Cochlear Canal Research Articles

MR imaging of endolymphatic hydrops in Ménière’s disease: feasibility at 1.5 T

BackgroundMénière’s disease is a chronic condition of the inner ear that causes vertigo, tinnitus and hearing loss. Its diagnosis relies on clinical criteria that are subjective and pure-tone audiometry results that are not specific. Its pathological substrate is endolymphatic hydrops. Its imaging was recently made possible by the late-enhanced 3D FLAIR sequence. This technique was primarily tested on 3 T. Our objective was to prove its feasibility using a 1.5 T magnet.MethodsWe conducted a prospective study including 30 patients who fulfilled the Bárány society criteria for Ménière’s disease. We performed the late-enhanced 3D FLAIR sequence on all patients. We used it to look for and grade endolymphatic hydrops in the utricle, the saccule and the cochlear canal using the Kahn method.ResultsWe found endolymphatic hydrops in all of the 30 patients who fulfilled the diagnostic criteria for Ménière’s disease. We had no false positives and only one false negative with a patient presenting with bilateral disease clinically but having endolymphatic hydrops only on one side. Thus, our correspondence rate between clinical and imaging findings was 97%.ConclusionsIt is possible to diagnose endolymphatic hydrops with the late-enhanced 3D FLAIR sequence using a 1.5 T MRI machine. Since Ménière’s disease diagnosis is sometimes tricky, imaging endolymphatic hydrops can aid in the diagnosis when the clinical picture is incomplete. It also helps guide invasive treatment plans. Feasibility at 1.5 T ensures broader access to the late-enhanced 3D FLAIR sequence. Beyond the scope of Ménière’s disease, this sequence offers the possibility to better understand pressure-related inner ear diseases.

The inner ear and stapes of the basal mammaliaform Morganucodon revisited: new information on labyrinth morphology and promontorial vascularization

Abstract Based on high-resolution computed tomography scanning, we provide new insights into the inner ear and stapedial morphology of Morganucodon from the Early Jurassic of St Brides. At the base of mammaliaforms, Morganucodon plays a pivotal role in understanding the sequence of character acquisition from basal cynodonts to mammals, including the detachment of the middle ear and the evolution of high-frequency hearing. Advancements in imaging technology enabled us to revise or newly describe crucial anatomy that was not accessible for the original description of Morganucodon. Based on 37 petrosals, we can confirm that the apex of the cochlear canal is expanded in Morganucodon, suggestive of a lagena macula. A gently raised crest along the abneural margin is reminiscent of (although much shallower than) the secondary lamina base of other Mesozoic mammaliaforms. The venous circum-promontorial plexus, which surrounded the inner ear in several basal mammaliaforms, was connected to the cochlear labyrinth in Morganucodon through numerous openings along the secondary lamina base. Two petrosals contain fragmentary stapes, which differ substantially from previously described isolated stapes attributed to Morganucodon in having peripherally placed crura and an oval and bullate footplate. Based on the revised stapedial morphology, we question the traditional view of an asymmetrical bicrural stapes as the plesiomorphic condition for Mammaliaformes.

Machine learning-based prediction of the outcomes of cochlear implantation in patients with inner ear malformation.

The objectives of this study are twofold: first, to visualize the structure of malformed cochleae through image reconstruction; and second, to develop a predictive model for postoperative outcomes of cochlear implantation (CI) in patients diagnosed with cochlear hypoplasia (CH) and incomplete partition (IP) malformation. The clinical data from patients diagnosed with cochlear hypoplasia (CH) and incomplete partition (IP) malformation who underwent cochlear implantation (CI) at Beijing Tongren Hospital between January 2016 and August 2020 were collected. Radiological features were analyzed through 3D segmentation of the cochlea. Postoperative auditory speech rehabilitation outcomes were evaluated using the Categories of Auditory Performance (CAP) and the Speech Intelligibility Rating (SIR). This study aimed to investigate the relationship between cochlear parameters and postoperative outcomes. Additionally, a predictive model for postoperative outcomes was developed using the K-nearest neighbors (KNN) algorithm. In our study, we conducted feature selection by using patients' imaging and audiological attributes. This process involved methods such as the removal of missing values, correlation analysis, and chi-square tests. The findings indicated that two specific features, cochlear volume (V) and cochlear canal length (CDL), significantly contributed to predicting the outcomes of hearing and speech rehabilitation for patients with inner ear malformations. In terms of hearing rehabilitation, the KNN classification achieved an accuracy of 93.3%. Likewise, for speech rehabilitation, the KNN classification demonstrated an accuracy of 86.7%. The measurements obtained from the 3D reconstruction model hold significant clinical relevance. Despite the considerable variability in cochlear morphology across individuals, radiological features remain effective in predicting cochlear implantation (CI) prognosis for patients with inner ear malformations. The utilization of 3D segmentation techniques and the developed predictive model can assist surgeons in conducting preoperative cochlear structural measurements for patients with inner ear malformations. This, in turn, can offer a more informed perspective on the anticipated outcomes of cochlear implantation.

Analysis of Cochlear Morphology for Cochlear Implantation Using Three-Dimensional Reconstruction of Computed Tomography Images

Plain Language SummarySubjects suffering from sensorineural deafness have been able to regain partial hearing and speech understanding using cochlear implants. The frequency mapping of the cochlea is important for postoperative success. However, the frequency distribution of the human cochlea varies among individuals due to variations in cochlear length. Accurate measures of cochlear duct length for preoperatively defining this length are needed to maximize the effect of frequency mapping. This study analyzed the length and shape of the cochlea using three-dimensional reconstructions of the temporal bone based on computed tomography scans. Eight angular points (P0–P7) every 90° were selected from 0° to 630° from the center of the round window using the reconstructed cochlear canal images. The radius (R) and thickness (T) of the cochlear canal at each point were measured. Each point was theoretically positioned 90° relative to the origin starting from the center of the round window. Therefore, P0 and P7 are the angular points at 0° and 630°, respectively. The coiling ratio of the cochlea was measured using the ratios R4/R0, R5/R1, R6/R2, and R7/R3. The cochlear canal length (CoCL) was estimated using an equation based on the radius at each point. The mean CoCL from 0° to 630° was 31.5 mm, and the cochlear volume was 55.9 mm3. Based on the Greenwood and Erixon equations, our CoCL 360° and 630° measurements corresponded to frequencies of 982 (759–1,405) Hz and 312 (158–499) Hz. These are comparable with previously reported values.

Parameterisation and Prediction of Intra-canal Cochlear Structures

Accurate 3D models of the cochlea are useful tools for research in the relationship between the electrode array and nerve fibres. The internal geometry of the cochlear canal plays an important role in understanding and quantifying that relationship. Predicting the location and shapes of the geometry is done by measuring histologic sections and fitting equations that can be used to predict parameters that fully define the geometry. A parameter sensitivity analysis is employed to prove that the size and location of the spiral lamina are the characteristics that most influence current distribution along target nerve fibres. The proposed landmark prediction method more accurately predicts the location of the points defining the spiral lamina in the apical region of the cochlea than methods used in previous modelling attempts. Thus, this technique can be used to generate 2D geometries that can be expanded to 3D models when high-resolution imaging is not available.

Quantitative Evaluation of the 3D Anatomy of the Human Osseous Spiral Lamina Using MicroCT

PurposeThe osseous spiral lamina (OSL) is an inner cochlear bony structure that projects from the modiolus from base to apex, separating the cochlear canal into the scala vestibuli and scala tympani. The porosity of the OSL has recently attracted the attention of scientists due to its potential impact on the overall sound transduction. The bony pillars between the vestibular and tympanic plates of the OSL are not always visible in conventional histopathological studies, so imaging of such structures is usually lacking or incomplete. With this pilot study, we aimed, for the first time, to anatomically demonstrate the OSL in great detail and in 3D.MethodsWe measured width, thickness, and porosity of the human OSL by microCT using increasing nominal resolutions up to 2.5-µm voxel size. Additionally, 3D models of the individual plates at the basal and middle turns and the apex were created from the CT datasets.ResultsWe found a constant presence of porosity in both tympanic plate and vestibular plate from basal turn to the apex. The tympanic plate appears to be more porous than vestibular plate in the basal and middle turns, while it is less porous in the apex. Furthermore, the 3D reconstruction allowed the bony pillars that lie between the OSL plates to be observed in great detail.ConclusionBy enhancing our comprehension of the OSL, we can advance our comprehension of hearing mechanisms and enhance the accuracy and effectiveness of cochlear models.

Tonotopic fitting of the sound processor cochlear implant in normal cochlea anatomy

Introduction. Cochlear implantation is very effective due to the known tonotopic organization of the cochlea. These data are used in the distribution of signals along the channels of the cochlear implant electrode. The more accurate and natural the stimulation of the auditory nerve fibers, the better the perception of speech, sounds and speech intelligibility.The aim of the study was to compare the clinical and anatomical settings of the cochlear implant processor.Materials and methods. The study included 63 patients aged 2 to 60 years using cochlear implantation system, implants with a standard long electrode array (31.5 mm). All participants underwent computed tomography (CT) of the temporal bones with a step of 0.6 mm or less. CT data were processed using Otoplan and Sliser 3D software. The geometric dimensions of the cochlea, the length of the cochlear canal, the angular position and tonotopic frequency of each electrode were calculated, and a 3D reconstruction of the cochlea and electrode was built.Results. The correction of the frequency filters of the electrodes and the anatomical adjustment of the processor were performed according to the data obtained in the Otoplan program. A comparison was made between the clinical and anatomical setting. After the redistribution of frequency filters, patients noted a more natural sound, improved speech intelligibility. Thus, with anatomical adjustment, an exact correspondence is achieved between the central frequency of each electrode channel and the tonotopic frequency of the cochlear zone, individually determined by computed tomography.Conclusions. A new tool has appeared that allows you to significantly improve the quality and provide an individual approach to setting up processors after cochlear implantation.

Evolution of semiaquatic habits in hippos and their extinct relatives: insights from the ear region

Abstract Since molecular data identified hippopotamids as the closest living relatives of cetaceans, a common aquatic/semiaquatic ancestor hypothesis for these modern taxa has naturally been proposed. However, recent molecular studies concluded that most molecular adaptations in extant cetaceans occurred after their split from hippopotamids. If the question of aquatic affinities of the first cetaceans has been investigated at large, it has not been the case for the forebears of hippopotamids. Sensory organs are drastically affected by underwater perception. In this work, we question the aquatic affinities of fossil hippopotamoids through an investigation of the morphology and morphometrics of the petrosal bone and cochlea of 12 extinct hippopotamoid taxa. Petrosal and bony labyrinth morphological characters constitute a source of structured phylogenetic signal, both supporting major hippopotamoid clades and bringing original relationships. The morphometric study of functional measurements of the cochlear canal shows that anthracotheres bridge the morphological gap between terrestrial artiodactyls and modern hippopotamids. The integrated functional signal of the ear region further supports convergent acquisitions of semiaquatic behaviour in hippopotamids and cetaceans and indicates that terrestrial hearing was an ancestral trait among Hippopotamoidea. We highlight multiple convergent acquisitions of semiaquatic traits in the ear region of hippopotamoids and new robust phylogenetic characters.

Bony Cochlear Nerve Canal as a Predictor for Cochlear Nerve Status in Prelingually Deaf Children.

Objectives: The presence of a functional cochlear nerve is a key issue in the preoperative evaluation of pediatric candidates for cochlear implants. Correlations between cochlear nerve deficiency (CND) and bony abnormalities of the labyrinth or bony canal of the cochlear nerve are not yet well understood. The aim of this study was to determine whether the width of the bony cochlear canal (BCNC) can serve as a reliable predictive factor for the existence of a CND. Materials and methods: A total of 11 children with a confirmed diagnosis of prelingual, severe sensorineural hearing loss were included in this study. In all patients, indication for CI was confirmed and according to the preoperative protocol, high-resolution CT and MR were performed. Reconstructions at a distance of 0.6 mm of the axial plane and images from the HRCT of temporal bones were used for measuring the width of the BCNC. The cochlear nerves were evaluated on axial and sagittal - oblique T2 - MRI images and classified as normal, hypoplastic or aplastic. Two factors were reviewed retrospectively: the presence of inner ear anomalies and the relationship between BCNC stenosis and the existence of CND. Results: From a total of 22 temporal bones analyzed (22 ears in 11 patients), inner ear malformations were detected in 6 ears from 3 patients (27.27%). All three children had a bilateral malformation, in one it was Michel deformity and in two it was IP2 (incomplete partition 2). The BCNC diameter ranged from 0.1mm to 2.33mm with a mean value of 1.46±0.6mm. CND was recorded in 4 of 22 ears and all were associated with stenosis of the BCNC. In a total of three ears with a stenotic canal, we obtained a normal finding for the cochlear nerve on MR. Conclusion: Children with BCNC stenosis have a high incidence of CND. A narrowed BCNC on CT can be an indicator for the selection of children with sensorineural hearing loss who will need to be additionally referred for MRI in order to definitively assess the status of the cochlear nerve.

Computational mathematics model of Passive spiral cochlea

The ear is an important sensory organ of the human body. Cochlea has a pivotal role in the hearing system of human. Nearly 300 million people around the world suffer from sensorineural deafness caused by cochlear lesions. Because the mechanism of cochlear sensing is very complex, it has not been understood completely so far, which has become one of the important problems in medicine today. The basilar membrane in the cochlear canal is the supporting structure of all microstructures, the complex coupling motion between basilar membrane and lymph in cochlear canal is the primary condition for generating the cochlear sound sensing function. Therefore, it is essential to study the dynamic behavior of the basement membranes. By dividing the length of the cochlea into a finite number of elements and giving the radial distribution, a set of governing equations is derived for coupling micromechanics with fluid. Then combining these equations with the matrix combination equation, the complete coupling response of basilar membrane and lymph is obtained. The instantaneous responses of the basilar membrane under different excitations, the time domain responses of the resonance position under different frequency excitations, and the effects of the changes of the mass and stiffness of the basilar membrane on its biomechanical properties and hearing function are analyzed. The results showthat the increase of the mass and stiffness of the basilar membrane leads to the weakening of the maximum response, and the increase of the mass causes the maximum response position to move to the bottom of the basilar membrane; the increase of the basilar membrane stiffness causes the maximum response position to move to the top of the basilar membrane; the changing basilar membrane cross-section can rapidly reduce the characteristic frequencies at the middle and top of the cochlea, thus achieving better filtering and amplification of specific frequency excitation, and enabling the cochlea to have a higher resolution in a specific frequency range of 1000–3000 Hz.This computational mathematics model can provide a numerical analysis platform for implementing the clinical evaluation of lesions in the basilar membrane of the inner ear. Compared with the existing finite element models, this method has faster calculation speed and higher efficiency of parameter analysis.

Morphology and morphometry of the inner ear of the dromedary camel and their influence on the efficiency of hearing and equilibrium

BackgroundThe inner ear morphology and size are linked to hearing and balance ability. The goal of this study was to determine the morphology and morphometrics of the dromedary camel's inner ear and how it influences hearing accommodation and equilibrium in the desert environment.Materials and methodsGross morphology, computed tomography images, and the endocast were used to show the inner ear morphology. A caliper and ImageJ software were used to take measurements on a plastic endocast.ResultsThe presence of the subarcuate fossa, flat cochlea, radii curvature of the semicircular canals, particularly the lateral semicircular canal, orthogonality, and the union between the semicircular canals, along with slightly increased saccule and utricle size, maintains camel balance on sandy ground, even during heavy sandstorms. The cochlear basilar membrane length and cochlea radii ratio aided low-frequency hearing and perception over a wide octave range.ConclusionThe camel's cochlear characteristics revealed a lengthy basilar membrane, a high radii ratio, 3.0 cochlear canal turns, and a very broad cochlea. The orthogonality of the semicircular canals, the high curvature of the lateral semicircular canal, the presence of the subarcuate fossa, and the confluence between the lateral and posterior semicircular canal were particular specifications that allowed the inner ear of the camel to adapt to desert living.

Comparative morphology and postnatal ontogeny of the bony labyrinth in Pantherinae (Felidae, Carnivora) with special emphasis on the lion

The bony labyrinth (inner ear) of mammals reveals systematic as well as morphofunctional information. However, detailed knowledge of bony labyrinth morphology and ontogeny in Pantherinae, that comprise some of the most iconic mammals, is still pending. Hence, we present the first comparative description of the bony labyrinth in all extant species of Panthera and Neofelis some of which are represented by several postnatal stages; particular focus is set on Panthera leo. Our study is based on µCT scans and virtual 3D reconstructions and accompanied by selected morphometric measurements. Even though quite similar in morphology, both genera as well as their species can be distinguished by several features, e.g., shape and relative size of the semicircular canals and presence or absence of an osseous secondary crus commune. In case of the latter, P. pardus shows some intraspecific variation. We also traced the reduction of the fossa subarcuata during ontogeny in P. leo which conforms with previous studies. Negative allometry of the bony labyrinth in relation to skull basal length can be observed during ontogeny as demonstrated by P. leo as well as between different sized species. Although not correlated with the length of the cochlear canal, the number of cochlear turns is higher in captive non-adult P. leo and P. tigris, but lower in adult captive P. pardus. If these intraspecific differences are related to captivity or represent an ontogenetic pattern, needs to be evaluated in future studies based on larger samples.

Synchrotron scanning sheds new light on Lumkuia fuzzi (Therapsida, Cynodontia) from the Middle Triassic of South Africa and its phylogenetic placement

Lumkuia fuzzi is a small non-mammalian cynodont from the Middle Triassic of South Africa. It has traditionally been phylogenetically identified as a basal Probainognathia, but some studies place it more basally as the sister-group to Eucynodontia. Lumkuia is known from a single specimen comprising a skull and partial skeleton. Only the skull has been thoroughly described. Here we use synchrotron X-ray computed tomography to describe the dental series and postcranial skeleton of Lumkuia. The shoulder girdle, forearm, manual phalanges, partial vertebral column, and ribs are described. To assess the effect of these new observations on the phylogenetic position of Lumkuia, the scoring of this taxon is updated and new characters are added to two previous analyses, one supporting Lumkuia as a Probainognathia and the other in which the taxon is usually retrieved as a basal Eucynodontia. Our phylogenetic analyses all unambiguously support the position of Lumkuia as a basal Probainognathia. The most commonly retrieved synapomorphies shared by Lumkuia and the probainognathians are cranial (absence of an ectopterygoid and pineal foramen), postcranial (the procoracoid does not contribute to the glenoid fossa), and palaeoneurological (reduction of the external nasal ramus of the maxillary canal, presence of a cochlear canal) characters. The degree of skeletal ossification and stages of dental replacement and wear support that the specimen is a subadult. The forelimbs were adapted to sprawling and occasional scratch-digging, thus suggesting a facultative fossorial ecology for Lumkuia.

Mammalian petrosal from the Lower Cretaceous high paleo-latitude Teete locality (Yakutia, Eastern Russia)

Abstract A mammalian petrosal from the Lower Cretaceous Teete locality in Yakutia (Russia) shows a prominent and complex system of venous channels in the bony wall of the pars cochlearis surrounding the straight cochlear canal. This complex venous system is distinctive and more strongly developed than in other mammalian petrosals. A bony ridge is present on the ventral side of the cochlear canal endocast, continuing from between fenestra vestibuli and fenestra cochleae in anterior direction. This ridge corresponds to the position of the scala tympani, and is similar to the secondary bony lamina of crown therians, but lacks the sharp laminar edge. The fenestra cochleae is separate from the canal for the aquaeductus cochleae (derived), but the fenestra retains a deep sulcus that resembles the perilymphatic sulcus (plesiomorphic). The fenestra cochleae is oval shaped and deep. The straight cochlear canal with a ridge on the ventral side strongly resembles that of eutriconodontans like Priacodon fruitaensis from the Upper Jurassic of North America. However, thick and extensive venous channels in the pars cochlearis are otherwise known from docodontans. In the Teete petrosal the channels are even more developed, and resemble the pattern recently reported from possible haramiyidan petrosals from the Middle Jurassic of western Siberia (Russia). Both eutriconodontan and haramiyidan dental remains are known from the Teete locality beside that of tritylodontids and docodontans.

A new mammal from the Lower Cretaceous Jehol Biota and implications for eutherian evolution.

Here we report on a new Early Cretaceous eutherian represented by a partial skeleton from the Jiufotang Formation at Sihedang site, Lingyuan City, Liaoning Province that fills a crucial gap between the earliest eutherians from the Yixian Formation and later Cretaceous eutherians. The new specimen reveals, to our knowledge for the first time in eutherians, that the Meckelian cartilage was ossified but reduced in size, confirming a complete detachment of the middle ear from the lower jaw. Seven hyoid elements, including paired stylohyals, epihyals and thyrohyals and the single basihyal are preserved. For the inner ear the ossified primary lamina, base of the secondary lamina, ossified cochlear ganglion and secondary crus commune are present and the cochlear canal is coiled through 360°. In addition, plesiomorphic features of the dentition include weak conules, lack of pre- and post-cingula and less expanded protocones on the upper molars and height differential between the trigonid and talonid, a large protoconid and a small paraconid on the lower molars. The new taxon displays an alternating pattern of tooth replacement with P3 being the last upper premolar to erupt similar to the basal eutherian Juramaia. Parsimony analysis places the new taxon with Montanalestes, Sinodelphys and Ambolestes as a sister group to other eutherians.This article is part of the theme issue ‘The impact of Chinese palaeontology on evolutionary research’.

Jurassic mammaliaform petrosals from Western Siberia (Russia) and implications for early mammalian inner-ear anatomy

Abstract Five partially preserved mammaliaform petrosals recovered from Middle Jurassic sediments of the Berezovsk coal mine (Krasnoyarsk Krai, Russia) show similarities to other early mammaliaforms like the morganucodontan Morganucodon and the docodontan Haldanodon in having an inflated promontorium and a curved and apically inflated cochlear canal, but they are distinct from dryolestoid and derived mammalian petrosals by the weak coiling of the cochlear duct and the presence of a perilymphatic foramen with an open perilymphatic sulcus. The two larger and robust specimens exhibit striking similarities to docodontan petrosals. Inside the bone an intricate circumpromontorial venous plexus was discovered, as recently described for the docodontan Borealestes, confirming that this structure is consistently present in basal non-mammalian mammaliaforms. The three smaller and slender petrosals probably belong to haramiyidans and are unique in showing a septum-like structure medially along the cochlear nerve entrance. The protruding perforated bony bar, which is preserved in two of the three, is interpreted here to be a remnant of a bony septum with multiple foramina for cochlear nerve fibres, representing an autapomorphic feature of Haramiyida. This newly described passageway for nerve fibres shows that the formation of the osteological structure surrounding the nervous pathways of the cochlea is more plastic among the non-mammalian mammaliaforms than previously thought.

New Skull Material of Taeniolabis taoensis (Multituberculata, Taeniolabididae) from the Early Paleocene (Danian) of the Denver Basin, Colorado.

Taeniolabis taoensis is an iconic multituberculate mammal of early Paleocene (Puercan 3) age from the Western Interior of North America. Here we report the discovery of significant new skull material (one nearly complete cranium, two partial crania, one nearly complete dentary) of T. taoensis in phosphatic concretions from the Corral Bluffs study area, Denver Formation (Danian portion), Denver Basin, Colorado. The new skull material provides the first record of the species from the Denver Basin, where the lowest in situ specimen occurs in river channel deposits ~730,000 years after the Cretaceous-Paleogene boundary, roughly coincident with the first appearance of legumes in the basin. The new material, in combination with several previously described and undescribed specimens from the Nacimiento Formation of the San Juan Basin, New Mexico, is the subject of detailed anatomical study, aided by micro-computed tomography. Our analyses reveal many previously unknown aspects of skull anatomy. Several regions (e.g., anterior portions of premaxilla, orbit, cranial roof, occiput) preserved in the Corral Bluffs specimens allow considerable revision of previous reconstructions of the external cranial morphology of T. taoensis. Similarly, anatomical details of the ascending process of the dentary are altered in light of the new material. Although details of internal cranial anatomy (e.g., nasal and endocranial cavities) are difficult to discern in the available specimens, we provide, based on UCMP 98083 and DMNH.EPV 95284, the best evidence to date for inner ear structure in a taeniolabidoid multituberculate. The cochlear canal of T. taoensis is elongate and gently curved and the vestibule is enlarged, although to a lesser degree than in Lambdopsalis.

Radiological measurement of cochlear dimensions in cochlear hypoplasia and its effect on cochlear implant selection.

To determine the effect of cochlear dimensions on cochlear implant selection in cochlear hypoplasia patients. Temporal bone computed tomography images of 36 patients diagnosed with cochlear hypoplasia between 2010 and 2016 were retrospectively reviewed and compared with those of 40 controls without sensorineural hearing loss. Basal turn length and mid-modiolar height were significantly lower in the cochlear hypoplasia patients with subtypes I, II and III than in the control group (p < 0.001). Mid-scalar length was significantly shorter in subtype I-III patients as compared with the control group (p < 0.001). In addition, cochlear canal length (measured along the lateral wall) was significantly shorter in subtype I-IV patients than in the control group (subtypes I-III, p < 0.001; subtype IV, p = 0.002). Cochlear hypoplasia should be considered if basal turn length is less than 7.5 mm and mid-modiolar height is less than 3.42 mm. The cochlear implant should be selected according to cochlear hypoplasia subgroup. It is critically important to differentiate subtype II from incomplete partition type I and subtype III from a normal cochlea, to ensure the most appropriate implant electrode selection so as to optimise cochlear implantation outcomes.

Histological examination of structural changes in the cochlear canal

Histological examination of structural changes in the cochlear canal

Inner ear morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar

ABSTRACT The cochlear canal of Adalatherium hui, from the Late Cretaceous of Madagascar, exhibits a combination of features previously unknown among mammaliaforms. The cochlear canal of Adalatherium is short and ‘C’-shaped (curved through at least 210°). A presumptive lagenar nerve canal extends from the apex of the cochlea to the internal acoustic meatus. In conjunction with an apical expansion of the cochlear canal, this morphology suggests that Adalatherium retained a lagenar macula. Adalatherium is derived among mammaliaforms in possessing primary and secondary osseous laminae, a cribriform plate, and a distinct cochlear ganglion canal. Strikingly, Adalatherium shows a single-layered primary osseous lamina that lacks internal, radially oriented canaliculi for auditory nerve fibers. In this respect, the primary lamina of Adalatherium is structurally different from the double-layered primary lamina containing habenulae perforatae of extant therians. Furthermore, Adalatherium resembles the gondwanatherian Vintana in possessing a secondary canal running parallel to the cochlear ganglion canal. Although its exact role and homology are uncertain, the morphology of this secondary canal and its tributary canaliculi is most consistent with a vascular function. The inner ear of Adalatherium augments a growing list of characters (or character combinations) in which gondwanatherians are not only different from the inferred plesiomorphic condition for mammaliaforms but also distinct from the derived characters of therians. Collectively, the new morphological and phylogenetic data support homoplastic transformation of such structures as the cribriform plate and primary osseous lamina in mammals and independent loss of the lagenar macula within gondwanatherians.