Semicircular Canal Research Articles

From Injury to Innovation: Margaret Dix's Pioneering Work in Neuro-Otology.

Margaret Ruth Dix made groundbreaking contributions to neuro-otology, particularly in the study of vestibular disorders. Together with Charles Hallpike, Dix developed the Dix-Hallpike maneuver, a diagnostic technique that is still widely used today for benign paroxysmal positional vertigo (BPPV). Their research provided critical insights into BPPV, although they initially misidentified its cause, attributing it to otolithic disturbances instead of semicircular canal dysfunction. In addition to her work on BPPV, Dix made important contributions to caloric testing, Meniere's disease, and pure tone audiometry for young children, among other areas. Her efforts led to more effective diagnostic and educational methods. Despite some early misconceptions, the work of Dix and Hallpike remains a cornerstone of neuro-otology. The Dix-Hallpike maneuver continues to be essential for diagnosing BPPV, and their research has had a lasting impact on clinical practice and scientific knowledge in the field.

Determination of Recovery by Total Restitution or Compensation Using Multifrequency Vestibular Tests and Subjective Functional Scales in a Human Model of Vestibular Neuritis.

Vestibular Neuritis (VN) can induce unilateral acute vestibular syndrome (AVS). This study aimed to identify predictive factors of recovery from vestibular neuritis considering total restitution and/or compensation. In this longitudinal study, 40 patients were included. The initial assessment, performed within 36 to 72 h from the onset (T0), included medical history taking (general and specific), including screening for cardiovascular risk factors (CVRFs), and a battery of diagnostic vestibular tests, comprising the bithermal caloric test (BCT), video head impulse test (VHIT), and skull vibration-induced nystagmus (SVIN) test. All patients also completed a Dizziness Handicap Inventory (DHI). All assessments were repeated 90 ± 15 days later (T3). Subjective compensation criteria were based on the DHI total score, and objective compensation criteria were based on laboratory test results. Four groups of patients (A, B, C, D) were delineated by combining patients with normal vs. abnormal vestibular tests and patients with normal vs. abnormal DHI. CVRFs (but not age or body mass index (BMI)) were associated with a poorer recovery of symptoms. The BCT (lateral semicircular canal paresis %), VHIT (lateral semicircular canal gain), and SVINT (nystagmus slow phase velocity) recovered to normal values in 20%, 20%, and 27% of patients, respectively, at T3. Vascular risk factors (hypercholesterolemia) are correlated with patients who do not recover their symptoms via either total restitution or compensation. There was no significant difference between high- and low-frequency vestibular tests in patients recovering from their symptoms. Some patients with objective recovery may continue to have persistent subjective symptoms.

When the Jugular Bulb Contacts the Facial Nerve.

Dehiscences of the intrapetrous canal of the facial nerve (FN) and those of a high jugular bulb (HJB) have various incidences. However, the HJB-FN common dehiscent osseous wall is a scarce finding and rarely reported. Thus, this work aimed to study this peculiar intrapetrous morphology on computed tomograms (CTs). A batch of 60 archived CTs was used. In 28.33% of cases, no HJBs were found; in 51.67% of cases, there were unilateral HJBs, and in 20% of cases, bilateral HJBs were found. 83.87% of the unilateral HJBs were on the right side, and the rest on the left side. In 3 cases with right-sided HJBs, 1 male and 2 females, FNs were found directly contacting the HJB. Therefore, the contact HJB-FN occurred in 5% of cases and 2.5% of the petrous bones/sides. HJBs' dehiscences to the retrotympanum or the posterior cranial fossa were also found in those cases. A dehiscent posterior semicircular canal to the HJB was found in one of these. Incidences for the HJB and the HJB-FN contacts seem higher than in previous studies. However, as only a 60-case batch of study was used, an overestimation may have resulted. Although scarce, the HJB-FN contact could determine specific symptoms and must be documented before specific surgical procedures involving the mastoid, retrotympanum, and posterior cranial fossa.

Abstract 350: Optimizing Stroke Assessment of Dizziness: The Role and Impact of Video Head Impulse Testing

Introduction Dizziness is a frequent and challenging symptom in patients with posterior ischemic stroke, often making it difficult to distinguish from peripheral vestibular disorders. The video head impulse test (vHIT) is a non‐invasive tool that measures the vestibulo‐ocular reflex (VOR) to assess semicircular canal function. This study evaluates the effectiveness of vHIT in the emergency department (ED) for differentiating between central (stroke‐related) and peripheral causes of dizziness. The primary objective is to confirm that vHIT is an effective tool for enhancing diagnostic confidence in ruling out stroke and avoiding unnecessary admissions, thereby optimizing resource allocation for other stroke patients. Methods In this prospective study, 30 patients who presented to the ED of the stroke center with dizziness and were subsequently admitted under standard stroke protocol were analyzed. Each patient underwent vHIT in addition to the standard stroke evaluation, which included MRI. The vHIT assessed the VOR in the lateral semicircular canal to detect vestibular hypofunction through measured gain reduction and saccadic eye movements. Two specialists independently analyzed the vHIT results, both blinded to the MRI findings. Results Of the 30 patients included in the study, MRI was performed on 27, serving as the gold standard for stroke detection. MRI confirmed the presence of a stroke in 10 cases (37%). Among these patients, the vHIT indicated a possible central etiology in 9 patients, with a sensitivity of 100% (95% CI: 66.37% to 100%). One patient's vHIT recordings were of poor quality, making the results uninterpretable. In the subgroup of 17 patients with negative MRI findings, vHIT suggested a peripheral cause of dizziness in 2 patients. The specificity of vHIT for central etiology was 15.38% (95% CI: 1.92% to 45.45%) with a negative predictive value of 100% (95% CI: 15.81% to 100.00%) and a positive predictive value of 40.97% (95% CI: 35.50% to 46.67%). One patient with a negative MRI but positive vHIT for peripheral etiology was unnecessarily admitted for 3 days. Conclusion Our findings suggest that incorporating vHIT into the ED workflow could be an effective strategy for ruling out stroke before proceeding with extensive stroke admissions and workups. vHIT appears to be a valuable tool in the initial assessment of patients with dizziness, facilitating the differentiation between central and peripheral causes. This approach has the potential to reduce unnecessary hospital admissions for patients without central pathology.

Retrolabyrinthine approach to the lateral skull base: The value of preoperative temporal bone CT analysis

PurposeThe most used neurosurgical approach to reach cerebellar-pontine angle is the retrosigmoid route. This article describes the presigmoid approach which requires excellent knowledge of the labyrinthine block together with quantitative analysis of temporal bone CT. MethodsCT-based quantitative measurements were obtained in patients undergoing vestibular neurectomy with a presigmoid approach. Eighteen patients were enrolled, and five measures were taken: Trautmann’s area, the petro-clival angle, presigmoid dura length and its angle. The relationship between these measurements and hospitalization days, operating times, and complications was explored. ResultsThe posterior semicircilar canal (PSC)-sigmoid sinus (SS) distance, presigmoid dura- internal auditory canal (IAC)-PSC angle, and duration of surgery are predictors of complications. Specifically, a PSC-sigmoid sinus distance <11 mm, a dura presig-IAC-PSC angle <14 are associated with the highest risk of complications. ConclusionPreoperative temporal bone CT scan can guide the surgeon through the narrowest areas of the surgical approach. Trautmann’s triangle area and petro-clival angle reduction are challenging and can be faced with combined microscopic-endoscopic technique, and with optics angulation-rotation. The retrolabyrinthine approach can enable hearing preservation and minimal cerebellar retraction.

Analysis of influencing factors of residual dizziness after repositioning of horizontal semicircular canal benign paroxysmal positional vertigo

Background Horizontal semicircular canal benign paroxysmal positional vertigo(HSC-BPPV) is the second most common type of BPPV. It is difficult to diagnose and treat, which has a serious impact on the prognosis of patients. Objectives To study the clinical features of HSC-BPPV and the influencing factors of residual dizziness (RD). Materials and methods The clinical data of 358 patients with BPPV were retrospectively collected. The differences between HSC-BPPV and posterior semicircular canal benign paroxysmal positional vertigo (PSC-BPPV) were compared, and the influencing factors of RD after HSC-BPPV repositioning were analyzed. Results ① Compared with PSC-BPPV, HSC-BPPV had a lower success rate of first repositioning (64.7 vs. 75.0%), a higher incidence of RD (57.3 vs. 43.8%), and a higher DHI score (40.0 vs. 34.0), and the differences were statistically significant (p < .05). ② Logistic regression analysis showed that age ≥60 years, secondary, DHI score, successful first repositioning were the influencing factors for the development of RD after HSC-BPPV repositioning (p < .05). Conclusions and significance The diagnosis and treatment of HSC-BPPV is difficult, and RD is prone to occur. Clinicians need to strengthen the training of HSC-BPPV diagnosis and treatment to reduce the occurrence and progression of RD.

Endocranial morphology of three early-diverging ceratopsians and implications for the behavior and the evolution of the endocast in ceratopsians

Abstract Ceratopsian dinosaurs underwent great changes, including a shift of locomotion mode, enlarged horns and frills, and increased body size. These changes occur alongside the evolution of endocranial morphology and physiology such as the size and shape of the flocculus, hearing range, olfactory ratio, and the reptile encephalization quotient (REQ). However, the evolution of endocranial structures in early ceratopsians is still unclear because of a lack of information on the earliest ceratopsians. Here, we reconstructed the endocasts of three early-diverging ceratopsians including the Late Jurassic Yinlong, and the Early Cretaceous Liaoceratops and Psittacosaurus. These ceratopsians display obvious flocculi, large and separate olfactory bulbs, long and high anterior semicircular canals, and relatively long cochlear ducts. In the evolution of the earliest ceratopsians to early neoceratopsians, changes include the increasing size of the flocculus (which is reduced or absent in late-diverging ceratopsids), the attenuation of the semicircular canals, and the heightening of the anterior semicircular canal (which is shortened in late-diverging ceratopsids). The endocranial structures suggest early-diverging ceratopsians had a higher olfactory acuity and were adapted to hearing higher frequencies than late-diverging ceratopsians. Furthermore, the REQ suggests that Yinlong and Psittacosaurus were more highly encephalized than late-diverging ceratopsians and most extant reptiles. The angle of the lateral semicircular canal suggests that heads in ceratopsians display a transition from a forward posture to a more downward posture. Our new findings are significant for understanding the physiological changes during ceratopsian evolution and also have implications for the evolution of physiology in extant tetrapods.

Model of superior semicircular canal dehiscence: asymmetrical vestibular dysfunction induces reversible balance impairment.

Superior semicircular canal dehiscence (SSCD) is a vestibular-cochlear disorder in humans in which a pathological third mobile window of the otic capsule creates changes to the flow of sound pressure energy through the perilymph/endolymph. The primary symptoms include sound-induced dizziness/vertigo, inner ear conductive hearing loss, autophony, headaches, and visual problems. We have developed an animal model of this human condition in the Mongolian Gerbil that uses surgically created SSCD to induce the condition. A feature that is unique in this model is that spontaneous resurfacing of the dehiscence occurs via osteoneogenesis without a subsequent intervention. In this study, we completed our assessment of this model to include reversible asymmetrical vestibular impairments that interfere with balance. Adult Mongolian gerbils (N = 6) were trained to complete a balance beam task. They were also trained to perform a Rotarod task. After 10 days of training, preoperative ABR and c+VEMP testing was followed by a surgical fenestration of the left superior semicircular canal. Balance beam testing recommenced at postoperative day 6 and continued through postoperative day 15 at which point final ABR and c+VEMP testing was carried out. Behavioral comparison of preoperative and postoperative performance show a significant decrease in Rotarod performance, increased rates of falling, and an increase in time to cross the balance beam. Impairments were the most significant at postoperative day 7 with a return toward preoperative performance by postoperative day 14. This behavioral impairment was correlated with residual impairments to auditory thresholds and vestibular myogenic amplitudes at postoperative day 14. These results confirm that aberrant asymmetric vestibular output in our model of SSCD results in reversible balance impairments. The level of these behavioral impairments is directly correlated with severity of the vestibular dysfunction as we have previously reported for peripheral ear physiology and cognition.

Specific features of bilateral otolith manifestations in patients with vestibular balance disorder

Bilateral asymmetry in the function of the semicircular canals underlies dizziness and vestibular balance disorders. According to the traditional view, otolith dysfunction does not have a significant effect on the clinical picture in individuals with peripheral vestibular disorders. In recent years, interest in studying the contribution of vestibular function to the control of posture and movements has increased. However, we have not identified any studies addressing the reactivity of otolith organs in vestibular balance disorders in the available literature.Aim: To study bilateral otolith reactions in patients with vestibular balance disorders using the method of cervical vestibular evoked myogenic potentials (cVEMP) in patients with episodic and chronic vestibular disorders.Material and Methods. A clinical examination was carried out in 63 patients complaining of dizziness and balance problems. They were hospitalized on an emergency and planned basis in the neurological departments of the clinics of the Siberian State Medical University and the Medical and Sanitary Unit No 2 in Tomsk. From the total group, 28 patients (8 men and 20 women aged from 22 to 84 years) were selected for assessment of vestibular function; the average age was 63.87 ± 11.52 years and 57.2 ± 18.5 years for men and women respectively. They had chronic and episodic vestibular dysfunction unrelated to acute or progressive neurological disease and inflammatory pathology of the inner ear.Results. 27 patients (96.4%) complained of dizziness. Systemic dizziness, characterized by a feeling of objects rotating around the subject, was detected in 29.63% of patients; non-systemic dizziness, including a feeling of “failing” – in 81.48%. Both types of complaints appeared in 10.71% of those examined, which made it possible to identify 2 groups of patients: Group A – with chronic vestibular disorders (7 patients) and Group B – with episodic vestibular disorders (21 patients). During the study of the groups of patients, differences were found in the amplitudes of cVEMP latency P13 and the coefficient of vestibular asymmetry between Groups A and B, as well as the absence of a difference in amplitudes in Group A and the presence of a difference in Group B on the right.Conclusion. Despite the fact that patients presented with predominantly one complaint of dizziness, clinical and instrumental tests of vestibular dysfunction showed the presence of damage to both the semicircular canals and otolithic organs; asymmetry of vestibular reflexes and/or bilateral damage to the vestibular organs. The results of the study allow us to consider the cVEMP method as one of the methods for objectively assessing the condition of the otolithic apparatus in patients with impaired vestibular function. In this regard, it is recommended to use this method in routine neurological practice.

Revised Classification of Inner Ear Schwannomas.

Over the past two decades, there has been increasing interest in the diagnosis and management of schwannomas of the inner ear including hearing rehabilitation with cochlear implants. However, tumor nomenclature and classification within the literature have been variable and oftentimes cumbersome. The term "intralabyrinthine schwannoma" is in common use when describing these tumors but is a potential source of confusion given that people often use the term "labyrinth" or "labyrinthine" to refer to the vestibular component of the inner ear only (i.e., labyrinthectomy or the translabyrinthine approach).During the Ninth Quadrennial Conference on Vestibular Schwannoma and Other Cerebellopontine Angle Lesions in Bergen, Norway, in May 2023, a multidisciplinary group of conference participants met and discussed issues pertaining to current terminology and classifications to enhance clarity and to reflect recent advances in tumor management and hearing rehabilitation.Although a variety of terms have been previously used to describe inner ear schwannomas, consensus was achieved on the term "inner ear schwannoma (IES)" to describe eighth nerve schwannomas of the cochlea, vestibule, or semicircular canals. Subgroups under this term comprise intravestibular, intracochlear, or intravestibulocochlear inner ear schwannomas (low complexity tumors), inner ear schwannomas with transfundal extension into the internal auditory canal but without modiolar involvement (intermediate complexity tumors), and inner ear schwannomas with transfundal extension with modiolar involvement (high complexity tumors).The details of the recommendations for an updated and simplified tumor nomenclature centered around tumor control and hearing rehabilitation with cochlear implantation are presented.

Minor's Syndrome or Dehiscence of the Superior Semicircular Canal: A Case Report

Semicircular canal dehiscence is a congenital syndrome that mainly affects the superior and, less commonly, the posterior semicircular canal in the temporal bone. This syndrome was first reported by Minor et al. in 1998. The prevalence is about 0.5% in the general population. The most characteristic symptom is the Tullio phenomenon, predominantly vertigo and nystagmus. Hearing loss (in particular conductive loss) often completes overall clinical picture. The dehiscence may be completely asymptomatic, in which case it is seen as an incidental finding on radiological investigations. Audiological evaluation includes audiometry and vestibular evoked myogenic potentials (VEMPs). Clinical symptoms are based on the pathophysiological concept of a third mobile window within the inner ear. Diagnosis is confirmed by high resolution petrous temporal bone CT with multiplanar reconstructions (MPRs) in the plane of the canal (Pöschls’ plane for the superior semicircular canal) and 3-D surface reconstructions. MR findings are less sensitive for this entity. The most common differential diagnosis is otosclerosis. Clinical–radiological correlations have therapeutic applications even though the indication for surgery depends on the severity of the vestibular symptoms.

The Impact of Sleep Deprivation on Video Head Impulse Test Results.

To investigate the association between sleep deprivation and vestibular dysfunction by Video Head Impulse Test (vHIT). This prospective clinical trial explores the impact of acute sleep deprivation on the vestibular-ocular reflex (VOR) in medical residents. The study involved healthy physicians from diverse medical disciplines. Participants underwent vHIT assessments before and after a 26-h shift. The examinations focused solely on the right lateral semicircular canal. Participants further completed a demographics and fatigue questionnaire, including the Fatigue Severity Scale (FSS) questionnaire and a Visual Analog Fatigue Score (VAFS). The study involved 30 medical residents. Participants experienced a statistically significant decrease in VOR gain in the right horizontal semicircular canal during a 26-h shift (p < 0.01). While the FSS and VAFS questionnaires showed no significant difference before and after the shift, the analysis of ∆VOR gain indicated a statistically significant increase associated with decreased sleep time during the shift (p = 0.018, 95% Confidence Interval [0.08, 0.68]). The most substantial increase in ∆VOR occurred between 22-26 h of sleep deprivation. No significant differences were observed in ∆VOR between genders, ages, disciplines, department shifts versus emergency room shifts, or years of residency. vHIT can be used as an objective, reliable screening tool for severe sleep deprivation among physicians. The decrease in the VOR gain may indicate that vestibular function is influenced by sleep deprivation. The clinical significance of these findings is still questioned, more studies may help to assess this effect. 3 Laryngoscope, 2024.

Automated volumetric analysis of the inner ear fluid space from hydrops magnetic resonance imaging using 3D neural networks

Due to the development of magnetic resonance (MR) imaging processing technology, image-based identification of endolymphatic hydrops (EH) has played an important role in understanding inner ear illnesses, such as Meniere’s disease or fluctuating sensorineural hearing loss. We segmented the inner ear, consisting of the cochlea, vestibule, and semicircular canals, using a 3D-based deep neural network model for accurate and automated EH volume ratio calculations. We built a dataset of MR cisternography (MRC) and HYDROPS-Mi2 stacks labeled with the segmentation of the perilymph fluid space and endolymph fluid space of the inner ear to devise a 3D segmentation deep neural network model. End-to-end learning was used to segment the perilymph fluid and the endolymph fluid spaces simultaneously using aligned pair data of the MRC and HYDROPS-Mi2 stacks. Consequently, the segmentation performance of the total fluid space and endolymph fluid space had Dice similarity coefficients of 0.9574 and 0.9186, respectively. In addition, the EH volume ratio calculated by experienced otologists and the EH volume ratio value predicted by the proposed deep learning model showed high agreement according to the interclass correlation coefficient (ICC) and Bland–Altman plot analysis.

Benign paroxysmal positional vertigo: diagnosis, treatment, rehabilitation. Current concepts on the role of betahistine in the complex treatment of patients with benign paroxysmal positional vertigo

The treatment of patients with benign paroxysmal positional vertigo (BPPV) is an urgent issue in modern medicine.Expert Council on the diagnosis and treatment of BPPV was held in Moscow on June 1, 2024. Timely diagnosis and effective treatment play a key role in the management of patients with BPPV, reduce the risk of falls and related injuries, prevent the development of emotional disorders and impairment of daily activities. Accurate patient routing and selection of appropriate treatment can significantly reduce the duration of disability and the burden on the healthcare system. Relatively simple positional tests aimed at detecting involvement of various semicircular canals have been found to be of paramount importance in the diagnosis of BPPV. Repositioning maneuvers are of paramount importance in the treatment of patients with BPPV. They vary depending on the canal affected and aim to move the otoliths out of the semicircular canals to the vestibule of the labyrinth. If repositioning maneuvers can not be performed, effective methods of vestibular gymnastics can be used. When discussing drug therapy, it was found that the use of betahistine in addition to repositioning maneuvers or vestibular gymnastics increases the efficacy of therapy, accelerates the recovery process and prevents the development of residual non-positional vertigo.

Spike-based rotation detection using a self-powered triboelectric sensor with mimicry of a vestibular system

The biological vestibular system in semicircular canals detects head rotation with high energy efficiency through its unique spike-based processing. We propose a self-powered vestibular sensory neuron inspired by the biological vestibular system and utilizing a triboelectric nanogenerator (TENG) as a rotation sensor and a neuron transistor (neuristor) as a spiking neuron. This artificial vestibular neuron simultaneously detects the angular velocity and encodes it into spikes. When the angular velocity that is applied to the TENG increases, the spiking frequency increases, and this is a desired property of the vestibular neuron. Therefore, the vestibular neuron can serve as an input neuron in a spiking neural network (SNN). We also demonstrate a fully hardware-based neuromorphic system that is attractive for its improved energy efficiency to recognize rotation axes. Compared to a vestibular system based on conventional von-Neumann computing, that based on the proposed neuromorphic computing can effectively reduce power consumption by adopting spike transmission and employing the self-powered sensor. The proposed system is promising for applications related to rotation that demands high energy-efficiency.

Photodynamic therapy-induced precise attenuation of light-targeted semicircular canals for treating intractable vertigo.

Vertigo is a common symptom of various diseases that affects a large number of people worldwide. Current leading treatments for intractable peripheral vertigo are to intratympanically inject ototoxic drugs such as gentamicin to attenuate the semicircular canal function but inevitably cause hearing injury. Photodynamic therapy (PDT) is a noninvasive therapeutic approach by precisely targeting the diseased tissue. Here, we developed a PDT-based method for treating intractable peripheral vertigo in a mouse model using a polymer-coated photosensitizer chlorin e6 excited by red light. We found that a high dose of PDT attenuated the function of both semicircular canals and otolith organs and damaged their hair cells. Conversely, the PDT exerted no effect on hearing function or cochlear hair-cell viability. These results suggest the therapeutic potential of PDT for treating intractable peripheral vertigo without hurting hearing. Besides, the attenuation level and affected area can be precisely controlled by adjusting the light exposure time. Furthermore, we demonstrated the potential of this therapeutic approach to be minimally invasive with light irradiation through bone results. Thus, our PDT-based approach for attenuating the function of the semicircular canals offers a basis for developing a less-invasive and targeted therapeutic option for treating vertigo.

Toward Intelligent Head Impulse Test: A Goggle-Free Approach Using a Monocular Infrared Camera.

To assess vestibular function, video head impulse test (vHIT) is taken as the gold standard by evaluating the vestibulo-ocular reflex (VOR). However, vHIT requires the patient to wear a specialized head-mounted goggle equipment that needs to be calibrated before each use. For this, we proposed an intelligent head impulse test (iHIT) setting with a monocular infrared camera instead of the head-mounted goggle and contributed correspondingly a video classification approach with deep learning to vestibular function determination. Within the iHIT framework, a monocular infrared camera was set in front of the patient to capture test videos, based on which a dataset DiHIT of HIT video clips was set up. We then proposed a two-stage multi-modal video classification network, trained on the dataset DiHIT, that took as input the eye motion and head motion data extracted from the facial keypoints via HIT clips and outputted the identification of the semicircular canal (SCC) being tested (SCC identification) and determination of VOR abnormality (SCC qualitation). Experiments on this dataset DiHIT showed that it achieved the accuracy of 100% in prediction of SCC identification. Furthermore, it attained predictive accuracies of 84.1% in horizontal and 79.0% in vertical SCC qualitation. Compared with existing video-based HIT, iHIT eliminates goggles, does not require equipment calibration, and achieves complete automation. Furthermore, iHIT will bring more benefits to users due to its low cost and ease of operation. Codes and use case pipeline are available at: https://github.com/dec1st2023/iHIT. 3 Laryngoscope, 2024.

Effects of aging on otolith morphology and functions in mice.

Increased fall risk caused by vestibular system impairment is a significant problem associated with aging. A vestibule is composed of linear acceleration-sensing otoliths and rotation-sensing semicircular canals. Otoliths, composed of utricle and saccule, detect linear accelerations. Otolithic organs partially play a role in falls due to aging. Aging possibly changes the morphology and functions of otoliths. However, the specific associations between aging and otolith changes remain unknown. Therefore, this study aimed to clarify these associations in mice. Young C56BL/6 N (8 week old) and old (108-117 weeks old) mice were used in a micro-computed tomography (μCT) experiment for morphological analysis and a linear acceleration experiment for functional analysis. Young C56BL/6 N (8 week old) and middle-aged (50 week old) mice were used in electron microscopy experiments for morphological analysis. μCT revealed no significant differences in the otolith volume (p = 0.11) but significant differences in the otolith density (p = 0.001) between young and old mice. μCT and electron microscopy revealed significant differences in the structure of striola at the center of the otolith (μCT; p = 0.029, electron microscopy; p = 0.017). Significant differences were also observed in the amplitude of the eye movement during the vestibulo-ocular reflex induced by linear acceleration (maximum amplitude of stimulation = 1.3G [p = 0.014]; maximum amplitude of stimulation = 0.7G [p = 0.015]), indicating that the otolith function was worse in old mice than in young mice. This study demonstrated the decline in otolith function with age caused by age-related morphological changes. Specifically, when otolith density decreased, inertial force acting on the hair cells decreased, and when the structure of striola collapsed, the function of cross-striolar inhibition decreased, thereby causing a decline in the overall otolith function.

Amplification of vibration induced nystagmus in patients with peripheral vestibular loss by head tilt.

In patients with unilateral loss of vestibular function (UVL) vibration of the skull leads to a response of the vestibulo-ocular reflex (VOR) called vibration-induced nystagmus (VIN), with slow phases usually directed toward the paretic ear. This response is thought to result from the difference between the neural discharge in semicircular canal afferents from the healthy and the affected labyrinth. The brain interprets this difference as a sustained imbalance in angular (rotational) vestibular tone, which in natural circumstances would only occur when the head was rotating at a constant acceleration. To study this effect, we used a contemporary model of the neural network that combines sensory information about head rotation, translation, and tilt relative to gravity to estimate head orientation and motion. Based on the model we hypothesize that in patients with UVL, the brain may estimate not only a "virtual" rotation from the induced canal imbalance but also a subsequent "virtual" translation from the incorrect computation of the orientation of the head relative to gravity. If this is the case, the pattern of vibration-induced nystagmus will depend on the orientation of the head relative to gravity during the stimulation. This model predicts that this "virtual" translation will alter the baseline VIN elicited with the head upright; augmenting it when the affected ear is down and diminishing it when the affected ear is up. Confirming this hypothesis, we recorded VIN in 3 patients with UVL (due to vestibular neuritis) in upright, right ear-down, and left ear-down positions and each showed the expected pattern. From a practical, clinical view, our results and modeling suggest that positional VIN might reveal a hidden imbalance in angular vestibular tone in patients with UVL, when patients have equivocal signs of a vestibular imbalance, such as a minute amount of spontaneous or vibration-induced nystagmus with the head upright. This research provides insights into the underlying mechanisms of vestibular processing, the analysis of nystagmus in patients with UVL, and guides the design of a new bedside diagnostic test to assess vestibular function in patients with dizziness and imbalance.

Atypical PC-BPPV - Cupulolithiasis and Short-Arm Canalithiasis: A Retrospective Observational Study.

Atypical posterior canal (pc) benign paroxysmal positional vertigo (BPPV) may be caused by cupulolithiasis (cu), short arm canalithiasis (ca), or jam. The purpose of this study was to describe the clinical presentation and differential diagnosis of pc-BPPV-cu and short arm canalithiasis. This retrospective observation study identified persons with atypical pc-BPPV based on history and findings from four positional tests. Patterns of nystagmus suggested canal involved and mechanism of BPPV. Interventions included canalith repositioning procedures (CRP). Fifteen persons, 17 episodes of care, met inclusion criteria, 65% referred following unsuccessful CRPs. Symptoms included persistent, non-positional unsteadiness, "floating" sensation, with half experiencing nausea/vomiting. Downbeat nystagmus with/without torsion in Dix-Hallpike (DH) and Straight Head Hang (SHH) position and no nystagmus upon sitting up, occurred in 76% of persons attributed to pc-BPPV-cu. Upbeat nystagmus with/without torsion and vertigo/retropulsion upon sitting up, occurred in 24% attributed to pc-BPPV-ca short arm. During SHH, canal conversion from pc-BPPV-cu to long arm canalithiasis occurred in 31%. The Half-Hallpike position identified pc-BPPV-cu in 71%. The Inverted Release position identified pc-BPPV-cu adjacent short arm and pc-BPPV-ca short arm. Persistent, peripheral nystagmus that is downbeat or downbeat/torsion away from involved ear in provoking positions and no nystagmus sitting up, may be attributed to pc-BPPV-cu, and nystagmus that is upbeat or upbeat/torsion towards involved ear upon sitting up may be attributed to pc-BPPV-ca short arm. Both are effectively treated with canal- and mechanism-specific CRPs. for more insights from the authors (see the Video, Supplemental Digital Content 1 available at: (http://links.lww.com/JNPT/A487).