Synchrotron Radiation-Based Reconstruction of the Human Spiral Ganglion: Implications for Cochlear Implantation.

OBJECTIVE: To three-dimensionally reconstruct Rosenthal's canal (RC) housing the human spiral ganglion (SG) using synchrotron radiation phase-contrast imaging (SR-PCI). Straight cochlear implant electrode arrays were inserted to better comprehend the electro-cochlear interface in cochlear implantation (CI). DESIGN: SR-PCI was used to reconstruct the human cochlea with and without cadaveric CI. Twenty-eight cochleae were volume rendered, of which 12 underwent cadaveric CI with a straight electrode via the round window (RW). Data were input into the 3D Slicer software program and anatomical structures were modeled using a threshold paint tool. RESULTS: The human RC and SG were reproduced three-dimensionally with artefact-free imaging of electrode arrays. The anatomy of the SG and its relationship to the sensory organ (Corti) and soft and bony structures were assessed. CONCLUSIONS: SR-PCI and computer-based three-dimensional reconstructions demonstrated the relationships among implanted electrodes, angular insertion depths, and the SG for the first time in intact, unstained, and nondecalcified specimens. This information can be used to assess stimulation strategies and future electrode designs, as well as create place-frequency maps of the SG for optimal stimulation strategies of the human auditory nerve in CI.

Three-dimensional imaging of the human internal acoustic canal and arachnoid cistern: a synchrotron study with clinical implications.

A thorough knowledge of the gross and micro-anatomy of the human internal acoustic canal (IAC) is essential in vestibular schwannoma removal, cochlear implantation (CI) surgery, vestibular nerve section, and decompression procedures. Here, we analyzed the acoustic-facial cistern of the human IAC, including nerves and anastomoses using synchrotron phase contrast imaging (SR-PCI). A total of 26 fresh human temporal bones underwent SR-PCI. Data were processed using volume-rendering software to create three-dimensional (3D) reconstructions allowing soft tissue analyses, orthogonal sectioning, and cropping. A scalar opacity mapping tool was used to enhance tissue surface borders, and anatomical structures were color-labeled for improved 3D comprehension of the soft tissues. SR-PCI reproduced, for the first time, the variable 3D anatomy of the human IAC, including cranial nerve complexes, anastomoses, and arachnoid membrane invagination (acoustic-facial cistern; an extension of the cerebellopontine cistern) in unprocessed, un-decalcified specimens. An unrecognized system of arachnoid pillars and trabeculae was found to extend between the arachnoid and cranial nerves. We confirmed earlier findings that intra-meatal vestibular schwannoma may grow unseparated from adjacent nerves without duplication of the arachnoid layers. The arachnoid pillars may support and stabilize cranial nerves in the IAC and could also play a role in local fluid hydrodynamics.

Effects of Various Trajectories on Tissue Preservation in Cochlear Implant Surgery: A Micro-Computed Tomography and Synchrotron Radiation Phase-Contrast Imaging Study.

OBJECTIVES: The purpose of this study was to evaluate the three-dimensional (3D) anatomy and potential damage to the hook region of the human cochlea following various trajectories at cochlear implantation (CI). The goal was to determine which of the approaches can avoid lesions to the soft tissues, including the basilar membrane and its suspension to the lateral wall. Currently, there is increased emphasis on conservation of inner ear structures, even in nonhearing preservation CI surgery. DESIGN: Micro-computed tomography and various CI approaches were made in an archival collection of macerated and freshly fixed human temporal bones. Furthermore, synchrotron radiation phase-contrast imaging was used to reproduce the soft tissues. The 3D anatomy was investigated using bony and soft tissue algorithms, and influences on inner ear structures were examined. RESULTS: Micro-computed tomography with 3D rendering demonstrated the topography of the round window (RW) and osseous spiral laminae, while synchrotron imaging allowed reproduction of soft tissues such as the basilar membrane and its suspension around the RW membrane. Anterior cochleostomies and anteroinferior cochleostomies invariably damaged the intracochlear soft tissues while inferior cochleostomies sporadically left inner ear structures unaffected. CONCLUSIONS: Results suggest that cochleostomy approaches often traumatize the soft tissues at the hook region at CI surgery. For optimal structural preservation, the RW approach is, therefore, recommended.

Three-Dimensional Analysis of the Fundus of the Human Internal Acoustic Canal.

OBJECTIVES: Documentation of the nerve components in the internal acoustic canal is essential before cochlea implantation surgery. Interpretations may be challenged by wide anatomical variations of the VIIIth nerve and their ramifications. Malformations may further defy proper nerve identification. DESIGN: Using microcomputed tomography, we analyzed the fundus bone channels in an archival collection of 113 macerated human temporal bones and 325 plastic inner molds. Data were subsequently processed by volume-rendering software using a bony tissue algorithm. Three-dimensional reconstructions were made, and through orthogonal sections, the topographic anatomy was established. RESULTS: The technique provided additional information regarding the anatomy of the nerve foramina/channels of the human fundus region, including variations and destinations. Channel anastomosis were found beyond the level of the fundus. A foramen of the transverse crest was identified. CONCLUSIONS: Three-dimensional reconstructions and cropping outlined the bone canals and demonstrated the highly variable VIIIth nerve anatomy at the fundus of the human inner acoustic canal. Myriad channel interconnections suggested an intricate system of neural interactive pathways in humans. Particularly striking was the variable anatomy of the saccule nerve channels. The results may assist in the preoperative interpretation of the VIIIth nerve anatomy.

Anatomical Characteristics of Facial Nerve and Cochlea Interaction.

OBJECTIVE: The aim was to study the relationship between the labyrinthine portion (LP) of the facial canal and the cochlea in human inner ear molds and temporal bones using micro-CT and 3D rendering. A reduced cochlea-facial distance may spread electric currents from the cochlear implant to the LP and cause facial nerve stimulation. Influencing factors may be the topographic anatomy and otic capsule properties. METHODS: An archival collection of human temporal bones underwent micro-CT and 3D reconstruction. In addition, cochlea-facial distance was assessed in silicone and polyester resin molds, and the association between the LP and upper basal turn of the cochlea was analyzed. RESULTS: Local thinning of the otic capsule and local anatomy may explain the development of cochlea-facial dehiscence, which was found in 1.4%. A reduced cochlea-facial distance was noted in 1 bone with a superior semicircular canal dehiscence but not in bones with superior semicircular canal "blue line." The otic capsule often impinged upon the LP and caused narrowing. CONCLUSION: Micro-CT with 3D rendering offers new possibilities to study the topographic anatomy of the human temporal bone. The varied shape of the cross-section of the LP could often be explained by an "intruding" cochlea.

Do Patients Aged 85 Years and above Benefit from Their Cochlear Implants?

The present study aims to investigate the usage and benefits of cochlear implants (CIs) in elderly patients aged ≥85 years, including their device-handling issues, follow-ups, and the influence on their well-being. The patients answered one questionnaire regarding quality of life, EQ5D-3L, and one questionnaire, obtained from the Swedish CI quality register, regarding usage, handling, satisfaction, remaining difficulties, etc. The medical records were searched for the implantation date, implant model, speech processor model, monosyllabic (MS) word scores, infections over the implant, and compliance regarding scheduled visits to the clinic. The results show that most elderly patients are satisfied full-time users of their implants. Even though most patients had no problems handling their CI, handling issues must be considered. Recurring guidance and training on device operation are needed. We suggest that follow-up visits are essentially needed for this group of patients on a regular basis. CI surgery is considered a safe treatment, even for the elderly. Upgrads to new external equipment (e.g., sound processors) should not be excluded because of their age. The results suggested that the CI positively affected their well-being. This study was approved by the Swedish Ethical Review Authority (5/10-2021, Dnr: 2021-04970).

Vestibular Organ and Cochlear Implantation-A Synchrotron and Micro-CT Study.

Background: Reports vary on the incidence of vestibular dysfunction and dizziness in patients following cochlear implantation (CI). Disequilibrium may be caused by surgery at the cochlear base, leading to functional disturbances of the vestibular receptors and endolymphatic duct system (EDS) which are located nearby. Here, we analyzed the three-dimensional (3D) anatomy of this region, aiming to optimize surgical approaches to limit damage to the vestibular organ. Material and Methods: A total of 22 fresh-frozen human temporal bones underwent synchrotron radiation phase-contrast imaging (SR-PCI). One temporal bone underwent micro-computed tomography (micro-CT) after fixation and staining with Lugol's iodine solution (I2KI) to increase tissue contrast. We used volume-rendering software to create 3D reconstructions and tissue segmentation that allowed precise assessment of anatomical relationships and topography. Macerated human ears belonging to the Uppsala collection were also used. Drilling and insertion of CI electrodes was performed with metric analyses of different trajectories. Results and Conclusions: SR-PCI and micro-CT imaging demonstrated the complex 3D anatomy of the basal region of the human cochlea, vestibular apparatus, and EDS. Drilling of a cochleostomy may disturb vestibular organ function by injuring the endolymphatic space and disrupting fluid barriers. The saccule is at particular risk due to its proximity to the surgical area and may explain immediate and long-term post-operative vertigo. Round window insertion may be less traumatic to the inner ear, however it may affect the vestibular receptors.

Cochlear implantation and residual hearing preservation long-term follow-up of the first consecutively operated patients using the round window approach in Uppsala, Sweden.

Objective: We conducted a long-term follow-up study to investigate the time course of residual hearing in our first 21 consecutively operated cochlear implant (CI) patients using the round window (RW) approach . The study may provide additional information about the influence of a flexible lateral wall electrode array on cochlear function. Methods: Data were available for long-term follow-up (>5 years) in 15 patients. Pure tone audiometry (PTA) was assessed at 0.125-8 kHz preoperatively, and at one, three and >5 years postoperatively. Insertion angle, number of electrodes inside the cochlea, user-time of the processor and stimulation strategy were documented. Results: Twelve out of 15 patients had residual hearing after a follow-up period of five years (mean 86 months, range: 61-103 months). Four out of 15 patients had >75% complete hearing preservation (HP), 8 out of 15 had 25-75% partial HP and 3 out of 15 patients had complete loss of hearing. There was a high correlation between insertion angle and HP. Conclusion: Long-term HP was possible in 12 out of 15 cases. Even patients with complete hearing loss at long-term follow-up showed high performance in speech understanding and were full-time users.

Special Anatomic Considerations in Otosclerosis Surgery.

The anatomy of the vestibular organs together with considerations of the middle and inner ear anatomy relevant to stapes surgery is discussed. An archival collection of macerated and freshly frozen human temporal bones underwent micro-computed tomography (CT) with subsequent volume-rendering. Three-dimensional (3D) reconstructions and the topographic anatomy of the oval window were considered. Micro-CT and 3D rendering revealed the relationship between the otolith organs and the oval window. Anatomic variations were extensive and included the distance between the footplate and the reconstructed macula margins. A "no-go" zone is suggested for the surgeon to avoid injury during stapes surgery.

The Human Cochlear Aqueduct and Accessory Canals: a Micro-CT Analysis Using a 3D Reconstruction Paradigm.

OBJECTIVE: We sought to study the anatomic variations of the cochlear aqueduct and its accessory canals in human temporal bones using micro-CT and a 3D reconstruction paradigm. More knowledge about the anatomic variations of these structures, particularly at the basal turn of the cochlea and round window niche, may be important to better preserve residual hearing as well as the neural supply during cochlear implant surgery. METHODS: An archival collection of 30 human temporal bones underwent micro-CT and 3D reconstruction. A surface enhancement paradigm was applied. The application displays reconstructed slices as a 3D object with realistic 3D visualization of scanned objects. Virtual sectioning or "cropping" of the petrous bone presented subsequent areas. Thereby, the bony canals could be followed from inside the basal turn of cochlea and middle ear to the jugular foramen. RESULTS: The cochlear aqueduct was always paralleled by an accessory canal containing the inferior cochlear vein. It ran from the basal turn of the cochlea and exited laterally in the jugular foramen. In 70% of the cases, a secondary accessory canal was observed and it derived mostly from a depression or infundibulum located in the floor of the round window niche. This canal also exited in the jugular foramen. The secondary accessory canal occasionally anastomosed with the primary accessory canal suggesting that it contains a vein that drains middle ear blood to the cranial sinus. CONCLUSION: Micro-CT with 3D surface reconstruction paradigm offers new possibilities to study the topographic anatomy of minor details in the human inner ear. The technique creates simulated transparent "castings" of the labyrinth with a coinciding surface view through enhancement of contrast between boundaries. Accessory canals that drain blood from the cochlea, spiral ganglion, and middle ear could be characterized three-dimensionally.

Peri-operative electrically evoked auditory brainstem response assessment of facial nerve/cochlea interaction at cochlear implantation.

OBJECTIVES: Dehiscence between the cochlear otic capsule and the facial nerve canal is a rare and relatively newly described pathology. In cochlear implantation (CI), this dehiscence may lead to adverse electric facial nerve stimulation (FNS) already at low levels, rendering its use impossible. Here, we describe an assessment technique to foresee this complication. METHODS: Pre- and postoperative computed tomography (CT) scans and intraoperative electrically evoked auditory brainstem response (e-ABR) measurements were analyzed in two patients with cochlear-facial dehiscence (CFD). RESULTS: Because of the relatively low resolution, the confirmation of CFD with a clinical CT was difficult. The e-ABR displayed a large potential with 6 and 7.5 ms latency, respectively, which did not occur otherwise. DISCUSSION: Potential strategies to resolve and manage FNS are described. CONCLUSION: Prediction of FNS by assessing the distance between the labyrinthine portion of the facial nerve and the cochlea is difficult using conventional CT scans. A large evoked late myogenic potential at low stimulation levels during intraoperative e-ABR measurement may foresee FNS at CI activation.

The secondary spiral lamina and its relevance in cochlear implant surgery.

OBJECTIVE: We used synchrotron radiation phase contrast imaging (SR-PCI) to study the 3D microanatomy of the basilar membrane (BM) and its attachment to the spiral ligament (SL) (with a conceivable secondary spiral lamina [SSL] or secondary spiral plate) at the round window membrane (RWM) in the human cochlea. The conception of this complex anatomy may be essential for accomplishing structural preservation at cochlear implant surgery. MATERIAL AND METHODS: Sixteen freshly fixed human temporal bones were used to reproduce the BM, SL, primary and secondary osseous spiral laminae (OSL), and RWM using volume-rendering software. Confocal microscopy immunohistochemistry (IHC) was performed to analyze the molecular constituents. RESULTS: SR-PCI reproduced the soft tissues including the RWM, Reissner's membrane (RM), and the BM attachment to the lateral wall (LW) in three dimensions. A variable SR-PCI contrast enhancement was recognized in the caudal part of the SL facing the scala tympani (ST). It seemed to represent a SSL allied to the basilar crest (BC). The SSL extended along the postero-superior margin of the round window (RW) and immunohistochemically expressed type II collagen. CONCLUSIONS: Unlike in several mammalian species, the human SSL is restricted to the most basal portion of the cochlea around the RW. It anchors the BM and may influence its hydro-mechanical properties. It could also help to shield the BM from the RW. The microanatomy should be considered at cochlear implant surgery.

Effects of mechanical trauma to the human tympanic membrane: an experimental study using transmission electron microscopy.

HYPOTHESIS: To examine the cellular events following induced superficial lesions of the human tympanic membrane (TM). Such information could lead to enhanced appreciation of repair mechanisms and novel strategies to restore TM perforations. BACKGROUND: Persistent perforation of the TM in chronic otitis media is a major global health problem and frequently necessitates surgical intervention. Most TM perforations heal spontaneously and swiftly, but sometimes healing fails. The underlying mechanisms and the reason for incomplete repair are often elusive, although some mechanisms have been proposed. METHODS: Here, five healthy adult human TMs were sampled during vestibular schwannoma surgery. Three days before harvesting, three TMs were superficially lesioned, including the epithelial and sub-epithelial layers, using a needle and two TMs served as controls. Light and transmission electron microscopy were performed. RESULTS: Surrounding lesion showed distinct ultrastructural changes. This included a keratinocyte frontier with electron-dense cells with abundant ribosomes and nuclei metamorphosis. Beneath, were activated fibroblasts and invaded/transformed free cells and signs of increased transcellular activity of adjacent blood vessels. CONCLUSIONS: The study describes dynamic morphological events of a human lesioned TM. The human model may be used for further investigations and understanding of TM healing mechanisms.