat inner ear disorders more efficiently. Intratympanic administration is minimally invasive but relies on diffusion through middle ear barriers for drug entry into the cochlea, whereas intracochlear administration offers direct access to the colchlea but is rather invasive. A wide range of drug delivery systems or devices were evaluated in research and clinic over the last decade for inner ear applications. In this review, different strategies including medical devices, hydrogels and nanoparticulate systems for intratympanic administration, and cochlear implant coating or advanced medical devices for intracoclear administration were explored with special attention to in vivo studies. This review highlights the promising systems for future clinical applications as well as the current hurdles that remain to be overcome for efficient inner ear therapy.

The role of intracochlear drug delivery devices in the management of inner ear disease

INTRODUCTION

Diseases of the inner ear include those of the auditory and vestibular systems, and frequently result in disabling hearing loss or vertigo. Despite a rapidly expanding pipeline of potential cochlear therapeutics, the inner ear remains a challenging organ for targeted drug delivery, and new technologies are required to deliver these therapies in a safe and efficacious manner. In addition to traditional approaches for direct inner ear drug delivery, novel microfluidics-based systems are under development, promising improved control over pharmacokinetics over longer periods of delivery, ultimately with application towards hair cell regeneration in humans.

AREAS COVERED

Advances in the development of intracochlear drug delivery systems are reviewed, including passive systems, active microfluidic technologies and cochlear prosthesis-mediated delivery. This article provides a description of novel delivery systems and their potential future clinical applications in treating inner ear disease.

EXPERT OPINION

Recent progresses in microfluidics and miniaturization technologies are enabling the development of wearable and ultimately implantable drug delivery microsystems. Progress in this field is being spurred by the convergence of advances in molecular biology, microfluidic flow control systems and models for drug transport in the inner ear. These advances will herald a new generation of devices, with near-term applications in preclinical models, and ultimately with human clinical use for a range of diseases of the inner ear.

A microfluidic reciprocating intracochlear drug delivery system with reservoir and active dose control

Reciprocating microfluidic drug delivery, as compared to steady or pulsed infusion, has unique features which may be advantageous in many therapeutic applications. We have previously described a device, designed for wearable use in small animal models, that periodically infuses and then withdraws a sub-microliter volume of drug solution to and from the endogenous fluid of the inner ear. This delivery approach results in zero net volume of liquid transfer while enabling mass transport of compounds to the cochlea by means of diffusion and mixing. We report here on an advanced wearable delivery system aimed at further miniaturization and complex dosing protocols. Enhancements to the system include the incorporation of a planar micropump to generate reciprocating flow and a novel drug reservoir that maintains zero net volume delivery and permits programmable modulation of the drug concentration in the infused bolus. The reciprocating pump is fabricated from laminated polymer films and employs a miniature electromagnetic actuator to meet the size and weight requirements of a head-mounted in vivo guinea pig testing system. The reservoir comprises a long microchannel in series with a micropump, connected in parallel with the reciprocating flow network. We characterized in vitro the response and repeatability of the planar pump and compared the results with a lumped element simulation. We also characterized the performance of the reservoir, including repeatability of dosing and range of dose modulation. Acute in vivo experiments were performed in which the reciprocating pump was used to deliver a test compound to the cochlea of anesthetized guinea pigs to evaluate short-term safety and efficacy of the system. These advances are key steps toward realization of an implantable device for long-term therapeutic applications in humans.

A Bone-Thickness Map as a Guide for Bone-Anchored Port Implantation Surgery in the Temporal Bone

The bone-anchored port (BAP) is an investigational implant, which is intended to be fixed on the temporal bone and provide vascular access. There are a number of implants taking advantage of the stability and available room in the temporal bone. These devices range from implantable hearing aids to percutaneous ports. During temporal bone surgery, injuring critical anatomical structures must be avoided. Several methods for computer-assisted temporal bone surgery are reported, which typically add an additional procedure for the patient. We propose a surgical guide in the form of a bone-thickness map displaying anatomical landmarks that can be used for planning of the surgery, and for the intra-operative decision of the implant’s location. The retro-auricular region of the temporal and parietal bone was marked on cone-beam computed tomography scans and tridimensional surfaces displaying the bone thickness were created from this space. We compared this method using a thickness map (n = 10) with conventional surgery without assistance (n = 5) in isolated human anatomical whole head specimens. The use of the thickness map reduced the rate of Dura Mater exposition from 100% to 20% and suppressed sigmoid sinus exposures. The study shows that a bone-thickness map can be used as a low-complexity method to improve patient’s safety during BAP surgery in the temporal bone.

Comparison of 3D reconstructive technologies used for morphometric research and the translation of knowledge using a decision matrix

The use of three-dimensional (3D) models for education, pre-operative assessment, presurgical planning, and measurement have become more prevalent. With the increase in prevalence of 3D models there has also been an increase in 3D reconstructive software programs that are used to create these models. These software programs differ in reconstruction concepts, operating system requirements, user features, cost, and no one program has emerged as the standard. The purpose of this study was to conduct a systematic comparison of three widely available 3D reconstructive software programs, Amira(®), OsiriX, and Mimics(®) , with respect to the software's ability to be used in two broad themes: morphometric research and education to translate morphological knowledge. Cost, system requirements, and inherent features of each program were compared. A novel concept selection tool, a decision matrix, was used to objectify comparisons of usability of the interface, quality of the output, and efficiency of the tools. Findings indicate that Mimics was the best-suited program for construction of 3D anatomical models and morphometric analysis, but for creating a learning tool the results were less clear. OsiriX was very user-friendly; however, it had limited capabilities. Conversely, although Amira had endless potential and could create complex dynamic videos, it had a challenging interface. These results provide a resource for morphometric researchers and educators to assist the selection of appropriate reconstruction programs when starting a new 3D modeling project.

Microsystems technologies for drug delivery to the inner ear

The inner ear represents one of the most technologically challenging targets for local drug delivery, but its clinical significance is rapidly increasing. The prevalence of sensorineural hearing loss and other auditory diseases, along with balance disorders and tinnitus, has spurred broad efforts to develop therapeutic compounds and regenerative approaches to treat these conditions, necessitating advances in systems capable of targeted and sustained drug delivery. The delicate nature of hearing structures combined with the relative inaccessibility of the cochlea by means of conventional delivery routes together necessitate significant advancements in both the precision and miniaturization of delivery systems, and the nature of the molecular and cellular targets for these therapies suggests that multiple compounds may need to be delivered in a time-sequenced fashion over an extended duration. Here we address the various approaches being developed for inner ear drug delivery, including micropump-based devices, reciprocating systems, and cochlear prosthesis-mediated delivery, concluding with an analysis of emerging challenges and opportunities for the first generation of technologies suitable for human clinical use. These developments represent exciting advances that have the potential to repair and regenerate hearing structures in millions of patients for whom no currently available medical treatments exist, a situation that requires them to function with electronic hearing augmentation devices or to live with severely impaired auditory function. These advances also have the potential for broader clinical applications that share similar requirements and challenges with the inner ear, such as drug delivery to the central nervous system.

Intracochlear drug delivery systems

INTRODUCTION

Advances in molecular biology and in the basic understanding of the mechanisms associated with sensorineural hearing loss and other diseases of the inner ear are paving the way towards new approaches for treatments for millions of patients. However, the cochlea is a particularly challenging target for drug therapy, and new technologies will be required to provide safe and efficacious delivery of these compounds. Emerging delivery systems based on microfluidic technologies are showing promise as a means for direct intracochlear delivery. Ultimately, these systems may serve as a means for extended delivery of regenerative compounds to restore hearing in patients suffering from a host of auditory diseases.

AREAS COVERED

Recent progress in the development of drug delivery systems capable of direct intracochlear delivery is reviewed, including passive systems such as osmotic pumps, active microfluidic devices and systems combined with currently available devices such as cochlear implants. The aim of this article is to provide a concise review of intracochlear drug delivery systems currently under development and ultimately capable of being combined with emerging therapeutic compounds for the treatment of inner ear diseases.

EXPERT OPINION

Safe and efficacious treatment of auditory diseases will require the development of microscale delivery devices, capable of extended operation and direct application to the inner ear. These advances will require miniaturization and integration of multiple functions, including drug storage, delivery, power management and sensing, ultimately enabling closed-loop control and timed-sequence delivery devices for treatment of these diseases.

Anatomic limitations in implantation of middle ear transducer and carina middle ear implants

OBJECTIVES/HYPOTHESIS

The objective of this study was to examine any anatomic limitations in implantation of the semi-implantable middle ear transducer (MET) and fully implantable Carina middle ear implants (Otologics, Boulder, CO).

STUDY DESIGN

Retrospective case series.

METHODS

This study involved high-resolution computed tomography (HRCT) of the temporal bone and surgical findings in 22 middle ear implantations (17 MET, five Carina). The distance between the dura and the superior-posterior wall of the external auditory canal (dura-meatal distance) on the incus projection level was measured in coronal high-resolution computed tomography (HRCT) sections. Extensive bone removal from the tegmen for the fitting of the implant was intraoperatively documented, using as criteria the dura exposure. The correlation between HRCT measurements and dura exposure was examined.

RESULTS

In 10 implantations (45.5%) the dura was exposed. In nine of 10 cases (90%) the dura-meatal distance was less than 8 mm. In 11 out of 12 implantations that were performed without exposing the dura (91.7%), the dura-meatal distance was greater than 8 mm. In two cases with dura-meatal distance less than 5 mm, extensive dura exposure and surgical time were needed. In one of these cases, opening of the dura occurred during later explantation.

CONCLUSIONS

When dura-meatal distance is greater than 8 mm, implantation of the MET or Carina is a safe procedure. By contrast, in cases with a dura-meatal distance of less than 8 mm, the surgery introduces a high risk of complications. When dura-meatal distance is less than 5 mm, MET or Carina implantation is not recommended.

Reconstruction and exploration of virtual middle-ear models derived from micro-CT datasets

BACKGROUND

Middle-ear anatomy is integrally linked to both its normal function and its response to disease processes. Micro-CT imaging provides an opportunity to capture high-resolution anatomical data in a relatively quick and non-destructive manner. However, to optimally extract functionally relevant details, an intuitive means of reconstructing and interacting with these data is needed.

MATERIALS AND METHODS

A micro-CT scanner was used to obtain high-resolution scans of freshly explanted human temporal bones. An advanced volume renderer was adapted to enable real-time reconstruction, display, and manipulation of these volumetric datasets. A custom-designed user interface provided for semi-automated threshold segmentation. A 6-degrees-of-freedom navigation device was designed and fabricated to enable exploration of the 3D space in a manner intuitive to those comfortable with the use of a surgical microscope. Standard haptic devices were also incorporated to assist in navigation and exploration.

RESULTS

Our visualization workstation could be adapted to allow for the effective exploration of middle-ear micro-CT datasets. Functionally significant anatomical details could be recognized and objective data could be extracted.

CONCLUSIONS

We have developed an intuitive, rapid, and effective means of exploring otological micro-CT datasets. This system may provide a foundation for additional work based on middle-ear anatomical data.

Development of a microfluidics-based intracochlear drug delivery device

BACKGROUND

Direct delivery of drugs and other agents into the inner ear will be important for many emerging therapies, including the treatment of degenerative disorders and guiding regeneration.

METHODS

We have taken a microfluidics/MEMS (MicroElectroMechanical Systems) technology approach to develop a fully implantable reciprocating inner-ear drug-delivery system capable of timed and sequenced delivery of agents directly into perilymph of the cochlea. Iterations of the device were tested in guinea pigs to determine the flow characteristics required for safe and effective delivery. For these tests, we used the glutamate receptor blocker DNQX, which alters auditory nerve responses but not cochlear distortion product otoacoustic emissions.

RESULTS

We have demonstrated safe and effective delivery of agents into the scala tympani. Equilibration of the drug in the basal turn occurs rapidly (within tens of minutes) and is dependent on reciprocating flow parameters.

CONCLUSION

We have described a prototype system for the direct delivery of drugs to the inner ear that has the potential to be a fully implantable means for safe and effective treatment of hearing loss and other diseases.