Atraumatic Scala Tympani Cochleostomy; Resolution of the Dilemma.

OBJECTIVES: While an accurate placement in cochleostomy is critical to ensure appropriate insertion of the cochlear implant (CI) electrode into the scala tympani (ST), the choice of preferred cochleostomy sites widely varied among experienced surgeons. We present a novel technique for precise yet readily applicable localization of the optimum site for performing ST cochleostomy. MATERIAL AND METHODS: Twenty fresh frozen temporal bones were dissected using the mastoidectomy-posterior tympanotomy approach. Based on the facial nerve and the margins of the round window membrane (RWM), the cochleostomy site was chosen to insert the electrode into the ST while preserving the surrounding intracochlear structures. RESULTS: There is a limited safe area suitable for the ST implantation in the area inferior and anterior to the RWM. There is a higher risk of scala vestibuli (SV) insertion anterior to that area. Posterior to that area, the cochlear aqueduct (CA) and inferior cochlear vein (ICV) are liable for the injury. CONCLUSION: For atraumatic CI, precise and easy localization of the site of cochleostomy play a pivotal role in preserving intracochlear structures. Accurate setting of the vertical and horizontal orientations is mandatory before choosing the site of cochleostomy. The facial nerve and the margins of the RWM offer a very helpful clue for such localization; meanwhile, it is readily identifiable in the surgical field.

Real-time intracochlear imaging of automated cochlear implant insertions in whole decalcified cadaver cochleas using ultrasound.

OBJECTIVES: This study aimed to determine the feasibility of combining high-frequency ultrasound imaging, automated insertion, and force sensing to yield more information about cochlear implant insertion dynamics. METHODS: An apparatus was developed combining these aspects along with software to control implant and imaging probe positions. Decalcified unfixed human cochleas were implanted at various speeds, insertion sites, and implant models while imaging near the implant tip throughout insertion and recording force data from the cochlea mounting stage. Ultrasound video data were also captured. RESULTS: The basilar membrane (BM) was frequently penetrated by the implant in either the mid-basal or lower middle turn. Measurements were also performed of apical BM motion in response to upstream implant movement at varying insertion speeds. Increasing insertion speed resulted in greater BM displacement. DISCUSSION: Multiple insertions per cochlea increase the volume of data per specimen while also reducing variability due to differences between cochleas. However, to image inside the cochlea with ultrasound, the bone had to be decalcified, which likely had a significant effect upon the response of tissue to contact by the implant. As calcified bone strongly reflects ultrasound, we also found ultrasound imaging to be an excellent method for easily assessing bone decalcification progress. CONCLUSION: This technique may be very useful for some studies, although the confounding effects of bone decalcification may make results of other studies too difficult to generalize. The approach could be adapted to other real-time imaging modalities, such as optical coherence tomography.

Systematic review: Radiological and histological evidence of cochlear implant insertion trauma in adult patients.

INTRODUCTION: Cochlear implantation (CI) has developed from its origins in the 1980s. Initially, CI was for profound bilateral hearing impairment. However, candidacy for CI have become more widespread in recent years with unilateral implantation and an emphasis on hearing preservation. Evidence supports full electrode insertion in an atraumatic fashion into the scala tympani (ST) provides optimal hearing outcomes. The main aim of this systematic review was to elucidate the degree of trauma associated with CI insertion. METHODS: A systematic literature search was undertaken using PubMed Medline. A grading system described by Eshraghi was used to classify cochlear trauma. Both radiological and histological studies were included. RESULTS: Twenty one papers were identified which were relevant to our search. In total, 653 implants were inserted and 115 (17.6%) showed evidence of trauma. The cochleas with trauma had basilar membrane elevation in 5.2%, ruptured in 5.2%, the electrode passed from the ST to the SV in 84.4% and there was grade 4 trauma in 5.2%. The studies used a variety of histological and radiological methods to assess for evidence of trauma in both cadaveric temporal bones and live recipients. CONCLUSIONS: Minimizing cochlear trauma during implant insertion is important to preserve residual hearing and optimize audiological performance. An overall 17.6% trauma rate suggests that CI insertion could be improved with more accurate and consistent electrode insertion such as in the form of robotic guidance. The correlation of cochlea trauma with post-operative hearing has yet to be determined.

Semiautomatic cochleostomy target and insertion trajectory planning for minimally invasive cochlear implantation.

A major component of minimally invasive cochlear implantation is atraumatic scala tympani (ST) placement of the electrode array. This work reports on a semiautomatic planning paradigm that uses anatomical landmarks and cochlear surface models for cochleostomy target and insertion trajectory computation. The method was validated in a human whole head cadaver model (n = 10 ears). Cochleostomy targets were generated from an automated script and used for consecutive planning of a direct cochlear access (DCA) drill trajectory from the mastoid surface to the inner ear. An image-guided robotic system was used to perform both, DCA and cochleostomy drilling. Nine of 10 implanted specimens showed complete ST placement. One case of scala vestibuli insertion occurred due to a registration/drilling error of 0.79 mm. The presented approach indicates that a safe cochleostomy target and insertion trajectory can be planned using conventional clinical imaging modalities, which lack sufficient resolution to identify the basilar membrane.

Surgical management of retinal detachment resulting from macular hole in a setting of high myopia.

PURPOSE: To evaluate the anatomical and visual outcomes of pars plana vitrectomy (PPV) with internal limiting membrane (ILM) peeling and use of retinal tamponade for retinal detachments resulting from macular hole (MHRD) in highly myopic eyes. METHODS: Twenty-nine highly myopic patients (29 eyes) underwent PPV with ILM peeling and retinal tamponade for MHRD were enrolled. Demographics and best-corrected visual acuity (BCVA) were measured preoperatively and at final follow-up. Anatomical success and macular hole closure were analyzed. RESULTS: Patients' mean age of patients was 58.7 ± 10.6 years, mean follow-up was 11.7 ± 7.4 months. Twenty three eyes (23/26, 88.5%) undergoing primary PPV combined with ILM peeling had successful initial retinal reattachment, including 19 eyes (19/19, 100%) with silicone oil tamponade and in 4 eyes (4/7, 57.1%) with sulfur hexafluoride (C3F8) tamponade. Overall anatomical success was achieved in 27 eyes (27/29, 93.1%). The macular hole closure was observed in 17 eyes (17/26, 65.4%) with final anatomical success. Compared to preoperative BCVA, the mean postoperative BCVA in the eyes with anatomical success was significantly improved (P = 0.007, Wilcoxon signed rank test). CONCLUSION: As a primary or secondary procedure, PPV combined with ILM peeling and usage of retinal tamponade serves as an effective method for MHRD in highly myopic eyes.

Cochlear implant insertion forces in microdissected human cochlea to evaluate a prototype array.

Cochlear implant array insertion forces are potentially related to cochlear trauma. We compared these forces between a standard (Digisonic SP; Neurelec, Vallauris, France) and an array prototype (Neurelec) with a smaller diameter. The arrays were inserted by a mechatronic tool in 23 dissected human cochlea specimens exposing the basilar membrane. The array progression under the basilar membrane was filmed together with dynamic force measurements. Insertion force profiles and depth of insertion were compared. The recordings showed lower insertion forces beyond 270° of insertion and deeper insertions with the thin prototype array. This will potentially allow larger cochlear coverage with less trauma.

A new cochlear implant electrode design for preservation of residual hearing: a temporal bone study.

CONCLUSIONS: Success in conservation of residual hearing after cochlear implantation has benefited patients with high levels of residual low frequency hearing who were not previously considered for conventional cochlear implantation. Technological developments play a key role in minimizing trauma to the cochlea during placement of electrodes. OBJECTIVES: The Nucleus Straight Research Array (SRA) has been designed and developed as a collaboration project between our centre and Cochlear Ltd with the objective of minimizing trauma to the cochlea with insertion of the electrode via the round window. METHODS: We studied 22 fresh or thawed fresh-frozen human temporal bones implanted by one otosurgeon with the SRA electrode with a standard round window technique used for cochlear implantation. An additional four temporal bones were implanted with a 'Standard' straight electrode using the same surgical technique. All insertions were performed in the scala tympani of the cochlea. RESULTS: Evaluation of insertion depth and position of the electrode array inside the cochlea showed little or no evidence of significant intracochlear trauma in the vast majority of bones implanted with the SRA. Handling of the electrode carrier was reported as very satisfactory, which was evident from low resistance to insertion in the majority of cases.

Anatomy of the middle-turn cochleostomy.

OBJECTIVE: Middle-turn cochleostomies are occasionally used for cochlear implant electrode placement in patients with labyrinthitis ossificans. This study evaluates the anatomic characteristics of the middle-turn cochleostomy and its suitability for placement of implant electrodes. METHODS: Ten cadaveric human temporal bones were dissected using a facial recess approach. A middle-turn cochleostomy was drilled 2 mm anterior to the oval window and just inferior to the cochleariform process. The preparations were then stained with osmium tetroxide and microdissections were performed. The location of the cochleostomy on the cochlear spiral and its path through the various cochlear compartments were evaluated in all 10 specimens. A Cochlear Corporation depth gauge was inserted in five of the specimens and insertion trauma, number of contact rings, and depth of insertion were recorded. RESULTS: Eight of the 10 cochleostomies were placed at approximately 360 degrees on the cochlear spiral, near the transition between the basal and middle turns. In one case, the cochleostomy was found to enter the cochlear apex and in another it entered scala vestibuli of the proximal basal turn. The cochleostomy entered scala media in six bones and scala vestibuli in four specimens. A depth gauge was inserted in five specimens. The number of contacts placed within the cochlear lumen ranged from four to nine. There was evidence of insertional trauma to the lateral wall of the cochlear duct, basilar membrane, and Reissner's membrane, but no evidence of fractures to the osseous spiral lamina or modiolus. CONCLUSION: This study demonstrates that electrodes inserted via a middle-turn cochleostomy are likely to enter scala vestibuli and have access to the middle- and apical-cochlear turns. It is also possible that the electrode could be directed into the descending portion of the basal turn depending on cochleostomy orientation. Middle-turn cochleostomy seems to be a viable alternative for electrode placement when preservation of residual hearing is not a concern.

Comparison of round window and cochleostomy approaches with a prototype hearing preservation electrode.

INTRODUCTION: Preservation of residual hearing in cochlear implant recipients has been demonstrated to be possible and provides the potential benefit of combined electric and acoustic auditory stimulation. A prototype 16-mm multichannel array has been designed to facilitate placement of 22 electrodes without damage to intracochlear structures. The electrode array is suitable for insertion via the round window membrane (RWM) or a small cochleostomy. AIM: To evaluate the insertion trajectory and the presence of trauma to intracochlear structures with the prototype electrode inserted by either the RWM or a scala tympani cochleostomy. MATERIALS AND METHODS: Eighteen fresh frozen human temporal bones were prepared for cochlear implantation using a standard transmastoid facial recess technique. Twelve electrodes were implanted at the University of Melbourne and 6 at the Medizinische Hochschule Hannover. In Melbourne fluoroscopy was used to monitor the insertions. Twelve prototype electrodes were inserted via the RWM. A further 6 electrodes were inserted via a small scala tympani cochleostomy. The cochleostomy was sited inferior to the RWM to avoid trauma to the basilar membrane and spiral ligament. Specimens were embedded and fixed with acrylic resin and the cochleae then examined histologically at 200-mum intervals using a grinding and polishing technique. RESULTS: Full insertion of the electrode was achieved without significant resistance in all RWM and cochleostomy specimens. In two RWM specimens fold-over of the electrode tip occurred, and in one specimen the electrode penetrated the spiral ligament to lie in an 'endosteal 'position. In one cochleostomy specimen the electrode was rotated within the cochlea to face laterally rather than towards the modiolus. The final electrode position differed for the two groups, with the electrodes inserted via the RWM lying in a more perimodiolar position along the first part of the basal turn. The average depth of insertion was 240 degrees for the RWM electrodes and 255 degrees for the cochleostomy electrodes. Histologic examination showed no damage in any specimen to the modiolus, osseous spiral lamina or basilar membrane. CONCLUSIONS: A prototype hearing preservation electrode array was inserted by either a RWM or a scala tympani cochleostomy without evidence of significant intracochlear trauma.

Deep electrode insertion in cochlear implants: apical morphology, electrodes and speech perception results.

Morphological examination of the human temporal bone in the apical region supports the benefits of deep electrode insertion. Initiation of spikes on peripheral processes close to the basilar membrane would provide improved channel selectivity during electrical stimulation but recruiting of nerve fibres requires a higher current. A clinical study was performed on 10 users of the MED-EL COMBI 40 + implant to evaluate the effect of the insertion depth of the cochlear implant electrode on speech perception. All subjects were implanted with the standard COMBI 40 + electrode with an insertion depth of > 30 mm. Acute speech tests were carried out in which stimulation was restricted to the apical, middle and basal regions of the cochlea in turn, and using electrode arrangements in which contacts were either distributed over the whole length of the cochlea or concentrated at the basal end, thus mimicking an insertion depth of approximately 20 mm only. The results showed that stimulation of the apical region of the cochlea supports a significant degree of speech understanding, and that distributing the contacts over the whole length of the cochlea improves speech perception in quiet and in noise.

The contour electrode array: safety study and initial patient trials of a new perimodiolar design.

OBJECTIVE: The aim of these studies was to investigate the insertion properties and safety of a new intracochlear perimodiolar electrode array design (Contour). BACKGROUND: An electrode array positioned close to the neural elements could be expected to reduce stimulation thresholds and might potentially reduce channel interaction. METHODS: Two sequential studies were conducted. In study 1, the Contour electrode array was inserted in 12 human temporal bones. After cochlear surface preparation, the position of the array was noted and the basilar membrane was examined for insertion damage. On the basis of the outcome of this temporal bone study, study 2 investigated the Contour array, mounted on a Nucleus CI-24 M device and implanted in three adult patients. RESULTS: Study I showed that in 10 temporal bones, the Contour array was positioned close to the modiolus, and the basilar membrane was intact. In the two remaining bones, the arrays had pierced the basilar membrane and were positioned in the scala vestibuli apical to the penetration. Statistical analysis showed an equivalent probability of insertion-induced damage of the two array designs. In study 2, image analysis indicated that the Contour electrodes were positioned closer to the modiolus than the standard Nucleus straight array. Lower T and C levels, but higher impedance values, were recorded from electrodes close to the modiolus. Initial speech perception data showed that all patients gained useful open-set speech perception, two patients achieving scores of 100% on sentence material 3 months postoperatively. CONCLUSIONS: The temporal bone studies showed the Contour electrode array to be generally positioned closer to the modiolus than the standard Nucleus straight array, and to have an equivalent probability of causing insertion-induced damage.

Radiologic evaluation of multichannel intracochlear implant insertion depth.

Postoperative plain film x-rays are necessary in all multichannel cochlear implant patients to confirm intracochlear position, detect possible electrode kinking, and provide a reference if postoperative slippage occurs. In addition, precise documentation of multichannel intracochlear electrode insertion depths is necessary for comparison of speech recognition results among patients and may be of use for future speech processing strategies. In the present study, a method has been devised, using a modified Stenver's view, to more accurately document insertion depths of the electrode array and location of individual electrodes on 50 multichannel cochlear implant patients. Surgical estimates of insertion depth are shown to have great variability in regard to distance along the basilar membrane when compared with x-ray documentation. Additionally, there is preliminary evidence that insertion depth, as determined by x-ray studies, has a strong correlation with open-set speech discrimination.

State of stress within the basilar membrane: a re-evaluation of the membrane misnomer.

By deforming and making incisions in the basilar membrane (BM), von Békésy showed that the BM seems to behave as a thin elastic plate, rather than as a membrane. However, it has never been shown whether a traveling wave could be sustained by a prestretched material in which the tension is insufficient to cause a visible retraction of the cut edges of an incision when viewed with a light microscope. We have shown that the necessary radial tension would decrease exponentially along the cochlea, from a value of 39 +/- 9 N/m at the base, with a space constant of 4.3 +/- 1.1 mm, for the guinea pig. This variable tension would be produced by a constant prestretching surface force of 2.4 +/- 0.1 X 10(6) N/m2, acting on the BM edges. Using values of Young's modulus in the radial direction, ranging from that of elastin to collagen, it is shown that this force would most likely cause a visible retraction of the cut edges of an incision. Therefore one must either conclude, once again, that the BM is effectively an unstretched material or question the original interpretation of the incision experiments.