Anatomy of the Round Window Region With Relation to Selection of Entry Site Into the Scala Tympani.

OBJECTIVES/HYPOTHESIS: The aim of cochlear implantation is to safely insert an electrode array into the scala tympani (ST) while avoiding damage to surrounding structures. There is disagreement on the optimal way of entering the ST-the round window (RW) approach versus cochleostomy. Regardless of the chosen approach, it is vital to understand the regional anatomy, which is complex, difficult to conceptualize, and rarely dissected in temporal bone courses. The goal of this study was to examine the anatomy of the RW to gain more in-depth knowledge on the local relationships of the anatomical structures and propose an approach for entering the ST in cochlear implant surgery tailored to the encountered anatomy. STUDY DESIGN: Cadaveric prevalence study and expert opinion with literature review. METHODS: Cadaveric temporal bone dissection (n = 13) by the first author assessing the RW anatomy. RESULTS: The round window membrane (RWM) and the osseous spiral lamina (OSL) are curved structures, each with a horizontal and a vertical part. The two horizontal portions are very closely apposed. The relationship between the OSL and the RWM determines the best site for a cochleostomy, which if required is best placed anteroinferiorly to the RWM. The distance between the oval window inferior margin and the RW membrane is less than 2 to 3 mm. The ST initially extends inferiorly and medially to the RW. CONCLUSIONS: The findings of our dissection have implications for cochlear implant surgery in aiming to avoid trauma to the OSL and basilar membrane and aid decision making in choosing the safest surgical approach. LEVEL OF EVIDENCE: 5. Laryngoscope, 131:E598-E604, 2021.

Grading of the Position of the Mastoid Tegmen in Human Temporal Bones - A Surgeon's Perspective.

OBJECTIVES: To establish a new surgically relevant classification system of the anatomic variations of the temporal bone tegmen plate as well as to perform a comparative analysis, with respect to the pneumatization patterns in the cadaveric temporal bones. MATERIALS AND METHODS: Microdissection of the human cadaveric temporal bones was performed after obtaining ethical approval from the Institutional Ethical Committee (F.8-522/A-522/2017/RS). The pneumatization pattern of the temporal bones was noted as "under-pneumatized" or "well-pneumatized." The tegmen mastoid (TM) was classified into two grades as per the position of the tegmen plate and the visibility of the superior semicircular canal (SSCC) and the aditus. The latter two structures were well visualized in Grade A and poorly visualized in Grade B. The data were analyzed using Stata 14.0 (Stata Corp, 4905, Lakway drive, College Station, Texas, USA). RESULTS: Ninety-three temporal bones were dissected under microscope. Fifty-eight bones were well-pneumatized and 35 were under-pneumatized. The tegmen plates were classified as Grade-A in 49 bones (well-pneumatized -37 and under-pneumatized -12), and as Grade-B in 44 bones (well-pneumatized-21, poorly-pneumatized-23). Grade-A classification was significantly more common in well-pneumatized temporal bones, while Grade-B was more common in under-pneumatized bones (p=0.0057). CONCLUSION: We propose a surgically relevant classification for TM positioning. A well-pneumatized temporal bone is associated with a significantly higher position of the tegmen plate (Grade-A TM).

Understanding the anatomy of ears from guinea pigs and rats and its use in basic otologic research.

UNLABELLED: The use of animal samples is important in otologic research and understanding the anatomy of their ears help make proper use of them in research projects. AIM: to study guinea pig's and rat's ears under light microscopy(LM) and scanning electron microscopy(SEM) and understand their anatomical advantages in basic otologic research. MATERIALS AND METHODS: The temporal bones, tympanic bullas and cochleas from three albino guinea pigs and rats were photographed and analyzed under LM and SEM. RESULTS: Rats aren't as simple to handle as guinea pigs, and often present with otitis media. Rats have a fragile junction of the tympanic bulla, two and half turns in the cochlea, and their tympanic membranes do not seal off the entire external auditory canal. Guinea pigs have full bullas, their incus and malleus are fused and they have three and half cochlear turns. Under SEM, guinea pigs and rats have Tectori Membrane, Raissner's Membrane and the Organ of Corti. Only guinea pigs have Hensen's Cells. CONCLUSION: Guinea pigs were considered easy to handle for microdissection purposes because of the size and robustness of their temporal bones, and for surgical experiments involving the stapes, the oval window and the tympanic membrane. Under SEM there are similarities guinea pigs and rats, and both can be used in inner ear studies.

Detection of mitochondrial DNA deletions in the cochlea and its structural elements from archival human temporal bone tissue.

Large-scale deletions of mitochondrial DNA (mtDNA) have been associated with aging and disease in post-mitotic tissues. These post-mitotic tissues, including skeletal muscle, heart and brain, are heavily dependent on intact functional mitochondria. The cochlear tissues are known to contain an abundance of mitochondria. This observation stimulated a search for mtDNA deletions in the cochlea and its elements using a sensitive nested PCR methodology and long range PCR to explain the functional deficits observed in age-related hearing loss. The presence of the so-called "common" deletion (CD) was detected in cochlear tissue from two individuals with age-related hearing loss, 73 and 78 years of age. Three additional deletions, that to our knowledge have not been previously reported, were also identified in these two individuals, including a 5354 bp deletion flanked with a 3 bp repeat, a 9682 bp deletion flanked by a 10 bp repeat and a 5142 bp deletion without a flanking repeat. The 9682 and 5142 bp deletions were also detected in an individual 39 years of age with normal hearing, however, these two deletions were not detected in a normal hearing individual 9 years of age. In contrast, the 5354 bp deletion was detected in all four of the individuals studied. To localize the deletions within the cochlea, the cochlear elements were removed by laser capture microdissection (LCM) and the mtDNA from these tissues was studied. The 5142 and 5354 bp deletions were detected in the organ of corti, spiral ligament, and ganglion cells, but not in the stria vascularis. These findings correlate with the reduction in the number of spiral ganglion cells and outer hair cells, and the normal stria vascularis volume observed in this individual. All four of these deletions involve the cytochrome c oxidase (COX) subunit III gene, encoded by mtDNA. These observations suggest that multiple mtDNA deletions may contribute to a deficit in mitochondrial function in the cochlea and result in hearing loss if a level of physiological significance is reached.

Ginkgo biloba extract (EGb 761) protects against cisplatin-induced ototoxicity in rats.

HYPOTHESIS: A standardized Ginkgo biloba extract, EGb 761, may have protective effect against cisplatin-induced ototoxicity in rats. BACKGROUND: Cisplatin-induced ototoxicity is a major dose-limiting side effect in anticancer chemotherapy. Cisplatin-induced ototoxicity has been correlated to depletion of the cochlear antioxidant system and increased lipid peroxidation. EGb 761 contains potent antioxidants capable of scavenging free radicals, inhibiting nitric oxide synthesis, reducing lipid peroxidation, and protecting against apoptosis. The purpose of this study was to investigate the effect of EGb 761 on cisplatin-induced ototoxicity in rats. METHODS: Male Wistar rats were divided into four groups and were treated as follows: 1) vehicle control; 2) cisplatin (13 mg/kg, intraperitoneally) plus vehicle; 3) EGb 761 (200 mg/kg, intraperitoneally); and 4) EGb 761 plus cisplatin. Auditory brainstem responses (ABRs) were measured pretreatment and 72 hours posttreatment, and threshold shifts were analyzed. Endocochlear potentials (EPs) were also obtained at 72 hours posttreatment. Cochleae were harvested and processed for scanning electron microscopy after completion of auditory testing. RESULTS: Cisplatin-treated rats showed significant ABR threshold shifts across all frequencies (click, and 2-, 4-, 8-, 16-, and 32-kHz tones) compared with each of the other groups (p < 0.001). Rats treated with EGb 761 plus cisplatin did not show significant ABR threshold shifts (p > 0.05). Similarly, the EPs of cisplatin-treated rats were decreased significantly approximately 50% in comparison with the other groups (p < 0.001). The EPs of EGb 761 plus cisplatin-treated rats were decreased less than 20% compared with vehicle control group or the EGb 761 only group (p < 0.01). The scanning electron microscopy observation indicated severe outer hair cell loss in the basal turn of cochleae of cisplatin-treated rats, whereas outer hair cells remained intact in the rats treated with EGb 761 plus cisplatin. CONCLUSION: These results demonstrate that EGb 761 protects against cisplatin-induced ototoxicity.

Spindle cell carcinoma of the external auditory meatus with intracranial extension: histological, immunohistochemical and electron microscopic evaluation.

We present a case of squamous spindle cell carcinoma of the external auditory meatus in a 38-year-old man. The tumour was extended to the inner ear, the temporal bone, the middle cranial fossa and the meningo-cerebral tissue. The surgical intervention of temporo-occipital craniotomy removed most of the neoplasia. At pathologic examination, the tumour showed an undifferentiated spindle cell pattern. Immunohistochemistry with a large antibody panel found a weak positivity only to EMA. The diagnosis was made when the electron microscopy showed rare junctional structures and tonofilaments.

Damage to inner ear structure during cochlear implantation: Correlation between insertion force and radio-histological findings in temporal bone specimens.

Cochlear implant insertion should be as least traumatic as possible in order to reduce trauma to the cochlear sensory structures. The force applied to the cochlea during array insertion should be controlled to limit insertion-related damage. The relationship between insertion force and histological traumatism remains to be demonstrated. Twelve freshly frozen cadaveric temporal bones were implanted with a long straight electrodes array through an anterior extended round window insertion using a motorized insertion tool with real-time measurement of the insertion force. Anatomical parameters, measured on a pre-implantation cone beam CT scan, position of the array and force metrics were correlated with post-implantation scanning electron microscopy images and histological damage assessment. An atraumatic insertion occurred in six cochleae, a translocation in five cochleae and a basilar membrane rupture in one cochlea. The translocation always occurred in the 150- to 180-degree region. In the case of traumatic insertion, different force profiles were observed with a more irregular curve arising from the presence of an early peak force (30 ± 18.2 mN). This corresponded approximately to the first point of contact of the array with the lateral wall of the cochlea. Atraumatic and traumatic insertions had significantly different force values at the same depth of insertion (p < 0.001, two-way ANOVA), and significantly different regression lines (y = 1.34x + 0.7 for atraumatic and y = 3.37x + 0.84 for traumatic insertion, p < 0.001, ANCOVA). In the present study, the insertion force was correlated with the intracochlear trauma. The 150- to 180-degree region represented the area at risk for scalar translocation for this straight electrodes array. Insertion force curves with different sets of values were identified for traumatic and atraumatic insertions; these values should be considered during motorized insertion of an implant so as to be able to modify the insertion parameters (e.g axis of insertion) and facilitate preservation of endocochlear structures.

Laser-Modified Surface Enhances Osseointegration and Biomechanical Anchorage of Commercially Pure Titanium Implants for Bone-Anchored Hearing Systems.

Osseointegrated implants inserted in the temporal bone are a vital component of bone-anchored hearing systems (BAHS). Despite low implant failure levels, early loading protocols and simplified procedures necessitate the application of implants which promote bone formation, bone bonding and biomechanical stability. Here, screw-shaped, commercially pure titanium implants were selectively laser ablated within the thread valley using an Nd:YAG laser to produce a microtopography with a superimposed nanotexture and a thickened surface oxide layer. State-of-the-art machined implants served as controls. After eight weeks' implantation in rabbit tibiae, resonance frequency analysis (RFA) values increased from insertion to retrieval for both implant types, while removal torque (RTQ) measurements showed 153% higher biomechanical anchorage of the laser-modified implants. Comparably high bone area (BA) and bone-implant contact (BIC) were recorded for both implant types but with distinctly different failure patterns following biomechanical testing. Fracture lines appeared within the bone ~30-50 µm from the laser-modified surface, while separation occurred at the bone-implant interface for the machined surface. Strong correlations were found between RTQ and BIC and between RFA at retrieval and BA. In the endosteal threads, where all the bone had formed de novo, the extracellular matrix composition, the mineralised bone area and osteocyte densities were comparable for the two types of implant. Using resin cast etching, osteocyte canaliculi were observed directly approaching the laser-modified implant surface. Transmission electron microscopy showed canaliculi in close proximity to the laser-modified surface, in addition to a highly ordered arrangement of collagen fibrils aligned parallel to the implant surface contour. It is concluded that the physico-chemical surface properties of laser-modified surfaces (thicker oxide, micro- and nanoscale texture) promote bone bonding which may be of benefit in situations where large demands are imposed on biomechanically stable interfaces, such as in early loading and in compromised conditions.

Microscopic anatomy of the carotid canal and its relations with cochlea and middle ear.

UNLABELLED: The knowledge of the relations between the noble and vital structures of temporal bone is still a great challenge for the otologic surgeon. The microscopic anatomic studies of the temporal bone are one of the greatest help to prevent lesions during surgical intervention. AIM: To study the anatomic correlations between the carotid canal and the cochlea, and the occurrence of dehiscence of the carotid canal in the middle ear tympanic cavity. MATERIAL AND METHODS: Microscopic study of 122 human temporal bones. RESULTS: The average distance between the carotid canal and the cochlea were: the shortest distance, 1.05 mm; basal turn, 2.04 mm; middle turn, 2.32 mm; and apical turn, 5.70 mm. The occurrence of dehiscence of the carotid canal inside the tympanic cavity was 35.2%. CONCLUSION: The small distances between the cochlea and carotid canal, and the high incidence of dehiscence in the tympanic cavity remind us that anatomical knowledge of the temporal bone is required for the best qualification of otologists.

Localisation of the nitric oxide (NO)/cGMP-pathway in the vestibular system of guinea pigs.

The exact distribution of nitric oxide-synthases (NOS) in the vestibular system has not been described satisfying yet. Immunostaining, using specific antibodies to the three known NOS-isoforms, to cyclic guanosine monophosphate (cGMP) and soluble guanylyl-cyclase (sGC), the second messenger system of nitric oxide (NO), was performed on paraffin sections of temporal bone from guinea pigs. eNOS could be detected in vestibular ganglion cells and in nerve fibres, including the calyces, surrounding the type 1 hair cells (HC). bNOS was found in the sensory epithelium, ganglion cells and in bone, while iNOS could not be found. NOS-detection was accompanied by reactivity to sGC and to cGMP. This finding implies that b- and eNOS-generated NO is involved in regulative processes in neurotransmission and regulation of blood flow.

Nature of the tympanic membrane insertion into the tympanic bone of the rat.

The nature of the insertion of the tympanic membrane into the tympanic bone was studied in the rat during the developmental period ranging from 18 days post conception (dpc) to 40 days after birth (dab). Techniques applied were light microscopy, electron microscopy and immunohistochemistry with antibodies to cytoskeletal proteins: vimentin, desmin and alpha-smooth muscle actin (sma) as fibroblast differentiation markers. It was established that the cartilaginous annulus of the pars tensa was connected to the tympanic bone by an interface of specialised connective tissue. Both the fibrocartilage and the interface were derived from the embryonal mesenchyme between the tympanic ring and meatal plate. Electron microscopy showed that the interface was composed of two types of fibroblast. The majority of these cells were myofibroblasts, which were interconnected by junctions and had intimate contact with the collagenous fibres. A small number were identified as genuine fibroblasts. Cytoskeletal characterisation revealed the presence of three types of cell: V cells which expressed vimentin, VA cells which expressed vimentin and alpha-sma and VAD cells which expressed vimentin, alpha-sma and desmin. The myofibroblasts expressed antigens of both smooth muscle cells (alpha-sma, desmin) and connective tissue cells (vimentin). It is suggested that the pars tensa is connected to the tympanic bone by a network of contractile cells and fibres. Contraction will move the membrane in an outward direction and antagonise the inward retraction by the tensor tympani.

Ultrastructural localization of ChAT-like immunoreactivity in the human vestibular periphery.

Acetylcholine (ACh) has long been considered a neurotransmitter candidate in the efferent vestibular system of mammals. Recently, choline acetyltransferase (ChAT), the synthesizing enzyme for ACh, was immunocytochemically localized in all five end-organs of the rat vestibule (Kong et al. (1994) Hear. Res. 75, 192-200). However, there is little information in the literature concerning the cholinergic innervation in the vestibular periphery of man. In the present study the ultrastructural localization of the ChAT-like immunoreactivity in the human vestibular periphery was investigated in order to reveal the cholinergic innervation in the human vestibular end-organs. A modified method of pre-embedding immunoelectron microscopy was applied. It was found that the ChAT-like immunoreactivity was located in the bouton-type vesiculated nerve terminals in the vestibular neurosensory epithelia of man. These ChAT-like immunostained nerve terminals make synaptic contacts either with afferent chalices surrounding type I vestibular sensory hair cells, or with type II vestibular sensory hair cells. These results show that the ChAT-like immunoreactivity in the human vestibular periphery is confined to the efferent vestibular system. The ChAT-containing efferents innervate both type I hair cells and type II hair cells, making postsynaptic and presynaptic contacts, respectively. This study presents evidence that ACh is a neurotransmitter candidate in the efferent vestibular system of man.

Processing and analyzing the mouse temporal bone to identify gross, cellular and subcellular pathology.

A technique has been developed for preparing the mouse temporal bone for histopathological examination: first, as a whole mount to detect any gross malformations of the bony or membranous labyrinths; second, in dissected segments to localize damage in the different sensory organs and to quantify sensory- and supporting-cell losses; and finally, in semi-thick and thin sections to identify and characterize subcellular pathology. Examples are given of the successful application of this technique to mice with very different inner-ear problems, including those with an abnormally short cochlear spiral, a defective lateral semicircular canal, abnormal otoliths over the saccular macula, an increased susceptibility to noise damage and those which lack fibroblast growth factor receptor 3.

Ultrastructural localization of GABA-like immunoreactivity in the human utricular macula.

In the vertebrate vestibular periphery, gamma-aminobutyric acid (GABA) has long been presumed to be a neurotransmitter candidate. However, experimental reports about the localization and function of GABA in the vestibular systems of vertebrates are contradictory. In addition, there is no information in the literature concerning the localization of GABA in the human vestibular periphery. The present study investigates the ultrastructural localization of GABA-like immunoreactivity in the human utricular macula. A modified pre-embedding immunostaining electron microscopy technique was applied using two different commercially available polyclonal antibodies to GABA. GABA-like immunoreactivity is confined to the vesiculated nerve fibers and terminals of the human vestibular neurosensory epithelia. The GABA-containing nerve terminals make asymmetrical axo-dendritic synapses with the afferent chalices surrounding the type I sensory hair cells. Type I and type II hair cells as well as afferent chalices are devoid of GABA-like immunoreactive staining. The present study demonstrates that GABA exists in the human vestibular periphery, and that GABA is a neurotransmitter candidate of the human efferent vestibular system.

A technique for reembedding celloidin sections for electron microscopy.

A new technique for reembedding celloidin sections of human temporal bones for transmission electron microscopy is described. It consists of four steps: 1. loosening of celloidin sections from glass slides with use of xylene and dissection of the area of interest, 2. removal of celloidin with use of clove oil, 3. staining with 1% osmium tetroxide and 1% tannic acid, and 4. embedding in epoxy resin. Autolytic changes were seen due to poor fixation. TEM of reembedded celloidin sections of optimally fixed tissue revealed that the celloidin-embedding procedure affected ultrastructural preservation to some degree. This included less well-preserved cell membranes and some increased electron density of the cytosol decreasing the EM resolution of intracytoplasmic organelles. The technique allows TEM analysis of the intact labyrinth at all regions in the same specimen without dissection of the fragile tissue components of the membranous labyrinth. This might make the technique useful for processing freshly fixed human inner ear tissue and temporal bones for ultrastructural histopathological analysis.

The temporal bone in multiple myeloma.

Multiple myeloma is a malignant disease of the skeleton. Anatomically, any bone may ultimately come to be involved in a given case. In a literature review, no published series of temporal bone findings have been reported. In this study, oto-histopathologic changes associated with multiple myeloma are analyzed and reported in 15 temporal bones from 8 patients. The bone marrow of 13 temporal bones was involved by the tumor. Osteolysis was evident in 11 temporal bones. Serous otitis media (SOM) or purulent otitis media (POM) was seen in 13 ears with 12 showing mastoid effusions. Eight ears exhibited pathological changes in inner ears, including degeneration of the organ of Corti, atrophy of stria vascularis, decreased ganglion cells, and labyrinthine hydrops. The inner ear changes were most severe in 2 patients who had otologic symptoms. Infiltration of myeloma cells was not apparent in the middle ear mucosa or the inner ears.

Immunoelectron microscopy of the human inner ear.

The immediate fixation required for satisfactory morphologic preservation of the human inner ear has not only limited the ultrastructural study of this region, but has also limited the application of immunohistochemistry. The technique of postembedding protein A-colloidal gold immunoelectron microscopy was used on human inner ear tissue taken at operation and on celloidin-embedded temporal bone sections from a traditional temporal bone bank. We describe the utility of postembedding immunoelectron microscopy for studying the localization of a wide variety of antigens including type I collagen, S-100, and calcitonin gene-related peptide. The use of this method in material available in temporal bone banks or that has been routinely processed for transmission electron microscopy provides the potential for broad application to collections of otologic material.

Proximal intratemporal facial nerve in Bell's palsy surgery. A study correlating anatomical and surgical findings.

This paper deals with the surgical approaches to that part of the intratemporal facial nerve lying proximal to the cochleariform process and focuses on two issues: the advisability of disarticulating the ossicular chain to reach this area and the accessibility of the labyrinthine segment via the transmastoid, extralabyrinthine, subtemporal route. Relevant anatomical features, which are based on 39 gross temporal bones, 47 histologic sections, and 10 cadaveric specimens are first considered. In the head specimens, it was possible to attempt exploration of the entire nerve with the transmastoid, extralabyrinthine, subtemporal operation and then remove the labyrinth to gauge the adequacy of this approach as an avenue to the labyrinthine segment. These anatomical findings, their bearing on the questions at hand, and the author's clinical experience are incorporated into descriptions of the operations currently in vogue for exploring the proximal nerve in patients with Bell's palsy.

Inner ear histopathology in patients treated with cis-platinum.

Temporal bone histopathology was studied in five patients (aged 51-67) who received cis-diamminedichloroplatinum (DDP) chemotherapy for head and neck squamous cell carcinoma. In each case, sensorineural hearing loss occurred during the course of treatment and temporal bones were acquired 3-5 hours postmortem for anatomical study. Scanning electron microscopy revealed acute degenerative changes in cochlear hair cells that appeared to be the result of drug treatment. However, the presence of age-related degeneration made it difficult to unequivocally identify hair cell loss due solely to ototoxicity. In one patient, a decrement in vestibular function was observed during DDP treatment. Postmortem examination showed severe degeneration of the maculae and cristae which could be correlated with the absence of caloric response seen after chemotherapy.

Three-dimensional images of the temporal bone and experimental otitis media in Japanese monkeys.

Since the middle ear structure of animals commonly used for experimental study is different from that of humans, we used the Japanese monkey (Macaca fuscatus) as an animal model for otitis media with effusion (OME). The exact similarities and differences of the ear structure between humans and Japanese monkeys were studied by the use of computer-aided three-dimensional reconstruction, in addition to light and electron microscopy. Otitis media with effusion was repeatedly induced by direct intratympanic inoculation of one of the following: keyhole limpet hemocyanin; following systemic immunization with keyhole limpet hemocyanin, Streptococcus pneumoniae; or endotoxin. The temporal bones were serially sliced with a diamond band saw, after which the histologic findings were examined by light and electron microscopy on the basis of macroscopic observations. Each substance induced OME equally, 2 to 3 days after inoculation. Inflammatory reaction of the middle ear mucosa extended to all of the air cells; subsequently, the inflamed mucosa returned to normal in each case along with normalization of both the tympanometric and otoscopic findings. No remarkable architectural change remained, even after OME was induced repeatedly. These findings are applicable to acute otitis media and acute mastoiditis. The development of chronic middle ear effusion was not observed in this study. The usefulness of the diamond band saw and computer-aided analysis for temporal bone histologic evaluations is emphasized.