A Morphometric Study of the Semicircular Canals Using Micro-CT Images in Three-Dimensional Reconstruction

Semicircular canals are long in patients with benign paroxysmal positional vertigo

OBJECTIVE

To search for any morphological variation contributing to aetiopathogenesis and the diagnosis of benign paroxysmal positional vertigo, we measured the sizes of the semicircular canals in patients with and without benign paroxysmal positional vertigo using multidetector computed tomography.

METHODS

Cranial bone computed tomography images of 30 benign paroxysmal positional vertigo patients and 30 control patients were acquired with a 128-slice computed tomography scanner and a transverse plane with a thickness of 0.67 mm. The inner diameter, height and width of the canals were measured.

RESULTS

The width of the anterior semicircular canals, and the width and height of the posterior semicircular canals of the affected ears in benign paroxysmal positional vertigo patients (n = 30) were significantly greater than in the control patients (n = 90; p = 0.001, p = 0.023, p = 0.003, respectively).

CONCLUSION

In benign paroxysmal positional vertigo patients, the posterior and anterior semicircular canals are longer than those in people without benign paroxysmal positional vertigo. These morphological changes may contribute to elucidating the aetiopathogenesis and be used as a radiological sign for diagnosis of benign paroxysmal positional vertigo disease.

Pathological Study of Light Cupula Syndrome on a Visual Bionic Semicircular Canal

A type of persistent direction-changing positional nystagmus with a null point during head position deflection is known as light cupula syndrome (LCS) in the clinic. To date, the pathogenesis and biomechanical response of human semicircular canals with light cupula syndrome (LCS) (HSCs-LCS) are still unclear. In this study, based on the anatomical structure and size of the one-dimensional human semicircular canal (HSC) and imitating the pathological changes of the endolymph in HSC with LCS, a visual bionic semicircular canal (BSC) with LCS was fabricated using three-dimensional printing technology, hydrogel modification, and target tracking technology. Through theoretical derivation, mathematical models of the HSC-LCS perception process were established. By conducting in vitro experiments on the bionic model, the biomechanical response process of HSC-LCS was studied, and the mathematical models were validated. The results of pulse acceleration stimulation showed that the pathological changes in the density and viscosity of the endolymph could reduce the deformation of the cupula of the BSC-LCS and increase the time constant. The results of the sinusoidal acceleration stimulation showed that the amplitude-frequency gain of the BSC-LCS decreased and the phase difference increased. The BSC-LCS can be used as a tool for pathological research of the HSC-LCS. The results of this study can provide a theoretical basis for clinical diagnosis.

Estimation of Normal Semi-circular Canal Dimensions on Computed Tomography

Aims

To measure and compare length, width and luminal diameters of semi-circular canals (SCC) on Multiplanar reformatted CT images in individuals without any features of vestibular dysfunction.

Materials And Methods

A prospective, cross sectional, observational study was conducted in a tertiary care hospital in October - November 2021. Multiplanar reformatted CT temporal bone images of 50 participants without features of vestibular dysfunction were used to measure the curved lengths, widths and luminal diameters of the three semi-circular canals. Unpaired t-test was used to ascertain and compare the values obtained.

Results

Fifty participants, 27 women and 23 men (mean age 38.5 years) were included in the study. Mean curved lengths of Superior, posterior and Lateral SCCs were 1.37 cm, 1.33 cm and 1.19 cm respectively. Semi-circular width of Superior SCC (4.8 mm) was significantly larger than Posterior SCC (4.17 mm, p = 0.03) which was significantly larger than Lateral SCC (3.65 mm, p = 0.04). No significant difference was found between mean mid luminal diameters of the three SCCs. Mid luminal diameters were significantly smaller than the diameters at either ends of all SCCs.

Conclusion

The results can potentially serve as reference values for Indians and for further studies on pathophysiology of disequilibrium.

Description of a New Labyrinthine Dehiscence: Horizontal Semicircular Canal Dehiscence at the Tympanic Segment of the Facial Nerve

Objective

This report is a case series of patients with findings suspicious for a labyrinthine dehiscence syndrome not previously described in the medical literature. We describe the clinical and test findings in 16 patients with CT findings suspicious for dehiscence of the ampullated end of the horizontal semicircular canal at the tympanic segment of the facial nerve.

Study Design

Observational case series.

Setting

Neurotology vestibular referral center.

Patients

To be included in this study the patients were seen at our center in 2019 and had a high-resolution CT scan with a collimation of 0.6 mm. Patients who were identified as having findings suspicious for dehiscence of bone where the facial nerve crosses the ampullated end of the horizontal semicircular canal (HSC-FND) were identified and further analyzed.

Interventions

Case series retrospective record review of patient symptoms, physical findings, audiometry, vestibular testing, and CT scans was performed. CT findings of other dehiscent sites were noted. A comparison to surgically treated perilymph fistula (PLF) patients of the same period was performed.

Main Outcome Measures

History and physical exam were reviewed for auditory symptoms, vestibular symptoms, and exacerbating factors. and. Audiometry and vestibular testing were reviewed to determine which tests were most likely to be abnormal. CT scans were independently graded according to degree of suspicion for HSC-FND. Finally, patients with HSC-FND as the sole dehiscence identified were compared to those who had HSC-FND plus other dehiscent sites (HSC-FND+O) and to the group of surgically treated PLF patients.

Results

Of 18 patients, 16 met inclusion criteria. Nine (56%) of those suspicious for HSC-FND had dehiscences in other parts of the labyrinth. Additional dehiscent sites included: six superior semicircular canal dehiscences (SSCD), two cochlear facial dehiscences and one cochlear carotid dehiscence. The most common auditory symptoms were autophony followed by tinnitus and aural fullness. The most common vestibular symptoms were pulsion sensation (feeling of being pushed to one side) followed by vertigo spells. The most common exacerbating factors for vertigo were straining, and sound. The most commonly abnormal vestibular test was nasal Valsalva testing, which was positive in all but one patient. Anamnesis and examination observations were similar in both groups, but the HSC-FND group were less likely to demonstrate a caloric weakness or an abnormal ECOG compared to the HSC-FND+O group. Of note, cVEMP was more often found to have lower thresholds in the HSC-FND group compared to the HSC-FND+O group. An example case is highlighted. Comparison to the PLF patients revealed statistically significant difference in the presenting symptoms of autophony, fullness and pulsion sensation. When comparing testing, HSC-FND patients were more likely to have an abnormal cVEMP and PLF patients were more likely to have asymmetric hearing. The incidence of bilateral disease was also more common among the HSC-FND patients than the PLF patients.

Conclusions

A new labyrinthine dehiscence has been described to occur where the tympanic segment of the facial nerve crosses over the ampullated end of the horizontal semicircular canal. HSC-FND patients can present in a similar manner as HSC-FND+O patients with similar test findings except as mentioned above. The identification of one dehiscence such as SSCD does not preclude the presence of another dehiscence such as HSC-FND. HSC-FND could be the source of persistent symptoms post SSCD surgery as illustrated in the case presented. HSC-FND patients seem to identify themselves compared to PLF patients by a much more likely presenting symptoms of autophony, fullness, pulsion, abnormal cVEMP, bilaterality of disease, and symmetric hearing.

Human semicircular canal form: Ontogenetic changes and variation of shape and size

The semicircular canals (SCCs) transduce angular acceleration of the head into neuronal signals, and their morphology has been used to infer function. Once formed, the bony labyrinth, that surrounds the canals, is tightly regulated and has a very low bone turnover. However, relaxed postnatal inhibition of bone remodelling later in ontogeny may allow for some organised adjustments of shape and size or for greater stochastic variation. In the present study, we test the hypotheses that after birth, the shape and size of the bony canal changes or becomes more variable, or both. We study microCT scans of human perinatal and adult temporal bones using a combination of geometric morphometric analysis and cross-sectional measures. Results revealed marginal differences of size (<5%), of cross-sectional shape and of measurement variability. Geometry of the three canals together and their cross-sectional areas were, however, indistinguishable between perinates and adults. These mixed findings are indicative of diminutive levels of relaxed inhibition superimposed over a constrained template of SCC morphology.

A New Coordinate System for Magnetic Resonance Imaging of the Vestibular System

Objectives: To develop and evaluate a new coordinate system for MRI of the vestibular system.

Methods: In this study, 53 internal auditory canal MRI and 78 temporal bone CT datasets were analyzed. Mimics Medical software version 21.0 was used to visualize and three-dimensionally reconstruct the image data. We established a new coordinate system, named W–X, based on the center of the bilateral eyeballs and vertex of the bilateral superior semicircular canals. Using the W–X coordinate system and Reid's coordinate system, we measured the orientations of the planes of the anterior semicircular canal (ASCC), the lateral semicircular canal (LSCC), and the posterior semicircular canal (PSCC).

Results: No significant differences between the angles measured using CT and MRI were found for any of the semicircular canal planes (p > 0.05). No statistical differences were found between the angles measured using Reid's coordinate system (CT) and the W–X coordinate system (MRI). The mean values of ∠ASCC & LSCC, ∠ASCC & PSCC, and ∠LSCC & PSCC were 84.67 ± 5.76, 94.21 ± 3.81, and 91.79 ± 5.22 degrees, respectively. The angle between the LSCC plane and the horizontal imaging plane was 15.64 ± 3.92 degrees, and the angle between the PSCC plane and the sagittal imaging plane was 48.79 ± 4.46 degrees.

Conclusion: A new W–X coordinate system was developed for MRI studies of the vestibular system and can be used to measure the orientations of the semicircular canals.

Measurement of Human Semicircular Canal Spatial Attitude

Located deep in the temporal bone, the semicircular canal is a subtle structure that requires a spatial coordinate system for measurement and observation. In this study, 55 semicircular canal and eyeball models were obtained by segmentation of MRI data. The spatial coordinate system was established by taking the top of the common crus and the bottom of the eyeball as the horizontal plane. First, the plane equation was established according to the centerline of the semicircular canals. Then, according to the parameters of the plane equation, the plane normal vectors were obtained. Finally, the average unit normal vector of each semicircular canal plane was obtained by calculating the average value of the vectors. The standard normal vectors of the and left posterior semicircular canal, superior semicircular canal and lateral semicircular canal were [−0.651, 0.702, 0.287], [0.749, 0.577, 0.324], [−0.017, −0.299, 0.954], [0.660, 0.702, 0.266], [−0.739, 0.588, 0.329], [0.025, −0.279, 0.960]. The different angles for the different ways of calculating the standard normal vectors of the right and left posterior semicircular canal, superior semicircular canal and lateral semicircular canal were 0.011, 0.028, 0.008, 0.011, 0.024, and 0.006 degrees. The technology for measuring the semicircular canal spatial attitudes in this study are reliable, and the measurement results can guide vestibular function examinations and help with guiding the diagnosis and treatment of BPPV.

IE-Map: a novel in-vivo atlas and template of the human inner ear

Brain atlases and templates are core tools in scientific research with increasing importance also in clinical applications. Advances in neuroimaging now allowed us to expand the atlas domain to the vestibular and auditory organ, the inner ear. In this study, we present IE-Map, an in-vivo template and atlas of the human labyrinth derived from multi-modal high-resolution magnetic resonance imaging (MRI) data, in a fully non-invasive manner without any contrast agent or radiation. We reconstructed a common template from 126 inner ears (63 normal subjects) and annotated it with 94 established landmarks and semi-automatic segmentations of all relevant macroscopic vestibular and auditory substructures. We validated the atlas by comparing MRI templates to a novel CT/micro-CT atlas, which we reconstructed from 21 publicly available post-mortem images of the bony labyrinth. Templates in MRI and micro-CT have a high overlap, and several key anatomical measures of the bony labyrinth in IE-Map are in line with micro-CT literature of the inner ear. A quantitative substructural analysis based on the new template, revealed a correlation of labyrinth parameters with total intracranial volume. No effects of gender or laterality were found. We provide the validated templates, atlas segmentations, surface meshes and landmark annotations as open-access material, to provide neuroscience researchers and clinicians in neurology, neurosurgery, and otorhinolaryngology with a widely applicable tool for computational neuro-otology.

A comparative analysis of the vestibular apparatus in Epipliopithecus vindobonensis: Phylogenetic implications

Pliopithecoids are an extinct group of catarrhine primates from the Miocene of Eurasia. More than 50 years ago, they were linked to hylobatids due to some morphological similarities, but most subsequent studies have supported a stem catarrhine status, due to the retention of multiple plesiomorphic features (e.g., the ectotympanic morphology) relative to crown catarrhines. More recently, some morphological similarities to hominoids have been noted, raising the question of whether they could be stem members of this clade. To re-evaluate these competing hypotheses, we examine the morphology of the semicircular canals of the bony labyrinth of the middle Miocene pliopithecid Epipliopithecus vindobonensis. The semicircular canals are suitable to test between these hypotheses because (1) they have been shown to embed strong phylogenetic signal and reliably discriminate among major clades; (2) several potential hominoid synapomorphies have been identified previously in the semicircular canals; and (3) semicircular canal morphology has not been previously described for any pliopithecoid. We use a deformation-based (landmark-free) three-dimensional geometric morphometric approach to compare Epipliopithecus with a broad primate sample of extant and extinct anthropoids. We quantify similarities in semicircular canal morphology using multivariate analyses, reconstruct ancestral morphotypes by means of a phylomorphospace approach, and identify catarrhine and hominoid synapomorphies based on discrete characters. Epipliopithecus semicircular canal morphology most closely resembles that of platyrrhines and Aegyptopithecus due to the retention of multiple anthropoid symplesiomorphies. However, Epipliopithecus is most parsimoniously interpreted as a stem catarrhine more derived than Aegyptopithecus due to the possession of a crown catarrhine synapomorphy (i.e., the rounded anterior canal), combined with the lack of other catarrhine and any hominoid synapomorphies. Some similarities with hylobatids and atelids are interpreted as homoplasies likely related to positional behavior. The semicircular canal morphology of Epipliopithecus thus supports the common view that pliopithecoids are stem catarrhines.

Drafting a Surgical Procedure Using a Computational Anatomy Driven Approach for Precise, Robust, and Safe Vestibular Neuroprosthesis Placement-When One Size Does Not Fit All

OBJECTIVE

To design and evaluate a new vestibular implant and surgical procedure that should reach correct electrode placement in 95% of patients in silico.

DESIGN

Computational anatomy driven implant and surgery design study.

SETTING

Tertiary referral center.

PARTICIPANTS

The population comprised 81 patients that had undergone a CT scan of the Mastoid region in the Maastricht University Medical Center. The population was subdivided in a vestibular implant eligible group (28) and a control group (53) without known vestibular loss.

INTERVENTIONS

Canal lengths and relationships between landmarks were calculated for every patient. The relationships in group-anatomy were used to model a fenestration site on all three semicircular canals. Each patient's simulated individual distance from the fenestration site to the ampulla was calculated and compared with the populations average to determine if placement would be successful.

MAIN OUTCOME MEASURES

Lengths of the semicircular canals, distances from fenestration site to ampulla (intralabyrinthine electrode length), and rate of successful electrode placement (robustness).

RESULTS

The canal lengths for the lateral, posterior, and superior canal were respectively 12.1 mm ± 1.07, 18.8 mm ± 1.62, and 17.5 mm ± 1.23, the distances from electrode fenestration site to the ampulla were respectively 3.73 mm ± 0.53, 9.02 mm ± 0.90, and 5.31 mm ± 0.73 and electrode insertions were successful for each respective semicircular canal in 92.6%, 66.7%, and 86.4% of insertions in silico. The implant electrode was subsequently revised to include two more electrodes per lead, resulting in a robustness of 100%.

CONCLUSIONS

The computational anatomy approach can be used to design and test surgical procedures. With small changes in electrode design, the proposed surgical procedure's target robustness was reached.

Position of the Internal Aperture of Vestibular Aqueduct in Patients With Enlarged Vestibular Aqueduct

OBJECTIVE

To investigate the position of the internal aperture of vestibular aqueduct and its relationship to hearing level in patients with enlarged vestibular aqueduct (EVA).

METHODS

The size of the common crus and the position of the internal aperture of vestibular aqueduct were compared among control subjects, EVA patients with and without other inner ear malformations. Auditory steady-state response thresholds were compared between EVA patients with different positions of internal apertures.

RESULTS

The common crus in EVA patients was shorter than in control subjects (p < 0.05). The internal aperture of the vestibular aqueduct opened solely into the common crus in control subjects, simultaneously into the common crus and vestibule in almost 45% of EVA patients, solely into the common crus, and the vestibule in almost 30 and 25% of EVA patients, respectively. Auditory steady-state response thresholds at 2000 and 4000 Hz were higher in EVA patients whose internal apertures of vestibular aqueducts opened simultaneously into the common crus and vestibule than in those whose internal apertures opened solely into the common crus.

CONCLUSION

The common crus is shorter in EVA patients than in control subjects. The internal aperture of the vestibular aqueduct opens solely into the common crus in control subjects. It opens simultaneously into the common crus and vestibule in almost half of the EVA patients. The EVA patients whose internal apertures of vestibular aqueducts open solely into the common crus may have better hearing than those whose internal apertures open simultaneously into the common crus and vestibule.

Semicircular canal angulation during fetal life: a computed tomography study of 54 human fetuses

OBJECTIVE

In humans, the inner ear reaches its final configuration and adult size during fetal life. According to the literature, this occurs between 18 and 25 weeks of amenorrhea (WA). The ossification of the otic capsule is believed to arrest any further configuration change. There have, however, been some observations of slight changes in the orientation of the semicircular canals (SCCs) occurring later in fetal life. The present study aim was to examine changes of angulations between bony SCCs during fetal life.

PATIENTS

Fifty-four human fetuses aged 22 to 40 WA.

INTERVENTION

Computed tomography scanner.

MAIN OUTCOME MEASURE

SCC angulation (in degrees) studied with Amira software.

RESULTS

We found mean angles between the lateral SCC and anterior SCC, the lateral SCC and posterior SCC, and the anterior SCC and posterior SCC of 88.67, 92.60, and 90.19 degrees, respectively. Inter-SCC angles did not change significantly between the different age groups (22 WA, 24 WA, 26 WA, 29-31 WA, 34-36 WA, 38-40 WA). There was no difference of angulation between males and females and no intraobserver or interobserver variability.

CONCLUSION

The absence of correlation of SCC angles with age in our sample of fetuses indicates that the three-dimensional configuration of the SCC has already reached its adult form at 22 WA. As often described in the literature, these angles are close to orthogonality, probably reflecting an optimal vestibular function configuration.

The human semicircular canals orientation is more similar to the bonobos than to the chimpanzees

For some traits, the human genome is more closely related to either the bonobo or the chimpanzee genome than they are to each other. Therefore, it becomes crucial to understand whether and how morphostructural differences between humans, chimpanzees and bonobos reflect the well known phylogeny. Here we comparatively investigated intra and extra labyrinthine semicircular canals orientation using 260 computed tomography scans of extant humans (Homo sapiens), bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). Humans and bonobos proved more similarities between themselves than with chimpanzees. This finding did not fit with the well established chimpanzee – bonobo monophyly. One hypothesis was convergent evolution in which bonobos and humans produce independently similar phenotypes possibly in response to similar selective pressures that may be associated with postural adaptations. Another possibility was convergence following a “random walk” (Brownian motion) evolutionary model. A more parsimonious explanation was that the bonobo-human labyrinthine shared morphology more closely retained the ancestral condition with chimpanzees being subsequently derived. Finally, these results might be a consequence of genetic diversity and incomplete lineage sorting. The remarkable symmetry of the Semicircular Canals was the second major finding of this article with possible applications in taphonomy. It has the potential to investigate altered fossils, inferring the probability of post-mortem deformation which can lead to difficulties in understanding taxonomic variation, phylogenetic relationships, and functional morphology.

Size of the semicircular canals measured by multidetector computed tomography in different age groups

PURPOSE

The purpose of the study was to obtain reference values for the sizes of the semicircular canals (SCCs) on multidetector computed tomographic (CT) images in different age groups.

METHODS

Computed tomographic images of the temporal bone of 210 patients, a total of 420 ears without inner ear pathology, have been evaluated. These patients were divided into 4 groups by age: young children (<7 years), older children and adolescents (8-17 years), adults (18-59 years), and the elderly patients (>60 years). The inner diameter, maximum height, and width of the SCCs were measured.

RESULTS

There was no significant difference in the size of SCC among the 4 age groups. The inner diameter measurements of the anterior SCC, lateral SCC, and posterior SCC were 0.101 ± 0.016, 0.135 ± 0.033, and 0.124 ± 0.021 cm, respectively. The height measurements of the anterior SCC, lateral SCC, and posterior SCC were 0.535 ± 0.086, 0.349 ± 0.090, and 0.490 ± 0.109 cm, respectively. The width measurements of the anterior SCC, lateral SCC, and posterior SCC were 0.567 ± 0.080, 0.302 ± 0.082, and 0.472 ± 0.099 cm, respectively.

CONCLUSIONS

The size of SCCs remains constant from children to the elderly people, unlike the other human organs. The reference values provided by multidetector CT can serve as an aid for the interpretation of CT images.