Scanning electron microscopic study of the human auditory ossicles

An anatomical investigation of alkaptonuria: Novel insights into ochronosis of cartilage and bone

Ochronotic pigmentation of connective tissue is the central pathological process in the rare metabolic disease alkaptonuria (AKU). Tissue pigmentation in AKU occurs due to unmetabolised homogentisic acid (HGA) in the circulation, caused by an enzyme deficiency in the liver. Ochronotic pigmentation, derived from HGA, has previously been reported and described in large joints obtained from arthroplasty surgeries, which typically have advanced disease. Many tissues that are affected by ochronosis are not accessible for study during life, including tissues subjected to early and mid-stage disease. Here, the opportunity arose to anatomically examine a 60-year-old AKU female body donor, allowing the investigation of previously understudied tissue, including those undergoing early-stage pathological changes. Dissection of fresh-frozen tissue was carried out and harvested tissues were fixed and examined histologically using H&E and Schmorl's stains to aid identification of ochronotic pigment. This work focusses on osteochondral tissues including extra-skeletal cartilage, viscera and eyes. Gross and histological images demonstrating pigmentation in the cartilage and perichondrium of the ear ossicles, tympanic membrane and the pubic symphysis fibrocartilaginous disc are described for the first time here. We also show the first examination of the temporomandibular joint, which macroscopically appeared unpigmented, with histological analysis of the fibrocartilaginous disc showing no pigmentation. Pigmentation of non-articular hyaline cartilage was observed in the respiratory tract, in both the hyaline cartilage and perichondrium, confirming previous findings. Within smaller joints, pigmentation of chondrons and the surrounding territorial matrix was observed, but was confined to calcified articular cartilage, and was not generally found in the hyaline articular cartilage. Dark pigmentation of the perichondrium adjacent to the articular surface was observed in numerous small joints. The calcified bone matrix was not pigmented but ochronosis was identified in a small fraction of trabecular osteocytes in the capitate and radius, with substantially more pigmented osteocytes observed in bone of the ear ossicles. Viscera examined were unpigmented. This anatomical examination of tissues from an AKU individual highlights that most osteochondral tissues are susceptible to HGA-derived pigmentation, including the ear ossicles which are the smallest bones in the body. Within joints, calcified cartilage and perichondrium appear to be the earliest affected tissues, but why this is the case is not understood. Furthermore, why the TMJ disc was unaffected by pigmentation is intriguing. The heterogenous appearance of pigmentation both within and between different tissues indicates that factors other than tissue type (i.e. cartilage, perichondrium) and matrix composition (i.e. collagen-rich, calcified) may affect the process of ochronosis, such as oxygen tension, loading patterns and tissue turnover. The effect of nitisinone treatment on the ochronotic disease state is considered, in this case 7 years of treatment, however comparisons could not be made to other cases due to inter-individual variability.

Morphological and Morphometrical Aspects of the Auditory Ossicles in the European Badger (Meles Meles)

Simple Summary

The little-described morphology of the ear ossicles in the badger provides some interesting morphological features alongside some metrical data. For the malleus, we notice the standard framing into the known shape, with the mentioned presence at the level of the column of all three processes (lateral, rostral and medial), from which the rostral one is the most developed. The malleal manubrium is long and triangularly shaped on a cross-section. For the incus we notice the overall shape of a biradicular molar with the existence of the two crura in acute angulation, while the long crus is continuing with the lenticular process. The presence of a bony blade that links to the lenticular process is also noted. For the stapes, the almost equal two crura and the quite round intercrural foramen is described.

Abstract

Given the scarce morphological data regarding the middle ear anatomy of this species, the paper attempts to describe the morphological and morphometrical data of the auditory ossicles in the badger. The study was performed using the standard morphological investigations and provides a complete morphological description of the ossicular assembly (malleus, incus and stapes) with some comparative features and attempts to provide a complete set of standardized metrical data for each ossicle. A more-detailed attempt to compare some functional aspects in the light of combined metrical ratios is also implied.

Internal vascular channel architecture in human auditory ossicles

The vascular supply of the human auditory ossicles has long been of anatomical and clinical interest. While the external blood supply has been well‐described, there is only limited information available regarding the internal vascular architecture of the ossicles, and there has been little comparison of this between individuals. Based on high‐resolution micro‐CT scans, we made reconstructions of the internal vascular channels and cavities in 12 sets of ossicles from elderly donors. Despite considerable individual variation, a common basic pattern was identified. The presence of channels within the stapes footplate was confirmed. The long process of the incus and neck of the stapes showed signs of bony erosion in all specimens examined. More severe erosion was associated with interruption of some or all of the main internal vascular channels which normally pass down the incudal long process; internal excavation of the proximal process could interrupt vascular channels in ossicles which did not appear to be badly damaged from exterior inspection. An awareness of this possibility may be helpful for surgical procedures that compromise the mucosal blood supply. We also calculated ossicular densities, finding that the malleus tends to be denser than the incus. This is mainly due to a lower proportion of vascular channels and cavities within the malleus.

Statistical analysis of the human middle ear mechanical properties

Many experimental data on the human middle ear (ME) mechanics and dynamics can be found in the literature. Nevertheless, discussions about the uncertainties of these data are scarce. The present study compiles experimental data on the mechanical properties of the human ME. The summary statistics of mean and standard deviation of the data were collected and the coefficients of variation were computed and pooled. Moreover, the linear correlation and distribution were assessed for the ossicles' mass. Results show that, generally, the uncertainties of the stiffness properties of the tympanic membrane, ligaments, and tendons are larger than the uncertainties of the ossicles' mass. In addition, the uncertainties of the ME response vary across frequency. The vibration measures, such as the stapes' velocity normalized by the sound pressure at the tympanic membrane, are more uncertain than ME input impedance and reflectance. It is expected that the results presented in this study will provide the basis for the development of probabilistic models of the human ME.

MECHANISM OF SENSORINEURAL HEARING LOSS CAUSED BY TYPICAL SCLEROSIS OF COCHLEA

It is difficult to measure the cochlea directly because of the ethical problems and the complexity of cochlear structure. Therefore, finite element model (FEM) can be used as an effective alternative research method. An accurate FEM of the human ear can not only help people understand the mechanisms of sound transmission, but also effectively assess the effects of otologic diseases and guide research on the treatment of hearing loss. In this paper, a three-dimensional (3D) FEM of the human normal cochlea is proposed to study the changes in the biomechanical behavior of the cochlear sensory structure caused by the anterior fissure sclerosis and bottom-turn and apex-turn ossification of the cochlear window. The degree and harm of hearing loss caused by diseases are quantitatively predicted, which can deepen the understanding of the biomechanical mechanism of cochlea, and provide theoretical basis for clinical medicine.

Human auditory ossicles as an alternative optimal source of ancient DNA

DNA recovery from ancient human remains has revolutionized our ability to reconstruct the genetic landscape of the past. Ancient DNA research has benefited from the identification of skeletal elements, such as the cochlear part of the osseous inner ear, that provides optimal contexts for DNA preservation; however, the rich genetic information obtained from the cochlea must be counterbalanced against the loss of morphological information caused by its sampling. Motivated by similarities in developmental processes and histological properties between the cochlea and auditory ossicles, we evaluate the ossicles as an alternative source of ancient DNA. We show that ossicles perform comparably to the cochlea in terms of DNA recovery, finding no substantial reduction in data quantity and minimal differences in data quality across preservation conditions. Ossicles can be sampled from intact skulls or disarticulated petrous bones without damage to surrounding bone, and we argue that they should be used when available to reduce damage to human remains. Our results identify another optimal skeletal element for ancient DNA analysis and add to a growing toolkit of sampling methods that help to better preserve skeletal remains for future research while maximizing the likelihood that ancient DNA analysis will produce useable results.

Human auditory ossicles as an alternative optimal source of ancient DNA

DNA recovery from ancient human remains has revolutionized our ability to reconstruct the genetic landscape of the past. Ancient DNA research has benefited from the identification of skeletal elements, such as the cochlear part of the osseous inner ear, that provides optimal contexts for DNA preservation; however, the rich genetic information obtained from the cochlea must be counterbalanced against the loss of morphological information caused by its sampling. Motivated by similarities in developmental processes and histological properties between the cochlea and auditory ossicles, we evaluate the ossicles as an alternative source of ancient DNA. We show that ossicles perform comparably to the cochlea in terms of DNA recovery, finding no substantial reduction in data quantity and minimal differences in data quality across preservation conditions. Ossicles can be sampled from intact skulls or disarticulated petrous bones without damage to surrounding bone, and we argue that they should be used when available to reduce damage to human remains. Our results identify another optimal skeletal element for ancient DNA analysis and add to a growing toolkit of sampling methods that help to better preserve skeletal remains for future research while maximizing the likelihood that ancient DNA analysis will produce useable results.

Synchrotron radiation imaging revealing the sub-micron structure of the auditory ossicles

PURPOSE

Synchrotron-based X-ray Phase Contrast Imaging (SR X-PCI) allows, thanks to a highly coherent and powerful X-ray beam, the imaging of surface and cross-sectional tissue properties with high absorption-contrast. The objective of this study is to investigate the sub-micron structure of the ossicular chain. The understanding of its morphological properties at sub-micron scale will help to refine the understanding of its structural properties. The investigation of intact, non-decalcified and unstained ossicular bones allows to study the spatial relationship between surface properties, internal structure and tomographical slides.

MAIN RESULTS

The tomography datasets with a pixel size of 0.65 μm were reconstructed and 3D volume rendering models of all specimens were analyzed. Based on surface models, the surfaces of the articulations, the insertion of the tensor tympani and stapedial muscle tendons and the nutritional foramina, where the vessels penetrate the ossicles, were visualized. Moreover, a branched network of inner channels could be represented and its connection to the nutritional foramen was demonstrated. Looking at the tomographic structure of the three ossicles a mineralization pattern for every auditory bone was described, indicating a considerable variation throughout the bones.

CONCLUSIONS

This study investigates the submicron-structure of the auditory ossicles at a pixel size of 0.65 μm, which is to the best of our knowledge the highest resolution reported in the investigation of the human auditory system so far. The provided data helps in the further understanding of the anatomical conformation of the ossicular chain.

Ciliated cell observation by SEM on the surface of human incudo-malleolar-joint articular cartilage: are they a new chondrocyte phenotype?

BACKGROUND

Scanning electron microscopy (SEM) study of the human incus bone is scanty whilst, to our knowledge, no information regarding human incudo-malleolar joint articular-cartilage morphology has previously been provided.

AIMS/OBJECTIVES

Our aim was to shed some light on this morphological issue and to propose some theoretical perspectives on its functional role.

MATERIAL AND METHODS

The human incudo-malleolar joint was documented with field emission SEM on samples recovered during ear surgery procedures after patients' informed consent.

RESULTS

Normal articular cartilage chondrocytes, flattened cells with prominent nucleus and short microvilli were observed. Interestingly, cells provided with long cilia were identified. Type A cilia are arranged in a pyramidal formation with extra-long cilia stemming from the cluster, projecting upwards in an antenna-like formation ending with a dilated structure that as a whole, resembles the stereocilia with kinocilium. Types B, C and D cilia resemble those of the genital and respiratory tracts.

CONCLUSIONS AND SIGNIFICANCE

It is therefore possible to hypothesize that the observed ciliated cells may be a new chondrocyte phenotype with sensory function. Motile cilia confer the ability to distinguish variations in synovial fluid chemical composition and, in addition, they perhaps may also play some role in the mechanism of sound transmission.

A technical review and evaluation of implantable sensors for hearing devices

Most commercially available cochlear implants and hearing aids use microphones as sensors for capturing the external sound field. These microphones are in general located in an external element, which is also responsible for processing the sound signal. However, the presence of the external element is the cause of several problems such as discomfort, impossibility of being used during physical activities and sleeping, and social stigma. These limitations have driven studies with the goal of developing totally implantable hearing devices, and the design of an implantable sensor has been one of the main challenges to be overcome. Different designs of implantable sensors can be found in the literature and in some commercial implantable hearing aids, including different transduction mechanisms (capacitive, piezoelectric, electromagnetic, etc), configurations microphones, accelerometers, force sensor, etc) and locations (subcutaneous or middle ear). In this work, a detailed technical review of such designs is presented and a general classification is proposed. The technical characteristics of each sensors are presented and discussed in view of the main requirements for an implantable sensor for hearing devices, including sensitivity, internal noise, frequency bandwidth and energy consumption. The feasibility of implantation of each sensor is also evaluated and compared.

Innovative 3D Model of the Human Middle Ear in High Resolution with a Histological Microgrinding Method: A Feasibility Study and Comparison with μCT

Conclusion. The development of a histological 3D model of the tympanic cavity visualizes the exact microanatomy of the sound conduction organ and is therefore essential for finite elements simulations and surgical training. Objectives. So far, no accurate histological 3D model of the sound conduction system existed in literature. For 3D reconstruction of the very fine structures inside and outside the auditory ossicles, a method based on histological slices allows a more differential analysis of both hard and soft tissues and could thus be superior to μCT. Method. A complete temporal bone was embedded in epoxy resin and microground in distances of about 34 μm. After photodocumentation of every plane, a 3D reconstruction was performed by using the Computer Aided Design (CAD) program Rhinoceros 5®. For comparison, a μCT of the same specimen resulted in a 3D model of the calcified structures in the middle ear. Results. The histological 3D model gives an excellent overview to all anatomical soft and bony tissues of the human auditory ossicles. Specifically the fine blood vessel system and the exact dimension of cartilage areas inside the ossicles can be illustrated much more precisely than with μCT data. The present technique also allows the evaluation of the fine connecting ligaments inside the tympanic cavity.

Systematic Review of Ossicular Chain Anatomy: Strategic Planning for Development of Novel Middle Ear Prostheses

Objective

To systematically review the anatomy of the ossicular chain.

Data Sources

Google Scholar, PubMed, and otologic textbooks.

Review Methods

A systematic literature search was performed on January 26, 2015. Search terms used to discover articles consisted of combinations of 2 keywords. One keyword from both groups was used: [ ossicular, ossicle, malleus, incus, stapes] and [ morphology, morphometric, anatomy, variation, physiology], yielding more than 50,000 hits. Articles were then screened by title and abstract if they did not contain information relevant to human ossicular chain anatomy. In addition to this search, references of selected articles were studied as well as suggested relevant articles from publication databases. Standard otologic textbooks were screened using the search criteria.

Results

Thirty-three sources were selected for use in this review. From these studies, data on the composition, physiology, morphology, and morphometrics were acquired. In addition, any correlations or lack of correlations between features of the ossicular chain and other features of the ossicular chain or patient were noted, with bilateral symmetry between ossicles being the only important correlation reported.

Conclusion

There was significant variation in all dimensions of each ossicle between individuals, given that degree of variation, custom fitting, or custom manufacturing of prostheses for each patient could optimize prosthesis fit. From published data, an accurate 3-dimensional model of the malleus, incus, and stapes can be created, which can then be further modified for each patient’s individual anatomy.

Bone quality and biomechanical function: a lesson from human ossicles

In humans, the middle ear contains a chain of three ossicles with a major highly specific mechanical property (transmission of vibrations) and modeling that stops rapidly after birth. Their bone quality has been rarely studied either in noninflammatory ossicles or in those from ears with chronic inflammation. Our primary goal was to assess bone microarchitecture, morphology and variables reflecting bone quality from incuses, in comparison with those from human femoral cortical bone as controls. Secondly, the impact of chronic inflammation on quality of ossicles was documented. The study was performed on 15 noninflammatory incuses from 15 patients (35±32 years, range: 2-91). Comparisons were performed with 13 inflammatory incuses from 13 patients (55±20 years, range: 1-79) with chronic inflammation of the middle ear, essentially cholesteatoma. Microarchitecture and bone mineral density (BMD) were assessed by microcomputed tomography. Microhardness was measured by microindentation. Mineral and organic characteristics were investigated by Fourier transform infrared microspectroscopy. Noninflammatory incuses were composed of a compact, well mineralized bone without bone marrow and with sparse vessels. Remodeling activity was rarely observed. Woven or lamellar textures and numerous osteocytes were observed. In inflammatory incuses, architecture was degraded, organic tissue was abundant and bone cavities contained fibrocellular tissue and adipocytes. BMD of noninflammatory incuses was significantly higher than BMD from both control bones (4 embedded cortical femoral bone samples; age: 72±15 years, range: 50-85) and inflammatory incuses. Noninflammatory incuses were less hard than both control bone (8 cortical femoral bone samples; age: 49±18 years, range: 24-74) and inflammatory incuses. All incuses were more mineralized and less mature than controls. In conclusion, bone quality of incuses (dense, well mineralized, hard) is well adapted to their function of sound transmission. In inflammatory condition, incuses were degraded, thus explaining the decline of hearing. Moreover, microhardness was found higher than in noninflammatory incuses. Compared to bone with remodeling, the mineralization index in incuses does not explain variation of microhardness. Interestingly, a linear multiple regression model indicated that a combination of two variables, i.e., crystallinity index (crystal size/perfection) and carbonation (incorporation of carbonate ions in apatite) explains 26% of the increase in microhardness variability. Because the low remodeling level of ossicles could not prevent the reversibility of their degradation which impacts audition quality, an early management of ear inflammation in chronic otitis is recommended.

RESEARCH ON THE DISTRIBUTION OF PRESSURE FIELD ON THE BASILAR MEMBRANE IN THE PASSIVE SPIRAL COCHLEA

The cochlea is the important auditory organ of the inner ear. It is responsible for transforming the acoustic signals into neural impulses that travel along the auditory nerve to the brain. The role of, perhaps, the most characteristic feature of the cochlea, its three-dimensional (3D) helical structure, has remained elusive. To address this problem, the present paper develops a 3D spiral cochlea mathematical model using orthogonal coordinate system. Based on the method of separation of variables and conformal transformation, equations of three cases for the velocity potential are derived to solve the steady flow problem of lymph in the cochlea. Then, the distribution of pressure field on the basilar membrane (BM) is obtained. By comparing the analytical results with FE analyses results, the derived formulas are demonstrated to be accurate and reliable. The conclusion can be drawn that the spiral shape and physical dimension of the cochlea have a significant influence on the distribution of pressure field. Interestingly, near the helicotrema, the velocity potential of the first case plays a leading role in pressure distribution on the BM. Therefore, it may enhance the vibration of BM and improve hearing ability in the low-frequency parts of human ears. The proposed model could provide an approach for further investigation of fluid-structure interaction problem in the cochlea.

Changes in auditory ossicles in rheumatoid arthritis: scanning electron microscopic study

The aim of this study was to define the existence of surface changes on auditory ossicles caused by rheumatoid arthritis. The study comprised of nine pairs of auditory ossicles (mallei and incudes) from autopsy of patients with rheumatoid arthritis, and five pairs of ossicles from persons without RA, taken during autopsies. The specimens were studied with JEOL JSM 5300 type scanning electron microscope. Surface changes of auditory ossicles were defined, affected areas were calculated, and expressed in percentage of total surface. Changes in auditory ossicles in patients with rheumatoid arthritis are significantly higher than in control ossicles, both on ossicular surface and articulations. Increased lysis of incudes, especially in the region of long propagation, corresponds to vascular damage. Articular degeneration is also present, indicating specific rheumatoid alteration. Both changes are statistically more intense in cases with longer duration of disease. In conclusion, rheumatoid arthritis reduces vascularity of auditory ossicles and causes degeneration of articular surfaces.