Spiral Lamina Research Articles

An optically-guided cochlear implant sheath for real-time monitoring of electrode insertion into the human cochlea

In cochlear implant surgery, insertion of perimodiolar electrode arrays into the scala tympani can be complicated by trauma or even accidental translocation of the electrode array within the cochlea. In patients with partial hearing loss, cochlear trauma can not only negatively affect implant performance, but also reduce residual hearing function. These events have been related to suboptimal positioning of the cochlear implant electrode array with respect to critical cochlear walls of the scala tympani (modiolar wall, osseous spiral lamina and basilar membrane). Currently, the position of the electrode array in relation to these walls cannot be assessed during the insertion and the surgeon depends on tactile feedback, which is unreliable and often comes too late. This study presents an image-guided cochlear implant device with an integrated, fiber-optic imaging probe that provides real-time feedback using optical coherence tomography during insertion into the human cochlea. This novel device enables the surgeon to accurately detect and identify the cochlear walls ahead and to adjust the insertion trajectory, avoiding collision and trauma. The functionality of this prototype has been demonstrated in a series of insertion experiments, conducted by experienced cochlear implant surgeons on fresh-frozen human cadaveric cochleae.

Otosclerosis under microCT: New insights into the disease and its anatomy.

Otospongiotic plaques can be seen on conventional computed tomography (CT) as focal lesions around the cochlea. However, the resolution remains insufficient to enable evaluation of intracochlear damage. MicroCT technology provides resolution at the single micron level, offering an exceptional amplified view of the otosclerotic cochlea. In this study, a non-decalcified otosclerotic cochlea was analyzed and reconstructed in three dimensions for the first time, using microCT technology. The pre-clinical relevance of this study is the demonstration of extensive pro-inflammatory buildup inside the cochlea which cannot be seen with conventional cone-beam CT (CBCT) investigation. A radiological and a three-dimensional (3D) anatomical study of an otosclerotic cochlea using microCT technology is presented here for the first time. 3D-segmentation of the human cochlea was performed, providing an unprecedented view of the diseased area without the need for decalcification, sectioning, or staining. Using microCT at single micron resolution and geometric reconstructions, it was possible to visualize the disease's effects. These included intensive tissue remodeling and highly vascularized areas with dilated capillaries around the spongiotic foci seen on the pericochlear bone. The cochlea's architecture as a morphological correlate of the otosclerosis was also seen. With a sagittal cut of the 3D mesh, it was possible to visualize intense ossification of the cochlear apex, as well as the internal auditory canal, the modiolus, the spiral ligament, and a large cochleolith over the osseous spiral lamina. In addition, the oval and round windows showed intense fibrotic tissue formation and spongiotic bone with increased vascularization. Given the recently described importance of the osseous spiral lamina in hearing mechanics and that, clinically, one of the signs of otosclerosis is the Carhart notch observed on the audiogram, a tonotopic map using the osseous spiral lamina as region of interest is presented. An additional quantitative study of the porosity and width of the osseous spiral lamina is reported. In this study, structural anatomical alterations of the otosclerotic cochlea were visualized in 3D for the first time. MicroCT suggested that even though the disease may not appear to be advanced in standard clinical CT scans, intense tissue remodeling is already ongoing inside the cochlea. That knowledge will have a great impact on further treatment of patients presenting with sensorineural hearing loss.

Insights into Inner Ear Function and Disease Through Novel Visualization of the Ductus Reuniens, a Seminal Communication Between Hearing and Balance Mechanisms.

The sensory end-organs responsible for hearing and balance in the mammalian inner ear are connected via a small membranous duct known as the ductus reuniens (also known as the reuniting duct (DR)). The DR serves as a vital nexus linking the hearing and balance systems by providing the only endolymphatic connection between the cochlea and vestibular labyrinth. Recent studies have hypothesized new roles of the DR in inner ear function and disease, but a lack of knowledge regarding its 3D morphology and spatial configuration precludes testing of such hypotheses. We reconstructed the 3D morphology of the DR and surrounding anatomy using osmium tetroxide micro-computed tomography and digital visualizations of three human inner ear specimens. This provides a detailed, quantitative description of the DR's morphology, spatial relationships to surrounding structures, and an estimation of its orientation relative to head position. Univariate measurements of the DR, inner ear, and cranial planes were taken using the software packages 3D Slicer and Zbrush. The DR forms a narrow, curved, flattened tube varying in lumen size, shape, and wall thickness, with its middle third being the narrowest. The DR runs in a shallow bony sulcus superior to the osseus spiral lamina and adjacent to a ridge of bone that we term the "crista reuniens" oriented posteromedially within the cranium. The DR's morphology and structural configuration relative to surrounding anatomy has important implications for understanding aspects of inner ear function and disease, particularly after surgical alteration of the labyrinth and potential causative factors for Ménière's disease.

High-speed flat-detector computed tomography for temporal bone imaging and postoperative control of cochlear implants.

PurposeFlat-detector computed tomography (FD-CT) is the standard for cochlear implant (CI) imaging. FD-CT systems differ in technical characteristics. Our aim was an evaluation of two different FD-CT generations with different protocols and hardware regarding image quality, radiation dose, and scan time.MethodsTwo temporal bone specimens (− / + CI = TB0/TB1) were scanned using three different scanners: two FD-CT systems with different scanning protocols (standard FD-CT: 20 s 70 kV, 20 s 109 kV; high-speed FD-CT [HS-FD-CT]: 7 s 109 kV, 9 s 109 kV, 14 s 72 kV) and MS-CT (5 s 120 kV). Acquired datasets were evaluated in consensus reading regarding qualitative and quantitative parameters: addressing CI- and cochlea-specific parameters, cochlea delineation, lamina spiralis ossea visibility, distinction of single CI electrodes, determination of intracochlear implant position, stapes delineation, and mastoidal septation were assessed. Addressing protocol-specific parameters, radiation dose (dose-length-product/DLP), and scan time were assessed.Results Two HS-FD-CT protocols (14 s/9 s) provide higher or equivalent diagnostic information regarding CI- and cochlea-specific parameters compared to both standard FD-CT protocols. The fastest HS-FD-CT protocol (7 s)—providing inferior diagnostic information compared to all other FD-CT protocols—still exceeds MS-CT. The highest DLP was recorded for the 14 s HS-FD-CT protocol (TB1 = 956 mGycm); the lowest DLPs were recorded for the 7 s HS-FD-CT protocol (TB0 = 188 mGycm) and for MS-CT (TB0 = 138 mGycm), respectively. HS-FD-CT allows a significant reduction of scan time compared to standard FD-CT.ConclusionHigh-speed FD-CT improves visualization of temporal bone anatomy and postoperative assessment of CIs by combining excellent image quality, fast scan time, and reasonable radiation exposure.

Age-Related Hearing Loss Is Accompanied by Chronic Inflammation in the Cochlea and the Cochlear Nucleus.

Age-related hearing loss (ARHL) is a major hearing impairment characterized by pathological changes in both the peripheral and central auditory systems. Low-grade inflammation was observed in the cochlea of deceased human subjects with ARHL and animal models of early onset ARHL, which suggests that inflammation contributes to the development of ARHL. However, it remains elusive how chronic inflammation progresses during normal aging in the cochlea, and especially the accompanying changes of neuroinflammation in the central auditory system. To address this, we investigated chronic inflammation in both the cochlea and the cochlear nucleus (CN) of CBA/CaJ mice, an inbred mouse strain that undergoes normal aging and develops human, like-late-onset ARHL. Using immunohistochemistry, confocal microscopy, and quantitative image processing, we measured the accumulation and activation of macrophages in the cochlea and microglia in the CN using their shared markers: ionized calcium binding adaptor molecule 1 (Iba1) and CD68—a marker of phagocytic activity. We found progressive increases in the area covered by Iba1-labeled macrophages and enhanced CD68 staining in the osseous spiral lamina of the cochlea that correlated with elevated ABR threshold across the lifespan. During the process, we further identified significant increases in microglial activation and C1q deposition in the CN, indicating increased neuroinflammation and complement activation in the central auditory system. Our study suggests that during normal aging, chronic inflammation occurs in both the peripheral and the central auditory system, which may contribute in coordination to the development of ARHL.

Human vestibular schwannoma reduces density of auditory nerve fibers in the osseous spiral lamina

Hearing loss in patients with vestibular schwannoma (VS) is commonly attributed to mechanical compression of the auditory nerve, though recent studies suggest that this retrocochlear pathology may be augmented by cochlear damage. Although VS-associated loss of inner hair cells, outer hair cells, and spiral ganglion cells has been reported, it is unclear to what extent auditory-nerve peripheral axons are damaged in VS patients. Understanding the degree of damage VSs cause to auditory nerve fibers (ANFs) is important for accurately modeling clinical outcomes of cochlear implantation, which is a therapeutic option to rehabilitate hearing in VS-affected ears. A retrospective analysis of human temporal-bone histopathology was performed on archival specimens from the Massachusetts Eye and Ear collection. Seven patients met our inclusion criteria based on the presence of sporadic, unilateral, untreated VS. Tangential sections of five cochlear regions were stained with hematoxylin and eosin, and adjacent sections were stained to visualize myelinated ANFs and efferent fibers. Following confocal microscopy, peripheral axons of ANFs within the osseous spiral lamina were quantified manually, where feasible, and with a “pixel counting” method, applicable to all sections. ANF density was substantially reduced on the VS side compared to the unaffected contralateral side. In the upper basal turn, a significant difference between the VS side and unaffected contralateral side was found using both counting methods, corresponding to the region tuned to 2000 Hz. Even spiral ganglion cells (SGCs) contralateral to VS were affected by the tumor as the majority of contralateral SGC counts were below average for age. This observation provides histological insight into the clinical observation that unilateral vestibular schwannomas pose a long-term risk of progression of hearing loss in the contralateral ear as well. Our pixel counting method for ANF quantification in the osseous spiral lamina is applicable to other pathologies involving sensorineural hearing loss. Future research is needed to classify ANFs into morphological categories, accurately predict their electrical properties, and use this knowledge to inform optimal cochlear implant programming strategies.

Pseudoreticulate-Subreticulate-Reticulate Nummulites and their possible evolution in the middle Eocene-lower Oligocene succession of Surat-Bharuch, Gujarat India

A biostratigraphically well constrained middle Eocene to lower Oligocene shelf succession (ca. 33 m) of the Amravati Formation in the Vagalkhod-Dinod area of Surat-Bharuch Districts, Gujarat, India contains Nummulites having varied septal filaments, among which complicated filaments show progressive changes in the succession. Complications by the intersection of filaments with spiral laminae/ridge, bifurcation of filaments at low angle and joining by transverse trabeculae, and bifurcation and re-joining of filaments at high and varied angles, and consecutive bifurcation and trifurcation of filaments allowed their categorization in different species. Successive appearances of pseudoreticulate filaments (Nummulites acutus, Nummulites broachensis and Nummulites longilocula), subreticulate filaments (Nummulites hormoensis and Nummulites ptukhiani) and reticulate filaments (Nummulites fabianii, Nummulites retiatus and Nummulites fichteli) reflect gradual complication with time, producing a bioseries that is also manifested by changes in canals and equatorial chambers. The eight species of Nummulites are differentiated and described within the pseudoreticulate subreticulate- reticulate group and based on their stratigraphic distribution, seven zones in ascending order namely, the Nummulites acutus Assemblage Zone, Nummulites broachensis Range Zone, SRG Barren zone, Nummulites hormoensis-Nummulites fabianii Interval Zone, Nummulites fabianii Range Zone, Nummulites fabianii-Nummulites retiatus Interval Zone and Nummulites fichteli Range Zone are recognized and described. The zones are tentatively correlated with the SB zones and their ages are assigned by planktonic foraminiferal zones. Complexity of septal filaments within the Nummulites of the succession began with the development of pseudoreticulation (by the intersection of radial filaments with spiral laminae) during the late Lutetian; afterward during the early Bartonian Stage bifurcation develops in a septal filament along with occasional joining by transverse trabeculae; subreticulation remained restricted to the late Bartonian,while reticulation appeared at the beginning of the Priabonian to flourish during the Priabonian to mid Rupelian.The bioseries by septal filaments shows three evolutionary trends in these species: 1) evolution of N. acutus to N. fichteli through N. broachensis-N. hormoensis-N. ptukhiani-N. fabianii; besides acquiring complication of septal filaments this trend shows a general increase in the size of the proloculus, an increase of the size of the B-form, increasing complication in canals, and lowering the height of equatorial chambers concomitant with the increase of length; 2) evolution of N. acutus to N. broachensis to N. longilocula; this trend is restricted to the pseudoreticulate group; discerning changes involve connecting adjacent septal filaments by transverse trabeculae and spiral laminae, and development of rudimentary mesh of septal filaments, complication in canals and slit-like long equatorial chambers; 3). evolution of N. hormoensis to N. retiatus; changes involve in the development of reticulation from subreticulate septal filaments, decrease in the height of chambers, complication in canals, and development of laminae and mesh as grooves. Nummulites acutus is ancestral to all the discussed species. The evolution of Nummulites leading to complicated septal filaments is known during the corresponding span in the Mediterranean region, East African region, and a few locations in western European and southeast Asian regions, but the trends of evolution as studied in the Amravati Formation differs in the distinct developments of pseudoreticulate lineage, N. ptukhiani as an intermediate evolutionary form between N. hormoensis and N. fabianii, and in the development of complex subreticulation from a simple one. The studied succession is the only one of its kind in the Indian region to have successive development of pseudoreticulate-subreticulate-reticulate Nummulites across the Lutetian/Bartonian, Bartonian/Priabonian and Priabonian/Rupelian boundaries.

Image-Based Planning of Minimally Traumatic Inner Ear Access for Robotic Cochlear Implantation.

Objective: During robotic cochlear implantation, an image-guided robotic system provides keyhole access to the scala tympani of the cochlea to allow insertion of the cochlear implant array. To standardize minimally traumatic robotic access to the cochlea, additional hard and soft constraints for inner ear access were proposed during trajectory planning. This extension of the planning strategy aims to provide a trajectory that preserves the anatomical and functional integrity of critical intra-cochlear structures during robotic execution and allows implantation with minimal insertion angles and risk of scala deviation.Methods: The OpenEar dataset consists of a library with eight three-dimensional models of the human temporal bone based on computed tomography and micro-slicing. Soft constraints for inner ear access planning were introduced that aim to minimize the angle of cochlear approach, minimize the risk of scala deviation and maximize the distance to critical intra-cochlear structures such as the osseous spiral lamina. For all cases, a solution space of Pareto-optimal trajectories to the round window was generated. The trajectories satisfy the hard constraints, specifically the anatomical safety margins, and optimize the aforementioned soft constraints. With user-defined priorities, a trajectory was parameterized and analyzed in a virtual surgical procedure.Results: In seven out of eight cases, a solution space was found with the trajectories safely passing through the facial recess. The solution space was Pareto-optimal with respect to the soft constraints of the inner ear access. In one case, the facial recess was too narrow to plan a trajectory that would pass the nerves at a sufficient distance with the intended drill diameter. With the soft constraints introduced, the optimal target region was determined to be in the antero-inferior region of the round window membrane.Conclusion: A trend could be identified that a position between the antero-inferior border and the center of the round window membrane appears to be a favorable target position for cochlear tunnel-based access through the facial recess. The planning concept presented and the results obtained therewith have implications for planning strategies for robotic surgical procedures to the inner ear that aim for minimally traumatic cochlear access and electrode array implantation.

ALADA Dose Optimization in the Computed Tomography of the Temporal Bone: The Diagnostic Potential of Different Low-Dose CT Protocols.

Objective: Repeated computed tomography (CT) is essential for diagnosis, surgical planning and follow-up in patients with middle and inner ear pathology. Dose reduction to “as low as diagnostically acceptable” (ALADA) is preferable but challenging. We aimed to compare the diagnostic quality of images of subtle temporal bone structures produced with low doses (LD) and reference protocols (RP). Methods: Two formalin-fixed human cadaver heads were scanned using a 64-slice CT scanner and cone-beam CT (CBCT). The protocols were: RP (120 kV, 250 mA, CTDIvol 83.72 mGy), LD1 (100 kV, 80 mA, CTDIvol 26.79 mGy), LD2 (100 kV, 35 mA, CTDIvol 7.66 mGy), LD3 (80 kV, 40 mA, CTDIvol 4.82 mGy), and CBCT standard protocol. Temporal bone structures were assessed using a 5-point scale. Results: A median score of ≥2 was achieved with protocols such as the tendons of m. tensor tympani (RP/LD1/LD2/CBCT) and m. stapedius (CBCT), the incudostapedial joint (RP/LD1/CBCT), the incudomalleolar joint (RP/LD1/LD2/CBCT), the stapes feet (RP/LD1/CBCT), the stapes head (RP/LD1/LD2/CBCT), the tympanic membrane (RP/LD1/LD2/CBCT), the lamina spiralis ossea (none), the chorda tympani (RP/LD1/CBCT), and the modiolus (RP/LD1/LD2/CBCT). Adaptive statistical iterative reconstructions did not show advantages over the filtered back projection. Conclusions: LD protocols using a CTDIvol of 7.66 mGy may be sufficient for the identification of temporal bone structures.

Time-domain analysis of a three-dimensional numerical model of the human spiral cochlea at medium intensity.

For the processing and detection of speech and music, the human cochlea has an exquisite sensitivity and selectivity of frequency and a dynamic range. How the cochlea performs these remarkable functions has fascinated auditory scientists for decades. Because it is not possible to measure sound-induced vibrations within the cochlea in a living human being, mathematical modeling has played an important role in cochlear mechanics. For this study, a three-dimensional human cochlear model with a fluid‒structure coupling was constructed. Time-domain analysis was performed to calculate the displacement, velocity, and stress of the basilar membrane (BM) and osseous spiral lamina (OSL) at different times in response to a pure tone stimulus. The model reproduced the traveling-wave motion of the BM. The model also showed that the cochlea's spiral shape can induce asymmetrical mechanical behavior of the BM and cause cochlear fluid to move in a radial direction; this may contribute to human sound perception. The cochlea's spiral shape not only enhances a low-frequency vibration of the BM but also changes the maximization of the positions of vibration. Therefore, the spiral's characteristics play a key role in the cochlea's frequency selectivity for low-frequency sounds. And this suggests that the OSL can react to sound as quickly as the BM. Furthermore, the basal region of the BM tends to have more stress than its other regions, and this may explain the clinical observation that human sensorineural hearing loss often occurs at high frequencies.

Prevalence of Macrophages Within the Cochlear Vessels Following Cochlear Implantation in the Human: An Immunohistopathological Study Using Anti-Iba1 Antibody.

The prevalence of monocyte-derived macrophages within cochlear vessels may increase following cochlear implantation. Recently, we reported an increase in the number of ionized calcium-binding adaptor molecule 1 (Iba1)-positive macrophages in selected cochlear sites such as the osseous spiral lamina and Rosenthal's canal following cochlear implantation. Activation of the immune system induces the recruitment of monocyte-derived macrophages. The prevalence of monocyte-derived macrophages within cochlear vessels may increase following cochlear implantation. However, the delivery system of macrophages to the human cochlea is incompletely understood. The prevalence of macrophages and monocytes within cochlear blood vessels in 10 human subjects who had undergone unilateral cochlear implantation was studied by light microscopy using anti-Iba1 immunostaining. The densities of Iba1-positve monocytes per area of lumen of cochlear vessels in the sections near the round window in implanted ears were compared with the contralateral unimplanted ears. The correlation between the densities of Iba1-positve monocytes and the duration (months after the cochlear implantation) was also evaluated. The prevalence of Iba1-positive macrophages/monocytes in vessels near the round window in implanted ears (mean 26%, median 21%) was greater than in opposite unimplanted ears (mean 5.2%, median 2.5%: p < 0.01). The density of Iba1-positive monocytes in implanted ears (mean 32, median 16 cells/105 μm2) tended to be greater than that in unimplanted ears (mean 6.6, median 0.93 cells/105 μm2: p = 0.08). The density of Iba1-positive monocytes was significantly correlated with duration of implantation but not in the unimplanted ears. An increase in prevalence of Iba1-positive macrophages/monocytes within cochlear blood vessels after cochlear implantation was demonstrated. These findings suggest a delivery system of Iba1-positive macrophages through cochlear vessels in human that is ongoing for long duration.

Visualization of Different Types of Cochlear Implants in Postoperative Cone-Beam CT Imaging

To evaluate cone-beam computed-tomography (CBCT) images of the temporal bone for radiological delineation, metal artifacts, and accuracy for localization of six different electrode arrays after cochlear device implantation. This retrospective study included 116 patients who underwent CBCT (120kV, 7.1mA) within 24 hours after cochlear device implantation. Exclusion criteria were anatomical abnormalities, and electrode misinsertion. Six different CI electrodes were implanted: Advanced Bionics HiFocus Mid-Scala, Cochlear Contour Advance, Cochlear Slim-Straight, Cochlear Slim-Modiolar, MED-EL Flex 24 and MED-EL Flex 28. Two radiologists rated independently presence of metal artifacts, overall image quality, as well as dedicated visualization of the osseous spiral lamina, inner and outer cochlear wall, single electrode contacts, and electrode position using 5-point-Likert scales. Inter-rater agreement was calculated by using Cohen's kappa and intraclass correlation. Of 116 patients, 94 (81.0%; 56.1 ± 16.9 years; age range, 13-86 years; 49 [52.1%] females) were included in the study. Overall image quality was rated good for all electrode models without significant differences (p = 0.061). Depiction of electrode contacts was rated significantly better for Advanced Bionics HiFocus Mid-Scala, Cochlear Slim-Straight, and MED-EL Flex 24 and 28 compared to Cochlear Contour Advance and Slim-Modiolar (p < 0.001). Depiction of the osseous spiral lamina (p = 0.20), inner (p = 0.42) and outer cochlear wall (p = 0.35), metal artifacts (p = 0.18), and electrode position (p = 0.31) did not show significant differences between electrode models. Inter-rater agreement varied from substantial to almost perfect (0.70-0.93). CBCT provides excellent visualization of all evaluated CI electrode types, in particular electrode arrays with greater spacing between contacts and contact size allow improved radiologic evaluation.

Insertion trauma of a new cochlear implant electrode: evaluated by histology in fresh human temporal bone specimens

Background Combining acoustic and electrical stimulation has been successfully used in patients with low-frequency residual hearing. Electrode insertion trauma, such as electrode translocation could result in loss of residual hearing. Objectives The aim of the study is to evaluate the LCI-20PI electrode array insertion trauma to the intra-cochlear structures in fresh human temporal bone specimens. Materials and methods The LCI-20PI electrode arrays were inserted into scalae tympani through round window membrane in 10 cochleae from ten fresh human cadavers. The intracochlear trauma was evaluated histologically by a scale of 0–4: 0 – no observable trauma, 1 – elevation of basilar membrane, 2 – rupture of basilar membrane or spiral ligament, 3–dislocation into scala vestibuli and 4 – fracture of modiolus or osseous spiral lamina. The insertion depth was measured by radiography. Results Histological results revealed no observable trauma in seven specimens; basal membrane elevation and rupture in two specimens; the electrode array misled into scala vestibuli in one specimen. The insertion depth varied from 228° to 288°. Conclusions and significance The insertion of the LCI-20PI electrode arrays caused no trauma in the majority of the fresh temporal bone specimens. No translocation of the electrode arrays from the scala tympani to the scala vestibuli was observed.

Cone-beam CT versus Multidetector CT in Postoperative Cochlear Implant Imaging: Evaluation of Image Quality and Radiation Dose.

Cone-beam CT is being increasingly used in head and neck imaging. We compared cone-beam CT with multidetector CT to assess postoperative implant placement and delineate finer anatomic structures, image quality, and radiation dose used. This retrospective multicenter study included 51 patients with cochlear implants and postoperative imaging via temporal bone cone-beam CT (n = 32 ears) or multidetector CT (n = 19 ears) between 2012 and 2017. We evaluated the visualization quality of single electrode contacts, the scalar position of the electrodes, cochlear walls, mastoid facial canal, metallic artifacts (using a 4-level visual score), and the ability to measure the insertion angle of the electrodes. The signal-to-noise ratio and radiation dose were also evaluated. Cone-beam CT was more sensitive for visualizing the scalar position of the electrodes (P = .046), cochlear outer wall (P = .001), single electrode contacts (P < .001), and osseous spiral lamina (P = .004) and had fewer metallic artifacts (P < .001). However, there were no significant differences between both methods in visualization of the modiolus (P = .37), cochlear inner wall (P > .99), and mastoid facial canal wall (P = .07) and the ability to measure the insertion angle of the electrodes (P > .99). The conebeam CT group had significantly lower dose-length product (P < .001), but multidetector CT showed a higher signal-to-noise ratio in both bone and air (P = .22 and P = .001). Cone-beam CT in patients with cochlear implants provides images with higher spatial resolution and fewer metallic artifacts than multidetector CT at a relatively lower radiation dose.

Histopathologic Evaluation of Intralabyrinthine Schwannoma

Objectives: The aim of this study is to perform a histopathologic analysis of temporal bones with an intralabyrinthine schwannoma (ILS) in order to characterize its extension. Methods: Archival temporal bones with a diagnosis of sporadic schwannoma were identified. Both symptomatic and occult nonoperated ILS were included for further analysis. Results: A total of 6 ILS were identified, with 4 intracochlear and 2 intravestibular schwannomas. All intracochlear schwannomas involved the osseous spiral lamina, with 2 extending into the modiolus. The intravestibular schwannomas were limited to the vestibule, but growth into the bone next to the crista of the lateral semicircular canal was observed in 1 patient. Conclusions: Complete removal of an ILS may require partial removal of the modiolus or bone surrounding the crista ampullaris as an ILS may extend into these structures, risking damage of the neuronal structures. Due to the slow growth of the ILS, it remains unclear if a complete resection is required with the risk of destroying neural structures hindering hearing rehabilitation with a cochlear implant.

A Micro-Computed Tomography Study of Round Window Anatomy and Implications for Atraumatic Cochlear Implant Insertion.

The goal of this study was to interrogate high-resolution three-dimensional reconstructions of round window anatomy to illustrate and characterize structural variability with implications for atraumatic cochlear implant insertion. Cochlear implants are increasingly used to improve sound detection in patients with substantial residual hearing. However, traumatic cochlear implant insertion through the round window involving upward deviation of the electrode into the spiral ligament, basilar membrane, and osseous spiral lamina, medial impaction on the modiolus, or interscalar excursion into the scala vestibuli are associated with lower rates of hearing preservation and poorer speech perception.Successful atraumatic insertion is dependent on an anatomical understanding of the middle and inner ear. The round window bony niche lacks distinct demonstrable anatomical landmarks for the position of the round window membrane, and there is limited guidance on the amount of bony overhang that can be safely drilled away. A greater understanding of the anatomical variation around the round window could enhance treatment efficacy. Fourteen human cadaver temporal bones were imaged using microcomputed tomography. Resulting scans were digitally reconstructed, segmented, and measured. Round window niche walls vary substantially in size and projection. Round window average short diameter measured 1.30 mm (range 1.07-1.44), and is limited by the crista fenestrae at the inferoanterior margin of the round window. Crista fenestrae size and morphology varied considerably. Reconstructions with solid and translucent panels are presented. Anatomical heterogeneity should be considered in cochlear implant selection, drilling, and choice of insertion vector.

BDNF-mediated preservation of spiral ganglion cell peripheral processes and axons in comparison to that of their cell bodies

Treatment with neurotrophins prevents degeneration of spiral ganglion cells (SGCs) after severe hair cell loss. In a previous study we demonstrated a long-lasting effect with brain-derived neurotrophic factor (BDNF) after cessation of treatment. In that study the survival of the SGC cell bodies was examined. Here we address the question whether their peripheral processes and central processes (axons) were protected by this treatment as well in the cochleas of the aforementioned study. Guinea pigs were deafened by co-administration of kanamycin and furosemide. Two weeks after deafening the right cochleas were implanted with an intracochlear electrode array combined with a cannula connected to an osmotic pump filled with BDNF solution. Four weeks later the treatment was stopped by surgically removing the osmotic pump. At that point, or another four or eight weeks later, the animals were sacrificed for histological analysis. Control groups consisted of normal-hearing animals, and three groups of deafened animals: two-weeks-deaf untreated animals, and six- and fourteen-weeks-deaf sham-treated animals. Cochleas were processed for analysis of: (1) the myelinated portion of peripheral processes in the osseous spiral lamina, (2) the cell bodies in Rosenthal's canal, and (3) axons in the internal acoustic meatus. Packing densities and cross-sectional areas were determined using light microscopy. Up to eight weeks after treatment cessation the numbers of peripheral processes and axons were significantly higher than in untreated cochleas of control animals. Whereas the numbers of cell bodies and axons were similar to those at the start of treatment, the peripheral processes were significantly less well preserved. This smaller protective effect was found mainly in the apical turns. Strategies to prevent SGC degeneration after hair cell loss should consider the differential effects on the various neural elements.

Forward-projected Model-based Iterative Reconstruction SoluTion in Temporal Bone Computed Tomography: A Comparison Study of All Reconstruction Modes.

Identify appropriate reconstruction modes of Forward-projected model-based Iterative Reconstruction SoluTion (FIRST) in temporal bone computed tomography (CT) and investigate the contribution of spatial resolution and noise to the visual assessment. Sixteen temporal bone CT images were reconstructed. Two blinded radiologists assessed 8 anatomical structures and classified the visual assessment. These visual scores were compared across reconstruction modes among each anatomical structure. Visual scores and contrast-to-noise ratio, noise power spectrum (NPS) at low (NPSLow) and high (NPSHigh) spatial frequencies, and 50% modulation transfer function relationships were evaluated. Visual scores differed significantly for the stapedius muscle and osseous spiral lamina, with CARDIAC SHARP, BONE, and LUNG modes for the osseous spiral lamina scoring highest. Visual scores significantly positively correlated with NPSLow, NPSHigh, and 50% modulation transfer function but negatively with contrast-to-noise ratio. Modes providing higher spatial resolution and lower noise reduction showed an improved visual assessment of CT images reconstructed with FIRST.

Phosphatidylinositol 4-kinase β mutations cause nonsyndromic sensorineural deafness and inner ear malformation

Congenital hearing loss is a common disorder worldwide. Heterogeneous gene variation accounts for approximately 20–25% of such patients. We investigated a five-generation Chinese family with autosomal-dominant nonsyndromic sensorineural hearing loss (SNHL). No wave was detected in the pure-tone audiometry, and the auditory brainstem response was absent in all patients. Computed tomography of the patients, as well as of two sporadic SNHL cases, showed bilateral inner ear anomaly, cochlear maldevelopment, absence of the osseous spiral lamina, and an enlarged vestibular aqueduct. Such findings were absent in nonaffected persons. We used linkage analysis and exome sequencing and uncovered a heterozygous missense mutation in the PI4KB gene (p.Gln121Arg) encoding phosphatidylinositol 4-kinase β (PI4KB) from the patients in this family. In addition, 3 missense PI4KB (p.Val434Gly, p.Glu667Lys, and p.Met739Arg) mutations were identified in five patients with nonsyndromic SNHL from 57 sporadic cases. No such mutations were present within 600 Chinese controls, the 1000 genome project, gnomAD, or similar databases. Depleting pi4kb mRNA expression in zebrafish caused inner ear abnormalities and audiosensory impairment, mimicking the patient phenotypes. Moreover, overexpression of 4 human missense PI4KB mutant mRNAs in zebrafish embryos resulted in impaired hearing function, suggesting dominant-negative effects. Taken together, our results reveal that PI4KB mutations can cause SNHL and inner ear malformation. PI4KB should be included in neonatal deafness screening.

Anatomy of the Round Window Region With Relation to Selection of Entry Site Into the Scala Tympani.

The aim of cochlear implantation is to safely insert an electrode array into the scala tympani (ST) while avoiding damage to surrounding structures. There is disagreement on the optimal way of entering the ST-the round window (RW) approach versus cochleostomy. Regardless of the chosen approach, it is vital to understand the regional anatomy, which is complex, difficult to conceptualize, and rarely dissected in temporal bone courses. The goal of this study was to examine the anatomy of the RW to gain more in-depth knowledge on the local relationships of the anatomical structures and propose an approach for entering the ST in cochlear implant surgery tailored to the encountered anatomy. Cadaveric prevalence study and expert opinion with literature review. Cadaveric temporal bone dissection (n = 13) by the first author assessing the RW anatomy. The round window membrane (RWM) and the osseous spiral lamina (OSL) are curved structures, each with a horizontal and a vertical part. The two horizontal portions are very closely apposed. The relationship between the OSL and the RWM determines the best site for a cochleostomy, which if required is best placed anteroinferiorly to the RWM. The distance between the oval window inferior margin and the RW membrane is less than 2 to 3 mm. The ST initially extends inferiorly and medially to the RW. The findings of our dissection have implications for cochlear implant surgery in aiming to avoid trauma to the OSL and basilar membrane and aid decision making in choosing the safest surgical approach. 5. Laryngoscope, 131:E598-E604, 2021.