Semicircular Canal Research Articles

Surgical Anatomy of the Retrosigmoid Approach with Endoscopic-Assisted Reverse Anterior Petrosectomy: Optimizing Meckel's Cave Access from the Posterior Fossa

Abstract Objectives We investigated the extent of access to Meckel's cave (MC) and the middle cranial fossa (MCF) protecting the internal carotid artery (ICA) using the retrosigmoid approach with endoscopic-assisted reverse anterior petrosectomy (EA-RAP). Methods Five specimens were dissected using the limited and extended EA-RAP. Based on the bone removal of the internal acoustic meatus (IAM) and subarcuate fossa, exposure of the MC and ICA were statistically compared. Results The limited and extended EA-RAP allowed access to the medial and anterior MC (4 mm posterior to the first genu of the cavernous ICA, and 20 mm posterior to foramen rotundum [FR]). The access to the lateral MC varied with distance of 12 and 8 mm medial to the foramen ovale for the limited and extended EA-RAP, respectively.In the extended EA-RAP, the exposure of the ICA was gained by drilling with the 0-degree endoscope (3 mm) versus 45-degree endoscope (9 mm). The working distances from the midpoint of the IAM to the most medial point of the exposed ICA was 24 mm. The most lateral point of the exposed ICA varied between 0- and 45-degree endoscopes with a distance of 21 and 13 mm, respectively. Conclusion A coronal plane from the posterior genu of the cavernous ICA and a sagittal plane to the common crus of the semicircular canals can define the area of MCF accessed by the EA-RAP. Drilling of the temporal bone should be carefully customized according to the patient and can be aided by endoscopic assistance for direct visualization to minimize the risk of injuries to ICA.

Bone conduction stimulation efficiency at coupling locations closer to the cochlea

Bone conduction implants enable patients to hear via vibrations transmitted to the skull. The main constraint of current bone conduction implants is their maximum output force level. Stimulating closer to the cochlea is hypothesized to increase efficiency and improve force transfer, addressing this limitation. This study evaluated stimulation at four positions in human cadaveric specimens: the cochlear promontory, the posterior wall of the outer ear canal, the lateral semi-circular canal, and the standard Bone-Anchored Hearing Aid (Baha) location. To assess potential hearing sensation, three objective measures were simultaneously recorded. For intracochlear pressure and promontory velocity, stimulating at the lateral semi-circular canal and promontory results in the highest response, with a gain of up to 20 dB. Ear canal pressure shows less conclusive results, with significant differences at only a few frequencies. These findings suggest that stimulation closer to the cochlea offers higher efficiency, which could benefit patients needing higher output force levels than currently available or those eligible for electro-vibrational stimulation, e.g. a cochlear implant combined with a bone conduction device.

Is endolymphatic hydrops, as detected in MRI, a truly cochleocentric finding?

IntroductionThe most common histopathological finding in Ménière’s disease (MD) is endolymphatic hydrops (EH), which involves the dilation of the membranous labyrinth. The direct relationship between EH and MD is debated, although EH plays a crucial role in auditory and vestibular functional tests. MRI sequences such as 3D-FLAIR and 3D-real-IR are used to study EH, with the latter being more effective. This study aimed to examine whether the severity of EH detected by MRI is always more pronounced in the cochlea than in the vestibule, indicating a cochleocentric progression of the condition.MethodsA retrospective longitudinal study was conducted at a tertiary care medical center from 2019 to 2023, involving patients diagnosed with unilateral Ménière’s disease. All patients underwent MRI hydrops assessments (3D-REAL-IR sequences) using 3 Tesla magnets and gadobutrol contrast agent. EH was graded qualitatively and quantitatively for both ears using scales for cochlear endolymphatic hydrops (cEH) and vestibular endolymphatic hydrops (vEH). Volumetric measurements of the vestibule and endolymph were performed, and the vestibular endolymphatic ratio (vELR) was calculated. The degree of perilymphatic enhancement (PE) and endolymphatic herniation was also assessed. Patient data, including demographics, disease features, comorbidities, hearing loss, and vestibular function, were collected from medical records. Statistical analysis involved various tests to compare groups and evaluate correlations, using a significance level of p < 0.05. The study aimed to classify the patients into cochleocentric (CC) or non-cochleocentric (NCC) groups based on the difference in the severity of EH in both compartments.ResultsWe included 137 patients, of whom 55 (40.15%) were classified as CC, and the remaining 82 (59.85%) were classified as NCC. The degree of vestibular EH (vEH) was more severe in the NCC group (p < 0.001), while cochlear EH (cEH) showed a moderate correlation with vEH. The mean vestibular endolymphatic ratio (vELR) was higher in the NCC group (80.5% ± 38%) compared to the CC group (55% ± 49.5%) (p < 0.0001). Vestibular herniation was more common in the NCC group, while vestibular perilymphatic enhancement was more prevalent in the CC group. Cardiovascular risk was associated with the CC group, while the NCC group reported more vestibular symptoms. Delayed Ménière’s disease was linked to the CC group. The hearing loss and vestibular function tests did not show significant differences between the groups.DiscussionIn conclusion, our study found that endolymphatic hydrops (EH) was more severe in the vestibule than in the cochlea in nearly 60% of the cases, with a clinical correlation to the initial symptoms. However, no significant differences were observed in the auditory or vestibular function tests during the follow-up.V Previous studies have indicated that vestibular EH occurs early in Ménière’s disease (MD) and subsequently progresses to the cochlea, a finding that challenges the traditional cochleocentric progression theory supported by experimental and clinical otopathology. MRI techniques have enhanced the detection of EH, revealing that the relative amount of endolymph is slightly higher in the vestibule than in the cochlea, thereby supporting the study’s findings. We considered the important technical limitations in the MRI visualization of EH and suggested that advanced imaging techniques and volumetric quantification could enhance the classification of cochleocentric and non-cochleocentric groups. The clinical findings revealed that cardiovascular risk factors and delayed MD phenotypes were more common in the cochleocentric group, while the non-cochleocentric group exhibited poorer vestibular MRI results and a higher incidence of endolymph herniation into the semicircular canals.

Comparative analysis of audiovestibular testing results in vestibular schwannomas

Objective:This study aimed to analyze the results of auditory and vestibular function tests in patients with unilateral vestibular schwannoma and explore their association with tumor size. Methods:Clinical data from 81 patients diagnosed with unilateral vestibular schwannoma who underwent pure-tone audiometry（PTA）, cervical and ocular vestibular evoked myogenic potentials（c/oVEMP）, as well as video head impulse test（vHIT）, and subsequently underwent surgical treatment, were retrospectively analyzed. Patients were categorized into groups based on tumor size: small （≤ 15 mm）, medium（16-30 mm）, and large （>30 mm）, determined by the maximum tumor diameter on contrast-enhanced MRI scans. Results:PTA results indicated hearing loss in 73 cases（90.1%）; vestibular function tests revealed abnormal rates for the anterior semicircular canal, horizontal semicircular canal, posterior semicircular canal, utricle, and saccule at 29.6%, 77.8%, 54.3%, 90.1%, and 92.6%, respectively. Statistically, no significant differences were found in preoperative hearing test results among patients in different groups（F=0.393, P=0.676）. However, significant differences were observed in horizontal semicircular canal gain（r=-0.248, P=0.025）, abnormal rates of horizontal semicircular canal catch-up saccades（r=0.507, P<0.001）, as well as cVEMP（χ²=15.111, P=0.004） and oVEMP thresholds（χ²=18.948, P<0.001） across varying tumor size groups. Conclusion:The extent of hearing loss in patients with vestibular schwannoma is not correlated with tumor size, whereas the degree of vestibular dysfunction demonstrates a correlation with tumor size.

Effect and differentiation of spontaneous nystagmus of acute unilateral vestibulopathy on saccade in the video head impulse test

Objective:Exploring the performance characteristics of spontaneous nystagmus（SN） in video-head impulse test（vHIT） and its possible effects on saccade. Methods:Vestibular function tests such as vHIT and SN were conducted in 48 patients with acute unilateral vestibulopathy（AUVP）. The saccade characteristics of vHIT in patients without SN and those with SN were analyzed, as well as the expression characteristics of SN in vHIT. Results:Among the 48 AUVP patients, there were 34 cases with SN, including 31 cases with saccade on the healthy side, 11 cases with both the same and opposite directions of eye movement, 19 with the opposite only, 1 with same direction only, and 3 cases without saccade. There were 14 patients without SN, of whom 10 showed saccade on the healthy side, including 4 with both eye movements in the same and opposite direction, 2 in the opposite direction only, 4 in the same direction only, and 4 without saccade. There is a correlation between reverse saccade on the healthy side and the presence of SN in patients. SN in vHIT can appear opposite to the direction of eye movement on the healthy side, while on the affected side it can appear the same as the direction of eye movement and may cause more discrete overt saccade. 32 patients in the acute phase（≤2 w）, 29 patients with SN, SN intensity of（6.7 ± 3.2） °/s, and 3 patients without SN. 16 cases in non acute phase（>2 w）, 5 cases with SN, SN intensity of（3.7 ± 2.1） °/s, and 11 cases without SN. In the acute phase there were 30 cases of saccade on the healthy side, 10 cases with both the same and opposite direction of eye movement, 18 cases with only the opposite direction, 2 cases with only the same direction and 2 cases without saccade. There is a correlation between the duration of the disease and the occurrence of reverse saccade on the healthy side. The intensity cut off point of SN for reverse saccade is 2.1 °/s in the healthy lateral semicircular canal vHIT. Conclusion:Compensatory saccades and SN waves with similar waveforms are mostly present in vHIT in AUVP patients. SN wave is in the opposite direction of the normal side and eye movement wave, and the affected side and dominant saccade direction are in the same direction and mixed together, which can affect the dispersion and amplitude of overt saccade in vHIT. Accurate identification of SN in vHIT of AUVP patients is not only the key factor to identify compensatory saccade, but also can provide help for the diagnosis and compensatory assessment of AUVP.

Estimating Cognitive Workload Using Task-Related Pupillary Responses in Simulated Drilling in Cochlear Implantation.

Training of temporal bone drilling requires more than mastering technical skills with the drill. Skills such as visual imagery, bimanual dexterity, and stress management need to be mastered along with precise knowledge of anatomy. In otorhinolaryngology, these psychomotor skills underlie performance in the drilling of the temporal bone for access to the inner ear in cochlear implant surgery. However, little is known about how psychomotor skills and workload management impact the practitioners' continuous and overall performance. To understand how the practitioner's workload and performance unfolds over time, we examine task-evoked pupillary responses (TEPR) of 22 medical students who performed transmastoid-posterior tympanotomy (TMPT) and removal of the bony overhang of the round window niche in a 3D-printed model of the temporal bone. We investigate how students' TEPR metrics (Average Pupil Size [APS], Index of Pupil Activity [IPA], and Low/High Index of Pupillary Activity [LHIPA]) and time spent in drilling phases correspond to the performance in key drilling phases. All TEPR measures revealed significant differences between key drilling phases that corresponded to the anticipated workload. Enlarging the facial recess lasted significantly longer than other phases. IPA captured significant increase of workload in thinning of the posterior canal wall, while APS revealed increased workload during the drilling of the bony overhang. Our findings contribute to the contemporary competency-based medical residency programs where objective and continuous monitoring of participants' progress allows to track progress in expertise acquisition. Laryngoscope, 134:5087-5095, 2024.

Superior semicircular canal dehiscence isolation by transmastoid two-point canal plugging with preservation of the vestibulo-ocular reflex. German version

This article describes the surgical treatment of superior semicircular canal dehiscence syndrome (SCDS) by isolating the dehiscence using transmastoid two-point canal plugging while preserving the high-frequency vestibulo-ocular reflex (VOR) of the affected semicircular canal. The superior semicircular canal is opened via atransmastoid approach anterior (as far from the ampulla as possible) and posterior to the dehiscence and then plugged with connective tissue and bone dust. In two clinical exemplary cases, vestibular testing showed that the VOR measured by video head impulse (vHIT) test was preserved (patient1: gain preoperative 0.7, long-term postoperative 0.75; patient2: gain preoperative 0.64, long-term postoperative 0.79; reduction of corrective saccades in each case) with asimultaneous reduction in pathologically increased amplitudes of vestibular evoked myogenic potentials (VEMPs) and asignificant improvement in clinical symptoms with almost complete freedom from symptoms. One possible explanation for preservation of the high-frequency VOR of the superior semicircular canal would be the deformability of the endolymphatic space described at high stimulation frequencies, which can lead to endolymph movements in the area of the ampulla with deflection of the cupula despite blockage of the semicircular canal.

Vestibular electrode position stability over time.

In vestibular implants (VI), the electrode position is thought to be important for optimal neural activation. The objective of this study was to evaluate the stability of the vestibular electrode position over time. Seven patients implanted with a VI were followed for one year. When possible, the fenestrations of the semicircular canals were kept very small (approximately 0.8mm) to stabilize the electrode lead. Additionally, the electrodes were fixed at their fenestration sites using bone cement. A temporal bone CT scan was performed intraoperatively, and one week and one year postoperatively. In one patient reliable analysis of the intraoperative CT scan was not possible due to a technical error. A displacement of the vestibular electrodes of more than 0.5mm was considered significant. Fourteen out of 18 electrodes did not show a significant displacement between the intraoperative scan and the first postoperative scan. In the remaining four electrodes, a displacement of ≥ 0.5mm occurred (mean 0.54mm, range 0.50-0.58mm). These four electrodes were found in the two first implanted patients. In both cases, the intraoperative CT scan had a slice thickness of 0.5mm and showed severe scattering. This might imply that the measured displacement was (partially) related to a higher measurement error. None of the vestibular electrodes migrated outside of the ampulla. No displacement was observed in any of the vestibular electrodes between the first postoperative scan and the one-year follow-up scan. The current surgical technique seems to securely stabilize the vestibular VI electrodes over time.

Comparing the efficacy of repositioning manoeuvres over medications in the treatment of posterior and lateral canal benign paroxysmal positional vertigo: a prospective, randomized and comparative study

Background: Benign paroxysmal positional vertigo (BPPV) is a benign peripheral disorder of vestibular system and is the most common cause of peripheral vertigo. The aim of our study was to compare and assess the efficacy of Epley’s and Barbeque roll over manoeuvres with labyrinthine sedatives in the management of Benign Paroxysmal Positional Vertigo (BPPV) over a period of one month and to know the prevalence of BPPV in different age and gender groups among the two semicircular canals(posterior and lateral). Methods-This prospective randomized comparative clinical trial included 60 patients with clinically diagnosed BPPV in a tertiary care centre and were investigated for a period on one year. The clinical diagnosis of specific canal type of BPPV was assessed based on the diagnostic tests, Dix Hallpike test and McClure test. In manoeuvre group, posterior canal BPPV, Epley’s manoeuvre was performed and for lateral canal BPPV, Barbeque roll over manoeuvre was performed as treatment. In pharmacological group, labyrinthine sedatives i.e. either cinnarizine 25mg twice a day or betahistine 16 mg twice a day were administered for one month as treatment. Results: Results were assessed at the end of 48 hours (immediate time period) and at four weeks’ time period after the treatment, under three different outcome categories namely disappeared, improving and unchanged. Treatment of Benign Paroxysmal Positional Vertigo with repositioning manoeuvre had higher success percentage of 83.3% than the medical treatment. Conclusion: The treatment of BPPV with repostioning manoeuvres had a better outcome than the medical treatment.

Video head impulse test (vHIT) unravels the hidden pathology in chronic vestibular deficit

BackgroundThe caloric test is persistently altered in chronic peripheral vestibular hypofunction (PVH). So, we cannot depend on it to measure the degree of compensation in chronic vestibulopathy patients who are still complaining. So our aim was to assess the utility of vHIT to discover the unrevealed pathology in those patients. Our study included 20 subjects with unilateral chronic PVH who were still complaining (study group) and 20 healthy volunteers (control group). Videonystagmography (VNG) and video head impulse test (vHIT) were applied to all the subjects.ResultsVNG and caloric test results showed compensation signs in the study group. The caloric test indicated unilateral weakness in the affected side. According to vHIT results, a comparison between the affected lateral canal, contralateral healthy lateral canal among the study group, Rt. lateral canal, and Lt. lateral canal among the control group revealed no significant difference (P = 0.789), while comparing anterior and posterior canals showed significant differences (P = 0.005, 0.025) respectively.ConclusionThe caloric test assesses only the horizontal semicircular canal and it is persistently altered in unilateral chronic PVH. So, we cannot depend on it to measure the degree of compensation in chronic vestibulopathy patients who are still complaining nor to detect unrevealed pathology regarding ant or post semi-circular canal. So we can use the vHIT test to discover the unrevealed pathology in those patients.

Differential energetic profile of signal processing in central vestibular neurons

BackgroundEnergetic aspects of neuronal activity have become a major focus of interest given the fact that the brain among all organs dominates the oxygen consumption. At variance with the importance of neuroenergetics, the knowledge about how electrical activity and metabolism is correlated in defined neuronal populations is still rather scarce.ResultsWe have estimated the ATP consumption in the two physiologically well characterized populations of frog central vestibular neurons, with tonic and phasic firing patterns, respectively. These two distinct groups of neurons jointly process head/body movements detected by semicircular canal and otolith organs in the inner ear. The ATP consumption for maintenance of the resting membrane potential (Vr) and postsynaptic action potential (AP) generation was calculated based on the wealth of previously reported morpho-physiological features of these two neuronal types. Accordingly, tonic vestibular neurons require less ATP across the physiological activity range for these major processes, than phasic vestibular neurons, despite the considerably higher firing rates of the former subtype. However, since both neuronal subtypes are indispensable for the encoding and processing of the entire head/body motion dynamics, the higher energy demand of phasic neurons represents an obvious and necessary price to pay. Although phasic and tonic neurons form the respective core elements of the frequency-tuned vestibular pathways, both cellular components are cross-linked through feedforward and feedback side loops. The prominent influence of inhibitory tonic neurons in shaping the highly transient firing pattern of phasic neurons is cost-intensive and contributes to energy consumption for electrical activity in addition to the already extensive energy costs of signal processing by the very leaky phasic vestibular neurons.ConclusionDespite the sparse production of action potentials by phasic vestibular neurons, the computation by this neuronal type dominates the ATP expense for processing head/body movements, which might have contributed to the late evolutionary arrival of this central neuronal element, dedicated to the encoding of highly dynamic motion profiles.

Evaluation of Posterior Superior Alveolar Canal in Individuals With Cleft Lip and Palate Using Cone Beam Computed Tomography.

To evaluate the posterior superior alveolar canal (PSAC) in individuals with cleft lip and palate (CLP) by comparing them with individuals with no cleft lip and palate (NC) using cone beam computed tomography (CBCT). This is a cross-sectional, analytical study with a prospective sample. CBCT scans of 29 individuals with no cleft and palate (Group I) and 29 individuals with cleft lip and palate (Group II) were used. PSAC was evaluated and compared for its position, diameter, and distance between the individuals with CLP and NC using CBCT scans. The mean age of individuals in Group I and II were 12.93 and 11.82 years, respectively. The distribution of individuals based on gender comprised of 51.7% males and 48.3% females in both the study groups. PSAC was present in both right and left maxillary sinus in 100% of the study subjects of Group I and Group II. The most prevalent position of PSAC in Group I and Group II was on the lower third and middle third of lateral wall of maxillary sinus, respectively. The mean diameter was higher in Group II (1.2962 mm) when compared to Group I (1.0897 mm) which showed statistically significant value (P = .008). The promising results obtained from the present study demonstrates the importance of knowing the precise anatomical location of the PSAC in individuals with cleft lip and palate by using CBCT which is reliable, less time consuming and cost effective imaging tool.

Reduced Vestibular Function is Associated with Cortical Surface Shape Changes in the Frontal Cortex.

Aging-associated decline in peripheral vestibular function is linked to deficits in executive ability, self-motion perception, and motor planning and execution. While these behaviors are known to rely on the sensorimotor and frontal cortices, the precise pathways involving the frontal and sensorimotor cortices in these vestibular-associated behaviors are unknown. To fill this knowledge gap, this cross-sectional study investigates the relationship between age-related variation in vestibular function and surface shape alterations of the frontal and sensorimotor cortices, considering age, intracranial volume, and sex. Data from 117 participants aged 60+ from the Baltimore Longitudinal Study of Aging, who underwent endorgan-specific vestibular tests (cVEMP for the saccule, oVEMP for the utricle, and vHIT for the horizontal canal) and T1-weighted MRI scans on the same visit, were analyzed. We examined ten brain structures in the putative "vestibular cortex": the middle-superior part of the prefrontal cortex (SFG_PFC), frontal pole (SFG_pole), and posterior pars of the superior frontal gyrus (SFG), the dorsal prefrontal cortex and posterior pars of middle frontal gyrus (MFG_DPFC, MFG), the pars opercularis, pars triangularis, and pars orbitalis of the inferior frontal gyrus, as well as the precentral gyrus and postcentral gyrus (PoCG) of the sensorimotor cortex. For each region of interest (ROI), shape descriptors were estimated as local compressions and expansions of the population average ROI surface using surface LDDMM. Shape descriptors were linearly regressed onto standardized vestibular variables, age, intracranial volume, and sex. Lower utricular function was linked with surface compression in the left MFG and expansion in the bilateral SFG_pole and left SFG. Reduced canal function was associated with surface compression in the right SFG_PFC and SFG_pole and left SFG. Both reduced saccular and utricular function correlated with surface compression in the posterior medial part of the left MFG. Our findings illuminate the complexity of the relationship between vestibular function and the morphology of the frontal and sensorimotor cortices in aging. Improved understanding of these relationships could help in developing interventions to enhance quality of life in aging and populations with cognitive impairment.

Congenital Internal Auditory Canal Stenosis

A 3-year-old boy underwent evaluation for possible cochlear implantation. He had failed a neonatal otoacoustic emission (OAE) hearing screen. A combined auditory brainstem response/auditory steady-state response (ABR/ASSR) test battery confirmed the presence of a severe hearing loss on the right and a profound hearing loss on the left. No Joint Committee on Infant Hearing (JCIH) risk factors for early childhood hearing loss1 were identified. Rehabilitation via hearing aid amplification and auditory-verbal speech therapy was unsuccessful. Computerized tomographic (CT) imaging of the temporal bone was performed to identify the presence of any inner ear abnormalities. No abnormalities of the cochlea, vestibule and semicircular canals on both sides were identified by the radiologist. The internal auditory canals were described as “fairly symmetrical without widening”, and the study was officially reported as an “unremarkable study of the temporal bones”. Independent review of the CT imaging revealed the presence of seemingly narrow internal auditory canals (IAC) on both sides. (Figure1A) The width of the IACs on the axial plane were measured by drawing a perpendicular line starting from the posterior wall of the IAC, 2 mm inside the posterior lip of the internal auditory meatus, and ending on the anterior canal wall, as described by McClay et al.2 Measurements taken utilizing the length measurement tool in the DICOM imaging software (RadiAnt DICOM Viewer, Version 2024.1, Medixant) indicated an IAC width of 1.78 mm on the right (with severe hearing loss) and 1.37 mm on the left (with profound hearing loss). (Figure 1B) These measurements confirmed the presence of bilateral internal auditory canal stenosis, a diagnosis defined by a canal of 2 mm or less on highresolution CT.3

Revisiting Diagnostic Criteria for Bilateral Vestibulopathy: A New Comprehensive Instrumental Model.

Background: Bilateral vestibulopathy (BVP) is a disabling condition characterized by a deficit in vestibular function on both sides. Current diagnostic criteria consider instrumental data only from horizontal canals, excluding vertical canals and otolithic function, with the possibility of not including some variants of BVP. This study aims to evaluate vestibular functions in people with chronic vestibular syndrome through a comprehensive battery of tests. Methods: This diagnostic accuracy study included patients who met criteria for probable BVP. The index test included a thorough evaluation of the vestibular system, using the video Head Impulse Test (vHIT) to measure the gain of the angular vestibulo-ocular reflex (aVOR) in all six semicircular canals and the cervical and ocular vestibular-evoked myogenic potentials (VEMPs) to assess otolith function. The diagnostic criteria established by the Barany Society were considered the standard reference, including only the horizontal vHIT as an instrumental assessment. Results: 78 patients (41 male, age 61.40 ± 12.99) were enrolled. The Barany criteria showed a low ability to rule out BPV (sensitivity = 46%). The median Dizziness Handicap Inventory (DHI) varied from 66 to 69 among the models studied, and a significant difference in DHI scores between positive and negative tests was observed for the Barany criteria and the six-canals vHIT model. Conclusions: Our findings highlight the potential to transform BPV diagnostic criteria. The identification of new bilateral vestibular dysfunction variants through improved diagnostic tools calls for revising current criteria, with promising implications for patient care and understanding of etiological and prognostic aspects.

The specialized inner ear labyrinth of worm-lizards (Amphisbaenia: Squamata).

High-resolution computed tomography (HRCT) has become a widely used tool for studying the inner ear morphology of vertebrates. Amphisbaenians are one of the most specialized groups of fossorial reptiles but are poorly understood relative to other squamate reptile. In this paper we survey the anatomy of the inner and middle ear of these fossorial reptiles using HRCT models and we describe qualitatively and quantitatively (using 3D morphometrics) the anatomy of the inner ear. Amphisbaenians are diverse in skull anatomy, especially in the configuration of the snout, which correlates with digging modes. We demonstrate that the ear also exhibits a diversity of configurations, which are independent of phylogenetic relationships. Results from morphological analyses also allow us to describe 11 new potentially informative phylogenetic characters including some that help to diagnose amphisbaenians, such as: 1) the globular vestibule, ii) semicircular canals arranged in a circular trajectory, and iii) an extensive area of interaction between the columella footplate and the lagenar recess. Among extant amphisbaenians, Rhineura floridana has the most unusual inner ear configuration, including a horizontal semicircular canal that is in the same orientation as the inclined snout. The new morphological information helps us to better understand the morphology of headfirst-burrowing fossorial reptiles and contributes new data for resolution of phylogenetic relationships among amphisbaenians.

Morphology of the human inner ear and vestibulocochlear nerve assessed using 7T MRI.

To optimize high-resolution 7T MRI of the cochlea and measure normal cochlea and the cochlear nerve morphometry in vivo. Eight volunteers with normal hearing were scanned at 7T using an optimized protocol. Two neuroradiologists independently scored image quality. The basal turn lumen diameter (BTLD), height, width, length and volume of the cochlear, long (LD) and short (SD) diameter the calculated cross-sectional area (CSA) of the cochlear nerve were measured. Intra and inter-observer reliability was assessed using intraclass correlation (ICC). 3D T2W DRIVE combined with dielectric pads, allowed acquisition of high-resolution images showing detailed structures, such as the crista ampullaris in the semicircular canals. The overall grading scores from neuroradiologists were excellent. In the left ear, averaging over all subjects gave BTLD of 2.6 ± 0.05mm, height of 4.9 ± 0.1mm, width of 4.4 ± 0.2mm, length of 36.5 ± 0.4mm, volume of 0.16 ± 0.02ml, LD of 1.31 ± 0.1mm, SD of 1.06 ± 0.1mm, and CSA of 1.1 ± 0.1 mm2. The right ear gave BTLD of 2.6 ± 0.04mm, height of 4.9 ± 0.1mm, width of 4.4 ± 0.3mm, length of 35.5 ± 0.4mm, volume of 0.16 ± 0.02ml, LD of 1.29 ± 0.1mm, SD of 1.07 ± 0.1mm, and CSA of 1.10 ± 0.2 mm2. No statistically significant difference was found between the sides of the head (p-value > 0.05). The intra-observer reliability was high (0.77-0.94), while the inter-observer reliability varied from moderate to high (0.55-0.81). 7T MRI can provide excellent visualization of the internal structure of the cochlear and of the vestibulocochlear nerve in vivo.

SURG-55. NOVEL IQ-DOME APPROACH FOR SUPERIOR SEMICIRCULAR CANAL DEHISCENCE REPAIR REDUCES REVISIONAL SURGERY RATE

Abstract Superior Semicircular Canal Dehiscence (SSCD) is characterized by a thinning of the bony ceiling of the superior semicircular canal, manifesting in auditory and vestibular deficits. Surgical repair is the standard treatment modality of SSCD, with conventional methods including plugging or recapping the defective canal with bone wax, bone chips, muscle, and others. Previous research has shown multiple complications with these conventional materials, including a high rate of failure of the primary repair and the need for revisional surgeries. To address this challenge, we investigated a novel surgical sealing technique using IQ-Dome, a titanium mesh plate overlying the arcuate eminence. We aim to assess the efficacy of IQ-Dome in the repair of SSCD compared to conventional material while evaluating outcome measures including postoperative symptom resolution, complication, and revisional surgery rates. We performed a retrospective analysis of patients undergoing SSCD repair via the middle cranial fossa approach at UCLA between 2017 and 2021. We compared demographics and post-operative outcomes between the application of IQ-Dome and conventional materials. A total of 160 patients undergoing SSCD repair were included in our study, with 80 patients receiving IQ-Dome and 80 patients receiving non-IQ-Dome approaches. 60% of patients in the IQ-Dome cohort and 66.7% of patients in the non-IQ-Dome cohort were female. The mean ages of patients were 45.7 years (range 13-78) in the IQ-Dome cohort and 48.9 years (range 17-69) in the non-IQ-Dome cohort. The surgical revision rates for the IQ-Dome and non-IQ-Dome cohorts were 5.7% and 8.5%, respectively. There was no significant difference in postoperative complications between groups. Thus, IQ-Dome is a safe approach for the surgical management of SSCD, decreasing failure and revision rate by nearly 3% in our patient population and offering an alternative surgical sealing repair intervention. Future studies with larger sample sizes are warranted to further assess the efficacy of IQ-Dome.

Surgical and dermatological management of asymptomatic congenital ear canal atresia in a male Wirehaired Pointing Griffon dog

AbstractA 1‐year‐old, male, entire Wirehaired Pointing Griffon was evaluated for asymptomatic right congenital ear canal atresia. Head computed tomography confirmed congenital ear canal atresia diagnosis. Surgical resection and anastomosis of the ear canal followed by video otoscopy was performed. An intact, but flaccid tympanic membrane, suspected from impacted ear canal debris, was identified. One week postoperatively, bilateral yeast otitis externa was diagnosed and successfully treated with topical anti‐fungal therapy. Five months postoperatively, the stoma remained patent, the dog was asymptomatic, and computed tomography with video otoscopy revealed a taut tympanic membrane bulging into the horizontal ear canal. Myringotomy, cytology, bacterial cultures, susceptibility testing, middle ear saline lavage and pre‐emptive topical antibiotic therapy were pursued. Cultures yielded no bacterial growth. Four weeks later, the tympanic membrane was visibly normal, and the stoma was unchanged. This case report is the first to describe interdisciplinary management of asymptomatic congenital ear canal atresia and might support early surgical intervention as a reasonable option.

Semicircular canal drug delivery safely targets the inner ear perilymphatic space.

Effective, reproducible, and safe delivery of therapeutics into the inner ear is required for the prevention and treatment of hearing loss. A commonly used delivery method is via the posterior semicircular canal (PSCC); however, its specific targeting within the cochlea remains unclear, impacting precision and reproducibility. To assess safety and target specificity, we conducted in vivo recordings of the pharmacological manipulations delivered through the PSCC. Measurements of auditory brainstem response (ABR), vibrometry, and vestibular behavioral and sensory-evoked potential (VsEP) revealed preserved hearing and vestibular functions after artificial perilymph injections. Injection of curare, a mechanoelectrical transducer (MET) channel blocker that affects hearing when in the endolymph, had no effect on ABR or VsEP thresholds. Conversely, injection of CNQX, an AMPA receptor blocker, or lidocaine, a Na+ channel blocker, which affects hearing when in the perilymph, significantly increased both thresholds, indicating that PSCC injections selectively target the perilymphatic space. In vivo tracking of gold nanoparticles confirmed their exclusive distribution in the perilymph during PSCC injection, supporting the pharmacological finding. Together, PSCC injection is a safe method for inner ear delivery, specifically targeting the perilymphatic space. Our findings will allow for precise delivery of therapeutics within the inner ear for therapeutic and research purposes.