The Age-Related Orientational Changes of Human Semicircular Canals

Age-related morphological change in bony segment and cartilage segment of Eustachian tube

Background

Eustachian tube dysfunction (ETD) is the predominant cause of otitis media with effusion in children and adults. Balloon dilatation of the Eustachian tube (BDET) provides a new method for restoring the ventilatory function of Eustachian tube (ET). However, the differences in age-related morphological changes in the dimensions and positions of ET in children and adults are unclear.

Purpose

This study aimed to examine age-related morphological changes in bony and cartilage segments of the ET in a three-dimensional space in normal population.

Methods

A total of 71 randomly selected computed tomography (CT) images of the temporal bones of 46 people were retrospectively studied in four age groups: A (0-3 years old); B (4-8 years old), C (9-18 years old), and D (19-65 years old). Space analytic geometry was assessed to calculate the dimensions and positions of ET.

Results

The bony segment of ET lengthened from infancy to adulthood with age in groups A, B and C (r = 0.562**/0.000). The cartilage segment of ET mostly extended with age from infancy to 8 years old in children (r = 0.633**/0.000), but with bending close to the sagittal plane and away from the horizontal plane with age in groups A, B and C (P < .05), and with a constant angle to the coronal plane among the four groups (P > .05).

Conclusion

The bony and cartilaginous segments of ET exhibit distinct morphological changes in space with age. The bony segment of ET extends in a constant position from infancy to adulthood. In contrast, the cartilaginous segment of the ET indicates multidimensional positional changes until adulthood, in addition to the elongation from infancy to children. This may provide an accurate morphological basis for comparing the differences in ETD pathogenesis and surgical treatment between children and adults.

Pediatric Benign Paroxysmal Positional Vertigo: Degree of Nystagmus and Concurrent Dizziness Differs from Adult BPPV

Background: Benign paroxysmal positional vertigo (BPPV) is characterized by brief, intense episodes of vertigo triggered by abrupt changes in head position. It is generally accepted as being most common in adults, while it is regarded as rare in children. It is necessary to compare the disease between pediatric and adult patients for a better understanding of the disease's characteristics and its natural history. This study aimed to identify the clinical characteristics of BPPV in children and compare them with those of adult BPPV patients. Methods: All children ≤ 18 years old who were diagnosed with BPPV were selected by searching the electronic database of our hospital. Clinical features were identified by medical record review. For adult patients, we collected data from patients > 19 years of age. Results: A total of 30 pediatric (13.65 ± 4.15 years old) and 264 adult patients (60.86 ± 13.74 years old) were included in the study. Among pediatric patients, the lateral canals were involved in 80% and the posterior canals in 16.67%. In adult patients, the lateral and posterior canals were involved similarly (p = 0.007). The degree of nystagmus in pediatric patients was 6.82 ± 12.09, while in adults it was 15.58 ± 20.90 (p < 0.001). The concurrent dizziness disorder was higher in the pediatric group and recurrence was higher in the adult group. In the regression analysis, it was found that adult patients had a stronger nystagmus with a value of 6.206 deg/sec, and the risk of concurrent dizziness disorder was found to be 5.413 times higher in the pediatric group (p < 0.05). Conclusions: BPPV occurs in pediatric patients with lower prevalence, but it cannot be overlooked. In the pediatric group, a relatively high proportion of patients demonstrated lateral canal involvement, weaker nystagmus, and additional dizziness disorder.

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.

Lower Levels of Vestibular Developmental Stability in Slow-Moving than Fast-Moving Primates

The vestibular system of the mammalian inner ear senses angular and linear velocity of the head and enables animals to maintain their balance. Vestibular anatomy has been studied extensively in order to link its structure to particular kinds of locomotion. Available evidence indicates that, in primates, slow-moving species show higher levels of vestibular variation than fast-moving taxa. We analysed intraspecific morphological variation and fluctuating asymmetry (FA) levels in the semicircular canal systems of six species of lorisiform primates: three slow-moving lorisids and three fast-moving galagids. Our results showed clear differences in levels of intraspecific variation between slow-moving and fast-moving taxa. Higher levels of variation were responsible for deviations from coplanarity for synergistic pairs of canals in slower taxa. Lorisids also presented higher levels of FA than galagids. FA is a better indicator of agility than intraspecific variation. These results suggest that in order to function efficiently in fast taxa, semicircular canal systems must develop as symmetrically as possible, and should minimise the deviation from coplanarity for synergistic pairs. Higher levels of variation and asymmetry in slow-moving taxa may be related to lower levels of stabilising selection on the vestibular system, linked to a lower demand for rapid postural changes.

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.

A test of the lateral semicircular canal correlation to head posture, diet and other biological traits in "ungulate" mammals

For over a century, researchers have assumed that the plane of the lateral semicircular canal of the inner ear lies parallel to the horizon when the head is at rest, and used this assumption to reconstruct head posture in extinct species. Although this hypothesis has been repeatedly questioned, it has never been tested on a large sample size and at a broad taxonomic scale in mammals. This study presents a comprehensive test of this hypothesis in over one hundred "ungulate" species. Using CT scanning and manual segmentation, the orientation of the skull was reconstructed as if the lateral semicircular canal of the bony labyrinth was aligned horizontally. This reconstructed cranial orientation was statistically compared to the actual head posture of the corresponding species using a dataset of 10,000 photographs and phylogenetic regression analysis. A statistically significant correlation between the reconstructed cranial orientation and head posture is found, although the plane of the lateral semicircular canal departs significantly from horizontal. We thus caution against the use of the lateral semicircular canal as a proxy to infer precisely the horizontal plane on dry skulls and in extinct species. Diet (browsing or grazing) and head-butting behaviour are significantly correlated to the orientation of the lateral semicircular canal, but not to the actual head posture. Head posture and the orientation of the lateral semicircular canal are both strongly correlated with phylogenetic history.

Three-Dimensional Reconstruction of the Semicircular Canals with a Two-Hands Model

Objective

To help understand the anatomy and the diseases of the semicircular canals (SCCs) by defining the three-dimensional reconstruction of the SCCs in a model reconstructed using the two hands (two-hands model) and to determine the three-dimensional configuration of the two hands by measuring the angle between the SCCs and the sagittal plane.

Methods

Patients older than 18 years of age with computed tomography (CT) scans of the temporal bones taken between 2017 and 2018 at the Yeditepe University Hospital were included in the study. CT images were evaluated by a radiologist. The angles between every SCC and the sagittal plane were measured with the MIMICS 12.1 program. Mean angles between the SCCs and the sagittal plane were measured. These angles were demonstrated on the two-hands model of the SCCs by means of a goniometer and photographed.

Results

Thirty patients and 60 temporal bones were included in the study. Mean angles between the superior, the posterior, and the horizontal SCCs and the sagittal plane were found as 37.1±3.3°, 50.4±4.1°, and 89.5±4.7°, respectively.

Conclusion

This is the first study to define the three-dimensional representation of the SCCs with a two-hands model. This may allow for a better understanding and the better teaching of the anatomy and diseases of SCCs.

Supratubal recess and sinus tympani: CT analysis of middle ear hidden areas

Background

High-resolution computed tomography (HRCT) magnifies the role of preoperative imaging for detailed middle ear anatomy particularly its hidden area. The purpose of the current study was to assess the sinus tympani (ST) and supratubal recess (STR) by HRCT, to create CT classification of the STR depth, and to study the relationship between ST types and the new STR grades.

Results

In HRCT of non-pathological temporal bones of 100 subjects (200 ears), measurements of the STR and ST were calculated, registered, and analyzed. The depth of the STR was classified into grade 1 with depth less than 3 mm, grade 2 with depth ranged between 3 and 5 mm, and grade 3 with depth more than 5 mm. The mean STR length, width, and height were 4.17 ± 0.86, 3.55 ± 0.65, and 3.64 ± 0.7 mm, respectively, while the ST mean length and width of were 2.52 ± 0.5 and 1.82 ± 0.78 mm, respectively, without significant differences between either sexes or sided. The ST types were found to be type A in 56 ears (28%), type B in 142 ears (71%), and type C in 2 ears (1%). The STR grading was grade 1 in 12 ears (6%), grade 2 in 160 ears (80%), and grade 3 in 28 ears (14%) without significant relationship between ST types and STR grading (P = 0.3).

Conclusion

The current study provided reliable and applicable methods of CT assessment of STR and ST that can help to predict the degree of surgical visibility of the ST and STR during ear surgery.

Jugular bulb and skull base pathologies: proposal for a novel classification system for jugular bulb positions and microsurgical implications

OBJECTIVE

There is no definitive or consensus classification system for the jugular bulb position that can be uniformly communicated between a radiologist, neurootologist, and neurosurgeon. A high-riding jugular bulb (HRJB) has been variably defined as a jugular bulb that rises to or above the level of the basal turn of the cochlea, within 2 mm of the internal auditory canal (IAC), or to the level of the superior tympanic annulus. Overall, there is a seeming lack of consensus, especially when MRI and/or CT are used for jugular bulb evaluation without a dedicated imaging study of the venous anatomy such as digital subtraction angiography or CT or MR venography.

METHODS

A PubMed analysis of “jugular bulb” comprised of 1264 relevant articles were selected and analyzed specifically for an HRJB. A novel classification system based on preliminary skull base imaging using CT is proposed by the authors for conveying the anatomical location of the jugular bulb. This new classification includes the following types: type 1, no bulb; type 2, below the inferior margin of the posterior semicircular canal (SCC), subclassified as type 2a (without dehiscence into the middle ear) or type 2b (with dehiscence into the middle ear); type 3, between the inferior margin of the posterior SCC and the inferior margin of the IAC, subclassified as type 3a (without dehiscence into the middle ear) and type 3b (with dehiscence into the middle ear); type 4, above the inferior margin of the IAC, subclassified as type 4a (without dehiscence into the IAC) and type 4b (with dehiscence into the IAC); and type 5, combination of dehiscences. Appropriate CT and MR images of the skull base were selected to validate the criteria and further demonstrated using 3D reconstruction of DICOM files. The microsurgical significance of the proposed classification is evaluated with reference to specific skull base/posterior fossa pathologies.

RESULTS

The authors validated the role of a novel classification of jugular bulb location that can help effective communication between providers treating skull base lesions. Effective utilization of the above grading system can help plan surgical procedures and anticipate complications.

CONCLUSIONS

The authors have proposed a novel anatomical/radiological classification system for jugular bulb location with respect to surgical implications. This classification can help surgeons in complication avoidance and management when addressing HRJBs.

Anatomical measurement of the ossicles in patients with congenital aural atresia and stenosis

OBJECTIVES

Our aims were to measure and compare anatomical parameters of the ossicles in normal, congenital aural stenosis (CAS), and congenital aural atresia (CAA) ears.

METHODS

This retrospective study was performed using three-dimensional reconstructed images derived from computed tomography scans of 20 normal subjects, 20 CAS patients, and 20 CAA patients.

RESULTS

The lengths of the malleus handle and long process of the incus were greater in normal ears than in CAS and CAA ears (all P < 0.05). The angles of the incudostapedial joint and between the short and long processes of the incus were smaller in normal ears than in CAS and CAA ears (all P < 0.05). There were no significant differences in the positions of the malleus head and incudomalleolar joint, the size of the malleus head, the length of the short process of the incus, or the angle of the incudomalleolar joint (P > 0.05).

CONCLUSIONS

Anatomical parameters of the lower part, but not of the upper part, of the ossicular chain in CAS and CAA ears differed from those in normal ears. Different branchial arch origins of the upper and lower parts of the ossicular chain may explain these findings. Dysplasia of the second arch, which develops into the lower part of the ossicular chain, may contribute to ossicular malformation in CAA and CAS. Accurate radiographic measurement of malformed ossicles may be useful for reconstructive surgery of CAA and CAS using the patient's native ossicular chain and for choosing an appropriate place for active middle ear implants.

Orientation of the lateral semicircular canal in Xenarthra and its links with head posture and phylogeny

The orientation of the semicircular canals of the inner ear in the skull of vertebrates is one of the determinants of the capacity of this system to detect a given rotational movement of the head. Past functional studies on the spatial orientation of the semicircular canals essentially focused on the lateral semicircular canal (LSC), which is supposedly held close to horizontal during rest and/or alert behaviors. However, they generally investigated this feature in only a few and distantly related taxa. Based on 3D-models reconstructed from µCT-scans of skulls, we examined the diversity of orientations of the LSC within one of the four major clades of placental mammals, that is, the superorder Xenarthra, with a data set that includes almost all extant genera and two extinct taxa. We observed a wide diversity of LSC orientations relative to the basicranium at both intraspecific and interspecific scales. The estimated phylogenetic imprint on the orientation of the LSC was significant but rather low within the superorder, though some phylogenetic conservatism was detected for armadillos that were characterized by a strongly tilted LSC. A convergence between extant suspensory sloths was also detected, both genera showing a weakly tilted LSC. Our preliminary analysis of usual head posture in extant xenarthrans based on photographs of living animals further revealed that the LSC orientation in armadillos is congruent with a strongly nose-down head posture. It also portrayed a more complex situation for sloths and anteaters. Finally, we also demonstrate that the conformation of the cranial vault and nuchal crests as well as the orientation of the posterior part of the petrosal may covary with the LSC orientation in Xenarthra. Possible inferences for the head postures of extinct xenarthrans such as giant ground sloths are discussed in the light of these results.