Round Window Region Research Articles

The Use of Clinically Measurable Cochlear Parameters in Cochlear Implant Surgery as Indicators for Size, Shape, and Orientation of the Scala Tympani.

(1) To assess variations of the human intracochlear anatomy and quantify factors which might be relevant for cochlear implantation (CI) regarding surgical technique and electrode design. (2) Search for correlations of these factors with clinically assessable measurements. Human temporal bone study with micro computed tomography (μCT) data and analysis of intracochlear geometrical variations: μCT data of 15 fresh human temporal bones was generated, and the intracochlear lumina scala tympani (ST) and scala vestibuli were manually segmented using custom software specifically designed for accurate cochlear segmentation. The corresponding datasets were processed yielding 15 detailed, three-dimensional cochlear models which were investigated in terms of the scalae height, cross-sectional size, and rotation as well as the interrelation of these factors and correlations to others. The greatest anatomical variability was observed within the round window region of the cochlea (basal 45°), especially regarding the cross-sectional size of the ST and its orientation relative to the scala vestibuli, which were found to be correlated (p < 0.001). The cross-sectional height of the ST changes substantially for both increasing cochlear angles and lateral wall distances. Even small cochleae were found to contain enough space for all commercially available CI arrays. Significant correlations of individual intracochlear parameters to clinically assessable ones were found despite the small sample size. While there is generally enough space within the ST for CI, strong intracochlear anatomical variations could be observed highlighting the relevance of both soft surgical technique as well as a highly flexible and self-adapting cochlear implant electrode array design. Cochlear dimensions (especially at the round window) could potentially be used to indicate surgically challenging anatomies.

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

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. Cadaveric prevalence study and expert opinion with literature review. Cadaveric temporal bone dissection (n = 13) by the first author assessing the RW anatomy. 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. 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. 5. Laryngoscope, 131:E598-E604, 2021.

Access to Round Window Niche via Posterior Tympanotomy and Impact of Drilling Its Overhangs: A Cadaveric Descriptive Study.

We intended to study the morphological parameters of round window region and assess the gain in exposure achieved by drilling the round window niche overhang. The Exposure of the round window membrane (RWM) is of prime importance to carry out atraumatic electrode insertion for cochlear implantation. The anatomy of round window has been a subject of considerable debate in literature. Fifty-one Formalin preserved adult cadaveric temporal bones were micro-dissected to carry out an 'optimal' posterior tympanotomy to expose the round window region. The bony overhangs of round window niche (RWN) were next drilled to achieve maximal possible exposure the RWM without violating the annulus of the same. The exposure was classified as per St Thomas' Hospital classification. The round window could not be visualized in 3 bones (5.9%). The commonest morphology of RWN was dome shaped, found in 18 (37.5%) and that of the RWM was oval shaped, found in 14 (29.2%) bones. Pre drilling 41 bones had a > 50% exposure of RWM while post drilling > 50% exposure could be achieved in all the bones except the 3 bones in which RWN could not be visualized to begin with. The drilling of the RWN overhangs exposed RWM in entirety in 91.7% of bones with a visible morphology of RWN pre drilling. RWN and RWM exhibit varied morphology. Drilling of the round window niche overhangs can considerably enhance the exposure of RWM.

Surgical anatomy of the round window-Implications for cochlear implantation.

The round window is an important portal for the application of active hearing aids and cochlear implants. The anatomical and topographical knowledge about the round window region is a prerequisite for successful insertion for a cochlear implant electrode. To sum up current knowledge about the round window anatomy and to give advice to the cochlear implant surgeon for optimal placement of an electrode. Systematic Medline search. Search term "round window[Title]" with no date restriction. Only publications in the English Language were included. All abstracts were screened for relevance, that is a focus on surgical anatomy of the round window. The search results were supplemented with hand searching of selected reviews and reference lists from included studies. Subjective assessment. There is substantial variability in size and shape of the round window. The round window is regarded as the most reliable surgical landmark to safely locate the scala tympani. Factors affecting the optimal trajectory line for atraumatic electrode insertion are anatomy of the round window, the anatomy of the intracochlear hook region and the variable orientation and size of the cochlea's basal turn. The very close relation to the sensitive inner ear structures necessitates a thorough anatomic knowledge and careful insertion technique, especially when implanting patients with residual hearing. In order to avoid electrode migration between the scalae and to achieve protect the modiolus and the basilar membrane, it is recommended to aim for an electrode insertion vector from postero-superior to antero-inferior.

Endoscope-Assisted Cochlear Implantation.

Objectives Our aim was to present our endoscope-assisted cochlear implantation (CI) technique, in which the middle ear landmarks were identified through the facial recess exposure by using an endoscopic view without elevating the tympanic annulus. The secondary goal was to assess whether the situation of difficult surgical exposure could be predicted by evaluating preoperative axial computed tomography (CT) examinations.Methods CT examinations and surgical outcomes of endoscope-assisted CI surgeries were analyzed.Results A total of 179 CI operations performed in 27 adults (15.1%) and 152 children (84.9%) were retrospectively evaluated. It was found that in 14 cases (7.8%), endoscopic examination contributed substantially in identifying the round window (RW) membrane correctly. Endoscopic identification of the RW through the posterior tympanotomy enabled us to perform a straightforward surgery in all these cases, without the need for switching to a bony cochleostomy or alternative surgical techniques. The difficulty in the surgical exposure was predicted preoperatively by examining the axial CT scans in six of the 14 cases (42.8%) for which endoscopic assistance was necessary in order to identify the RW correctly.Conclusion The main benefit of endoscope-assisted CI is the improved visibility leading to a panoramic view of the RW region. The implementation of transfacial recess endoscopic examination into the conventional CI technique is helpful to avoid problems during surgical orientation. However, the difficulty in the surgical exposure of the RW cannot be reliably predicted by the subjective evaluation of preoperative CT scans and more studies are needed to obtain reliable criteria.

Surgical Anatomy of the Human Round Window Region: Implication for Cochlear Endoscopy Through the External Auditory Canal.

To enable development of an endoscope for cellular-level optical imaging of the inner ear. A prospective study of 50 cadaveric human temporal bones to define detailed surgical anatomy of the round window (RW) region and the range of angles necessary to reach the RW membrane perpendicularly via the external ear canal. The transcanal angle to the RW membrane was surgically measured in 3D intact specimens, and correlated with the angle calculated from temporal bone computed tomography (CT) scans of the same specimens obtained before and after measurements in situ. Surgically measured transcanal angles to the RW membrane correlated well with the radiographically measured angles. The angles ranged from 110 to 127 degrees, with the median of 115 degrees and the middle 50% ranging from 109 to 119 degrees. Four temporal bones were excluded because of pathology. The opening of the RW niche was located posteriorly in six bones (13%), inferiorly in 18 bones (39%), and postero-inferiorly in 22 bones (48%). The angles were not statistically different among the three orientations of the RW niche. By correlating measurement from cadaveric human temporal bones and their CT scans, we defined key parameters necessary for designing an endoscope for intracochlear imaging using a minimally invasive approach through the external auditory canal. The excellent correlation between the measurement on the CT scan and the actual shape of the probe that was able to reach the RW through the ear canal enables selection of the probe using the CT data.

Round window chamber and fustis: endoscopic anatomy and surgical implications

The round window region is of critical importance in the anatomy of the middle ear. The aim of this paper is to describe its anatomy from an endoscopic point of view, emphasizing structures that have important surgical implications, in particular the fustis and the subcochlear canaliculus. The fustis, a smooth bony structure that forms the floor of the round window region, is a constant and important structure. It seems to indicate the round window membrane and the correct position of scala tympani. A structure connecting the round window region to the petrous apex, named the subcochlear canaliculus, is also described. A retrospective review of video recordings of endoscopic dissection and surgical procedures, carried out between June 2014 and February 2015, was conducted across two Tertiary university referral centers. A total of 42 dissections were analyzed in the study. We observed the fustis in all the cases and we identify two different anatomical conformations. The subcochlear canaliculus was found in 81.0%, with a pneumatization direct to the petrous apex in 47.7%. Conformation and limits of the round window niche may influence the surgical view of the round window membrane. Endoscopic approaches allow a very detailed view, which enables a comprehensive exploration of the round window region. Accurate knowledge of the anatomical relationships of this region has important advantages during middle ear surgery.

Role of high resolution multislice CT scan in otosclerosis

This prospective study was carried out to assess the radiological findings in patients with otosclerosis using high resolution multislice CT scan and to correlate these findings with audiological findings in those patients. This study was done at Al Azhar University hospitals during the period from Jan 2012 to Jun 2014. Thirty-two patients were enrolled in this study; 13 (40.63%) males and 19 (59.37%) females. Their age ranged from 13 to 55 with a mean of 36.21±8.7years. Written consent was taken from all patients. Multislice CT scan was done to all patients and reports were done by computer assisted analysis with thorough audiological assessment including pure tone audiometry, tympanometry and stapedial reflex. Positive findings were present in 40/58 ears (69%) while negative findings were present in 18/58 ears (31%). Otosclerotic foci were more detected when slice thickness was lesser than one millimeter especially at fissula ante fenestrum and round window region. There was a good correlation between air bone gap and CT score (p=0.002). High resolution multislice CT helps in the diagnosis of otosclerosis with sensitivity (69%) and it aids in the diagnosis of doubtful cases. Otosclerosis has a special predilection to affect certain sites mainly the fissula ante fenestrum followed by the round window and the cochlear promontory.

Scala tympani cochleostomy survey: a follow-up study.

To reassess cochleostomy techniques among North American cochlear implant surgeons after a 6-year period of widespread education and research on the topic. Prospective cohort study. A multiple-choice survey of cochlear implant techniques was distributed to surgeons attending the William House Cochlear Implant Study Group in 2006 and 2012. This survey contained questions regarding routine surgical access and cochleostomy techniques. Responses were anonymous, and >50% were repeat respondents. Statistical analysis sought changes in technique in the past 6 years. Comparisons between 2006 and 2012 responses revealed no significant changes in the proportion of surgeons identifying the facial nerve or chorda tympani. By contrast, respondents in 2012 were more likely to drill off the round window niche overhang (P < .001), use a round window insertion (P < .001), or make a smaller cochleostomy (P = .003). In two images of a transfacial recess approach, there was a significant increase in the proportion choosing an inferior or anterior cochleostomy site over a superior location (image 1, 76% in 2006 to 92% in 2012, P = .003; image 3, 78% to 90%, respectively, P = .044). This repeat survey documents a change in practice among cochlear implant surgeons. Specifically, scala tympani access techniques now appear to be more consistent with known anatomical relationships in the round window region. These findings may have resulted from the concerted education and research efforts over the past 6 years.

The round window region and contiguous areas: endoscopic anatomy and surgical implications

The round window region is a critical area of the middle ear; the aim of this paper is to describe its anatomy from an endoscopic perspective, emphasizing some structures, the knowledge of which could have important implications during surgery, as well as to evaluate what involvement cholesteatoma may have with these structures. Retrospective review of video recordings of endoscopic ear surgeries and retrospective database review were conducted in Tertiary university referral center. Videos from endoscopic middle ear procedures carried out between June 2010 and September 2012 and stored in a shared database were reviewed retrospectively. Surgeries in which an endoscopic magnification of the round window region and the inferior retrotympanum area was performed intraoperatively were included in the study. Involvement by cholesteatoma of those regions was also documented based on information obtained from the surgical database. Conformation of the tegmen of the round window niche may influence the surgical view of round window membrane. A structure connecting the round window area to the petrous apex, named the subcochlear canaliculus, is described. Cholesteatoma can invade the round window areas in some patients. Endoscopic approaches can guarantee a very detailed view and allow the exploration of the round window region. Exact anatomical knowledge of this region can have important advantages during surgery, since some pathology can invade inside cavities or tunnels otherwise not seen by instrumentation that produces a straight-line view (e.g. microscope).

Scala Tympani Cochleostomy Survey: A Follow‐up Study

Objectives: Reassess cochleostomy techniques among North American cochlear implant surgeons after a 6-year period of widespread education and research on the topic. Methods: A multiple-choice survey of cochlear implant techniques was distributed to surgeons attending the William House Cochlear Implant Study Group in 2006 and 2012. This survey contained questions regarding routine surgical access and cochleostomy techniques. Responses were anonymous and more than 50% were repeat respondents. Statistical analysis sought changes in technique in the last 6 years. Results: Comparisons between 2006 and 2012 responses revealed no significant changes in the proportion of surgeons identifying the facial nerve or chorda tympani. By contrast, respondents in 2012 were more likely to drill off the round window-niche overhang ( P &lt; 0.001), use a round window insertion ( P &lt; 0.001), or make a smaller cochleostomy ( P = 0.003). In two images of a trans-facial recess approach, there was a significant increase in the proportion choosing an inferior or anterior cochleostomy site over a superior location (Image1-76% in 2006 to 92% in 2012 ( P = 0.003), Image 3 78% to 90%, respectively ( P = 0.044). Conclusions: This repeat survey documents a change in practice among cochlear implant surgeons. Specifically, scala tympani access techniques now appear to be more consistent with known anatomical relationships in the round window region. These findings may have resulted from the concerted education and research efforts over the last six years.

Congenital aural atresia treated with floating mass transducer on the round window: 5 years of imaging experience

The aim of this paper is to illustrate imaging features of patients affected by congenital aural atresia (CAA) before and after treatment with a Vibrant SoundBridge (VSB) device implanted on the round window. Ten patients (5 males and 5 females; mean age 22.1 years) with CAA underwent preoperative high-resolution computed tomography (HRCT) to estimate the degree of involvement of the middle- and inner-ear structures and highlight radiological landmarks useful for surgical planning. Bilateral CAA, mostly of the mixed type, was present in 7 patients and ossicular chain abnormalities in 16 ears (94% of cases). The round window region was normal in all patients, whereas facial-nerve course and/or caliber abnormalities were present in 6 ears (35.3%). The tympanic cavity was small in 13 ears (76.5%), whereas the mastoid was well pneumatized in 8/17 (47%). HRCT provides accurate information about anatomy and malformations of the middle and inner ear and can thus assist the surgeon in planning the procedure.

Anatomy of the Round Window and Hook Region of the Cochlea With Implications for Cochlear Implantation and Other Endocochlear Surgical Procedures

The goal of this study was to create a three-dimensional model of the anatomy of the hook region to identify the optimal site for cochleostomy in cochlear implant surgery. The anatomy of the hook region is complex, and spatial relationships can be difficult to evaluate using two-dimensional histological slides or cadaveric temporal bones. The right temporal bone of a 14-year-old adolescent boy was used to create a three-dimensional model. Sections containing the round window membrane (RWM) and surrounding cochlear structures were stained, digitized, and imported into a general purpose three-dimensional rendering and analysis software program (Amira, version 4.1). Three-dimensional models of the RWM, basilar membrane, osseous spiral lamina, spiral ligament, cochlear aqueduct, inferior cochlea vein, scala media, ductus reuniens, scala vestibuli, scala tympani, and surrounding bone were generated. The relationship between these structures and the RWM and adjacent otic capsule was evaluated. Histological sections from a different temporal bone were also analyzed. This temporal bone was sectioned in a plane perpendicular to the axis corresponding to the surgical view of the RWM, seen through the facial recess. The anteroinferior margin of the RWM or adjacent otic capsule was identified as the site for a cochleostomy that will avoid damage to critical cochlear structures and allow implantation directly into the scala tympani. The model can be downloaded from: https://research.meei.harvard.edu/otopathology/3dmodels. This three-dimensional model has implications for surgical procedures to the inner ear that aim to minimize insertional trauma.

Anatomy of the Round Window and Hook Region of the Cochlea With Implications for Cochlear Implantation and Other Endocochlear Surgical Procedures

Anatomy of the Round Window and Hook Region of the Cochlea With Implications for Cochlear Implantation and Other Endocochlear Surgical Procedures

Developmental study of the round window region.

A silicone impression method to study the anatomy of the round window region was used in 102 temporal bones belonging to individuals aged from 4 months of fetal life to 3-year-old children as well as adults. A total of 2,142 measurements of the round window, oval window and round window fossula was made in the molds. The data demonstrate that the round window shows a diameter from 1.21 mm (average for the short axis) to 1.74 mm (average for the long axis) and the circular shape was present in 55% of the adult temporal bones and in 18.18% of the fetal and infantile ones. The adult dimensions of the measured structures are reached during fetal development.

Accuracy of High‐Resolution Computed Tomography in Cochlear Implantation

Multichannel cochlear implants are a proven method for the auditory rehabilitation of individuals who have severe-to-profound sensorineural hearing loss. These devices typically require insertion into the scala tympani of the cochlea to provide auditory stimulations. A patent scala provides the best chance for an adequate insertion of the electrode array. Preoperative high-resolution computed tomography imaging has traditionally been used to determine the patency of the scala tympani. Its ability to accurately predict the patency of the cochlea has been questioned in several retrospective studies. A prospective study was undertaken in 28 consecutive individuals undergoing cochlear implant surgery to compare the findings on high-resolution computed tomography with the surgical findings in an attempt to determine high-resolution computed tomography's accuracy. Cochlear obstruction caused by ossification was accurately predicted in six of six individuals but overestimated in the round window region in three individuals. High-resolution computed tomography accurately predicted patent cochleas in 19 individuals. No false-negative results were encountered. In this study sensitivity of high-resolution computed tomography was 100%, and specificity was 86%. High-resolution computed tomography appears to be more helpful than previously reported for determining cochlear patency.

Accuracy of high-resolution computed tomography in cochlear implantation

Multichannel cochlear implants are a proven method for the auditory rehabilitation of individuals who have severe-to-profound sensorineural hearing loss. These devices typically require insertion into the scala tympani of the cochlea to provide auditory stimulations. A patent scala provides the best chance for an adequate insertion of the electrode array. Preoperative high-resolution computed tomography imaging has traditionally been used to determine the patency of the scala tympani. Its ability to accurately predict the patency of the cochlea has been questioned in several retrospective studies. A prospective study was undertaken in 28 consecutive individuals undergoing cochlear implant surgery to compare the findings on high-resolution computed tomography with the surgical findings in an attempt to determine high-resolution computed tomography's accuracy. Cochlear obstruction caused by ossification was accurately predicted in six of six individuals but overestimated in the round window region in three individuals. High-resolution computed tomography accurately predicted patent cochleas in 19 individuals. No false-negative results were encountered. In this study sensitivity of high-resolution computed tomography was 100%, and specificity was 86%. High-resolution computed tomography appears to be more helpful than previously reported for determining cochlear patency. (Otolaryngol Head Neck Surg 1996;114:38-43.)

Density of myelinated nerve fibers in the chinchilla cochlea.

Baseline values for the density of myelinated nerve fibers at 11 locations in the chinchilla cochlea were obtained as a prerequisite for studying the relationship between sensory cell degeneration and spiral ganglion cell loss. Myelinated nerve fibers were counted within the osseous spiral lamina near the habenulae perforata. The data were expressed as myelinated nerve fibers per inner hair cell (MNF/IHC). Since the vast majority of the afferent fibers innervate the inner hair cells and since the percentage of myelinated efferent fibers at the level of the osseous spiral lamina is estimated to be quite small, MNF/IHC is a useful value which will permit the comparison of data from normal and damaged specimens. An average density of 9.4 MNF/IHC was found at the apex. This rose to a peak of 18.8 MNF/IHC in the first turn and then decreased to 14.2 MNF/IHC in the round window region. The standard deviations at the different locations ranged from 0.8 to 1.5 MNF/IHC.

Distribution of the crossed olivocochlear bundle in the chinchilla's cochlea.

The efferent crossed olivocochlear bundle (COCB) was transected in the brain stem of the chinchilla, and the animals sacrificed 7 to 96 days later. Electron microscopy revealed that all the large efferent nerve endings on outer hair cells in the basalmost 2 mm (round window region) of the cochlea had degenerated, 87.5% in the remainder of the first turn, 70% in the second turn and 43% in the third turn. Only a few degenerating nerve fibers were seen in the medial spiral tract (inner spiral and tunnel bundles) of the experimental animals. Nerve fibers were counted in the medial spiral tracts of the cochleas of control animals as well as in those animals whose COCB had been transected. There were considerable individual variations in the fiber numbers, and statistical analysis showed no significant difference between the numbers of nerve fibers in normal and experimental animals. The cochlear microphonics (CM) and nerve action potentials (AP) of acute animals were assessed before and after COCB section. The CM and AP of the chronic experimental animals were compared with responses from normals. Overall, no changes in a physiological response of the anesthetized chinchilla could be attributed to complete section of the COCB.

Histological Otosclerosis in a Japanese —A Case With Multiple Foci and Crista Neglecta—

A case of histological otosclerosis in an 82 year-old Japanese male was presented. On histological examination of the left temporal bone, three distinct foci were found. One focus, located at the round window region, broke through the endosteal layer and protruded into the scala tympani of the basal turn. This focus showed inner active and outer inactive lesions. The other two foci were located in the antero-lateral portion of the cochlear capsule and in the anterior wall of the internal acoustic meatus. Both showed relatively inactive lesions. No otosclerotic process was demonstrated at the region anterior to the oval window. Crista neglecta was present in the posterior ampulla of the semicircular canal of the patient.