Anatomical Study of the Facial Recess with Implications in Round Window Visibility for Cochlear Implantation: Personal Observations and Review of the Literature

Abstract Introduction Posterior tympanotomy through facial recess (FR) is the conventional and most preferred approach to facilitate cochlear implantation, especially when the electrode is inserted through the round window. The complications of the FR approach can be minimized by proper understanding of the anatomy of the FR. Objective The present study was undertaken to assess the various parameters of FR and round window visibility, which may be of relevance for cochlear implant surgery. Methods Thirty-five normal wet human cadaveric temporal bones were studied by dissection for anatomy of FR and posterior tympanum. Photographs were taken with an 18megapixels digital camera, which were then imported to a computer to determine various parameters. Results The mean distance from the take-off point/crotch of the chorda tympani nerve (CTN) to the stylomastoid foramen was 4.08 ± 0.8 mm(range of 2.06 - 5.5mm). The variations in the course of the CTN included origin at the level of the lateral semicircular canal. Themean chorda-facial angle in our study was 26.91° ± 1.19°, with a range of 25° to 28.69°. The mean FR length ranged between 9.4 mm and 18.56 mm (mean of 12.41 ± 2.91mm) and varied with the origin of the CTN and pneumatization of temporal bone. The average maximum width of the FR was 2.93 ± 0.4 mm (range 2.24-3.45 mm) and the mean width of the FR at the level of the round window was 2.65 ± 0.41 mm. Conclusion The FR approach provides good access to the round windowmembrane in all cases. In some cases, table adjustment is required.

Blocking NR2B Receptor Reversed the Process of Cytotoxicity to Spiral Ganglion Neurons Induced by Sodium Salicylate in Guinea Pig / 听力学及言语疾病杂志

Objective To investigate whether blocking NR2B receptor can reverse the process of cytotoxicity to spiral ganglion neurons induced by sodium salicylate in guinea pig by applying ifenprodil (a NR2B antagonist) at the round window niche .Methods Sixty healthy guinea pigs provided by the experimental animal center of Guangxi medical university were randomly and evenly divided into a control group (Group I ,no treatment) ,an APL group (Group II ,60μl APL directly applied to the round window ) ,a sodium salicylate group (Group III ,60 μl APL di-rectly applied to the round window and then be given intraperitoneal sodium salicylate injection ) ,and an ifenprodil group (Group IV ,60μl of 10μmol/l ifenprodil in APL directly applied to the round window and then be given intra-peritoneal sodium salicylate injection ) .Sodium salicylate was given at 400 mg · kg -1 · d-1 for 7 days .Auditory brainstem responses (ABRs) were recorded before animal sacrifice by decapitation .The left cochlea was removed and prepared for detection of caspase -3 expression in spiral ganglion neurons via immunohistochemistry .From each group ,6 cochleae were used to test apoptosis index in spiral ganglion neurons using the TUNEL technique .Results Before salicylate administration ,the ABR threshold was less than 40 dB SPL in all animals .After salicylate ad-ministration ,the ABR threshold was 33 .33 ± 5 .17 dB SPL in Group II ,64 .17 ± 7 .36 dB SPL in Group III and 49 .17 ± 5 .85 dB SPL in Group IV ,in contrast to 31 .67 ± 5 .16 dB SPL in Group I (controls) .The caspase -3 ex-pression was not changed obviously in Group I and Group II ,but was significantly changed in Group III and Group IV (P<0 .01) .The caspase-3 expression appeared to be decreased in Group IV compared to those in Groups III (P<0 .05) ,but still increased compared to those of in Group I and II (P<0 .05) .The apoptosis index among spiral ganglion neurons in Groups III and IV increased significantly compared to those of in Group I and II (P<0 .001) .It was however ,lower in Group IV than in Group III (P<0 .01) .Conclusion Blocking NR2B receptor with specificity can reverse the process of cytotoxicity to spiral ganglion neurons induced by sodium salicylate in guinea pig .

Protection Against Gentamicin Ototoxicity by the Administration of Dexamethasone on the Cochlear Round Window Membrane / 听力学及言语疾病杂志

Objective To investigate the protective effects of round window membrane administration of dex-amethasone(Dex) on ototoxicity induced by gentamicin(GM) .Methods Sixty guinea pigs with normal hearing were randomly divided into four groups ,①GM group :treated with gentamicin by 120 mg · kg -1 · d-1 for 10 days;②GM -S-Dex group:treated as the GM group and dexamethasone by intraperitoneal injection 2 .5 mg · kg -1 · d-1 for 10 days;③GM -T -Dex group :treated as the GM group and dexamethasone by round window administration on right ear ;④NS -T -Dex group:treated with sodium chloride by 120 mg · kg -1 · d-1 for 10 days and with dex-amethasone topically as GM -T -Dex group .The auditory brainstem response (ABR) was respectively measured before the treatment and on day 1 ,day 10 after the treatment .After the treatment ,animals were killed instantly and the middle ear mucosa and the Corti's organ were observed with SEM .Results There was no change of ABR threshold in NS -T -Dex group on day 10 after the treatment ,whereas ABR thresholds in the other groups were elevated and GM group was the most significant .The massive outer hair cells loss was observed in GM group while the loss in GM -T -Dex group and GM -S-Dex group was trivial .The middle ear mucosa was normal and no inflammation was found in any of the groups .Conclusion The results indicated that round window administration of dexamethasone had protective effects aganist the gentamicin -induced hearing loss .

The Study of a New Approach to postauricular microinjection via the Round Window Membrane for Cochlear Gene transfection in Mouse / 听力学及言语疾病杂志

Objective To assess the feasibility of adenoviral vectors mediate cochlear gene transfer by postau-ricular microinjection through the round window membrane in mouse. Methods Twelve 5-week old C57BL/6J mice were selected for the study: 8 were implanted with Ad-EGFP by postauricular microinjection through the round window membrane, and 4 with artificial perilymphatic fluid. On postoperative days 5 and 14, the animals were sac-rificed and the surface preparation of cochleae was observed. Results Two animals died after operation. Bright green fluorescence in the cochleae was observed in Ad- EGFP groups. Gene expression on day 14 after operation was higher than that on day 5. However, the control group was free of fluorescence. Oonclusion The postauricular route of the cochlear gene transfer in mice is simple to operate with little side-effect. The technique of transgenic delivery into the inner ear through RWM by mieroinjection is feasible and effective.

Ultrastructural Characteristics of the Round Window Membrane During Pneumococcal Otitis Media in Rat

To understand better the pathogenesis of inner ear (IE) damage caused by otitis media (OM), the round window membrane(RWM) structure was investigated in a rat model for pneumococcal otitis media (POM). The RWM of 25 rats were evaluated light and electron microscopically on 1 day, 3 days, 6 days, 10 days, and 20 days after the unilateral inoculation of type 3 pneumococcus suspension into their middle ear cavities. The thickness of the RWM increased in various stages of the pneumococcus-evoked otitis media, compared with that of the normal. The thickening was most pronounced on day 1, being about 4 to 5 times greater than that of the normal RWM. All layers of the RWM were affected by the pneumococcal infection, but the major changes were confined to the subepithelial space close to the basement membrane (BM). Together with alterations to the BM, the most distinct pathological features were characterized by an increase and hypertrophy of fibroblasts in association with abundant collagen fibers. Elastic fibers observed close to the inner mesothelial layer under a high power magnification also increased during the experiment. These results will be relevant to a better understanding of the histologic implication of RWM in stages of acute otitis media involving pneumococcus-evoked otitis media.

ULTRASTRUCTURE OF THE ROUND WINDOW MEMBRANE IN HUMAN FETUS / 解剖学报

The normal round window membrane in human fetus was examined by transmission electron microscopy. The membranes in 5 to 9 months old fetus consist of the following three layers: (1) an outer squamous epithelial layer facing the middle ear, there was no epithelium in 4-month-old stage, (2) a middle fibrous layer consists of collagenous and elastic fibrils, fibroblasts, fibrocytes, blood vessels, and nerves, (3) an inner layer of simple flat cell(mesothelial cell) facing the scala tympani. With the advance of age the epithelium is getting thinner, the number of fibroblasts is reduced but that of fibrocytes is increased, collagenous and elastic fibrils grow gradually in density.The round window membrane in 8-month-old fetus is simillar to the ultrastrucrural characteristics of that in adult. The round window membrane has an important and complicated physiological function. The epithelium of the tympanic layer with tight junction and many desmosomes appear to present a barrier to free diffusion through the intact membrane. The stability and elasticity of the membrane provide protection against rupture and elasticity plays a role in the physiology of hearing as well.